Applying feature extraction of acoustic emission and machine learning for coal failure forecasting
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摘要: 同步采集了煤樣單軸壓縮破壞過程的聲發射全波形數據和應力數據,提取了聲發射梅爾倒譜系數作為樣本特征,定義煤樣當前受力與其峰值載荷的比值為煤樣的應力狀態并將其作為樣本標簽,利用機器學習方法構建了煤樣破壞狀態的預測模型。結果表明:梅爾倒譜系數可以很好地表征煤樣的破壞狀態,該參量在煤樣達到受力峰值80%后表現出明顯突增或突降或先增加然后突降的規律,機器學習能夠利用該樣本特征建立煤樣破壞狀態預測模型進而預測煤樣的危險狀態,利用五折交叉驗證方法評價模型的預測準確度達到88.61%,模型預測效果和穩定性良好;進一步討論了不同重要度的梅爾倒譜系數組合作為樣本特征對于模型預測效果的影響,發現樣本特征中含有重要度高的特征和關鍵特征是模型預測準確度高的關鍵。這可為進一步完善煤巖動力災害預測預警提供借鑒。Abstract: Recently, with increasing mining scale, intensity, and depth, the geological and mining conditions in coal mines are becoming more complicated; therefore, it has resulted in a more difficult situation of coal mine dynamic hazards, including rockburst, coal and gas outburst etc. Dynamic hazards are now posing a serious threat to the safety of coal mining. The precise forecasting of dynamic hazards is significant to their effective control. The acoustic emission (AE) monitoring technique is an effective geophysical monitoring and early warning method which can effectively reveal the characteristics and laws of coal and rock failure under loading. It has been successfully applied in the laboratory and engineering fields. To deeply analyze the characteristics of AE signals in the process of coal-rock damage and failure, thus, to help realize the precise monitoring and early warning of coal mine dynamic hazards, this study first conducted a uniaxial compression test on coal samples in the laboratory, and at the meantime, synchronously collected the full waveform data of AE and the loading data in the entire process of coal failure. Subsequently, using the feature extraction technique in the field of automatic speech recognition, this study extracted the Mel-frequency cepstral coefficient (MFCC) of AE and used it as the sample feature; the stress state of the coal sample was defined as the ratio of the current load the sample bore to its peak load and was employed as the sample label; a model for coal failure state forecasting was established by adopting machine learning methodology. Finally, the model’s forecasting accuracy was evaluated using the five-fold cross-validation method; the influence of different MFCC combinations as sample features on the forecasting accuracy of the model was discussed. The results show that MFCC can well characterize the failure state of coal samples. This parameter behaves in regular variation with increasing loading and shows the law of an obvious sudden increase or sudden decrease or increase followed by a sudden decrease when the loading exceeds 80% of the coal sample’s peak load. The established model can be well used to forecast coal failure state. The accuracy (ACC), true positive rate (TPR), true negative rate (TNR), and area under the curve (AUC) of the model forecasting reach 88.61%, 72.34%, 93.16%, and 0.93, respectively. Machine learning methodology can fully use MFCC features of AE and can identify essential sample features that are difficult to identify with the human eyes. Significant and key features included in the samples are the keys to the high forecasting accuracy of the model. TPR, TNR, and AUC of the model forecasting would be significantly influenced if crucial features were excluded from the samples. Adding features with low importance to the samples has little influence on the forecasting result of the model. This study’s results can provide a reference for further improving the prediction and early warning of coal and rock dynamic hazards.
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圖 4 4-1煤樣MFCC與應力隨時間的變化. (a) MFCC-1;(b) MFCC-2;(c) MFCC-3;(d) MFCC-4;(e) MFCC-5;(f) MFCC-6;(g) MFCC-7;(h) MFCC-8;(i) MFCC-9;(j) MFCC-10;(k) MFCC-11;(l) MFCC-12
Figure 4. Variation of MFCC and stress of coal sample No. 4-1 with increasing time: (a) MFCC-1; (b) MFCC-2; (c) MFCC-3; (d) MFCC-4; (e) MFCC-5; (f) MFCC-6; (g) MFCC-7; (h) MFCC-8; (i) MFCC-9; (j) MFCC-10; (k) MFCC-11; (l) MFCC-12
圖 5 不同煤樣在不同加載速率下MFCC-1的變化. (a) No. 1-2, 3 μm·s–1;(b) No. 2-1, 7 μm·s–1;(c) No. 3-1, 11 μm·s–1;(d) No. 4-2, 15 μm·s–1;(e) No. 5-1, 20 μm·s–1
Figure 5. Variation of MFCC-1 of different coal samples under different loading rates: (a) No. 1-2, 3 μm·s–1; (b) No. 2-1, 7 μm·s–1; (c) No. 3-1, 11 μm·s–1; (d) No. 4-2, 15 μm·s–1; (e) No. 5-1, 20 μm·s–1
圖 6 不同煤樣在不同加載速率下MFCC-2的變化. (a) No. 1-2, 3 μm·s–1;(b) No. 2-1, 7 μm·s–1;(c) No. 3-1, 11 μm·s–1;(d) No. 4-2, 15 μm·s–1;(e) No. 5-1, 20 μm·s–1
Figure 6. Variation of MFCC-2 of different coal samples under different loading rates: (a) No. 1-2, 3 μm·s–1; (b) No. 2-1, 7 μm·s–1; (c) No. 3-1, 11 μm·s–1; (d) No. 4-2, 15 μm·s–1; (e) No. 5-1, 20 μm·s–1
表 1 Light GBM算法參數設置
Table 1. Parameter setting of Light GBM algorithm
Parameter Value Role Learning_rate 0.1 Control model training speed Objective Binary Assigned learning tasks n_estimators 20 Control the number of training sessions Early_stopping_rounds 50 Control the maximum number of training sessions Max_depth 3 Set the depth of the decision tree Num_leaves 8 Adjust the complexity of the decision tree Subsample 0.8 Control the sampling ratio per tree Colsample_bytree 0.8 Control the proportion of features used per tree Min_child_weight 2 Control the weights of the minimum leaf nodes Reg_alpha 0 Prevent overfitting Reg_lambda 1 Prevent overfitting Verbose 100 Output model results 表 2 煤樣聲發射樣本統計
Table 2. Statistics of acoustic emission samples of each coal sample
Coal samples Number of acoustic emission fragments Safety sample Dangerous sample Total number of samples 1-1 11032 3365 14397 1-2 11762 2066 13828 2-1 4173 1211 5394 2-2 4013 725 4738 3-1 2728 813 3541 3-2 2014 602 2616 4-1 1362 687 2049 4-2 2178 486 2664 5-1 1347 344 1691 5-2 1277 305 1582 Total 41886 10604 52490 表 4 煤樣加載實驗方案
Table 4. Coal sample loading scheme
Coal samples Sample size Sample number Loading rate/(μm·s?1) Kuangou Mine ?50 mm×100 mm 1-1,1-2 3 2-1,2-2 7 3-1,3-2 11 4-1,4-2 15 5-1,5-2 20 表 5 五折交叉驗證方法分組情況
Table 5. Grouping of the five-fold cross validation
Fold number Training set Validation set Fold-1 1-2, 2-1, 2-2, 3-1, 4-1, 4-2, 5-1, 5-2 1-1, 3-2 Fold-2 1-1, 2-1, 2-2, 3-1, 3-2, 4-2, 5-1, 5-2 1-2, 4-1 Fold-3 1-1, 1-2, 2-2, 3-1, 3-2, 4-1, 5-1, 5-2 2-1, 4-2 Fold-4 1-1, 1-2, 2-1, 3-1, 3-2, 4-1, 4-2, 5-2 2-2, 5-1 Fold-5 1-1, 1-2, 2-1, 2-2, 3-2, 4-1, 4-2, 5-1 3-1, 5-2 表 6 基于五折交叉驗證的模型ACC、TPR、TNR和AUC結果
Table 6. Results showing the ACC, TPR, TNR, and AUC of the forecasting based on five-fold cross validation
Fold number TN FP FN TP ACC/% TPR/% TNR/% AUC Fold-1 10213 223 1193 1980 89.60 62.40 97.86 0.97 Fold-2 10224 273 198 2006 96.29 91.02 97.40 0.99 Fold-3 4777 303 484 883 87.79 64.59 94.04 0.90 Fold-4 3668 354 499 621 83.41 55.45 91.20 0.88 Fold-5 2732 471 105 789 85.94 88.26 85.30 0.92 Average value 88.61 72.34 93.16 0.93 Note: TN is true negative and means the number of negative predicted as negative classes; TP is true positive and means the number of positive predicted as positive classes; FN is false negative and means the number of positive predicted as negative classes; FP is false positive and means the number of negative predicted as positive classes; ACC is the accuracy; TPR is the true positive rate; TNR is the true negative rate; AUC is the area under the ROC curve. 表 7 23種MFCC特征組合
Table 7. 23 MFCC feature combinations
Serial number MFCC combination Serial number MFCC combination 1 [2] 13 [12,3,1,10,8,11,4,7,5,9,6] 2 [2,12] 14 [3,1,10,8,11,4,7,5,9,6] 3 [2,12,3] 15 [1,10,8,11,4,7,5,9,6] 4 [2,12,3,1] 16 [10,8,11,4,7,5,9,6] 5 [2,12,3,1,10] 17 [8,11,4,7,5,9,6] 6 [2,12,3,1,10,8] 18 [11,4,7,5,9,6] 7 [2,12,3,1,10,8,11] 19 [4,7,5,9,6] 8 [2,12,3,1,10,8,11,4] 20 [7,5,9,6] 9 [2,12,3,1,10,8,11,4,7] 21 [5,9,6] 10 [2,12,3,1,10,8,11,4,7,5] 22 [9,6] 11 [2,12,3,1,10,8,11,4,7,5,9] 23 [6] 12 [2,12,3,1,10,8,11,4,7,5,9,6] www.77susu.com -
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