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<front>
<journal-meta>
<journal-id journal-id-type="pmc">CMES</journal-id>
<journal-id journal-id-type="nlm-ta">CMES</journal-id>
<journal-id journal-id-type="publisher-id">CMES</journal-id>
<journal-title-group>
<journal-title>Computer Modeling in Engineering &#x0026; Sciences</journal-title>
</journal-title-group>
<issn pub-type="epub">1526-1506</issn>
<issn pub-type="ppub">1526-1492</issn>
<publisher>
<publisher-name>Tech Science Press</publisher-name>
<publisher-loc>USA</publisher-loc>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="publisher-id">64179</article-id>
<article-id pub-id-type="doi">10.32604/cmes.2025.064179</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Article</subject>
</subj-group>
</article-categories>
<title-group>
<article-title>SSA-LSTM-Multi-Head Attention Modelling Approach for Prediction of Coal Dust Maximum Explosion Pressure Based on the Synergistic Effect of Particle Size and Concentration</article-title>
<alt-title alt-title-type="left-running-head">SSA-LSTM-Multi-Head Attention Modelling Approach for Prediction of Coal Dust Maximum Explosion Pressure Based on the Synergistic Effect of Particle Size and Concentration</alt-title>
<alt-title alt-title-type="right-running-head">SSA-LSTM-Multi-Head Attention Modelling Approach for Prediction of Coal Dust Maximum Explosion Pressure Based on the Synergistic Effect of Particle Size and Concentration</alt-title>
</title-group>
<contrib-group>
<contrib id="author-1" contrib-type="author">
<name name-style="western"><surname>Liu</surname><given-names>Yongli</given-names></name><xref ref-type="aff" rid="aff-1">1</xref><xref ref-type="aff" rid="aff-2">2</xref></contrib>
<contrib id="author-2" contrib-type="author" corresp="yes">
<name name-style="western"><surname>Li</surname><given-names>Weihao</given-names></name><xref ref-type="aff" rid="aff-1">1</xref><xref ref-type="aff" rid="aff-2">2</xref><xref rid="cor1" ref-type="corresp">&#x002A;</xref><email>lwh158619@126.com</email></contrib>
<contrib id="author-3" contrib-type="author">
<name name-style="western"><surname>Wang</surname><given-names>Haitao</given-names></name><xref ref-type="aff" rid="aff-1">1</xref><xref ref-type="aff" rid="aff-2">2</xref><xref ref-type="aff" rid="aff-3">3</xref></contrib>
<contrib id="author-4" contrib-type="author">
<name name-style="western"><surname>Du</surname><given-names>Taoren</given-names></name><xref ref-type="aff" rid="aff-4">4</xref></contrib>
<aff id="aff-1"><label>1</label><institution>Institute of Interdisciplinary Research on Intelligent Mines, Heilongjiang University of Science and Technology</institution>, <addr-line>Harbin, 150022</addr-line>, <country>China</country></aff>
<aff id="aff-2"><label>2</label><institution>School of Mining Engineering, Heilongjiang University of Science and Technology</institution>, <addr-line>Harbin, 150022</addr-line>, <country>China</country></aff>
<aff id="aff-3"><label>3</label><institution>School of Resources and Engineering Department, Heilongjiang University of Technology</institution>, <addr-line>Jixi, 158100</addr-line>, <country>China</country></aff>
<aff id="aff-4"><label>4</label><institution>Heilongjiang Longmei Jixi Mining Co., Ltd., Xinfa Coal Mine</institution>, <addr-line>Jixi, 158199</addr-line>, <country>China</country></aff>
</contrib-group>
<author-notes>
<corresp id="cor1"><label>&#x002A;</label>Corresponding Author: Weihao Li. Email: <email>lwh158619@126.com</email></corresp>
</author-notes>
<pub-date date-type="collection" publication-format="electronic">
<year>2025</year>
</pub-date>
<pub-date date-type="pub" publication-format="electronic">
<day>30</day><month>05</month><year>2025</year>
</pub-date>
<volume>143</volume>
<issue>2</issue>
<fpage>2261</fpage>
<lpage>2286</lpage>
<history>
<date date-type="received">
<day>07</day>
<month>2</month>
<year>2025</year>
</date>
<date date-type="accepted">
<day>17</day>
<month>4</month>
<year>2025</year>
</date>
</history>
<permissions>
<copyright-statement>&#x00A9; 2025 The Authors.</copyright-statement>
<copyright-year>2025</copyright-year>
<copyright-holder>Published by Tech Science Press.</copyright-holder>
<license xlink:href="https://creativecommons.org/licenses/by/4.0/">
<license-p>This work is licensed under a <ext-link ext-link-type="uri" xlink:type="simple" xlink:href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</ext-link>, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.</license-p>
</license>
</permissions>
<self-uri content-type="pdf" xlink:href="TSP_CMES_64179.pdf"></self-uri>
<abstract>
<p>Coal dust explosions are severe safety accidents in coal mine production, posing significant threats to life and property. Predicting the maximum explosion pressure (<inline-formula id="ieqn-1"><mml:math id="mml-ieqn-1"><mml:msub><mml:mrow><mml:mtext>P</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>) of coal dust using deep learning models can effectively assess potential risks and provide a scientific basis for preventing coal dust explosions. In this study, a 20-L explosion sphere apparatus was used to test the maximum explosion pressure of coal dust under seven different particle sizes and ten mass concentrations (<inline-formula id="ieqn-2"><mml:math id="mml-ieqn-2"><mml:msub><mml:mrow><mml:mtext>C</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>dust</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>), resulting in a dataset of 70 experimental groups. Through Spearman correlation analysis and random forest feature selection methods, particle size (<inline-formula id="ieqn-3"><mml:math id="mml-ieqn-3"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>10</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, <inline-formula id="ieqn-4"><mml:math id="mml-ieqn-4"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>20</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, <inline-formula id="ieqn-5"><mml:math id="mml-ieqn-5"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>) and mass concentration (<inline-formula id="ieqn-6"><mml:math id="mml-ieqn-6"><mml:msub><mml:mrow><mml:mtext>C</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>dust</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>) were identified as critical feature parameters from the ten initial parameters of the coal dust samples. Based on this, a hybrid Long Short-Term Memory (LSTM) network model incorporating a Multi-Head Attention Mechanism and the Sparrow Search Algorithm (SSA) was proposed to predict the maximum explosion pressure of coal dust. The results demonstrate that the SSA-LSTM-Multi-Head Attention model excels in predicting the maximum explosion pressure of coal dust. The four evaluation metrics indicate that the model achieved a coefficient of determination (R<sup>2</sup>), root mean square error (RMSE), mean absolute percentage error (MAPE), and mean absolute error (MAE) of 0.9841, 0.0030, 0.0074, and 0.0049, respectively, in the training set. In the testing set, these values were 0.9743, 0.0087, 0.0108, and 0.0069, respectively. Compared to artificial neural networks (ANN), random forest (RF), support vector machines (SVM), particle swarm optimized-SVM (PSO-SVM) neural networks, and the traditional single-model LSTM, the SSA-LSTM-Multi-Head Attention model demonstrated superior generalization capability and prediction accuracy. The findings of this study not only advance the application of deep learning in coal dust explosion prediction but also provide robust technical support for the prevention and risk assessment of coal dust explosions.</p>
</abstract>
<kwd-group kwd-group-type="author">
<kwd>Coal dust explosion</kwd>
<kwd>deep learning</kwd>
<kwd>maximum explosion pressure</kwd>
<kwd>predictive model</kwd>
<kwd>SSA-LSTM</kwd>
<kwd>multi-head attention mechanism</kwd>
</kwd-group>
<funding-group>
<award-group id="awg1">
<funding-source>Research on Intelligent Mining Geological Model and Ventilation Model for Extremely Thin Coal Seam in Heilongjiang Province</funding-source>
<award-id>2021ZXJ02A03</award-id>
</award-group>
<award-group id="awg2">
<funding-source>Demonstration of Intelligent Mining for Comprehensive Mining Face in Extremely Thin Coal Seam in Heilongjiang Province</funding-source>
<award-id>2021ZXJ02A04</award-id>
</award-group>
<award-group id="awg3">
<funding-source>Natural Science Foundation of Heilongjiang Province</funding-source>
<award-id>LH2024E112</award-id>
</award-group>
</funding-group>
</article-meta>
</front>
<body>
<sec id="s1">
<label>1</label>
<title>Introduction</title>
<p>In the coal production process, coal dust, as one of the primary hazard sources in underground mines, poses a significant threat to both the safety of coal mining operations and economic efficiency. Hertzberg [<xref ref-type="bibr" rid="ref-1">1</xref>] demonstrated through experimental research that the combustion and explosion of coal dust are caused by the release of flammable gases (volatiles) when coal dust is heated. These gases mix with air to form a combustible gas mixture, which is then ignited by a high-temperature heat source. A common hazard source of coal dust disasters is the dust cloud formed by coal dust particles suspended in the air. When exposed to high-temperature heat sources such as blasting flames, mechanical friction sparks, or electrical sparks, coal dust explosion accidents may occur [<xref ref-type="bibr" rid="ref-2">2</xref>]. Yuan et al. [<xref ref-type="bibr" rid="ref-3">3</xref>] analyzed hundreds of dust explosion incidents and found that the number of dust explosion accidents worldwide has decreased over time; however, this trend does not apply to China. On 12 January 2019, a roof collapse at the Baiji Coal Mine in Shaanxi Province, China triggered a coal dust explosion, resulting in 21 fatalities. On 27 September 2021, a ventilation system failure at the Songzao Coal Mine in Chongqing, China caused a dust explosion, leading to 10 deaths. On 16 July 2022, an equipment malfunction at the Tashan Coal Mine of the Datong Coal Mine Group in Shanxi Province, China caused a coal dust cloud explosion, resulting in 8 fatalities. Therefore, studying the influence of coal dust&#x2019;s intrinsic factors on explosion characteristics and conducting effective risk assessments are crucial for the safe production of coal mines.</p>
<p>One of the key parameters in the coal dust explosion process is the maximum explosion pressure (<inline-formula id="ieqn-7"><mml:math id="mml-ieqn-7"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>), which serves as a critical indicator of the severity of dust explosions. By measuring and analyzing <inline-formula id="ieqn-8"><mml:math id="mml-ieqn-8"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>, a better understanding of the characteristics of dust explosions can be achieved, facilitating the development of effective explosion prevention measures. <inline-formula id="ieqn-9"><mml:math id="mml-ieqn-9"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> is primarily influenced by factors such as humidity, moisture content, ambient temperature, particle size, and dust concentration. In this study, dust concentration and particle size were selected as independent variables to investigate their effects on <inline-formula id="ieqn-10"><mml:math id="mml-ieqn-10"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>. Previous research has extensively explored the influence of these factors on dust explosion characteristics. Tan et al. [<xref ref-type="bibr" rid="ref-4">4</xref>] conducted experiments showing that, at the same concentration, the explosion pressure increases as the coal dust particle size decreases. Azam et al. [<xref ref-type="bibr" rid="ref-5">5</xref>] found that finer coal dust, due to its larger specific surface area and more significant inter-particle heat conduction, requires the addition of more rock dust to suppress explosions. Additionally, Yang et al. [<xref ref-type="bibr" rid="ref-6">6</xref>] discovered that the explosion intensity <inline-formula id="ieqn-11"><mml:math id="mml-ieqn-11"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> value of coal dust increases and then decreases with increasing mass concentration. This phenomenon may be due to the restricted flame propagation at low concentrations, resulting in a lower explosion intensity. As the concentration increases, the explosion intensity increases. However, at high concentrations, the limited availability of oxygen leads to a decrease in explosion intensity.</p>
<p>Prevention and suppression of dust explosions are two core measures to ensure the safety of coal mine production. To effectively prevent dust explosions, researchers employ various measurement methods to determine key safety parameters and assess the potential risks of dust explosions based on these parameters. To this end, researchers have conducted extensive experimental studies and utilized artificial neural network technology to develop models for predicting the characteristics of combustible materials in fire and explosion environments. Qi et al. [<xref ref-type="bibr" rid="ref-7">7</xref>] developed a machine learning model to predict the spontaneous combustion temperature of boreholes by combining Random Forest (RF) with the Hunger Games Search optimization algorithm (HGS). The results demonstrated that the HGS-RF hybrid model exhibited the best performance. Lei et al. [<xref ref-type="bibr" rid="ref-8">8</xref>] compared the accuracy of RF and Support Vector Machine (SVM) models in predicting coal spontaneous combustion and found that RF provided accurate predictions without requiring specific parameter settings, making it more suitable for practical applications. Shankar et al. [<xref ref-type="bibr" rid="ref-9">9</xref>] employed the Extreme Gradient Boosting (XGB) model for predicting the susceptibility of coal seams to spontaneous combustion, and the results indicated that this model outperformed the other four methods evaluated. Prasanjit et al. [<xref ref-type="bibr" rid="ref-10">10</xref>] developed a hybrid framework model that utilizes t-distributed Stochastic Neighbor Embedding (t-SNE) for dimensionality reduction and Variational Autoencoder (VAE) for gas feature extraction, combined with a Bidirectional Long Short-Term Memory (bi-LSTM) network for prediction. This model demonstrated lower Mean Squared Error (MSE). Borhani et al. [<xref ref-type="bibr" rid="ref-11">11</xref>] predicted the auto-ignition temperatures of 813 hydrocarbons using a Genetic Algorithm-optimized Multiple Linear Regression (GA-MLR) model and an Artificial Neural Network (ANN) model. The results indicated that the ANN model provided more accurate predictions and was more convenient for practical applications. Liu et al. [<xref ref-type="bibr" rid="ref-12">12</xref>] employed Principal Component Analysis (PCA) combined with a Backpropagation (BP) Neural Network to predict the flame propagation characteristics of coal dust explosions. The experimental results demonstrated that PCA effectively enhanced the prediction accuracy of the BP neural network. Qi et al. [<xref ref-type="bibr" rid="ref-13">13</xref>] measured the explosion characteristic parameters of four different coal dust and gas mixtures in a standard 20-L explosion vessel and established an effective prediction method. The results indicated that the Bartknecht model exhibited certain applicability for coal dust and gas mixtures. Khan et al. [<xref ref-type="bibr" rid="ref-14">14</xref>] conducted explosibility tests on coal samples from three different regions of Khyber-Pakhtunkhwa, Pakistan, using a 1.2-L Hartmann apparatus. They investigated the factors triggering coal dust explosions and utilized the RF model to predict the maximum explosion pressure. The model&#x2019;s prediction accuracy was relatively low, with experimental results showing an R<sup>2</sup> value of 0.89.</p>
<p>The aforementioned studies indicate that prediction models based on artificial neural networks possess strong theoretical support and practical relevance in the prevention and control of fires involving combustible materials and dust explosions. However, conducting <inline-formula id="ieqn-12"><mml:math id="mml-ieqn-12"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> testing not only requires significant time and cost but also entails safety risks. Therefore, establishing an accurate prediction model for coal dust <inline-formula id="ieqn-13"><mml:math id="mml-ieqn-13"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> is of great significance for the prevention of coal dust explosions and risk assessment in coal mines. In this study, a 20-L explosion spherical vessel was used to test the <inline-formula id="ieqn-14"><mml:math id="mml-ieqn-14"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> values of 7 coal dust samples (C1&#x2013;C7) at 10 different mass concentrations. Meanwhile, based on the coal dust explosion experimental data, a hybrid modeling method combining Long Short-Term Memory (LSTM) and Multi-Head Attention Mechanism was proposed. By integrating the advantages of both approaches, a <inline-formula id="ieqn-15"><mml:math id="mml-ieqn-15"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> prediction model for coal dust is constructed. In this model, LSTM controls the flow of input data through gating mechanisms and outputs hidden states containing historical information. The Multi-Head Attention module receives the hidden state sequence output by the LSTM and utilizes the global attention mechanism and multi-head parallel computing capabilities to capture the dependencies between different positions of the input sequence. To further improve the model&#x2019;s performance, the Sparrow Search Algorithm (SSA) is used to optimize the hyperparameters, and the model&#x2019;s predictive performance is compared with existing machine learning models.</p>
</sec>
<sec id="s2">
<label>2</label>
<title>Experimental Method and Materials</title>
<sec id="s2_1">
<label>2.1</label>
<title>Samples of Coal Dust</title>
<p>The coal samples used in this study were obtained from the Shuangyang Coal Mine in Shuangyashan City, China. The coal samples were ground into seven different particle size distributions, and the particle size of the sieved coal dust was measured using a laser particle size analyzer. Each coal sample was classified into ten different mass concentrations (2.5 g, 5 g, 7.5 g, 10 g, 12.5 g, 15 g, 17.5 g, 20 g, 22.5 g, and 25 g) for experimental investigation of the <inline-formula id="ieqn-16"><mml:math id="mml-ieqn-16"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> of coal dust. Prior to the experiments, the samples were dried at 50&#x00B0;C for at least 12 h, while the laboratory ambient temperature was maintained at approximately 27&#x00B0;C. The particle size distribution of the seven coal dust samples (C1&#x2013;C7) is shown in <xref ref-type="table" rid="table-1">Table 1</xref>. The mass concentration of each dust sample was calculated according to <xref ref-type="disp-formula" rid="eqn-1">Eq. (1)</xref> [<xref ref-type="bibr" rid="ref-15">15</xref>].<disp-formula id="eqn-1"><label>(1)</label><mml:math id="mml-eqn-1" display="block"><mml:msub><mml:mrow><mml:mtext>C</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>dust</mml:mtext></mml:mrow><mml:mo>=</mml:mo></mml:mrow></mml:msub><mml:mfrac><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow></mml:mfrac></mml:math></disp-formula>where, <inline-formula id="ieqn-17"><mml:math id="mml-ieqn-17"><mml:msub><mml:mrow><mml:mtext>C</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>dust</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> represents the mass concentration of coal dust, <inline-formula id="ieqn-18"><mml:math id="mml-ieqn-18"><mml:mi>m</mml:mi></mml:math></inline-formula> is the mass of the coal dust, and <inline-formula id="ieqn-19"><mml:math id="mml-ieqn-19"><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow></mml:math></inline-formula> is the volume of the 20-L spherical explosion chamber (0.02 m<sup>3</sup>). The calculated coal dust mass concentration values are 125.0, 250.0, 375.0, 500.0, 625.0, 750.0, 875.0, 1000.0, 1125.0, and 1250.0 g/m<sup>3</sup>.</p>
<table-wrap id="table-1">
<label>Table 1</label>
<caption>
<title>Measurement results of particle size parameters of coal dust samples</title>
</caption>
<table>
<colgroup>
<col/>
<col/>
<col/>
<col/>
<col/>
<col/>
<col/>
<col/>
</colgroup>
<thead>
<tr>
<th>Particle size parameters</th>
<th>C1</th>
<th>C2</th>
<th>C3</th>
<th>C4</th>
<th>C5</th>
<th>C6</th>
<th>C7</th>
</tr>
</thead>
<tbody>
<tr>
<td><inline-formula id="ieqn-20"><mml:math id="mml-ieqn-20"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>10</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> (&#x03BC;m)</td>
<td>6.78</td>
<td>4.62</td>
<td>4.29</td>
<td>3.97</td>
<td>2.12</td>
<td>1.74</td>
<td>1.33</td>
</tr>
<tr>
<td><inline-formula id="ieqn-21"><mml:math id="mml-ieqn-21"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>20</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> (&#x03BC;m)</td>
<td>15.99</td>
<td>11.13</td>
<td>9.29</td>
<td>7.75</td>
<td>4.50</td>
<td>3.75</td>
<td>3.13</td>
</tr>
<tr>
<td><inline-formula id="ieqn-22"><mml:math id="mml-ieqn-22"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>30</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> (&#x03BC;m)</td>
<td>26.95</td>
<td>22.98</td>
<td>15.99</td>
<td>15.99</td>
<td>7.75</td>
<td>5.39</td>
<td>4.50</td>
</tr>
<tr>
<td><inline-formula id="ieqn-23"><mml:math id="mml-ieqn-23"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>40</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> (&#x03BC;m)</td>
<td>36.58</td>
<td>33.02</td>
<td>22.98</td>
<td>19.17</td>
<td>11.13</td>
<td>7.47</td>
<td>6.46</td>
</tr>
<tr>
<td><inline-formula id="ieqn-24"><mml:math id="mml-ieqn-24"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> (&#x03BC;m)</td>
<td>44.59</td>
<td>40.34</td>
<td>33.49</td>
<td>30.33</td>
<td>17.44</td>
<td>11.47</td>
<td>8.70</td>
</tr>
<tr>
<td><inline-formula id="ieqn-25"><mml:math id="mml-ieqn-25"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>60</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> (&#x03BC;m)</td>
<td>51.87</td>
<td>47.44</td>
<td>39.58</td>
<td>39.58</td>
<td>22.98</td>
<td>15.99</td>
<td>13.34</td>
</tr>
<tr>
<td><inline-formula id="ieqn-26"><mml:math id="mml-ieqn-26"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>70</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> (&#x03BC;m)</td>
<td>59.31</td>
<td>52.15</td>
<td>47.44</td>
<td>47.44</td>
<td>27.55</td>
<td>22.98</td>
<td>19.17</td>
</tr>
<tr>
<td><inline-formula id="ieqn-27"><mml:math id="mml-ieqn-27"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>80</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> (&#x03BC;m)</td>
<td>65.17</td>
<td>56.87</td>
<td>55.41</td>
<td>56.87</td>
<td>39.58</td>
<td>27.55</td>
<td>27.55</td>
</tr>
<tr>
<td><inline-formula id="ieqn-28"><mml:math id="mml-ieqn-28"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>90</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> (&#x03BC;m)</td>
<td>77.93</td>
<td>67.43</td>
<td>63.12</td>
<td>64.16</td>
<td>45.73</td>
<td>36.60</td>
<td>33.81</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s2_2">
<label>2.2</label>
<title>Experimental Conditions and Methods</title>
<p>The experiment was conducted using a 20-L dust explosion experimental apparatus (HY16426D) manufactured by Jilin Hongyuan Scientific Instruments Co., Ltd. (Jilin, China). The <inline-formula id="ieqn-29"><mml:math id="mml-ieqn-29"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> values were measured in accordance with the GB/T 16426-1996 standard [<xref ref-type="bibr" rid="ref-16">16</xref>]. The experimental system configuration of the apparatus is shown in <xref ref-type="fig" rid="fig-1">Fig. 1</xref>. The 20-L explosion experimental apparatus primarily consists of an explosion tank, a control system, a dust dispersion system, an ignition system, and a data acquisition system. The control system is responsible for automatically initiating dust dispersion and ignition, as well as setting the ignition delay time. The nozzle of the dust dispersion system adopts an outwardly flared blade design. During the dust dispersion preparation process, the tank is first evacuated to an absolute pressure of 0.04 MPa, and then the dust storage is pressurized to an absolute pressure of 2.1 MPa. The control system then releases compressed air to disperse the dust within the dust storage, ensuring that the coal dust is ignited under normal atmospheric pressure. The ignition system consists of an electrode spark rod and a chemical ignition head. The electrode current ignites the chemical ignition head, generating 5 kJ of ignition energy to ignite the dust cloud. The chemical ignition head is composed of metallic zirconium, barium nitrate, and barium peroxide in a mass ratio of 4:3:3, with a total mass of 0.48 g. To ensure experimental reproducibility, all coal sample tests are conducted using the same ignition head and following the same procedure. The ignition delay time is set to 60 ms to ensure sufficient turbulence within the tank, allowing the dust to be uniformly dispersed at the time of ignition. The data acquisition system primarily relies on pressure transducers installed on the tank wall. When an explosion occurs, the system software collects the time-pressure change curve within 0.2 ms and transmits the data to the computer.</p>
<fig id="fig-1">
<label>Figure 1</label>
<caption>
<title>20-L dust explosion experimental apparatus: (<bold>a</bold>) Physical diagram of the experimental apparatus; (<bold>b</bold>) Structure of the experimental apparatus</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-1.tif"/>
</fig>
<p>To ensure the reliability of the experimental data, coal dust samples C1&#x2013;C7 were tested at least three times, and the average values were taken. The experimental results are shown in <xref ref-type="table" rid="table-2">Table 2</xref>. The pressure variation within the spherical tank during the experiment is shown in <xref ref-type="fig" rid="fig-2">Fig. 2</xref>. After the coal dust is released from the dust storage, the pressure in the tank gradually rises to the normal atmospheric pressure range. After the ignition delay, the dust explodes, and the pressure curve sharply increases to the maximum value. As the coal dust combustion in the explosion tank completes, the reaction terminates, and the pressure curve shows a decreasing trend. The explosion test data includes the maximum pressure (<inline-formula id="ieqn-30"><mml:math id="mml-ieqn-30"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>) reached within the tank during a single deflagration process, as well as the ignition delay time (<inline-formula id="ieqn-31"><mml:math id="mml-ieqn-31"><mml:msub><mml:mi>t</mml:mi><mml:mrow><mml:mi>d</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula>).</p>
<table-wrap id="table-2">
<label>Table 2</label>
<caption>
<title>Explosion experiment results of 7 kinds of coal dust samples</title>
</caption>
<table>
<colgroup>
<col align="center"/>
<col align="center"/>
<col align="center"/>
<col align="center"/>
<col align="center"/>
<col align="center"/>
<col align="center"/>
<col align="center"/>
</colgroup>
<thead>
<tr>
<th>No.</th>
<th align="center">Coal powder sample</th>
<th align="center">Concentration</th>
<th><inline-formula id="ieqn-32"><mml:math id="mml-ieqn-32"><mml:msub><mml:mi mathvariant="bold-italic">P</mml:mi><mml:mrow><mml:mrow><mml:mtext mathvariant="bold">m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula></th>
<th>No.</th>
<th align="center">Coal powder sample</th>
<th align="center">Concentration</th>
<th><inline-formula id="ieqn-33"><mml:math id="mml-ieqn-33"><mml:msub><mml:mi mathvariant="bold-italic">P</mml:mi><mml:mrow><mml:mrow><mml:mtext mathvariant="bold">m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula></th>
</tr>
<tr>
<th></th>
<th></th>
<th>g/m<sup>3</sup></th>
<th>MPa</th>
<th></th>
<th></th>
<th>g/m<sup>3</sup></th>
<th>MPa</th>
</tr>
</thead>
<tbody>
<tr>
<td>1</td>
<td>C1</td>
<td>125</td>
<td>0.483</td>
<td>36</td>
<td>C1</td>
<td>750</td>
<td>0.661</td>
</tr>
<tr>
<td>2</td>
<td>C2</td>
<td>125</td>
<td>0.512</td>
<td>37</td>
<td>C2</td>
<td>750</td>
<td>0.673</td>
</tr>
<tr>
<td>3</td>
<td>C3</td>
<td>125</td>
<td>0.526</td>
<td>38</td>
<td>C3</td>
<td>750</td>
<td>0.683</td>
</tr>
<tr>
<td>4</td>
<td>C4</td>
<td>125</td>
<td>0.659</td>
<td>39</td>
<td>C4</td>
<td>750</td>
<td>0.702</td>
</tr>
<tr>
<td>5</td>
<td>C5</td>
<td>125</td>
<td>0.678</td>
<td>40</td>
<td>C5</td>
<td>750</td>
<td>0.716</td>
</tr>
<tr>
<td>6</td>
<td>C6</td>
<td>125</td>
<td>0.683</td>
<td>41</td>
<td>C6</td>
<td>750</td>
<td>0.739</td>
</tr>
<tr>
<td>7</td>
<td>C7</td>
<td>125</td>
<td>0.693</td>
<td>42</td>
<td>C7</td>
<td>750</td>
<td>0.754</td>
</tr>
<tr>
<td>8</td>
<td>C1</td>
<td>250</td>
<td>0.538</td>
<td>43</td>
<td>C1</td>
<td>875</td>
<td>0.657</td>
</tr>
<tr>
<td>9</td>
<td>C2</td>
<td>250</td>
<td>0.568</td>
<td>44</td>
<td>C2</td>
<td>875</td>
<td>0.669</td>
</tr>
<tr>
<td>10</td>
<td>C3</td>
<td>250</td>
<td>0.598</td>
<td>45</td>
<td>C3</td>
<td>875</td>
<td>0.675</td>
</tr>
<tr>
<td>11</td>
<td>C4</td>
<td>250</td>
<td>0.669</td>
<td>46</td>
<td>C4</td>
<td>875</td>
<td>0.694</td>
</tr>
<tr>
<td>12</td>
<td>C5</td>
<td>250</td>
<td>0.683</td>
<td>47</td>
<td>C5</td>
<td>875</td>
<td>0.707</td>
</tr>
<tr>
<td>13</td>
<td>C6</td>
<td>250</td>
<td>0.696</td>
<td>48</td>
<td>C6</td>
<td>875</td>
<td>0.724</td>
</tr>
<tr>
<td>14</td>
<td>C7</td>
<td>250</td>
<td>0.709</td>
<td>49</td>
<td>C7</td>
<td>875</td>
<td>0.739</td>
</tr>
<tr>
<td>15</td>
<td>C1</td>
<td>375</td>
<td>0.583</td>
<td>50</td>
<td>C1</td>
<td>1000</td>
<td>0.646</td>
</tr>
<tr>
<td>16</td>
<td>C2</td>
<td>375</td>
<td>0.631</td>
<td>51</td>
<td>C2</td>
<td>1000</td>
<td>0.652</td>
</tr>
<tr>
<td>17</td>
<td>C3</td>
<td>375</td>
<td>0.651</td>
<td>52</td>
<td>C3</td>
<td>1000</td>
<td>0.668</td>
</tr>
<tr>
<td>18</td>
<td>C4</td>
<td>375</td>
<td>0.679</td>
<td>53</td>
<td>C4</td>
<td>1000</td>
<td>0.689</td>
</tr>
<tr>
<td>19</td>
<td>C5</td>
<td>375</td>
<td>0.687</td>
<td>54</td>
<td>C5</td>
<td>1000</td>
<td>0.696</td>
</tr>
<tr>
<td>20</td>
<td>C6</td>
<td>375</td>
<td>0.704</td>
<td>55</td>
<td>C6</td>
<td>1000</td>
<td>0.717</td>
</tr>
<tr>
<td>21</td>
<td>C7</td>
<td>375</td>
<td>0.714</td>
<td>56</td>
<td>C7</td>
<td>1000</td>
<td>0.727</td>
</tr>
<tr>
<td>22</td>
<td>C1</td>
<td>500</td>
<td>0.617</td>
<td>57</td>
<td>C1</td>
<td>1125</td>
<td>0.633</td>
</tr>
<tr>
<td>23</td>
<td>C2</td>
<td>500</td>
<td>0.659</td>
<td>58</td>
<td>C2</td>
<td>1125</td>
<td>0.647</td>
</tr>
<tr>
<td>24</td>
<td>C3</td>
<td>500</td>
<td>0.669</td>
<td>59</td>
<td>C3</td>
<td>1125</td>
<td>0.666</td>
</tr>
<tr>
<td>25</td>
<td>C4</td>
<td>500</td>
<td>0.683</td>
<td>60</td>
<td>C4</td>
<td>1125</td>
<td>0.679</td>
</tr>
<tr>
<td>26</td>
<td>C5</td>
<td>500</td>
<td>0.691</td>
<td>61</td>
<td>C5</td>
<td>1125</td>
<td>0.689</td>
</tr>
<tr>
<td>27</td>
<td>C6</td>
<td>500</td>
<td>0.711</td>
<td>62</td>
<td>C6</td>
<td>1125</td>
<td>0.699</td>
</tr>
<tr>
<td>28</td>
<td>C7</td>
<td>500</td>
<td>0.719</td>
<td>63</td>
<td>C7</td>
<td>1125</td>
<td>0.719</td>
</tr>
<tr>
<td>29</td>
<td>C1</td>
<td>625</td>
<td>0.675</td>
<td>64</td>
<td>C1</td>
<td>1250</td>
<td>0.627</td>
</tr>
<tr>
<td>30</td>
<td>C2</td>
<td>625</td>
<td>0.683</td>
<td>65</td>
<td>C2</td>
<td>1250</td>
<td>0.635</td>
</tr>
<tr>
<td>31</td>
<td>C3</td>
<td>625</td>
<td>0.688</td>
<td>66</td>
<td>C3</td>
<td>1250</td>
<td>0.653</td>
</tr>
<tr>
<td>32</td>
<td>C4</td>
<td>625</td>
<td>0.691</td>
<td>67</td>
<td>C4</td>
<td>1250</td>
<td>0.669</td>
</tr>
<tr>
<td>33</td>
<td>C5</td>
<td>625</td>
<td>0.701</td>
<td>68</td>
<td>C5</td>
<td>1250</td>
<td>0.682</td>
</tr>
<tr>
<td>34</td>
<td>C6</td>
<td>625</td>
<td>0.716</td>
<td>69</td>
<td>C6</td>
<td>1250</td>
<td>0.695</td>
</tr>
<tr>
<td>35</td>
<td>C7</td>
<td>625</td>
<td>0.724</td>
<td>70</td>
<td>C7</td>
<td>1250</td>
<td>0.699</td>
</tr>
</tbody>
</table>
</table-wrap><fig id="fig-2">
<label>Figure 2</label>
<caption>
<title>Classical pressure-time curve for 20-L dust explosion experiment</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-2.tif"/>
</fig>
</sec>
</sec>
<sec id="s3">
<label>3</label>
<title>Model Theoretical Basis and Establishment</title>
<sec id="s3_1">
<label>3.1</label>
<title>Long Short-Term Memory Network</title>
<p>Deep learning models are a type of deep neural network with multiple non-linear mapping layers, capable of extracting features from input signals layer by layer and uncovering deeper potential patterns [<xref ref-type="bibr" rid="ref-17">17</xref>]. Among many deep learning models, Long Short-Term Memory (LSTM) is a special architecture of Recurrent Neural Networks (RNNs) that alleviates the vanishing or exploding gradient problem in RNNs by adding a gating mechanism to regulate information flow, making it more adept at capturing semantic dependencies in long sequences. LSTM was created by Hochreiter and Schmidhuber in 1997 [<xref ref-type="bibr" rid="ref-18">18</xref>]. Its core structure consists of four components: the forget gate, input gate, memory cell state, and output gate, as shown in <xref ref-type="fig" rid="fig-3">Fig. 3</xref>. The LSTM network structure is calculated as shown in <xref ref-type="disp-formula" rid="eqn-2">Eqs. (2)</xref>&#x2013;<xref ref-type="disp-formula" rid="eqn-7">(7)</xref> [<xref ref-type="bibr" rid="ref-19">19</xref>,<xref ref-type="bibr" rid="ref-20">20</xref>]:
<disp-formula id="eqn-2"><label>(2)</label><mml:math id="mml-eqn-2" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mi mathvariant="normal">&#x03C3;</mml:mi></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x22C5;</mml:mo><mml:mrow><mml:mo>[</mml:mo><mml:msub><mml:mrow><mml:mtext>h</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mtext>x</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>]</mml:mo></mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mrow><mml:mtext>b</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
<disp-formula id="eqn-3"><label>(3)</label><mml:math id="mml-eqn-3" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:msub><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mi mathvariant="normal">&#x03C3;</mml:mi></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x22C5;</mml:mo><mml:mrow><mml:mo>[</mml:mo><mml:msub><mml:mrow><mml:mtext>h</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mtext>x</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>]</mml:mo></mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mrow><mml:mtext>b</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
<disp-formula id="eqn-4"><label>(4)</label><mml:math id="mml-eqn-4" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:msub><mml:mrow><mml:mtext>o</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mi mathvariant="normal">&#x03C3;</mml:mi></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>o</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mrow><mml:mo>[</mml:mo><mml:msub><mml:mrow><mml:mtext>h</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mtext>x</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>]</mml:mo></mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mrow><mml:mtext>b</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>o</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
<disp-formula id="eqn-5"><label>(5)</label><mml:math id="mml-eqn-5" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:msub><mml:mrow><mml:mrow><mml:mover><mml:mi mathvariant="normal">C</mml:mi><mml:mo stretchy="false">&#x007E;</mml:mo></mml:mover></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mi>tanh</mml:mi><mml:mo>&#x2061;</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>c</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x22C5;</mml:mo><mml:mrow><mml:mo>[</mml:mo><mml:msub><mml:mrow><mml:mtext>h</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mtext>x</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>]</mml:mo></mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mrow><mml:mtext>b</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>c</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
<disp-formula id="eqn-6"><label>(6)</label><mml:math id="mml-eqn-6" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:msub><mml:mrow><mml:mtext>C</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2217;</mml:mo><mml:msub><mml:mrow><mml:mtext>C</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2217;</mml:mo><mml:msub><mml:mrow><mml:mrow><mml:mover><mml:mi mathvariant="normal">C</mml:mi><mml:mo stretchy="false">&#x007E;</mml:mo></mml:mover></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
<disp-formula id="eqn-7"><label>(7)</label><mml:math id="mml-eqn-7" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:msub><mml:mrow><mml:mtext>h</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mrow><mml:mtext>o</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2217;</mml:mo><mml:mi>tanh</mml:mi><mml:mo>&#x2061;</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mtext>C</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>where, <inline-formula id="ieqn-34"><mml:math id="mml-ieqn-34"><mml:mrow><mml:mi mathvariant="normal">&#x03C3;</mml:mi></mml:mrow></mml:math></inline-formula> denotes the sigmoid activation function, <inline-formula id="ieqn-35"><mml:math id="mml-ieqn-35"><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> represents the forget gate, <inline-formula id="ieqn-36"><mml:math id="mml-ieqn-36"><mml:msub><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> denotes the input gate, and <inline-formula id="ieqn-37"><mml:math id="mml-ieqn-37"><mml:msub><mml:mrow><mml:mtext>o</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> represents the output gate. <inline-formula id="ieqn-38"><mml:math id="mml-ieqn-38"><mml:msub><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>, <inline-formula id="ieqn-39"><mml:math id="mml-ieqn-39"><mml:msub><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>, and <inline-formula id="ieqn-40"><mml:math id="mml-ieqn-40"><mml:msub><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>o</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> correspond to the weights for each gate, while <inline-formula id="ieqn-41"><mml:math id="mml-ieqn-41"><mml:msub><mml:mrow><mml:mtext>b</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>, <inline-formula id="ieqn-42"><mml:math id="mml-ieqn-42"><mml:msub><mml:mrow><mml:mtext>b</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>, and <inline-formula id="ieqn-43"><mml:math id="mml-ieqn-43"><mml:msub><mml:mrow><mml:mtext>b</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>o</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> are the bias terms. <inline-formula id="ieqn-44"><mml:math id="mml-ieqn-44"><mml:msub><mml:mrow><mml:mtext>h</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> and <inline-formula id="ieqn-45"><mml:math id="mml-ieqn-45"><mml:msub><mml:mrow><mml:mtext>C</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> denote the hidden state and the memory cell state at the moment of t, respectively, <inline-formula id="ieqn-46"><mml:math id="mml-ieqn-46"><mml:mrow><mml:mover><mml:msub><mml:mrow><mml:mtext>C</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x007E;</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula> is the candidate memory cell state at moment t obtained by the tanh activation function, and <inline-formula id="ieqn-47"><mml:math id="mml-ieqn-47"><mml:msub><mml:mrow><mml:mtext>x</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> is the input sequence at moment t.</p>
<fig id="fig-3">
<label>Figure 3</label>
<caption>
<title>Internal structure of LSTM network</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-3.tif"/>
</fig>
</sec>
<sec id="s3_2">
<label>3.2</label>
<title>Multi-Head Attention Mechanism</title>
<p>The Multi-Head Attention Mechanism [<xref ref-type="bibr" rid="ref-21">21</xref>] is a technique that enhances the self-attention mechanism. By decomposing the attention computation into multiple parallel self-attention heads, it allows the model to simultaneously capture various relationships and features from different parts of the input sequence. Each head independently calculates the self-attention scores for the query (Q), key (K), and value (V) in its subspace and outputs the result, thereby enhancing the model&#x2019;s ability to capture complex dependencies and improving its effectiveness in processing sequential data. Multi-Head Attention calculation process is as shown in <xref ref-type="disp-formula" rid="eqn-8">Eqs. (8)</xref>&#x2013;<xref ref-type="disp-formula" rid="eqn-11">(11)</xref> [<xref ref-type="bibr" rid="ref-22">22</xref>,<xref ref-type="bibr" rid="ref-23">23</xref>]:
<disp-formula id="eqn-8"><label>(8)</label><mml:math id="mml-eqn-8" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:msup><mml:mrow><mml:mtext>HW</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
<disp-formula id="eqn-9"><label>(9)</label><mml:math id="mml-eqn-9" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:msup><mml:mrow><mml:mtext>HW</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
<disp-formula id="eqn-10"><label>(10)</label><mml:math id="mml-eqn-10" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:msup><mml:mrow><mml:mtext>HW</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
<disp-formula id="eqn-11"><label>(11)</label><mml:math id="mml-eqn-11" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:mrow><mml:mtext>Attention</mml:mtext></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mo>=</mml:mo><mml:mrow><mml:mtext>softmax</mml:mtext></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mfrac><mml:msup><mml:mrow><mml:mtext>QK</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>T</mml:mtext></mml:mrow></mml:mrow></mml:msup><mml:msqrt><mml:msub><mml:mrow><mml:mtext>d</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>k</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:msqrt></mml:mfrac><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>where, <inline-formula id="ieqn-48"><mml:math id="mml-ieqn-48"><mml:mrow><mml:mtext>H</mml:mtext></mml:mrow></mml:math></inline-formula> is the output vector after LSTM computation, <inline-formula id="ieqn-49"><mml:math id="mml-ieqn-49"><mml:msup><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:math></inline-formula>, <inline-formula id="ieqn-50"><mml:math id="mml-ieqn-50"><mml:msup><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:math></inline-formula>, and <inline-formula id="ieqn-51"><mml:math id="mml-ieqn-51"><mml:msup><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:math></inline-formula> are the three parameter matrices. The softmax function serves to normalize the computed attentional weights to values of attentional weights between (0, 1) and all weights summing to 1. <inline-formula id="ieqn-52"><mml:math id="mml-ieqn-52"><mml:msub><mml:mrow><mml:mtext>d</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>k</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> represents the dimensionality of matrix <inline-formula id="ieqn-53"><mml:math id="mml-ieqn-53"><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow></mml:math></inline-formula>, and <inline-formula id="ieqn-54"><mml:math id="mml-ieqn-54"><mml:msqrt><mml:msub><mml:mrow><mml:mtext>d</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>k</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:msqrt></mml:math></inline-formula> serves as a scaling factor, which is used to balance the dot product results and avoid the issue of gradient vanishing due to excessively large dot product values of large vectors. In the Multi-Head Attention mechanism, <inline-formula id="ieqn-55"><mml:math id="mml-ieqn-55"><mml:msup><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:math></inline-formula>, <inline-formula id="ieqn-56"><mml:math id="mml-ieqn-56"><mml:msup><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:math></inline-formula>, and <inline-formula id="ieqn-57"><mml:math id="mml-ieqn-57"><mml:msup><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:math></inline-formula> perform multiple linear transformations on the vector <inline-formula id="ieqn-58"><mml:math id="mml-ieqn-58"><mml:mrow><mml:mtext>H</mml:mtext></mml:mrow></mml:math></inline-formula>, mapping it into different <inline-formula id="ieqn-59"><mml:math id="mml-ieqn-59"><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow></mml:math></inline-formula>, <inline-formula id="ieqn-60"><mml:math id="mml-ieqn-60"><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow></mml:math></inline-formula>, and <inline-formula id="ieqn-61"><mml:math id="mml-ieqn-61"><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow></mml:math></inline-formula> spaces. Each self-attention head calculates the attention weights using the respective <inline-formula id="ieqn-62"><mml:math id="mml-ieqn-62"><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow></mml:math></inline-formula> and <inline-formula id="ieqn-63"><mml:math id="mml-ieqn-63"><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow></mml:math></inline-formula> matrices and performs a weighted summation on the value vector <inline-formula id="ieqn-64"><mml:math id="mml-ieqn-64"><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow></mml:math></inline-formula>. Finally, the outputs of all self-attention heads are concatenated into a matrix, and a linear transformation matrix <inline-formula id="ieqn-65"><mml:math id="mml-ieqn-65"><mml:msup><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>o</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:math></inline-formula> is applied to obtain the final output, as shown in <xref ref-type="fig" rid="fig-4">Fig. 4</xref>. The output expression of each self-attention head is shown in <xref ref-type="disp-formula" rid="eqn-12">Eq. (12)</xref>, and the multi-head attention calculation expression is shown in <xref ref-type="disp-formula" rid="eqn-13">Eq. (13)</xref> [<xref ref-type="bibr" rid="ref-24">24</xref>].
<disp-formula id="eqn-12"><label>(12)</label><mml:math id="mml-eqn-12" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:msub><mml:mrow><mml:mtext>head</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mtext>Attention</mml:mtext></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:msubsup><mml:mrow><mml:mtext>QW</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>,</mml:mo><mml:msubsup><mml:mrow><mml:mtext>KW</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>,</mml:mo><mml:msubsup><mml:mrow><mml:mtext>VW</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>)</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
<disp-formula id="eqn-13"><label>(13)</label><mml:math id="mml-eqn-13" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:mrow><mml:mtext>MultiHead</mml:mtext></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mo>=</mml:mo><mml:mrow><mml:mtext>Concat</mml:mtext></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mtext>head</mml:mtext></mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mo>&#x2026;</mml:mo><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mtext>head</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>h</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:msup><mml:mrow><mml:mtext>W</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>o</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>where, <inline-formula id="ieqn-66"><mml:math id="mml-ieqn-66"><mml:msub><mml:mrow><mml:mtext>head</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> represents the attention output of the <inline-formula id="ieqn-67"><mml:math id="mml-ieqn-67"><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:math></inline-formula>-th head, <inline-formula id="ieqn-68"><mml:math id="mml-ieqn-68"><mml:mrow><mml:mtext>Concat</mml:mtext></mml:mrow></mml:math></inline-formula> refers to the concatenation operation, and <inline-formula id="ieqn-69"><mml:math id="mml-ieqn-69"><mml:mrow><mml:mtext>MultiHead</mml:mtext></mml:mrow></mml:math></inline-formula> is the output result of the multi-head attention layer.</p>
<fig id="fig-4">
<label>Figure 4</label>
<caption>
<title>Calculation structure of the multi-head attention mechanism</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-4.tif"/>
</fig>
</sec>
<sec id="s3_3">
<label>3.3</label>
<title>Sparrow Search Algorithm</title>
<p>The Sparrow Search Algorithm (SSA) [<xref ref-type="bibr" rid="ref-25">25</xref>] is a swarm intelligence optimization algorithm inspired by the foraging and anti-predation behaviors of sparrows. Due to its excellent stability and powerful search capability, SSA has been widely applied in deep learning modeling. The sparrow population is randomly initialized into discoverers and joiners. Discoverers are responsible for guiding the movement direction of the population and iteratively searching for the global optimal solution. Joiners perform local searches based on the optimal solutions generated by the discoverers. The anti-predation behavior refers to the ability of sparrows to detect danger and promptly issue warning signals, prompting the population to rapidly move to a safe area and update their positions, thereby preventing the algorithm from being trapped in local optima. The population updating process of SSA algorithm is as shown in <xref ref-type="disp-formula" rid="eqn-14">Eqs. (14)</xref>&#x2013;<xref ref-type="disp-formula" rid="eqn-16">(16)</xref> [<xref ref-type="bibr" rid="ref-26">26</xref>,<xref ref-type="bibr" rid="ref-27">27</xref>]:</p>
<p>Discoverers location update:
<disp-formula id="eqn-14"><label>(14)</label><mml:math id="mml-eqn-14" display="block"><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup><mml:mo>=</mml:mo><mml:mrow><mml:mo>{</mml:mo><mml:mtable columnalign="left left" rowspacing="4pt" columnspacing="1em"><mml:mtr><mml:mtd><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>&#x22C5;</mml:mo><mml:mi>exp</mml:mi><mml:mo>&#x2061;</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mo>&#x2212;</mml:mo><mml:mfrac><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mi mathvariant="normal">&#x03B1;</mml:mi></mml:mrow><mml:mo>&#x22C5;</mml:mo><mml:msub><mml:mrow><mml:mtext>iter</mml:mtext></mml:mrow><mml:mrow><mml:mo movablelimits="true" form="prefix">max</mml:mo></mml:mrow></mml:msub></mml:mrow></mml:mfrac><mml:mo>)</mml:mo></mml:mrow><mml:mo>,</mml:mo></mml:mtd><mml:mtd><mml:msub><mml:mrow><mml:mtext>R</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>&#x003C;</mml:mo><mml:mrow><mml:mtext>ST</mml:mtext></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>+</mml:mo><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow><mml:mo>&#x22C5;</mml:mo><mml:mi mathvariant="bold-italic">L</mml:mi><mml:mo>,</mml:mo></mml:mtd><mml:mtd><mml:msub><mml:mrow><mml:mtext>R</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>&#x2265;</mml:mo><mml:mrow><mml:mtext>ST</mml:mtext></mml:mrow></mml:mtd></mml:mtr></mml:mtable><mml:mo fence="true" stretchy="true" symmetric="true"></mml:mo></mml:mrow></mml:math></disp-formula>where, <inline-formula id="ieqn-70"><mml:math id="mml-ieqn-70"><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:math></inline-formula> denotes the current iteration number, <inline-formula id="ieqn-71"><mml:math id="mml-ieqn-71"><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msubsup></mml:math></inline-formula> represents the position information of the <inline-formula id="ieqn-72"><mml:math id="mml-ieqn-72"><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:math></inline-formula>-th sparrow in the <inline-formula id="ieqn-73"><mml:math id="mml-ieqn-73"><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:math></inline-formula>-th dimension, <inline-formula id="ieqn-74"><mml:math id="mml-ieqn-74"><mml:msub><mml:mrow><mml:mtext>iter</mml:mtext></mml:mrow><mml:mrow><mml:mo movablelimits="true" form="prefix">max</mml:mo></mml:mrow></mml:msub></mml:math></inline-formula> denotes the maximum number of iterations, <inline-formula id="ieqn-75"><mml:math id="mml-ieqn-75"><mml:mrow><mml:mi mathvariant="normal">&#x03B1;</mml:mi></mml:mrow><mml:mo>&#x2208;</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mn>0</mml:mn><mml:mo>,</mml:mo><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo></mml:math></inline-formula> is a random number, <inline-formula id="ieqn-76"><mml:math id="mml-ieqn-76"><mml:msub><mml:mrow><mml:mtext>R</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>(<inline-formula id="ieqn-77"><mml:math id="mml-ieqn-77"><mml:msub><mml:mrow><mml:mtext>R</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>&#x2208;</mml:mo><mml:mo stretchy="false">[</mml:mo><mml:mn>0</mml:mn><mml:mo>,</mml:mo><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo></mml:math></inline-formula>) and <inline-formula id="ieqn-78"><mml:math id="mml-ieqn-78"><mml:mrow><mml:mtext>ST</mml:mtext></mml:mrow></mml:math></inline-formula>(<inline-formula id="ieqn-79"><mml:math id="mml-ieqn-79"><mml:mrow><mml:mtext>ST&#xA0;</mml:mtext></mml:mrow><mml:mo>&#x2208;</mml:mo><mml:mo stretchy="false">[</mml:mo><mml:mn>0.5</mml:mn><mml:mo>,</mml:mo><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo></mml:math></inline-formula>) represent the warning threshold and safety threshold, respectively. <inline-formula id="ieqn-80"><mml:math id="mml-ieqn-80"><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow></mml:math></inline-formula> is a random number following a normal distribution, and <inline-formula id="ieqn-81"><mml:math id="mml-ieqn-81"><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:math></inline-formula> is a 1 &#x00D7; d matrix with all elements equal to 1.</p>
<p>Joiners location update:
<disp-formula id="eqn-15"><label>(15)</label><mml:math id="mml-eqn-15" display="block"><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup><mml:mo>=</mml:mo><mml:mrow><mml:mo>{</mml:mo><mml:mtable columnalign="left left" rowspacing="4pt" columnspacing="1em"><mml:mtr><mml:mtd><mml:msub><mml:mrow><mml:mtext>Q</mml:mtext></mml:mrow><mml:mrow><mml:mo>.</mml:mo></mml:mrow></mml:msub><mml:mi>exp</mml:mi><mml:mo>&#x2061;</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mfrac><mml:mrow><mml:msub><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>worst</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2212;</mml:mo><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msubsup></mml:mrow><mml:msup><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mfrac><mml:mo>)</mml:mo></mml:mrow><mml:mo>,</mml:mo></mml:mtd><mml:mtd><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>&#x003E;</mml:mo><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup><mml:mo>+</mml:mo><mml:mo>&#x2223;</mml:mo><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>&#x2212;</mml:mo><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup><mml:mo>&#x2223;</mml:mo><mml:mo>&#x22C5;</mml:mo><mml:msup><mml:mrow><mml:mtext>A</mml:mtext></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:mo>&#x22C5;</mml:mo><mml:mi mathvariant="bold-italic">L</mml:mi><mml:mo>,</mml:mo></mml:mtd><mml:mtd><mml:mrow><mml:mtext>otherwise</mml:mtext></mml:mrow></mml:mtd></mml:mtr></mml:mtable><mml:mo fence="true" stretchy="true" symmetric="true"></mml:mo></mml:mrow></mml:math></disp-formula>where, <inline-formula id="ieqn-82"><mml:math id="mml-ieqn-82"><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:math></inline-formula> represents the number of Joiners, <inline-formula id="ieqn-83"><mml:math id="mml-ieqn-83"><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow></mml:math></inline-formula> denotes the total number of sparrows, <inline-formula id="ieqn-84"><mml:math id="mml-ieqn-84"><mml:msub><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> is the current optimal position occupied by the discoverer, <inline-formula id="ieqn-85"><mml:math id="mml-ieqn-85"><mml:msub><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>worst</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> denotes the current global worst position, and <inline-formula id="ieqn-86"><mml:math id="mml-ieqn-86"><mml:mrow><mml:mtext>A</mml:mtext></mml:mrow></mml:math></inline-formula> is a 1 &#x00D7; d matrix with each element randomly assigned as either 1 or &#x2212;1, and <inline-formula id="ieqn-87"><mml:math id="mml-ieqn-87"><mml:msup><mml:mrow><mml:mtext>A</mml:mtext></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:mo>=</mml:mo><mml:msup><mml:mrow><mml:mtext>A</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>T</mml:mtext></mml:mrow></mml:mrow></mml:msup><mml:mo stretchy="false">(</mml:mo><mml:mrow><mml:mtext>A</mml:mtext></mml:mrow><mml:mrow><mml:msup><mml:mrow><mml:mtext>A</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>T</mml:mtext></mml:mrow></mml:mrow></mml:msup></mml:mrow><mml:msup><mml:mo stretchy="false">)</mml:mo><mml:mrow><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:math></inline-formula>.</p>
<p>Sparrows in Danger location update:
<disp-formula id="eqn-16"><label>(16)</label><mml:math id="mml-eqn-16" display="block"><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup><mml:mo>=</mml:mo><mml:mrow><mml:mo>{</mml:mo><mml:mtable columnalign="left center" rowspacing="4pt" columnspacing="1em"><mml:mtr><mml:mtd><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>best</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>+</mml:mo><mml:mrow><mml:mi mathvariant="normal">&#x03B2;</mml:mi></mml:mrow><mml:mo>&#x2223;</mml:mo><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>&#x2212;</mml:mo><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>best</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo stretchy="false">&#x2223;</mml:mo></mml:mtd><mml:mtd><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x003E;</mml:mo><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>g</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>+</mml:mo><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mfrac><mml:mrow><mml:mo stretchy="false">&#x2223;</mml:mo><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>,</mml:mo><mml:mrow><mml:mtext>j</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>&#x2212;</mml:mo><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>worst</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo stretchy="false">&#x2223;</mml:mo></mml:mrow><mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2212;</mml:mo><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>w</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mo>+</mml:mo><mml:mrow><mml:mi mathvariant="normal">&#x03B5;</mml:mi></mml:mrow></mml:mrow></mml:mfrac><mml:mo>)</mml:mo></mml:mrow></mml:mtd><mml:mtd><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>g</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:mtd></mml:mtr></mml:mtable><mml:mo fence="true" stretchy="true" symmetric="true"></mml:mo></mml:mrow></mml:math></disp-formula>where, <inline-formula id="ieqn-88"><mml:math id="mml-ieqn-88"><mml:msub><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>best</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> represents the current global best position, <inline-formula id="ieqn-89"><mml:math id="mml-ieqn-89"><mml:mrow><mml:mi mathvariant="normal">&#x03B2;</mml:mi></mml:mrow></mml:math></inline-formula> denotes a random number following a normal distribution with a mean of 0 and a variance of 1, <inline-formula id="ieqn-90"><mml:math id="mml-ieqn-90"><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow><mml:mo>&#x2208;</mml:mo><mml:mo stretchy="false">[</mml:mo><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo></mml:math></inline-formula> is a random number indicating the movement direction of the sparrow, <inline-formula id="ieqn-91"><mml:math id="mml-ieqn-91"><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> is the fitness value of the current sparrow, while <inline-formula id="ieqn-92"><mml:math id="mml-ieqn-92"><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>g</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> and <inline-formula id="ieqn-93"><mml:math id="mml-ieqn-93"><mml:msub><mml:mrow><mml:mtext>f</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>w</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> represent the current global maximum and minimum fitness values, respectively. <inline-formula id="ieqn-94"><mml:math id="mml-ieqn-94"><mml:mrow><mml:mi mathvariant="normal">&#x03B5;</mml:mi></mml:mrow></mml:math></inline-formula> is a small constant to avoid division by zero in the denominator.</p>
</sec>
<sec id="s3_4">
<label>3.4</label>
<title>SSA-LSTM-Multi-Head Attention Prediction Model Construction</title>
<p>In this study, an LSTM-Multi-Head Attention model is employed as the main framework for predicting the maximum explosion pressure of coal dust, and the SSA optimization algorithm is utilized to identify the optimal hyperparameters of the model to enhance prediction accuracy. The original data samples are obtained through coal dust explosion experiments, where the input features and labels of the model are represented as <inline-formula id="ieqn-95"><mml:math id="mml-ieqn-95"><mml:mrow><mml:mo>{</mml:mo><mml:msub><mml:mrow><mml:mtext>x</mml:mtext></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>,</mml:mo></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mtext>x</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>,</mml:mo></mml:mrow></mml:msub><mml:mo>&#x22EF;</mml:mo><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mtext>x</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow><mml:mo>,</mml:mo></mml:mrow></mml:msub><mml:mo>}</mml:mo></mml:mrow></mml:math></inline-formula> and <inline-formula id="ieqn-96"><mml:math id="mml-ieqn-96"><mml:mrow><mml:mo>{</mml:mo><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>,</mml:mo></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>,</mml:mo></mml:mrow></mml:msub><mml:mo>&#x22EF;</mml:mo><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow><mml:mo>,</mml:mo></mml:mrow></mml:msub><mml:mo>}</mml:mo></mml:mrow></mml:math></inline-formula>, respectively. Here, <inline-formula id="ieqn-97"><mml:math id="mml-ieqn-97"><mml:msub><mml:mrow><mml:mtext>x</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> denotes the n-th sample data, and <inline-formula id="ieqn-98"><mml:math id="mml-ieqn-98"><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> represents the corresponding explosion pressure. <xref ref-type="fig" rid="fig-5">Fig. 5</xref> illustrates the architecture of the model, and the specific construction process is as follows:<list list-type="simple">
<list-item><label>(1)</label><p>Coal dust explosion pressure experiments were conducted in a 20 L explosion tank to investigate the explosion behaviors under varying particle sizes and concentrations, resulting in the collection of 70 raw data samples. Data normalization was applied to eliminate dimensional differences among the features. In the dataset, particle size and concentration were utilized as input features, while the <inline-formula id="ieqn-99"><mml:math id="mml-ieqn-99"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> was designated as the output label. Additionally, 56 data points were randomly selected as the training set, and the remaining 14 data points were used as the test set to evaluate and compare the predictive performance of the developed model.</p></list-item>
<list-item><label>(2)</label><p>The LSTM module processes input sequential data using a gating mechanism, effectively extracting the dynamic features of particle size and concentration variations over time during the coal dust explosion process. By storing and updating historical information through memory cells, LSTM captures long-term dependencies within the sequential data, ensuring that the hidden state at each time step not only retains current feature information but also incorporates historical information. These hidden states are then fed into the Multi-Head Attention module to further enhance the model&#x2019;s ability to focus on key features.</p></list-item>
<list-item><label>(3)</label><p>The Multi-Head Attention module, through its global attention mechanism, is capable of understanding the dependencies between different time steps throughout the entire explosion process. It utilizes multi-head parallel computation to obtain attention weights, thereby adaptively focusing on the important features in the input sequence. This module not only further enhances the LSTM&#x2019;s ability to handle long sequence data but also improves the model&#x2019;s understanding of the complex nonlinear relationships in the explosion process by capturing the global dependencies among input features, thereby enhancing the predictive performance.</p></list-item>
<list-item><label>(4)</label><p>During the model training and optimization process, the SSA algorithm improves the training performance by adjusting hyperparameters. Specifically, SSA uses the model&#x2019;s mean squared error (MSE) as the fitness value to evaluate the optimization effect, ensuring that the model obtains the best hyperparameters and achieves optimal performance during training.</p></list-item>
<list-item><label>(5)</label><p>To validate the accuracy and applicability of the SSA-LSTM-Multi-Head Attention model, the prediction results were compared with those of existing models, including PSO-SVM, LSTM, SVM, RF, and ANN, using the test set. The predictive performance of each model was thoroughly evaluated.</p></list-item>
</list></p>
<fig id="fig-5">
<label>Figure 5</label>
<caption>
<title>SSA-LSTM-multi-head attention prediction model architecture</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-5.tif"/>
</fig>
</sec>
<sec id="s3_5">
<label>3.5</label>
<title>Model Performance Evaluation Metrics</title>
<p>In this study, four evaluation metrics were used to assess the prediction performance of each model for coal dust maximum explosion pressure on the test set:</p>
<p>Root mean square error (RMSE): The smaller the value, the less the divergence between results predicted by the model and the real value, and the better the forecast is [<xref ref-type="bibr" rid="ref-28">28</xref>]. The expression is shown in <xref ref-type="disp-formula" rid="eqn-17">Eq. (17)</xref>.
<disp-formula id="eqn-17"><label>(17)</label><mml:math id="mml-eqn-17" display="block"><mml:mrow><mml:mtext>RMSE</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:msqrt><mml:mfrac><mml:mn>1</mml:mn><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mfrac><mml:munderover><mml:mo>&#x2211;</mml:mo><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:munderover><mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mo stretchy="false">&#x005E;</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2212;</mml:mo><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:msqrt></mml:math></disp-formula></p><p>Mean absolute error (MAE): It represents the mean absolute error between the predicted values and the actual values. The smaller this value, the smaller the deviation between the predicted and actual values, indicating higher prediction accuracy of the model [<xref ref-type="bibr" rid="ref-29">29</xref>]. The expression is shown in <xref ref-type="disp-formula" rid="eqn-18">Eq. (18)</xref>.
<disp-formula id="eqn-18"><label>(18)</label><mml:math id="mml-eqn-18" display="block"><mml:mrow><mml:mtext>MAE</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mfrac><mml:munderover><mml:mo>&#x2211;</mml:mo><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:munderover><mml:mrow><mml:mo>|</mml:mo><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mo stretchy="false">&#x005E;</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2212;</mml:mo><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>|</mml:mo></mml:mrow></mml:math></disp-formula></p><p>Mean absolute percentage error (MAPE): It measures the relative error between the predicted values and the actual values by calculating the percentage of the prediction error relative to the actual value [<xref ref-type="bibr" rid="ref-30">30</xref>]. The expression is shown in <xref ref-type="disp-formula" rid="eqn-19">Eq. (19)</xref>.
<disp-formula id="eqn-19"><label>(19)</label><mml:math id="mml-eqn-19" display="block"><mml:mrow><mml:mtext>MAPE</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mfrac><mml:munderover><mml:mo>&#x2211;</mml:mo><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:munderover><mml:mfrac><mml:mrow><mml:mo>|</mml:mo><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mo stretchy="false">&#x005E;</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2212;</mml:mo><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>|</mml:mo></mml:mrow><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:mfrac></mml:math></disp-formula></p><p>Coefficient of determination (R<sup>2</sup>): The value ranges from 0 to 1 and is used to interpret the degree of fit between the model&#x2019;s predictions and the actual values [<xref ref-type="bibr" rid="ref-31">31</xref>]. The expression is shown in <xref ref-type="disp-formula" rid="eqn-20">Eq. (20)</xref>.
<disp-formula id="eqn-20"><label>(20)</label><mml:math id="mml-eqn-20" display="block"><mml:msup><mml:mrow><mml:mtext>R</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mo>&#x2212;</mml:mo><mml:mfrac><mml:mrow><mml:munderover><mml:mo movablelimits="false">&#x2211;</mml:mo><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:munderover><mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mo stretchy="false">&#x005E;</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2212;</mml:mo><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mrow><mml:munderover><mml:mo movablelimits="false">&#x2211;</mml:mo><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:munderover><mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2212;</mml:mo><mml:mover><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mo accent="false">&#x00AF;</mml:mo></mml:mover><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:mfrac></mml:math></disp-formula>where, <inline-formula id="ieqn-100"><mml:math id="mml-ieqn-100"><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:math></inline-formula> represents the number of samples, <inline-formula id="ieqn-101"><mml:math id="mml-ieqn-101"><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> is the actual value of the <inline-formula id="ieqn-102"><mml:math id="mml-ieqn-102"><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:math></inline-formula>-th sample, <inline-formula id="ieqn-103"><mml:math id="mml-ieqn-103"><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mo stretchy="false">&#x005E;</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> is the predicted value of the <inline-formula id="ieqn-104"><mml:math id="mml-ieqn-104"><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:math></inline-formula>-th sample, and <inline-formula id="ieqn-105"><mml:math id="mml-ieqn-105"><mml:mover><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mo accent="false">&#x00AF;</mml:mo></mml:mover></mml:math></inline-formula> is the mean of the actual values in the sample set.</p>
</sec>
</sec>
<sec id="s4">
<label>4</label>
<title>Results and Discussion</title>
<sec id="s4_1">
<label>4.1</label>
<title>Feature Correlation Analysis</title>
<p>The maximum explosion pressure (<inline-formula id="ieqn-106"><mml:math id="mml-ieqn-106"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>) of coal dust is influenced by multiple factors, and changes in these factors can trigger chain reactions in other conditions. Additionally, interactions exist among various factors in the experimental results. Therefore, analyzing the correlation between different particle size parameters, mass concentration, and <inline-formula id="ieqn-107"><mml:math id="mml-ieqn-107"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>, identifying key influencing factors, and eliminating redundant features can not only intuitively reflect the impact of different factors on the maximum explosion pressure but also effectively reduce model complexity, shorten training time, enhance generalization ability, and prevent overfitting. In this study, the Spearman correlation coefficient and random forest feature selection methods were employed to screen the most influential feature parameters from nine particle size parameters and coal dust concentration, aiming to analyze the influence patterns of key factors and optimize model performance.</p>
<p>Correlation coefficient is a statistical method used to measure the degree of relationship between two sets of variables. In practical applications, common correlation coefficients include Pearson, Spearman, and Kendall [<xref ref-type="bibr" rid="ref-32">32</xref>,<xref ref-type="bibr" rid="ref-33">33</xref>]. In this study, since the experimental parameters are continuous variables and have a nonlinear relationship with the maximum explosion pressure, the Spearman correlation coefficient is chosen for analysis.</p>
<p>The Spearman correlation coefficient evaluates the monotonic relationship between two variables through ranking, avoiding reliance on specific values. <xref ref-type="fig" rid="fig-6">Fig. 6</xref> presents the results of the Spearman correlation coefficient in the form of a heatmap, where darker colors indicate stronger correlations. The correlation coefficients of different parameters with <inline-formula id="ieqn-108"><mml:math id="mml-ieqn-108"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> are calculated as shown in <xref ref-type="disp-formula" rid="eqn-21">Eqs. (21)</xref> and <xref ref-type="disp-formula" rid="eqn-22">(22)</xref>:
<disp-formula id="eqn-21"><label>(21)</label><mml:math id="mml-eqn-21" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:munderover><mml:mo>&#x2211;</mml:mo><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow></mml:mrow></mml:munderover><mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>&#x2212;</mml:mo><mml:msub><mml:mrow><mml:mtext>P</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
<disp-formula id="eqn-22"><label>(22)</label><mml:math id="mml-eqn-22" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:mrow><mml:mi mathvariant="normal">&#x03C1;</mml:mi></mml:mrow><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mo>&#x2212;</mml:mo><mml:mfrac><mml:mrow><mml:mn>6</mml:mn><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:msup><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:mfrac></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>where, <inline-formula id="ieqn-109"><mml:math id="mml-ieqn-109"><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow></mml:math></inline-formula> represents the number of samples, <inline-formula id="ieqn-110"><mml:math id="mml-ieqn-110"><mml:msubsup><mml:mrow><mml:mtext>X</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:mrow></mml:msubsup></mml:math></inline-formula> denotes the rank of the <inline-formula id="ieqn-111"><mml:math id="mml-ieqn-111"><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:math></inline-formula>-th feature in the original sample <inline-formula id="ieqn-112"><mml:math id="mml-ieqn-112"><mml:msub><mml:mrow><mml:mtext>x</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> after sorting, <inline-formula id="ieqn-113"><mml:math id="mml-ieqn-113"><mml:msub><mml:mrow><mml:mtext>P</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> represents the rank of the true value <inline-formula id="ieqn-114"><mml:math id="mml-ieqn-114"><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> of the <inline-formula id="ieqn-115"><mml:math id="mml-ieqn-115"><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:math></inline-formula>-th sample after sorting, and <inline-formula id="ieqn-116"><mml:math id="mml-ieqn-116"><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow></mml:math></inline-formula> is the sum of squared differences after ranking. <inline-formula id="ieqn-117"><mml:math id="mml-ieqn-117"><mml:mrow><mml:mi mathvariant="normal">&#x03C1;</mml:mi></mml:mrow></mml:math></inline-formula> represents the Spearman correlation coefficient, with a range of [&#x2212;1, 1]. A value of 1 indicates a perfect positive correlation, &#x2212;1 indicates a perfect negative correlation, and 0 indicates no monotonic relationship.</p>
<fig id="fig-6">
<label>Figure 6</label>
<caption>
<title>Heat map of Spearman correlation coefficient</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-6.tif"/>
</fig>
<p>The Spearman correlation coefficient can effectively determine the monotonic relationship between features and the target variable. However, due to the complex interactions between features and the intricate linear relationships between features and the target variable, Spearman analysis alone is insufficient to comprehensively assess the impact of features on the target variable. Random Forest is an ensemble learning method that constructs multiple decision trees and uses the voting results of these trees to obtain the final prediction value [<xref ref-type="bibr" rid="ref-34">34</xref>]. It not only excels in classification and regression tasks but has also been applied to feature selection by Genuer et al. [<xref ref-type="bibr" rid="ref-35">35</xref>] and Marie et al. [<xref ref-type="bibr" rid="ref-36">36</xref>]. Research has shown that random forests can effectively capture nonlinear relationships and interactions between features and the target variable, demonstrating excellent stability in feature selection. In this study, the impact of each parameter on the explosion pressure in coal dust explosion experiments is ranked based on the mean squared error change in the random forest. The parameter rankings after feature selection are illustrated in <xref ref-type="fig" rid="fig-7">Fig. 7</xref>. The random forest feature importance calculation process is as shown in <xref ref-type="disp-formula" rid="eqn-23">Eqs. (23)</xref>&#x2013;<xref ref-type="disp-formula" rid="eqn-25">(25)</xref>:<disp-formula id="eqn-23"><label>(23)</label><mml:math id="mml-eqn-23" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:msub><mml:mrow><mml:mtext>MSE</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>original</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow></mml:mfrac><mml:munderover><mml:mo>&#x2211;</mml:mo><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow></mml:mrow></mml:munderover><mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2212;</mml:mo><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mo stretchy="false">&#x005E;</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
<disp-formula id="eqn-24"><label>(24)</label><mml:math id="mml-eqn-24" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:msubsup><mml:mrow><mml:mtext>MSE</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>perturbed</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow></mml:mfrac><mml:munderover><mml:mo>&#x2211;</mml:mo><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow></mml:mrow></mml:munderover><mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>&#x2212;</mml:mo><mml:msubsup><mml:mrow><mml:mover><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mo stretchy="false">&#x005E;</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula></p>

<p><disp-formula id="eqn-25"><label>(25)</label><mml:math id="mml-eqn-25" display="block"><mml:mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"><mml:mtr><mml:mtd /><mml:mtd><mml:mrow><mml:mtext>Importance</mml:mtext></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mo>=</mml:mo><mml:msubsup><mml:mrow><mml:mtext>MSE</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>perturbed</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:mrow></mml:msubsup><mml:mo>&#x2212;</mml:mo><mml:msub><mml:mrow><mml:mtext>MSE</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>original</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>where, <inline-formula id="ieqn-118"><mml:math id="mml-ieqn-118"><mml:mrow><mml:mtext>n</mml:mtext></mml:mrow></mml:math></inline-formula> represents the number of samples, <inline-formula id="ieqn-119"><mml:math id="mml-ieqn-119"><mml:msub><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> denotes the true value of the <inline-formula id="ieqn-120"><mml:math id="mml-ieqn-120"><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:math></inline-formula>-th sample, <inline-formula id="ieqn-121"><mml:math id="mml-ieqn-121"><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mo stretchy="false">&#x005E;</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> represents the predicted value of the <inline-formula id="ieqn-122"><mml:math id="mml-ieqn-122"><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:math></inline-formula>-th sample, and <inline-formula id="ieqn-123"><mml:math id="mml-ieqn-123"><mml:msubsup><mml:mrow><mml:mover><mml:mrow><mml:mtext>p</mml:mtext></mml:mrow><mml:mo stretchy="false">&#x005E;</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:mrow></mml:msubsup></mml:math></inline-formula> denotes the predicted value of the <inline-formula id="ieqn-124"><mml:math id="mml-ieqn-124"><mml:mrow><mml:mtext>i</mml:mtext></mml:mrow></mml:math></inline-formula>-th sample after perturbing feature <inline-formula id="ieqn-125"><mml:math id="mml-ieqn-125"><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:math></inline-formula>. <inline-formula id="ieqn-126"><mml:math id="mml-ieqn-126"><mml:msub><mml:mrow><mml:mtext>MSE</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>original</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> is the mean squared error of the original data, <inline-formula id="ieqn-127"><mml:math id="mml-ieqn-127"><mml:msubsup><mml:mrow><mml:mtext>MSE</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>perturbed</mml:mtext></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:mrow></mml:msubsup></mml:math></inline-formula> is the mean squared error after perturbing feature <inline-formula id="ieqn-128"><mml:math id="mml-ieqn-128"><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:math></inline-formula>, and <inline-formula id="ieqn-129"><mml:math id="mml-ieqn-129"><mml:mrow><mml:mtext>Importance</mml:mtext></mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow><mml:mo stretchy="false">)</mml:mo></mml:math></inline-formula> represents the importance coefficient of feature <inline-formula id="ieqn-130"><mml:math id="mml-ieqn-130"><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:math></inline-formula>.</p>
<fig id="fig-7">
<label>Figure 7</label>
<caption>
<title>Random forest feature selection results</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-7.tif"/>
</fig>
<p>The relationship between the 10 parameters of coal dust and <inline-formula id="ieqn-131"><mml:math id="mml-ieqn-131"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>, as well as the rankings of feature importance, were determined by combining Spearman correlation analysis with the Random Forest feature selection method. <xref ref-type="table" rid="table-3">Table 3</xref> displays the importance and correlation coefficients for each parameter.</p>
<table-wrap id="table-3">
<label>Table 3</label>
<caption>
<title>Feature importance coefficients and Spearman correlation coefficients with <italic>t</italic>-test <italic>p</italic>-values</title>
</caption>
<table>
<colgroup>
<col align="center"/>
<col align="center"/>
<col align="center"/>
<col align="center"/>
</colgroup>
<thead>
<tr>
<th>Coal dust sample parameters</th>
<th colspan="3"><inline-formula id="ieqn-132"><mml:math id="mml-ieqn-132"><mml:msub><mml:mi mathvariant="bold-italic">P</mml:mi><mml:mrow><mml:mrow><mml:mtext mathvariant="bold">M</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula></th>
</tr>
<tr>
<th></th>
<th align="center">Random forest importance coefficients</th>
<th align="center">Spearman correlation coefficients</th>
<th align="center"><italic>p</italic> values of the <italic>t</italic>-test</th>
</tr>
</thead>
<tbody>
<tr>
<td><inline-formula id="ieqn-133"><mml:math id="mml-ieqn-133"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>10</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula></td>
<td>0.098</td>
<td>&#x2212;0.875</td>
<td>0.000</td>
</tr>
<tr>
<td><inline-formula id="ieqn-134"><mml:math id="mml-ieqn-134"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>20</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula></td>
<td>0.100</td>
<td>&#x2212;0.875</td>
<td>0.000</td>
</tr>
<tr>
<td><inline-formula id="ieqn-135"><mml:math id="mml-ieqn-135"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>30</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula></td>
<td>0.088</td>
<td>&#x2212;0.858</td>
<td>0.000</td>
</tr>
<tr>
<td><inline-formula id="ieqn-136"><mml:math id="mml-ieqn-136"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>40</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula></td>
<td>0.093</td>
<td>&#x2212;0.875</td>
<td>0.000</td>
</tr>
<tr>
<td><inline-formula id="ieqn-137"><mml:math id="mml-ieqn-137"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula></td>
<td>0.096</td>
<td>&#x2212;0.875</td>
<td>0.000</td>
</tr>
<tr>
<td><inline-formula id="ieqn-138"><mml:math id="mml-ieqn-138"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>60</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula></td>
<td>0.084</td>
<td>&#x2212;0.858</td>
<td>0.000</td>
</tr>
<tr>
<td><inline-formula id="ieqn-139"><mml:math id="mml-ieqn-139"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>70</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula></td>
<td>0.069</td>
<td>&#x2212;0.858</td>
<td>0.000</td>
</tr>
<tr>
<td><inline-formula id="ieqn-140"><mml:math id="mml-ieqn-140"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>80</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula></td>
<td>0.077</td>
<td>&#x2212;0.796</td>
<td>0.000</td>
</tr>
<tr>
<td><inline-formula id="ieqn-141"><mml:math id="mml-ieqn-141"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>90</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula></td>
<td>0.069</td>
<td>&#x2212;0.825</td>
<td>0.000</td>
</tr>
<tr>
<td><inline-formula id="ieqn-142"><mml:math id="mml-ieqn-142"><mml:msub><mml:mrow><mml:mtext>C</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext>dust</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula></td>
<td>0.223</td>
<td>0.164</td>
<td>&#x2013;</td>
</tr>
</tbody>
</table>
</table-wrap>
<p>In dust explosion research, the median particle size (<inline-formula id="ieqn-143"><mml:math id="mml-ieqn-143"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>) is commonly used to represent the average particle size of dust samples. However, Castellanos et al. [<xref ref-type="bibr" rid="ref-37">37</xref>] proposed that using <inline-formula id="ieqn-144"><mml:math id="mml-ieqn-144"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> alone may not accurately describe the impact of particle size on explosion severity. This is further confirmed by the Spearman correlation analysis shown in <xref ref-type="fig" rid="fig-6">Fig. 6</xref>. Overall, all particle size parameters of coal dust exhibit a negative correlation with <inline-formula id="ieqn-145"><mml:math id="mml-ieqn-145"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>, indicating that <inline-formula id="ieqn-146"><mml:math id="mml-ieqn-146"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> decreases as particle size increases. In contrast, the monotonic correlation between dust mass concentration and <inline-formula id="ieqn-147"><mml:math id="mml-ieqn-147"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> is relatively weak. Among the nine particle size percentile parameters, the particle size components at the 10th, 20th, 40th, and 50th percentiles exhibit the strongest monotonic correlation with the maximum explosion pressure, followed by the 30th percentile. This indicates that, in addition to <inline-formula id="ieqn-148"><mml:math id="mml-ieqn-148"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, <inline-formula id="ieqn-149"><mml:math id="mml-ieqn-149"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>10</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, <inline-formula id="ieqn-150"><mml:math id="mml-ieqn-150"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>20</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, and <inline-formula id="ieqn-151"><mml:math id="mml-ieqn-151"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>40</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> are also suitable parameters for characterizing the influence of coal dust particle size on explosion pressure. Therefore, relying solely on the distribution of the <inline-formula id="ieqn-152"><mml:math id="mml-ieqn-152"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> parameter cannot accurately assess the impact of particle size on explosion pressure and may lead to the erroneous assumption that the hazard of smaller particle sizes applies to the entire dust cloud. This is because, during the reaction process, smaller particles are typically ignited first, acting as new ignition sources to form flame fronts that subsequently ignite surrounding coal dust particles, thereby promoting the progression of the explosion reaction. <xref ref-type="table" rid="table-3">Table 3</xref> presents the <italic>p</italic>-values of the particle size parameters after statistical significance testing. The results indicate that the Spearman correlation analysis between the independent variable (particle size) and the dependent variable (<inline-formula id="ieqn-153"><mml:math id="mml-ieqn-153"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>) is statistically reliable.</p>

<p>From the feature selection results in <xref ref-type="fig" rid="fig-7">Fig. 7</xref>, it is evident that the parameter with the greatest influence on the target variable <inline-formula id="ieqn-154"><mml:math id="mml-ieqn-154"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> is the mass concentration, with an importance coefficient of 0.223, followed by the particle size parameters. This phenomenon arises because, in the 20-L explosion tank experiment, although smaller particles have a larger specific surface area, which increases the contact area with oxygen and promotes the explosion reaction, as the dust concentration increases further, the oxygen content within the tank becomes insufficient to ensure the complete combustion of all coal dust particles, which becomes the primary factor limiting the explosion reaction. As a result, the mass concentration of coal dust has a more significant effect on explosion pressure than particle size. Among the particle size parameters, the top three with the greatest influence are <inline-formula id="ieqn-155"><mml:math id="mml-ieqn-155"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>10</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, <inline-formula id="ieqn-156"><mml:math id="mml-ieqn-156"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>20</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, and <inline-formula id="ieqn-157"><mml:math id="mml-ieqn-157"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>. This further indicates that in explosion experiments, smaller particle sizes are more likely to serve as ignition sources, igniting nearby particles, and therefore have a greater impact on <inline-formula id="ieqn-158"><mml:math id="mml-ieqn-158"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> compared to larger particle sizes.</p>
<p>Based on the above conclusions, this study will use mass concentration and the particle size percentages of <inline-formula id="ieqn-159"><mml:math id="mml-ieqn-159"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>10</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, <inline-formula id="ieqn-160"><mml:math id="mml-ieqn-160"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>20</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, and <inline-formula id="ieqn-161"><mml:math id="mml-ieqn-161"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> to analyze their influence on the maximum explosion pressure of coal dust. These five parameters will also be used as input features for the coal dust <inline-formula id="ieqn-162"><mml:math id="mml-ieqn-162"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> prediction model. The test set after feature selection is shown in <xref ref-type="table" rid="table-4">Table 4</xref>.</p>
<table-wrap id="table-4">
<label>Table 4</label>
<caption>
<title>Test dataset after feature selection</title>
</caption>
<table>
<colgroup>
<col/>
<col/>
<col/>
<col/>
<col/>
<col/>
<col/>
</colgroup>
<thead>
<tr>
<th rowspan="2">No.</th>
<th rowspan="2">Coal dust sample</th>
<th colspan="4">Input</th>
<th rowspan="2">Output</th>
</tr>
<tr>
<th><inline-formula id="ieqn-163"><mml:math id="mml-ieqn-163"><mml:msub><mml:mrow><mml:mtext mathvariant="bold">D</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext mathvariant="bold">10</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> (<bold>&#x03BC;</bold>m)</th>
<th><inline-formula id="ieqn-164"><mml:math id="mml-ieqn-164"><mml:msub><mml:mrow><mml:mtext mathvariant="bold">D</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext mathvariant="bold">20</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> (<bold>&#x03BC;</bold>m)</th>
<th><inline-formula id="ieqn-165"><mml:math id="mml-ieqn-165"><mml:msub><mml:mrow><mml:mtext mathvariant="bold">D</mml:mtext></mml:mrow><mml:mrow><mml:mrow><mml:mtext mathvariant="bold">50</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> (<bold>&#x03BC;</bold>m)</th>
<th>Concentration (g/m<sup>3</sup>)</th>
</tr>
</thead>
<tbody>
<tr>
<td>1</td>
<td>C3</td>
<td>4.29</td>
<td>9.29</td>
<td>33.49</td>
<td>125</td>
<td>0.526</td>
</tr>
<tr>
<td>2</td>
<td>C5</td>
<td>2.12</td>
<td>4.50</td>
<td>17.44</td>
<td>125</td>
<td>0.678</td>
</tr>
<tr>
<td>3</td>
<td>C2</td>
<td>4.62</td>
<td>11.13</td>
<td>40.34</td>
<td>250</td>
<td>0.568</td>
</tr>
<tr>
<td>4</td>
<td>C4</td>
<td>3.97</td>
<td>7.75</td>
<td>30.33</td>
<td>250</td>
<td>0.669</td>
</tr>
<tr>
<td>5</td>
<td>C1</td>
<td>6.78</td>
<td>15.99</td>
<td>44.59</td>
<td>375</td>
<td>0.583</td>
</tr>
<tr>
<td>6</td>
<td>C4</td>
<td>3.97</td>
<td>7.75</td>
<td>30.33</td>
<td>375</td>
<td>0.679</td>
</tr>
<tr>
<td>7</td>
<td>C1</td>
<td>6.78</td>
<td>15.99</td>
<td>44.59</td>
<td>500</td>
<td>0.617</td>
</tr>
<tr>
<td>8</td>
<td>C5</td>
<td>2.12</td>
<td>4.50</td>
<td>17.44</td>
<td>500</td>
<td>0.691</td>
</tr>
<tr>
<td>9</td>
<td>C1</td>
<td>6.78</td>
<td>15.99</td>
<td>44.59</td>
<td>625</td>
<td>0.675</td>
</tr>
<tr>
<td>10</td>
<td>C4</td>
<td>3.97</td>
<td>7.75</td>
<td>30.33</td>
<td>750</td>
<td>0.702</td>
</tr>
<tr>
<td>11</td>
<td>C1</td>
<td>6.78</td>
<td>15.99</td>
<td>44.59</td>
<td>875</td>
<td>0.657</td>
</tr>
<tr>
<td>12</td>
<td>C6</td>
<td>1.74</td>
<td>3.75</td>
<td>11.47</td>
<td>1000</td>
<td>0.717</td>
</tr>
<tr>
<td>13</td>
<td>C2</td>
<td>4.62</td>
<td>11.13</td>
<td>40.34</td>
<td>1125</td>
<td>0.647</td>
</tr>
<tr>
<td>14</td>
<td>C6</td>
<td>1.74</td>
<td>3.75</td>
<td>11.47</td>
<td>1250</td>
<td>0.695</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4_2">
<label>4.2</label>
<title>Impact of Coal Dust Concentration on P<sub>m</sub></title>
<p>In this study, the influence of mass concentrations ranging from 125.0 g/m<sup>3</sup> to 1250.0 g/m<sup>3</sup> on the maximum explosion pressure (<inline-formula id="ieqn-166"><mml:math id="mml-ieqn-166"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>) of coal dust was investigated for seven different particle sizes, as shown in <xref ref-type="fig" rid="fig-8">Fig. 8</xref>. Overall, at a constant particle size, <inline-formula id="ieqn-167"><mml:math id="mml-ieqn-167"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> initially increases with rising mass concentration but begins to decline after reaching a certain threshold. For coal dust samples C1&#x2013;C3, <inline-formula id="ieqn-168"><mml:math id="mml-ieqn-168"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> shows a significant initial increase with concentration, peaking at 625.0 g/m<sup>3</sup>, after which it gradually decreases. Thus, 625.0 g/m<sup>3</sup> is identified as the optimal explosion concentration for samples C1&#x2013;C3. For samples C4&#x2013;C7, when the concentration exceeds 750.0 g/m<sup>3</sup>, <inline-formula id="ieqn-169"><mml:math id="mml-ieqn-169"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> exhibits a notable decreasing trend with further increases in concentration. This trend is primarily influenced by the dispersion characteristics of coal dust and the oxygen content within the explosion tank. When the coal dust concentration is below the optimal explosion concentration (625.0 g/m<sup>3</sup> and 750.0 g/m<sup>3</sup> in this study), the particles are dispersed under turbulent flow, resulting in relatively large inter-particle spacing. Although combustion occurs in an oxygen-rich environment, the large spacing slows down the propagation of the combustion wave, making flame propagation difficult and leading to a lower <inline-formula id="ieqn-170"><mml:math id="mml-ieqn-170"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>. As the concentration increases, the inter-particle spacing decreases while oxygen remains sufficient, promoting flame propagation and heat transfer, which raises <inline-formula id="ieqn-171"><mml:math id="mml-ieqn-171"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> to its peak. However, when the concentration exceeds the optimal level, the particle density becomes excessively high. While heat transfer between particles is further enhanced, the limited oxygen supply in the tank becomes insufficient to support the complete combustion of all coal dust particles. Consequently, unburned particles are generated, which hinder flame propagation and absorb heat, ultimately causing <inline-formula id="ieqn-172"><mml:math id="mml-ieqn-172"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> to decline.</p>
<fig id="fig-8">
<label>Figure 8</label>
<caption>
<title>Impact of various concentrations of coal dust samples on <inline-formula id="ieqn-173"><mml:math id="mml-ieqn-173"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>: (<bold>a</bold>) The <inline-formula id="ieqn-174"><mml:math id="mml-ieqn-174"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> of coal dust samples C1&#x2013;C3 at different concentrations; (<bold>b</bold>) The <inline-formula id="ieqn-175"><mml:math id="mml-ieqn-175"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> of coal dust samples C4&#x2013;C7 at different concentrations</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-8.tif"/>
</fig>
<p>Additionally, as the particle size of coal dust decreases, the specific surface area increases, providing a larger contact area for oxygen and particles, accelerating the combustion rate, and releasing more energy per unit time, thereby intensifying the explosion reaction. Therefore, under conditions of sufficient oxygen, smaller coal dust particles produce higher peak <inline-formula id="ieqn-176"><mml:math id="mml-ieqn-176"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> values compared to larger particles. However, due to the faster combustion rate of smaller particles and the limitation of oxygen content, smaller particles generate more unburned particles, which suppress the progression of the explosion reaction, causing a more pronounced decline in <inline-formula id="ieqn-177"><mml:math id="mml-ieqn-177"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> compared to larger particles.</p>
</sec>
<sec id="s4_3">
<label>4.3</label>
<title>Impact of Coal Dust Particle Size on P<sub><bold>m</bold></sub></title>
<p><xref ref-type="fig" rid="fig-9">Fig. 9</xref> presents the variation curves of <inline-formula id="ieqn-178"><mml:math id="mml-ieqn-178"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> for seven different coal dust samples under dust concentrations of 375, 500, 625, 750, 1000, and 1250 g/m<sup>3</sup>. As shown in the figure, at a constant concentration, <inline-formula id="ieqn-179"><mml:math id="mml-ieqn-179"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> exhibits an increasing trend with decreasing coal dust particle size. Among the seven coal dust samples, sample C7, which has the smallest mean particle size <inline-formula id="ieqn-180"><mml:math id="mml-ieqn-180"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, produces the highest <inline-formula id="ieqn-181"><mml:math id="mml-ieqn-181"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> values across all six concentrations, measuring 0.699, 0.714, 0.719, 0.724, 0.727, and 0.754 MPa, respectively. In contrast, samples C1, C2, and C3, which have larger mean particle sizes <inline-formula id="ieqn-182"><mml:math id="mml-ieqn-182"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, exhibit maximum explosion pressures below 0.7 MPa compared to the other four samples. This phenomenon can be attributed to the increase in the specific surface area as particle size decreases, which shortens the diffusion time of oxygen to the particle surface, enhances combustion efficiency, and releases more heat. Consequently, the explosion reaction becomes more intense, leading to a higher <inline-formula id="ieqn-183"><mml:math id="mml-ieqn-183"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> with decreasing particle size.</p>
<fig id="fig-9">
<label>Figure 9</label>
<caption>
<title>Impact of various particle sizes of coal dust samples on <inline-formula id="ieqn-184"><mml:math id="mml-ieqn-184"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula></title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-9.tif"/>
</fig>
<p>When the particle size of coal dust is sufficiently fine, the combustion has already developed sufficiently, and particle size is no longer a major limiting factor for the maximum explosion pressure. As shown in <xref ref-type="fig" rid="fig-9">Fig. 9</xref>, the explosion pressure of samples C1&#x2013;C3 shows a clear increasing trend, while the increasing trend of samples C4&#x2013;C7 begins to slow down. This is because the <inline-formula id="ieqn-185"><mml:math id="mml-ieqn-185"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>10</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> and <inline-formula id="ieqn-186"><mml:math id="mml-ieqn-186"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>20</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> values of samples C4&#x2013;C7 are smaller than those of C1&#x2013;C3, resulting in a larger specific surface area of the coal dust particles. The larger specific surface area makes the coal dust more easily ignited, quickly absorbing heat and increasing the combustion temperature, thereby promoting the explosion reaction. However, the larger specific surface area also accelerates the reaction between coal dust and oxygen, leading to a higher rate of oxygen consumption. As the particle size continues to decrease, oxygen becomes insufficient in the sealed explosion tank, limiting the explosion reaction and causing the increase in <inline-formula id="ieqn-187"><mml:math id="mml-ieqn-187"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> to gradually plateau.</p>
</sec>
<sec id="s4_4">
<label>4.4</label>
<title>Validation of the Prediction Results for P<sub><bold>m</bold></sub> of Coal Dust</title>
<p>The model in this study is developed using the TensorFlow framework and written in Python. During the model training phase, the optimization algorithm SSA searches for the model&#x2019;s hyperparameters globally by evaluating the MSE, continuing the process until no further improvement can be made. <xref ref-type="fig" rid="fig-10">Fig. 10</xref> illustrates the detailed process of SSA&#x2019;s iterative optimization and the resulting best hyperparameters of the model. The learning rate, number of iterations, number of LSTM hidden layer nodes (for both layers), and batch size found for the model were 0.0002, 204, 52, 81, and 14, respectively. <xref ref-type="fig" rid="fig-11">Fig. 11</xref> shows the MSE validation process of the LSTM-Multi-Head Attention model after optimization by SSA, including iterations on both the training and test datasets. At the 212th iteration, the MSE on the training and test sets reached their minimum values of 0.000936 and 0.00103, respectively, indicating that the model&#x2019;s training was optimal and training was stopped at this point.</p>
<fig id="fig-10">
<label>Figure 10</label>
<caption>
<title>Iteration results of SSA in searching for model hyperparameters</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-10.tif"/>
</fig><fig id="fig-11">
<label>Figure 11</label>
<caption>
<title>Model iteration and MSE validation</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-11.tif"/>
</fig>
<p>To validate the superiority of the SSA optimization algorithm and the Multi-Head Attention mechanism in improving the LSTM model&#x2019;s prediction of coal dust <inline-formula id="ieqn-188"><mml:math id="mml-ieqn-188"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> values, the prediction performance of commonly used models in fire and explosion prediction, including ANN, RF, SVM, PSO-SVM, and LSTM, was compared under the same experimental conditions. Additionally, the prediction performance of each model was quantified using four evaluation metrics. The calculated results of the model&#x2019;s performance metrics are shown in <xref ref-type="table" rid="table-5">Table 5</xref>. From <xref ref-type="table" rid="table-5">Table 5</xref>, it can be observed that the SSA-LSTM-Multi-Head Attention model performs slightly better than the PSO-SVM model, with the R<sup>2</sup> for the test and training sets increasing by 0.0049 and 0.0194, respectively. Compared to the LSTM, SVM, RF, and ANN models, the R<sup>2</sup> values for the test and training sets improved by 0.0049 and 0.0302, 0.0634 and 0.063, 0.0095 and 0.0802, and 0.0062 and 0.1307, respectively. Furthermore, the SSA-LSTM-Multi-Head Attention model exhibited the lowest RMSE, MAPE, and MAE values for both the test and training sets, with R<sup>2</sup> values of 0.9841 and 0.9743, respectively, which are closest to 1. The performance of each model in the training set, after rolling prediction cross-validation, is shown in <xref ref-type="fig" rid="fig-12">Figs. 12</xref> and <xref ref-type="fig" rid="fig-13">13</xref>. From the figures, it is clear that the SSA-LSTM-Multi-Head Attention model has the lowest MSE and achieves the best values across all four evaluation metrics, demonstrating superior generalization ability.</p>
<table-wrap id="table-5">
<label>Table 5</label>
<caption>
<title>Comparison of prediction evaluation metrics for <inline-formula id="ieqn-189"><mml:math id="mml-ieqn-189"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> of coal dust in different models</title>
</caption>
<table>
<colgroup>
<col/>
<col/>
<col/>
<col/>
<col/>
<col/>
<col/>
<col/>
<col/>
</colgroup>
<thead>
<tr>
<th align="center" rowspan="2">Model</th>
<th colspan="2">MAPE</th>
<th colspan="2">RMSE</th>
<th colspan="2">MAE</th>
<th colspan="2">R<sup>2</sup></th>
</tr>
<tr>
<th align="center">Training set</th>
<th>Test set</th>
<th align="center">Training set</th>
<th>Test set</th>
<th align="center">Training set</th>
<th>Test set</th>
<th>Training set</th>
<th>Test set</th>
</tr>
</thead>
<tbody>
<tr>
<td>ANN</td>
<td>0.0070</td>
<td>0.0226</td>
<td>0.0074</td>
<td>0.0215</td>
<td>0.0044</td>
<td>0.0135</td>
<td>0.9779</td>
<td>0.8436</td>
</tr>
<tr>
<td>RF</td>
<td>0.0073</td>
<td>0.0210</td>
<td>0.0079</td>
<td>0.0177</td>
<td>0.0044</td>
<td>0.0125</td>
<td>0.9746</td>
<td>0.8941</td>
</tr>
<tr>
<td>SVM</td>
<td>0.0186</td>
<td>0.0192</td>
<td>0.0140</td>
<td>0.0162</td>
<td>0.0124</td>
<td>0.0124</td>
<td>0.9207</td>
<td>0.9113</td>
</tr>
<tr>
<td>LSTM</td>
<td>0.0077</td>
<td>0.0153</td>
<td>0.0072</td>
<td>0.0128</td>
<td>0.0051</td>
<td>0.0096</td>
<td>0.9792</td>
<td>0.9441</td>
</tr>
<tr>
<td>PSO-SVM</td>
<td>0.0093</td>
<td>0.01423</td>
<td>0.0071</td>
<td>0.0115</td>
<td>0.0062</td>
<td>0.0088</td>
<td>0.9792</td>
<td>0.9549</td>
</tr>
<tr>
<td>SSA-LSTM-Multi-Head Attention</td>
<td>0.0074</td>
<td>0.0108</td>
<td>0.0030</td>
<td>0.0087</td>
<td>0.0049</td>
<td>0.0069</td>
<td>0.9841</td>
<td>0.9743</td>
</tr>
</tbody>
</table>
</table-wrap><fig id="fig-12">
<label>Figure 12</label>
<caption>
<title>MSE variation of each model in rolling prediction cross-validation</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-12.tif"/>
</fig><fig id="fig-13">
<label>Figure 13</label>
<caption>
<title>Results of four evaluation metrics for each model after cross-validation</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-13.tif"/>
</fig>
<p>The prediction results of all models on the test set are shown in <xref ref-type="fig" rid="fig-14">Fig. 14</xref>. From the figure, the coal dust maximum explosion pressure prediction models based on the RF and ANN algorithms exhibit good fitting performance on the training set, with predicted values closely matching the true values. However, these models are prone to overfitting. When predicting the test set, the prediction accuracy of these two models significantly decreases, and the degree of dispersion increases, leading to a decline in model robustness. In contrast, the SSA-LSTM-Multi-Head Attention, PSO-SVM, and LSTM prediction models show small deviations between predicted and true values on the training set, demonstrating strong generalization ability. Among these, the LSTM-Multi-Head Attention model significantly outperforms the other two models, with smaller errors between predicted and true values. For the test set predictions, all three models maintain relatively high accuracy; however, the LSTM prediction model without SSA optimization exhibits the poorest performance. This further proves that the introduction of the SSA optimization algorithm and the Multi-Head Attention module enhances the model&#x2019;s prediction performance. The SVM prediction model shows slightly larger deviations between predicted and true values on the training set, but its generalization ability on the test set is superior to that of the RF and ANN models. Comparing the MAPE, RMSE, and MAE values of different models, in the test set, the LSTM-Multi-Head Attention model reduces the MAPE by 0.0034, 0.0045, 0.0084, 0.0102, and 0.0118 compared to PSO-SVM, LSTM, SVM, RF, and ANN, respectively. The RMSE is reduced by 0.0028, 0.0041, 0.0075, 0.009, and 0.0128, while the MAE is reduced by 0.0019, 0.0027, 0.0055, 0.0056, and 0.0066.</p>
<fig id="fig-14">
<label>Figure 14</label>
<caption>
<title>Comparison of model prediction results in test set and training set: (<bold>a</bold>) SSA-LSTM-multi-head attention model coal dust <inline-formula id="ieqn-190"><mml:math id="mml-ieqn-190"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> prediction results; (<bold>b</bold>) PSO-SVM model coal dust <inline-formula id="ieqn-191"><mml:math id="mml-ieqn-191"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> prediction results; (<bold>c</bold>) LSTM model coal dust <inline-formula id="ieqn-192"><mml:math id="mml-ieqn-192"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> prediction results; (<bold>d</bold>) SVM model coal dust <inline-formula id="ieqn-193"><mml:math id="mml-ieqn-193"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> prediction results; (<bold>e</bold>) RF model coal dust <italic>P</italic><sub>m</sub> prediction results; (<bold>f</bold>) ANN model coal dust <inline-formula id="ieqn-194"><mml:math id="mml-ieqn-194"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> prediction results</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-14a.tif"/>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-14b.tif"/>
</fig>
<p>In summary, for the prediction of coal dust <inline-formula id="ieqn-195"><mml:math id="mml-ieqn-195"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>, compared to traditional prediction models, the introduction of the Multi-Head Attention mechanism into the LSTM model enhances prediction accuracy by leveraging the strengths of both modules in capturing temporal dependencies in sequence data and global dependencies among features. Additionally, the use of SSA to automatically search for the optimal hyperparameters of the model further improves its stability and generalization capability, making it suitable for predicting the maximum explosion pressure of coal dust.</p>
</sec>
<sec id="s4_5">
<label>4.5</label>
<title>Validation of the SSA-LSTM-Multi-Head Attention Model in Predicting the P<sub><bold>m</bold></sub> of Coal Dust</title>
<p>Based on the analysis of the above studies, compared to the currently available fire and explosion prediction models. The SSA-LSTM-Multi-Head Attention model constructed with coal dust particle size and concentration as the original dataset has the best prediction accuracy for the value of coal dust <inline-formula id="ieqn-196"><mml:math id="mml-ieqn-196"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>, and showed better generalization in the test set. In order to verify the applicability of the model proposed in this study in predicting the <inline-formula id="ieqn-197"><mml:math id="mml-ieqn-197"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> of coal dust, coal samples were selected in the &#x201C;2 Experimental method and materials&#x201D;, and the same equipment and experimental methods for coal dust <inline-formula id="ieqn-198"><mml:math id="mml-ieqn-198"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> experiments, and a new set of 10 data points was obtained. According to &#x201C;<xref ref-type="sec" rid="s3_4">Section 3.4</xref> SSA-LSTM-Multi-Head Attention prediction model construction&#x201D; combined with newly acquired experimental data, SSA-LSTM-Multi-Head Attention model is used to predict the <inline-formula id="ieqn-199"><mml:math id="mml-ieqn-199"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> of coal dust. The results are shown in <xref ref-type="fig" rid="fig-15">Fig. 15</xref>.</p>
<fig id="fig-15">
<label>Figure 15</label>
<caption>
<title>Prediction of <inline-formula id="ieqn-200"><mml:math id="mml-ieqn-200"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> of coal dust and error distribution by SSA-LSTM-multi-head attention model: (<bold>a</bold>) Prediction of <inline-formula id="ieqn-201"><mml:math id="mml-ieqn-201"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> of coal dust by SSA-LSTM-multi-head attention model; (<bold>b</bold>) Error distribution of SSA-LSTM-multi-head attention model in predicting the <inline-formula id="ieqn-202"><mml:math id="mml-ieqn-202"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> of coal dust</title>
</caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CMES_64179-fig-15.tif"/>
</fig>
<p>From the validation results, the SSA-LSTM-Multi-Head Attention model&#x2019;s predicted values generally show a distribution characteristic greater than the actual values. The average absolute error rate between the actual and predicted maximum explosion pressures of coal dust samples is 0.88%, with the differences in maximum and minimum explosion pressures being 0.0122 MPa and 0.001 MPa, respectively. The average absolute error is 0.0059 MPa. The results indicate that this model can accurately and reliably reflect the maximum explosion pressure generated during coal dust explosions, providing an effective reference for coal mine dust explosion risk assessment.</p>
</sec>
</sec>
<sec id="s5">
<label>5</label>
<title>Conclusions</title>
<p>The Spearman correlation coefficient indicates a positive correlation between coal dust particle size and the maximum explosion pressure. The random forest screening results further reveal that concentration has the greatest impact on <italic>P</italic><sub>m</sub>. By using mass concentration and particle sizes <inline-formula id="ieqn-203"><mml:math id="mml-ieqn-203"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>10</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>, <inline-formula id="ieqn-204"><mml:math id="mml-ieqn-204"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>20</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> and <inline-formula id="ieqn-205"><mml:math id="mml-ieqn-205"><mml:msub><mml:mrow><mml:mtext>D</mml:mtext></mml:mrow><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> as feature parameters for the coal dust maximum explosion pressure prediction model, the effects of mass concentration and particle size on <italic>P</italic><sub>m</sub> are analyzed to more accurately assess coal dust explosion pressure.</p>
<p>At the same particle size, <inline-formula id="ieqn-206"><mml:math id="mml-ieqn-206"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula> shows a trend of initially increasing and then decreasing as the mass concentration increases. Samples C1&#x2013;C3 reach a peak at a mass concentration of 625.0 g/m<sup>3</sup> and then gradually decrease, while samples C4&#x2013;C7 continuously decrease after the mass concentration exceeds 750.0 g/m<sup>3</sup>. This trend is influenced by the dispersion and flowability of the dust: at low concentrations, the particle spacing is large, hindering flame propagation, resulting in lower pressure; at high concentrations, flame propagation is improved, but oxygen deficiency limits the reaction, leading to a decrease in pressure. At the same time, when the mass concentration remains constant, a decrease in particle size leads to an increase in <inline-formula id="ieqn-207"><mml:math id="mml-ieqn-207"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>. Fine coal dust, with a larger specific surface area, accelerates oxygen diffusion and combustion reactions, thereby increasing pm. Although smaller particle sizes enhance oxygen contact, the larger specific surface area also increases oxygen consumption. In a closed explosion chamber, the oxygen content limits the further increase of <inline-formula id="ieqn-208"><mml:math id="mml-ieqn-208"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub><mml:mo>.</mml:mo></mml:math></inline-formula></p>
<p>Compared to the PSO-SVM, LSTM, SVM, RF, and ANN models, the SSA-LSTM-Multi-Head Attention model outperforms these models in predicting the maximum explosion pressure of coal dust, demonstrating higher prediction accuracy and generalization ability. Verified through the 20 L explosion tank experiment, the model&#x2019;s prediction results show an average absolute error rate of 0.88%, a maximum explosion pressure difference of 0.0122 MPa, a minimum pressure difference of 0.001 MPa, and an average absolute error of 0.0059 MPa. These results confirm that the model can effectively predict the maximum explosion pressure of coal dust, providing strong support for coal dust explosion prevention and risk assessment in coal mines.</p>
<p>In this study, owing to the inherent safety limitations of explosion experiments, we primarily focus on the influence of coal dust particle size and concentration on explosion pressure <inline-formula id="ieqn-209"><mml:math id="mml-ieqn-209"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>. However, other physicochemical properties of coal dust (e.g., volatile content, moisture content) and different experimental conditions (e.g., oxygen concentration, methane concentration) may also significantly affect <inline-formula id="ieqn-210"><mml:math id="mml-ieqn-210"><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mrow><mml:mtext>m</mml:mtext></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>. Comprehensive consideration of these factors could further optimize the model&#x2019;s predictive performance. The 70 datasets used in this study are relatively small for deep learning models. Data augmentation and synthetic data generation could be considered to expand the dataset, but it is crucial to ensure that the augmented data aligns with the dynamic principles of dust explosions.</p>
</sec>
</body>
<back>
<ack><p>The authors acknowledge the support from the Institute of Interdisciplinary Research on Intelligent Mines, Heilongjiang University of Science and Technology, Harbin, China; the School of Resources and Engineering, Heilongjiang University of Technology, Jixi, China; and Heilongjiang Longmei Jixi Mining Co., Ltd., Xinfa Coal Mine, Jixi, China.</p>
</ack>
<sec>
<title>Funding Statement</title>
<p>This research was funded by the Research on Intelligent Mining Geological Model and Ventilation Model for Extremely Thin Coal Seam in Heilongjiang Province, China (2021ZXJ02A03), the Demonstration of Intelligent Mining for Comprehensive Mining Face in Extremely Thin Coal Seam in Heilongjiang Province, China (2021ZXJ02A04), and the Natural Science Foundation of Heilongjiang Province, China (LH2024E112).</p>
</sec>
<sec>
<title>Author Contributions</title>
<p>The authors confirm contribution to the paper as follows: Conceptualization, Haitao Wang; methodology, Weihao Li; software, Weihao Li and Haitao Wang; validation, Weihao Li; formal analysis, Weihao Li; investigation, Haitao Wang; resources, Yongli Liu; data curation, Weihao Li, Haitao Wang and Taoren Du; writing&#x2014;original draft preparation, Weihao Li; writing&#x2014;review and editing, Weihao Li and Haitao Wang; visualization, Taoren Du; supervision, Yongli Liu; project administration, Yongli Liu; funding acquisition, Yongli Liu. All authors reviewed the results and approved the final version of the manuscript.</p>
</sec>
<sec sec-type="data-availability">
<title>Availability of Data and Materials</title>
<p>The data that support the findings of this study are available from the Corresponding Author, Weihao Li, upon reasonable request.</p>
</sec>
<sec>
<title>Ethics Approval</title>
<p>Not applicable.</p>
</sec>
<sec sec-type="COI-statement">
<title>Conflicts of Interest</title>
<p>The authors declare no conflicts of interest to report regarding the present study.</p>
</sec>
<ref-list content-type="authoryear">
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