scholarly journals Evaluation of the weakening behavior of gas on the coal strength and its quantitative influence on the coal deformation

2021 ◽  
Author(s):  
Haijun Guo ◽  
Kai Wang ◽  
Yuchen Wu ◽  
Hanlu Tang ◽  
Jianguo Wu ◽  
...  
Keyword(s):  
Coal Deformation ◽  
Quantitative Influence ◽  
Coal Strength

scholarly journals Mechanical criterion for coal and gas outburst: a perspective from multiphysics coupling

2021 ◽  
Author(s):  
Ting Liu ◽  
Baiquan Lin ◽  
Xuehai Fu ◽  
Ang Liu
Keyword(s):  
Control Method ◽  
Risk Identification ◽  
Controlling Factors ◽  
Gas Pressure ◽  
Critical Values ◽  
Coal And Gas Outburst ◽  
Strong Interactions ◽  
Gas Outburst ◽  
Multiphysics Coupling ◽  
Coal Strength

AbstractAlthough a series of hypotheses have been proposed, the mechanism underlying coal and gas outburst remains unclear. Given the low-index outbursts encountered in mining practice, we attempt to explore this mechanism using a multiphysics coupling model considering the effects of coal strength and gas mass transfer on failure. Based on force analysis of coal ahead of the heading face, a risk identification index Cm and a critical criterion (Cm ≥ 1) of coal instability are proposed. According to this criterion, the driving force of an outburst consists of stress and gas pressure gradients along the heading direction of the roadway, whereas resistance depends on the shear and tensile strengths of the coal. The results show that outburst risk decreases slightly, followed by a rapid increase, with increasing vertical stress, whereas it decreases with increasing coal strength and increases with gas pressure monotonically. Using the response surface method, a coupled multi-factor model for the risk identification index is developed. The results indicate strong interactions among the controlling factors. Moreover, the critical values of the factors corresponding to outburst change depending on the environment of the coal seams, rather than being constants. As the buried depth of a coal seam increases, the critical values of gas pressure and coal strength decrease slightly, followed by a rapid increase. According to its controlling factors, outburst can be divided into stress-dominated, coal-strength-dominated, gas-pressure-dominated, and multi-factor compound types. Based on this classification, a classified control method is proposed to enable more targeted outburst prevention.

Top-coal deformation control of gob-side entry with narrow pillars and its application for fully mechanized mining face

2016 ◽  
Vol 26 (3) ◽  
pp. 417-422 ◽  
Author(s):  
Fangkun Qi ◽  
Yuejin Zhou ◽  
Jiawei Li ◽  
Erqian Wang ◽  
Zhengzheng Cao ◽  
...  
Keyword(s):  
Deformation Control ◽  
Coal Deformation ◽  
Mining Face

Coal strength and Young's modulus related to coal rank, compressional velocity and maceral composition

2013 ◽  
Vol 54 ◽  
pp. 129-135 ◽  
Author(s):  
Jienan Pan ◽  
Zhaoping Meng ◽  
Quanlin Hou ◽  
Yiwen Ju ◽  
Yunxing Cao
Keyword(s):  
Young’S Modulus ◽  
Young's Modulus ◽  
Coal Rank ◽  
Compressional Velocity ◽  
Coal Strength

scholarly journals Influence of misalignments on the performance of externally occulted solar coronagraphs

2018 ◽  
Vol 612 ◽  
pp. A82 ◽  
Author(s):  
S. V. Shestov ◽  
A. N. Zhukov
Keyword(s):  
European Space Agency ◽  
Numerical Approach ◽  
Primary Objective ◽  
Optical Elements ◽  
Trade Off ◽  
Space Agency ◽  
Minimal Height ◽  
Different Types ◽  
Points Of View ◽  
Quantitative Influence

Context. The ASPIICS instrument is a novel externally occulted coronagraph that will be launched on board the PROBA-3 mission of the European Space Agency. The external occulter will be placed on one satellite ~150 m ahead of the second satellite that will carry an optical instrument. During 6 h out of 19.38 h of orbit, the satellites will fly in a precise (accuracy around a few millimeters) formation, constituting a giant externally occulted coronagraph. The large distance between the external occulter and the primary objective will allow observations of the white-light solar corona starting from extremely low heights ~ 1.1R⊙. Aims. We intend to analyze influence of shifts of the satellites and misalignments of optical elements on the ASPIICS performance in terms of diffracted light. Based on the quantitative influence of misalignments on diffracted light, we provide a recipe for choosing the size of the internal occulter (IO) to achieve a trade-off between the minimal height of observations and sustainability to possible misalignments. Methods. We considered different types of misalignments and analyzed their influence from optical and computational points of view. We implemented a numerical model of the diffracted light and its propagation through the optical system and computed intensities of diffracted light throughout the instrument. Our numerical approach is based on a model from the literature that considered the axisymmetrical case. Here we extend the model to include nonsymmetrical cases and possible misalignments. Results. The numerical computations fully confirm the main properties of the diffracted light that we obtained from semi-analytical consideration. We obtain that relative influences of various misalignments are significantly different. We show that the internal occulter with RIO = 1.694 mm = 1.1R⊙ is large enough to compensate possible misalignments expected to occur in PROBA-3/ASPIICS. Besides that we show that apodizing the edge of the internal occulter leads to additional suppression of the diffracted light. Conclusions. We conclude that the most important misalignment is the tilt of the telescope with respect to the line connecting the center of the external occulter and the entrance aperture. Special care should be taken to co-align the external occulter and the coronagraph, which means co-aligning the diffraction fringe from the external occulter and the internal occulter. We suggest that the best orientation strategy is to point the coronagraph to the center of the external occulter.

scholarly journals Quantitative Influence and Performance Analysis of VR Laparoscopic Surgical Training System

2021 ◽  
Author(s):  
Peng Yu ◽  
Junjun Pan ◽  
Zhaoxue Wang ◽  
Yang Shen ◽  
Jialun Li ◽  
...  
Keyword(s):  
Medical Students ◽  
Performance Analysis ◽  
Cognitive Load ◽  
Surgical Training ◽  
Clinical Education ◽  
Training System ◽  
Physiological Data ◽  
Flow Experience ◽  
And Performance ◽  
Quantitative Influence

Abstract Background VR surgery training becomes a trend in clinical education. Many research papers validate the effectiveness of VR based surgical simulators in training surgeons. However, most existing papers employ subjective methods to study the residents’ surgical skills improvement. Few of them investigates how to substantially improve the surgery skills on specific dimensions.Methods In this paper, we resort to physiological approaches to objectively research quantitative influence and performance analysis of VR laparoscopic surgical training system for medical students. 41 participants were recruited from a pool of medical students. They conducted four pre and post experiments in the training box. In the middle of pre and post experiments, they were trained on VR laparoscopic surgery simulators (VRLS). When conducting pre and post experiments, their operation process and physiological data (heart rate and electroencephalogram) are recorded. Their performance is graded by senior surgeons using newly designed hybrid standards for fundamental tasks and GOALS standards for colon resection tasks. Finally, the participants were required to fill the questionnaires about their cognitive load and flow experience.Results The results show that the VRLS could highly improve medical students' performance (p < 0.01) especially in depth perception and enable the participants to obtain flow experience with a lower cognitive load.Conclusion The performance of participants is negatively correlated with cognitive load through quantitatively physiological analysis. This might provide a new way of assessing skill acquirement.

Modelling Methane Extraction from Stimulated Coalbed Influenced by Multidomain and Thermal Effects

2021 ◽  
Author(s):  
Wai Li ◽  
Jishan Liu ◽  
Jie Zeng ◽  
Yee-Kwong Leong ◽  
Derek Elsworth ◽  
...  
Keyword(s):  
Thermal Effects ◽  
Coalbed Methane ◽  
Thermal Strain ◽  
Fracture Network ◽  
Extraction Process ◽  
Mine Safety ◽  
Shanxi Province ◽  
Well Production ◽  
Proposed Model ◽  
Coal Deformation

Abstract The process of extracting coalbed methane (CBM) is not only of significance for unconventional energy supply but also important in mine safety. The recent advance in fracking techniques, such as carbon dioxide (CO2) fracking, intensifies the complexity of stimulated coalbeds. This work focuses on developing a fully coupled multidomain model to describe and get insight into the process of CBM extraction, particularly from those compound-fractured coalbeds. A group of partial differential equations (PDEs) are derived to characterize gas transport from matrix to fractures and borehole. A stimulated coalbed is defined as an assembly of three interacting porous media: matrix, continuous fractures (CF) and radial primary hydraulic fracture (RF). Matrix and CF constitute a dual-porosity-dual-permeability system, while RF is simplified as an 1-D cracked medium. These media further form three distinct domains: non-stimulated reservoir domain (NSRD), stimulated reservoir domain (SRD) and RF. The effects of coal deformation, heat transfer, and non-thermal sorption are coupled into the model to reflect the multiple processes in CBM extraction. The finite element method is employed to numerically solve the PDEs. The proposed model is verified by comparing its simulation results to a set of well production data from Southern Qinshui Basin in Shanxi Province, China. Great consistency is observed, showing the satisfactory accuracy of the model for CBM extraction. After that, the difference between various stimulation patterns is presented by simulating the CBM extraction process with different stimulation patterns including (1) unstimulated coalbed; (2) double-wing fracture + NSRD; (3) multiple RFs + NSRD; (4) SRD + NSRD and (5) multiple RFs + SRD + NSRD. The results suggest that Pattern (5) (often formed by CO2 fracking) boosts the efficiency of CBM extraction because it generates a complex fracture network at various scales by both increasing the number of radial fractures and activating the micro-fractures in coal blocks. Sensitivity analysis is also performed to understand the influences of key factors on gas extraction from a stimulated coalbed with multiple domains. It is found that the distinct properties of different domains originate various evolutions, which in turn influences the CBM production. Ignoring thermal effects in CBM extraction will either overestimate or underestimate the production, which is the net effect of thermal strain and non-isothermal sorption. The proposed model provides a useful approach to accurately evaluate CBM extraction by taking the complex evolutions of coalbed properties and the interactions between different components and domains into account. The importance of multidomain and thermal effects for CBM reservoir simulation is also highlighted.

EXPERIMENTAL INVESTIGATION ON MULTI-FRACTAL CHARACTERISTICS OF ACOUSTIC EMISSION OF COAL SAMPLES SUBJECTED TO TRUE TRIAXIAL LOADING–UNLOADING

Fractals ◽  
2020 ◽  
Vol 28 (05) ◽  
pp. 2050092 ◽  
Author(s):  
RAN ZHANG ◽  
JIE LIU ◽  
ZHANYOU SA ◽  
ZAIQUAN WANG ◽  
SHOUQING LU ◽  
...  
Keyword(s):  
Damage Evolution ◽  
Dynamic Changes ◽  
Deformation And Failure ◽  
True Triaxial ◽  
Coal Deformation ◽  
Coal Rock ◽  
True Triaxial Stress ◽  
Fractal Characteristics ◽  
Loading And Unloading ◽  
Precursory Information

Coal–rock dynamic disasters seriously threaten safe production in coal mines, and an effective early warning is especially important to reduce the losses caused by these disasters. The occurrence of coal–rock dynamic disasters is determined by mining-induced stress loading and unloading. Therefore, it is of great significance to analyze the precursory information of coal deformation and failure during true triaxial stress loading and unloading. In this study, the deformation and failure of coal samples subjected to true triaxial loading and unloading, including fixed axial stress and unloading confining stress (FASUCS), are experimentally investigated. Meanwhile, acoustic emission (AE) during the deformation of coal samples is monitored, and the multi-fractal characteristics of AE are analyzed. Furthermore, combined with the deformation and failure of coal samples, the precursory information of coal deformation and rupture during true triaxial stress loading and unloading is obtained. Finally, the relationship between multi-fractal characteristics and damage evolution of coal samples under FASUCS is discussed. The results show that the multi-fractal spectral widths of AE time series under the conditions of FASUCS with different initial confining stresses or unloading rates are quite different, but the dynamic changes of multi-fractal parameters [Formula: see text] and [Formula: see text] are similar. This indicates that the microscopic complexity of AE events of coal samples under different conditions of FASUCS differs, but the macroscopic generation mechanism of AE events has inherent uniformity. The dynamic changes of [Formula: see text] and [Formula: see text] can reflect the stress and damage degree of coal samples. The dynamic change process of [Formula: see text] well accords with the damage evolution process of coal samples. A gradual decrease of [Formula: see text] corresponds to a slow increase of damage, while a sharp increase of it corresponds to a rapid growth of damage. At the same time, the mutation point of damage curve at distinct stress difference levels shares the same variation trend with the [Formula: see text] mutation point. The change of [Formula: see text] can reflect the damage process of coal samples, which can be used as precursor information for predicting coal–rock rupture. The finding is of great significance for the early warning of coal–rock dynamic disasters.

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