scholarly journals Multifield Coupling Mechanism of Unloading Deformation and Fracture of Composite Coal-Rock

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Zhen Yang ◽  
Yan Li ◽  
Xin Li ◽  
Jiayu Zhuang ◽  
Hao Li ◽  
...  
Keyword(s):  
Electromagnetic Field ◽  
Electromagnetic Radiation ◽  
Field Variation ◽  
Rock Body ◽  
Deformation And Fracture ◽  
Initial Stage ◽  
Multiphysics Coupling ◽  
Coal Rock ◽  
Loading And Unloading ◽  
Simulation Results

The deformation and fracture evolution of coal and rock under unloading are prone to sudden instability or dynamic damage. To solve the problem, this paper combines interdisciplinary theories such as damage mechanics and electromagnetic field theory. The mathematical model of multiphysics coupling during loading and unloading of composite coal-rock is deduced. In addition, numerical simulations along with experimental verification are carried out to study multi-physical field variation and coupling mechanisms. The composite coal-rock deforms and ruptures under unloading, and the brittle failure of the rock body becomes more sudden when the confining pressure is unloaded. Macroscopically, many microcracks are generated and expanded during the loading and unloading of composite coal-rock. Microscopically, the internal old molecular chains are broken to form new molecular chains by the force. Simulation results show that, during the loading and unloading process, the three physical fields of the composite coal-rock all change regularly. During the unloading of coal and rock, there is a transition period in which the temperature increases sharply and reaches the maximum. Then, the temperature decreases due to the gradual decrease of its bearing capacity. Besides, the electromagnetic field is strongest on the surface of the coal body, and its propagation in the air decays exponentially. There are small fluctuations that appear at the junction of the coal body and the air. The experimental results show that the internal infrared radiation temperature of the composite coal-rock decreases during the initial stage of loading and unloading due to the discharge of internal gas. In the first stage of “loading and unloading,” it increases with the increase in stress, and the temperature suddenly increases in a short time after unloading. The electromagnetic radiation fluctuates in small amplitudes at the initial stage. When the stress is about to reach the peak, the electromagnetic radiation intensity increases and reaches the peak suddenly. Then, the coal-rock ruptures, the stress decreases, and the electromagnetic radiation weakens. The experiment and simulation results are consistent. The multiphysics coupling model is used to study the characteristics of coal and rock unloading under complex conditions, providing a theoretical basis and new method for the prediction and forecast of coal and rock mining dynamic disasters.

Rockburst Prediction Based on Electromagnetic Radiation Technology and its Application

2014 ◽  
Vol 1010-1012 ◽  
pp. 1564-1567 ◽  
Author(s):  
Chao Wang ◽  
Wei Peng
Keyword(s):  
Electromagnetic Radiation ◽  
Rock Burst ◽  
Monitoring Method ◽  
Radiation Technology ◽  
Working Face ◽  
Deformation And Fracture ◽  
Short Period ◽  
Coal Rock ◽  
Relationship Of ◽  
The Relationship

Rock bursts are serious threats to safety and production in coalmines, which are becoming more serious with the increase in mining intensity and depth. Electromagnetic radiation (EMR) always occurs along with coal rock deformation and fracture. EMR monitoring technique, the method using the short period changes of EMR signals before rock burst, has been widely applied to monitor and predict rock burst. This paper mainly studied the relationship of EMR generated by coal rock mass to applied loads and monitored the working face and roadways of coalmine by monitoring instrument, the results show that the EMR monitoring method has excellent performance in predicting rock burst.

A New Method to Concentrate Electromagnetic Field Within ROI Using a High Dielectric Material in 3T Body MRI

2013 ◽  
Author(s):  
Bu S. Park ◽  
Sunder S. Rajan ◽  
Leonardo M. Angelone
Keyword(s):  
Numerical Simulation ◽  
Electromagnetic Field ◽  
Human Body ◽  
Region Of Interest ◽  
Dielectric Materials ◽  
The Body ◽  
Human Body Model ◽  
Body Model ◽  
Simulation Results ◽  
High Dielectric

We present numerical simulation results showing that high dielectric materials (HDMs) when placed between the human body model and the body coil significantly alter the electromagnetic field inside the body. The numerical simulation results show that the electromagnetic field (E, B, and SAR) within a region of interest (ROI) is concentrated (increased). In addition, the average electromagnetic fields decreased significantly outside the region of interest. The calculation results using a human body model and HDM of Barium Strontium Titanate (BST) show that the mean local SAR was decreased by about 56% (i.e., 18.7 vs. 8.2 W/kg) within the body model.

scholarly journals Transient electromagnetic radiation of the lithosphere in a seismically active region

2019 ◽  
Vol 127 ◽  
pp. 03006
Author(s):  
Yiyang Luo ◽  
Nguyen Xuan An ◽  
Vladislav Lutsenko ◽  
Vladimir Uvarov
Keyword(s):  
Electromagnetic Field ◽  
Active Region ◽  
Electromagnetic Radiation ◽  
Seismic Waves ◽  
Earth’S Crust ◽  
Schumann Resonance ◽  
Short Term ◽  
Transient Electromagnetic ◽  
Earth's Crust ◽  
High Level

To study the electromagnetic radiation of the lithosphere associated with seismic waves, we used the recordings of the natural electromagnetic radiation obtained under conditions of weak industrial noise and a high level of microseismicity in the ELF-VLF wave bands. It is shown that these data contain information about the surface waves of the Earth’s crust and are accompanied by a frequency close to the first harmonic of the Schumann resonance. The distribution of spikes over thresholds is obtained, which can be indicators of the activity in the processes of the Earth’s crust. The averaged form of the spikes for different components of the electromagnetic field is obtained. Attention is drawn to the differences in the various components of the electromagnetic field and their diurnal differences are analyzed. The possibility of using the approach to predict the short-term movement of the Earth’s crust is considered.

scholarly journals Electromagnetic Radiation from the Geometrical Point of View

2018 ◽  
Vol 186 ◽  
pp. 01002
Author(s):  
Divakov Dmitriy ◽  
Malykh Mikhail ◽  
Tiutiunnik Anastasiia
Keyword(s):  
Electromagnetic Field ◽  
Electromagnetic Radiation ◽  
Coordinate System ◽  
Maxwell's Equations ◽  
Plane Waves ◽  
Geometrical Optics ◽  
Point Of View ◽  
Curvilinear Coordinates ◽  
Point To Point ◽  
The Relationship

The article describes the relationship between the solutions of Maxwell's equations which can be considered at least locally as plane waves and the curvilinear coordinates of geometrical optics. We introduce phase-ray coordinate system for any electromagnetic field if vectors E and H are orthogonal to each other and their directions do not change with time t, but may vary from point to point in the domain G.

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.

The Influence of Rotor Bar Wear of Impact Crusher on Impact Effect

2010 ◽  
Vol 42 ◽  
pp. 135-138 ◽  
Author(s):  
Shu Juan Cao ◽  
Hai Zhang ◽  
Sen Li
Keyword(s):  
Impact Force ◽  
Fem Simulation ◽  
Data Simulation ◽  
Simulation Data ◽  
Impact Effect ◽  
Large Influence ◽  
Initial Stage ◽  
Simulation Results ◽  
Experiment And Simulation

The influence of the wear of the rotor bar on its impact effect was investigated with FEM simulation. The effectiveness of FEM simulation on the research of impact force was verified through the comparison of experiment and simulation data. Simulation results showed that the wear of rotor bar has not so large influence on impact force. In its initial stage, the bar is worn easily, and the wear becomes slow with the wear increasing.

Study on the characteristics of coal rock electromagnetic radiation (EMR) and the main influencing factors

2018 ◽  
Vol 148 ◽  
pp. 216-225 ◽  
Author(s):  
Xiaoyan Song ◽  
Xuelong Li ◽  
Zhonghui Li ◽  
Zhibo Zhang ◽  
Fuqi Cheng ◽  
...  
Keyword(s):  
Electromagnetic Radiation ◽  
Influencing Factors ◽  
Coal Rock

scholarly journals Study on Ultrasonic Response to Mechanical Structure of Coal under Loading and Unloading Condition

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Xiaofei Liu ◽  
Xiaoran Wang ◽  
Enyuan Wang ◽  
Zhentang Liu ◽  
Xiaoyang Xu
Keyword(s):  
Stress Level ◽  
Dominant Frequency ◽  
Test System ◽  
Ultrasonic Signals ◽  
Linear Elastic ◽  
Cyclic Loading And Unloading ◽  
Deformation And Fracture ◽  
Ultrasonic Technology ◽  
Loading And Unloading ◽  
Ultrasonic Parameters

Ultrasonic technology can be applied to study the changes in the internal defects of coal under quantitative loading, which can provide the theoretical basis for applying the technology to determine the structural stability of coal and predict disasters related to the dynamics of coal or rock. In this paper, to investigate the propagation laws of ultrasonic signals through a coal material under various loading conditions, an ultrasonic test system for the deformation and fracture of coal rock was used and a cyclic loading and unloading pattern is adopted. In addition, changes in ultrasonic parameters such as amplitude, dominant frequency, and velocity were analyzed. At the initial loading stage, the ultrasonic amplitude, amplitude of the dominant frequency, and wave velocity slightly decrease as the loading process progresses, and these three ultrasonic parameters gradually increase to their maxima when the stress level reaches approximately 46%. When it progresses from the linear elastic stage to the elastic plastic stage, the material inside the coal distorts and fractures more drastically, the inner defects are fully developed, and the acoustic parameters decrease significantly. Therefore, the corresponding measures should be adapted to reduce the loading stress before the coal is loaded to its critical stress level.

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