Blasting wave pattern recognition based on Hilbert-Huang transform

Li, Xuelong,Wang, Enyuan,Li, Zhonghui,Bie, Xiaofei,Chen, Liang,Feng, Junjun,Li, Nan Techno-Press 2016 Geomechanics & engineering Vol.11 No.5

Rockburst is becoming more serious in Chinese coal mine. One of the effective methods to control rockburst is blasting. In the paper, we monitored and analyzed the blasting waves at different blast center distances by the Hilbert-Huang transform (HHT) in a coal mine. Results show that with the increase of blast center distance, the main frequency and amplitude of blasting waves show the decreasing trend. The attenuation of blasting waves is slower in the near blast field (10-75 m), compared with the far blast field (75-230 m). Besides, the frequency superposition phenomenon aggravates in the far field. A majority of the blasting waves energy at different blast center distances is concentrated around the IMF components 1-3. The instantaneous energy peak shows attenuation trend with the blast center distance increase, there are two obvious energy peaks in the near blast field (10-75 m), the energy spectrum appears "fat", and the total energy is greater. By contrast, there is only an energy peak in the far blast field, the energy spectrum is "thin", and the total energy is lesser. The HHT three dimensional spectrum shows that the wave energy accumulates in the time and frequency with the increasing of blast center distance.

Cerebral Arterial Stiffness as Measured Based on the Pulse Wave Velocity Is Associated With Intracranial Artery Calcification in Patients With Acute Stroke

Xuelong Li,Heng Du,Jia Li,Xianliang Li,Qingchun Gao,Xiangyan Chen 대한신경과학회 2023 Journal of Clinical Neurology Vol.19 No.4

Background and Purpose By measuring a newly defined parameter, the carotid–cerebral pulse wave velocity (ccPWV), this study aimed to determine the association of intracranial artery calcification (IAC) with arterial stiffness as reflected by the pulse wave velocity between the carotid and middle cerebral arteries using transcranial Doppler sonography in patients with acute stroke. Methods We recruited 146 patients with ischemic stroke from our stroke center. Computed tomography of the head was used to assess the presence and severity of IAC. Arterial stiffness was evaluated using ccPWV. Data are presented as quartiles of ccPWV. A multivariable logistic regression model was used to assess the independent relationship between ccPWV and IAC. Results The IAC prevalence increased with the ccPWV quartile, being 54%, 76%, 83%, and 89% for quartiles 1, 2, 3, and 4, respectively (p<0.001) as did IAC scores, with median [interquartile range] values of 0 [0–2], 3 [2–4], 4 [2–5], and 5 [4–6], respectively (p<0.001). After additionally adjusting for age and hypertension, a significant correlation was only found between quartiles 3 and 4 of ccPWV and IAC scores. The odds ratio (95% confidence interval) for the IAC scores was 1.78 (1.28–2.50) (p=0.001) in quartile 4 of ccPWV and 1.45 (1.07–1.95) (p=0.015) in quartile 3 compared with quartile 1. Conclusions We found that in patients with acute ischemic stroke, ccPWV was positively related to the degree of IAC. Future longitudinal cohort studies may help to identify the potential role of IAC in the progression of cerebral arterial stiffness.

Finite Element Simulation and Theoretical Analysis of Induction Fusing of Coating

Jianhua Liu,Xuelong Hao,Songmei Li,Liang Xu 한국표면공학회 2008 한국표면공학회 학술발표회 초록집 Vol.2008 No.-

Numerical investigation on the recirculation in annular jet pumps

Longzhou Xiao,Xinping LONG,Xiaohong Li,Qinglong Zeng,Xuelong Yang 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.6

The flow within the annular jet pump (AJP), in some degree, resembles the annular wall jet developing in a pipe with great axial pressure gradient. In some working conditions, there exists the backflow near the centerline. However this differs from the case in a center jet pump (CJP) that the recirculation emerges near the inner wall of the throat. The recirculation in AJP affects a lot to its performance, especially when AJP is utilized to convey something alive, such as fish. This paper aims to numerically study the impact of two parameters, the flow ratio M and the area ratio A, on the location, size and formation of the recirculation in AJP. After being validated by the experimental results, the RNG k-ε turbulent model was adopted. It is found that: (1) As M increases, the width and height of the recirculation in AJP decreases, and the separation point of the recirculation shifts gradually far away from the nozzle exit while the reattachment point slightly moves; (2) As A becomes larger, the width and height of the recirculation enlarged, with M keeping constant; (3) For AJP with constant A, the recirculation emerges when M declines to a critical value, and the value varies linearly with A; (4) The Craya-Curtet number Ct and the momentum ratio J, which take A and M into whole consideration, are also feasible in describing the disappearance of the recirculation. However the critical value of Ct and J are different from that discovered in CJP. The critical Ct increases with decreasing A and the critical momentum ratio Jc experiences a linear relationship with A.

Numerical simulation on gas continuous emission from face during roadway excavation

Chen, Liang,Wang, Enyuan,Feng, Junjun,Li, Xuelong,Kong, Xiangguo,Zhang, Zhibo Techno-Press 2016 Geomechanics & engineering Vol.10 No.3

With the mining depth continuously increasing, gas emission behaviors become more and more complex. Gas emission is an important basis for choosing the method of gas drainage, gas controlling. Thus, the accurate prediction of gas emission is of great significance for coal mine. In this work, based on the sources of gas emission from the heading faces and the fluid-solid coupling process, we established a gas continuous dynamic emission model, numerically simulated and applied it to the engineering. The result was roughly consistent with the actual situation and shows the model is correct. We proposed the measures of reducing the excavation distance and borehole gas drainage based on the model. The measures were applied and the result shows the overproof problem of gas emission disappears. The model considered the influence factors of gas emission wholly, and has a wide applicability, promotional value. The research is of great significance for the controlling of gas disaster, gas drainage and pre-warning coal and gas outbursts based on gas emission anomaly at the heading face.

Hazard prediction of coal and gas outburst based on fisher discriminant analysis

Chen, Liang,Wang, Enyuan,Feng, Junjun,Wang, Xiaoran,Li, Xuelong Techno-Press 2017 Geomechanics & engineering Vol.13 No.5

Coal and gas outburst is a serious dynamic disaster that occurs during coal mining and threatens the lives of coal miners. Currently, coal and gas outburst is commonly predicted using single indicator and its critical value. However, single indicator is unable to fully reflect all of the factors impacting outburst risk and has poor prediction accuracy. Therefore, a more accurate prediction method is necessary. In this work, we first analyzed on-site impacting factors and precursors of coal and gas outburst; then, we constructed a Fisher discriminant analysis (FDA) index system using the gas adsorption index of drilling cutting ${\Delta}h_2$, the drilling cutting weight S, the initial velocity of gas emission from borehole q, the thickness of soft coal h, and the maximum ratio of post-blasting gas emission peak to pre-blasting gas emission $B_{max}$; finally, we studied an FDA-based multiple indicators discriminant model of coal and gas outburst, and applied the discriminant model to predict coal and gas outburst. The results showed that the discriminant model has 100% prediction accuracy, even when some conventional indexes are lower than the warning criteria. The FDA method has a broad application prospects in coal and gas outburst prediction.

Investigation on energy dissipation and its mechanism of coal under dynamic loads

Feng, Junjun,Wang, Enyuan,Shen, Rongxi,Chen, Liang,Li, Xuelong,Xu, Zhaoyong Techno-Press 2016 Geomechanics & engineering Vol.11 No.5

The energy dissipation of coal under dynamic loads is a major issue in geomechanics and arising extensive concerns recently. In this study, dynamic loading tests of coal were conducted using a split Hopkinson pressure bar (SHPB) system, the characteristics of dynamic behavior and energy dissipation of coal were analyzed, and the mechanism of energy dissipation was discussed based on the fracture processes of coal under dynamic loads. Experimental results indicate that the energy dissipation of coal under dynamic loads has a positive linear correlation with both incident energy and dynamic compressive strength, and the correlation coefficients between incident energy, dynamic compressive strength and the energy dissipation rate are 0.74 and 0.98, respectively. Theoretical analysis demonstrates that higher level of stress leads to greater energy released during unstable crack propagation, thus resulting in larger energy dissipation rate of coal under dynamic loads. At last, a semi-empirical energy dissipation model is proposed for describing the positive relationship between dissipated energy and stress.