Development Of Law Research Articles

Experimental study and application of similar materials in thick coal seam mining

The orthogonal experiments of similar materials were optimized and analyzed in order to accurately simulate the mechanical properties and the fracture evolution law of thick coal seam overlying strata during mining in this study. The experimental results indicated that similar materials using gypsum and calcium carbonate as cementing agents had a wide range of compressive strength (173.80 kPa–425.95 kPa) and were suitable for simulating various rock properties. Adding an appropriate amount of calcium carbonate can improve the brittleness and mechanical properties of similar materials using gypsum as cementing agents. The failure mode of similar materials transitioned from shear to tensile failure with the increase of the mass ratio of aggregate to cementing agents and the mass ratio of calcium carbonate to gypsum. Moreover, the compressive strength of similar materials rapidly decreased with an increase in the mass ratio of aggregate to cementing materials. And the compressive strength showed an increasing trend with the decrease of the mass ratio of calcium carbonate to gypsum. Moisture content had a significant impact on the density of similar materials, other parameters had small impacts. A thick coal seam mining experimental model was designed based on the experimental results of similar materials, which showed that Qianjiaying Mine may experience basic roof collapse when mining reached 58.1 m. The recommended periodic weighting pace for face pressure on the working face was approximately 15.0 m. Appropriate measures are necessary to adopt to prevent disasters after mining to a length of 58.1 m, followed by every 15.0 m of mining.

Numerical simulation study on the evolution law of mechanical properties of different metamorphic coals after heat treatment.

In order to study the effect of temperature on the structure and mechanical properties of coal with different metamorphic degree. Three coal samples with varying degrees of metamorphism were chosen for analysis. The discrete element software PFC2D is used to simulate the heat treatment and compression of coal. The findings indicate that during the heating process, low-order coal exhibits noticeable thermal cracks at an early stage, while thermal crack development in middle-order coal is concentrated in the later stages. In contrast, high-order coal demonstrates a more stable macroscopic structure. The strength and stiffness of low rank coal show the lowest value and decrease significantly within 135°C. However, the strength and stiffness of medium rank coal decrease significantly after 135°C. The changes of mechanical properties and damage modes of coal caused by thermal damage are often ignored, which may lead to the deviation of design and research results from the actual situation. Therefore, this study is of great significance to the prevention and control of coal mine disasters.

Unsupervised learning of history-dependent constitutive material laws with thermodynamically-consistent neural networks in the modified Constitutive Relation Error framework

This article proposes a consistent and general approach to train physics-augmented neural networks with observable data to enrich and represent nonlinear history-dependent material behaviors in terms of both state equations and evolution laws. In this learning strategy consistent with thermodynamics, the constitutive model is expressed using two potentials (free energy and dissipation potential) which are represented by input-convex neural networks, thus automatically satisfying the principles of thermodynamics. The neural network is trained thanks to an unsupervised procedure that does not rely on strain–stress pairs but needs only partial strain or displacement measurements inside the structure, moreover with uncertain boundary conditions. This method is based on the minimization of the modified Constitutive Relation Error functional, and it extends previous works on this error measure for neural networks to the case of history-dependent behaviors, which requires to design a specific minimization procedure. Given that neural networks for typical structural health monitoring applications often need to be trained online, there is here a significant emphasis placed on automatically and adaptively tuning crucial hyperparameters such as learning rate or weighting between losses.The method is evaluated on elastoplastic and elastoviscoplastic test cases with synthetic data collected from optic fiber or full-field measurements. It is shown that the method can properly learn hidden behaviors, achieves high robustness to noise level, and low sensitivity to user-defined hyperparameters.

Evolution law of pulsating seepage and thermal deformation by injecting high‐temperature steam into coal for thermal coalbed methane recovery

AbstractChinese coal reservoirs are characterized by low pressure and low permeability, which need to be enhanced so as to increase production. However, conventional methods for permeability enhancement can only increase the permeability in fractures, but not the ultra‐low permeability in coal matrices. Attempts to enhance such impermeable structures lead to rapid attenuation of gas production, especially in the late stage of gas extraction. Thermal stimulation by injecting high‐temperature steam is a promising method to increase gas production. The critical scientific challenges that still hinder its widespread application are related to the evolution law of permeability of high‐temperature steam in coal and the thermal deformation of coal. In this study, an experimental approach is developed to explore the high‐temperature steam seepage coupled with the thermal deformation in coal under triaxial stress. The tests were conducted using cylindrical coal specimens of ϕ50 mm × 100 mm. The permeability and thermal strain in coal were investigated when high‐temperature steam was injected at 151.11, 183.20, 213.65, and 239.76°C. The experimental results reveal for the first time that as the amount of injected fluid increases, the steam permeability shows periodic pulsation changes. This paper introduces and explains the main traits of this discovery that may shed more light on the seepage phenomenon. When the injected steam temperature increases, the amplitude of pulsating permeability decreases, whereas the frequency increases; meanwhile, the period becomes shorter, the pulsation peak appears earlier, and the stabilization time becomes longer. The average peak permeability shows a “U‐shaped” trend, decreasing first and then increasing as the steam temperature increases. Meanwhile, with the extension of steam injection time, the axial, radial, and volumetric strains of coal show a stage‐wise expansion characteristic at different temperatures of steam injection, except for the radial strains at 151.11°C. A two‐phase flow theory of gas–liquid is adopted to elucidate the mechanism of pulsating seepage of steam. Moreover, the influencing mechanism of inward and outward thermal expansion on the permeability of coal is interpreted. The results presented in this paper provide new insight into the feasibility of thermal gas recovery by steam injection.

Surface microtopography evolution of monocrystalline silicon in chemical mechanical polishing

Chemical mechanical polishing (CMP) is a widely utilized technique for achieving ultra-smooth surfaces, yet a comprehensive understanding of the surface microtopography evolution remains elusive due to the intricate chemical and mechanical interactions inherent in chemical mechanical polishing. Accordingly, this study explores the evolution law of different spatial frequency features of surface microtopography of monocrystalline silicon by analyzing the changes in the power spectral density (PSD) curve. More importantly, the evolution mechanism of the chemical mechanical polishing surface micromorphology is revealed through the analysis of the power spectral density under different mechanical and chemical conditions. The results emphasize the noticeable impact of both mechanical and chemical actions on the evolution of different spatial frequency features in surface microtopography. The mechanical action of a large particle, less likely to contact the valley region with a small curvature radius, enhances the smoothing speed of high-spatial frequency roughness. Moreover, the mechanical action of polishing pad demonstrates a greater efficiency in smoothing mid-spatial frequency roughness when utilizing a hard pad. This is attributed to the limited impact of pad hardness on the removal depth of single particles within the reaction layer, rendering it less significant for high-spatial frequency roughness. Upon elevating the chemical reaction rate, a notable acceleration in the reduction of roughness in both mid- and high-spatial frequency regions is observed. Furthermore, insights derived from molecular dynamics (MD) simulations of monocrystalline silicon and quartz glass show that the manner of surface atom removal, whether through single atom removal or cluster removal, exerts a significant effect on the final high-spatial frequency components of the power spectral density. This study contributes valuable insights into the intricate formation mechanism of a smooth surface in chemical mechanical polishing.

NMR-based analysis of fractal characteristics of the pore structure of fully aeolian sand concrete under carbonation-dry-wet cycles

The evolution law of the pore structure of concrete is important for the study of concrete durability. To study the quantitative relationship between pore structure and macroscopic mechanics of aeolian sand concrete(ASC) under carbonation-dry-wet cycle(DWCs), the fractal characteristics of ASC under carbonation DWCs were analyzed by means of nuclear magnetic resonance(NMR) technology. The results showed that the carbonization product CaCO3 filled the pores and the compressive strength of ASC increased as the carbonization time increasing. When the DWCs was 0 times, the compressive strength of C1 and C2 groups increased by 9% and 13.6%, respectively, compared with C0. The compressive strength of C0 and C1 groups reached the maximum value when the DWCs was 40 times, while the C2 group reached the maximum value when the DWCs was 20 times. Compared with C0, the compressive strength of C1 and C2 increased by only 4% and 6%, respectively, after 100 DWCs. The fractal dimension Dmax reflected the proportion of harmless and multiple harmful pores in the damaged ASC. The fractal dimension Dmax was proportional to the proportion of harmless pores, and the correlation coefficient was 0.9303. The fractal dimension Dmax was inversely proportional to the proportion of harmful pores, and the correlation coefficient was 0.9565. The macroscopic mechanical properties were mainly affected by harmless pores and harmful pores, while the influence of less harmful pores and harmful pores was weak. This study will provide a theoretical justification for the use of ASC in practical engineering.

STZ-Clay: A shear-transformation-zone theory based constitutive model for clay

The shear-transformation-zone (STZ) theory is a mesoscale-based approach that attributes material macroscopic plastic deformation to the flipping, creation, and annihilation of mesoscopic structures known as STZs. In this study, the potential of the STZ theory in soil constitutive modeling is demonstrated through the development of a model coined STZ-Clay, by extending the conventional STZ theory to incorporate two essential characteristics of clay, i.e., plastic volumetric strain and pressure dependence. The STZ-Clay model assumes that the plastic volumetric strain arises from the creation and annihilation of STZs, while the pressure-dependency is accounted for by the dissipation rate function and evolution law of two internal variables, namely STZ density and orientational bias. Remarkably, the STZ-Clay model achieves a unique critical state under different loading paths and reasonably reproduces the influence of consolidation history on the hardening and dilatancy of clay. Overall, the STZ-Clay model offers a fresh perspective for understanding the yielding mechanism and critical state of clay through the lens of mesostructural evolution.

Study on the evolution of limestone damage and permeability under the tunnel driving stress path

The tunnel water inrush problems threaten the safety of tunneling. To understand the water inrush mechanism in tunnel tunneling, triaxial water seepage test and COMSOL numerical simulation were applied to study the water seepage law of tunnel surrounding rock according to the tunnel driving stress path. The results show that the permeability changes slowly, increases sharply and decreases sharply, respectively, during seepage and mechanical loading-unloading. However, during the σ1−σ3 active unloading stage, the permeability cannot return to the state before the plastic stage. The permeability presents a highly fitting exponential relationship with the stress of deviatoric and effective volume. During different loading and unloading stages, the index relationship is different, which is related to the rock damage degree. Through uniaxial cyclic loading-unloading acoustic emission test, it is verified that axial strain ε1 is related to cumulative AE count, that is rock damage degree. The damage variable D based on axial strain ε1 was established, and the permeability evolution law was effectively characterized by damage variable D. The permeability and crack evolution process cannot be directly observed during seepage test. The numerical model of real heterogeneous rock samples is established based on COMSOL. The simulated rock shear fracture feature is close to that of laboratory tests. In the numerical simulation of seepage, the evolution laws of damage, fracture and permeability in rock are effectively quantified. It is proved that the necessary numerical simulation can serve as an effective supplement to the laboratory test.

Rural revitalization in China: Measurement indicators, regional differences and dynamic evolution

It is crucial to scientifically assess China's rural revitalization and grasp its evolution laws. This paper constructs an indicator system to measure the level of rural revitalization in China from 2011 to 2021 using the entropy weight method. Then, we explore the spatial and temporal divergence and dynamic evolutionary characteristics of rural revitalization using the Dagum Gini coefficient and Kernel density. We found that the level of rural revitalization in China is low but fluctuating and increasing. Regionally, eastern China scores higher than central, western and northeastern China. In terms of dimensions, ecological livability scores are higher than prosperous industry, effective governance, affluent living and civilized countryside in that order. The regional differences in the level of rural revitalization are mainly reflected between regions, especially between eastern and western China, but the gap between regions is narrowing year by year. And the results of the Kernel density show that the level of rural revitalization in China shows a slow and balanced growth, but the eastern China shows a polarization growth. These findings can provide a comprehensive and objective outline of the advantages and shortcomings of rural revitalization development in China, and provide a policy reference for the comprehensive and stable promotion of rural revitalization construction.

Finite element simulation and experiment of residual stress evolution in MEMS structures

The MEMS device structure is usually formed by the combination of thick film and thin film deposition of many different materials, and the residual stress generated in the process of integration/superposition of different materials has a significant impact on the performance and reliability of the device.In this study, a test structure of a multilayer thin film was designed and processed. Based on this, finite element modeling analysis and reliability experiment, analyze the evolution of residual stress and construct the corresponding theoretical analysis model. The finite element modeling analysis can characterize the evolution and distribution laws of residual stress. The reliability experiment is mainly by carrying out the temperature shock experiment, and measuring the resistance value, resonance frequency and the surface morphology of the device, so as to better reflect the change of residual stress. Through this study, the resonant frequency and surface morphology of the device can reflect the residual stress of the device, which provides help for the test and analysis of the residual stress. To a certain extent, it can help reduce the harm caused by the residual stress in the design and manufacturing process, and improve the performance and reliability of MEMS devices.

Effect of the vertical magnetic field on the bubble dynamic behaviors during photoelectrochemical water splitting

The bubble dynamic behaviors on the electrode surface are significantly affected by the magnetohydrodynamic (MHD) flow induced by the Lorentz force resulting from the applied magnetic field. However, the mechanism of the impact of a magnetic field perpendicular to the electrode on the dynamic behaviors of bubble remain unclear. In this study, the evolution law of a single oxygen bubble on the surface of a TiO2 photoelectrode under the influence of a vertical magnetic field with different magnetic induction intensities was investigated. The presence of a vertical magnetic field effectively promoted the rapid detachment of bubbles from the electrode surface and greatly improved the gas evolution efficiency. The mass transfer was dominated by single-phase free convection during bubble evolution. Under the influence of the vertical magnetic field, the mass transfer coefficient near the electrode was enhanced, and the adverse effects of bubbles on mass transfer were counteracted when they entered the reaction-controlled growth phase. The further multiphysics simulation found that the MHD convection decreased the local supersaturation of reaction product oxygen molecules near the electrode, thereby reducing concentration overpotential and increasing the reaction rate. This study provides an experimental and theoretical basis for promoting the bubble detachment and the reaction rate on the gas evolving electrode surface during photoelectrochemical water splitting.

Seepage Evolution Law of Coal during Loading Process Based on Digital Core

Seepage Evolution Law of Coal during Loading Process Based on Digital Core

Research on Computer Aided Deformation Control Strategy for Welding of Large Long Straight Beams

<p>Long straight string beams are often used as supporting structures in large equipment. Due to the large size of string beams, welding technology is generally used to complete their production. This article first constructs the finite element model and heat source model of the chord beam based on the structure of the long straight beam, and then obtains the distribution and evolution law of the temperature field, as well as the temperature rise law of the temperature field under dynamic simulation. Based on this law data, an improved BP neural network model is used to predict the deformation of the beam. In order to verify the authenticity of the prediction results, the article finally builds a Matlab simulation experimental environment and conducts simulation experiments on the welding deformation prediction of the beam.</p> <p> </p>

The analysis of extension evolution law and damage behavior characteristic for line microcracks on Si3N4 bearing balls

To predict the relation between extension evolution law and damage of line microcracks on silicon nitride bearing balls. Firstly, the 3D point cloud features of line microcracks are obtained based on multi-image 3D reconstruction. Next, the point cloud diagram data is optimized to fit the molecular dynamics geometric model of line microcracks extension process. Then, according to the Si3N4 molecular dynamics deep learning potential, the molecular dynamics mechanical model is established. Finally, Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) is used to numerically solve the extension evolution of line microcracks. The experiment result shows that from the change analysis of single-layer surface mesh, the microcracks extension is concentrated in the central region of the indentation. The new microcracks spread along both sides of the original microcracks. After uniformly distributed load is applied to line microcracks, there is a phenomenon of concentrated swirling microcracks formation under the indentation region. By analyzing the atomic coordination number nephogram, the microcracks extension occurs when the proportion of amorphous atoms is up to 7 % during loading. And the plastic deformation occurs when the proportion of amorphous atoms is dropped to 6 % during unloading. In addition, in the process of indentation loading, plastic deformation and slip zone occur on Si3N4 bearing balls surface. However, the strain is accumulated in the middle region during unloading. The slip zone moves inward and becomes thin, and the elastic deformation partially is recovered.

Magnetic Field of Gas Giant Exoplanets and Its Influence on the Retention of Their Exomoons

We study the magnetic and tidal interactions of a gas-giant exoplanet with its host star and with its exomoons, and focus on their retention. We briefly revisit the scaling law for planetary dynamo in terms of its mass, radius, and luminosity. Based on the virial theorem, we construct an evolution law for planetary magnetic field and find that its initial entropy is important for the field evolution of a high-mass planet. We estimate the magnetic torques on orbit arising from the star–planet and planet–moon magnetic interactions, and find that it can compensate tidal torques and bypass frequency valleys where dynamical-tide response is ineffective. For exomoon’s retention, we consider two situations. In the presence of a circumplanetary disk (CPD), by comparison between CPD’s inner and outer radii, we find that planets with too strong magnetic fields or too small distance from its host star tend not to host exomoons. During the subsequent CPD-free evolution, we find, by comparison between a planet’s spin-down and a moon’s migration timescales, that hot Jupiters with periods of several days are unlikely to retain large exomoons, albeit they could be surrounded by rings from the debris of tidally disrupted moons. In contrast, moons, if formed around warm or cold Jupiters, can be preserved. Finally, we estimate the radio power and flux density due to the star–planet and planet–moon magnetic interactions and give the upper limit of detection distance by FAST.

Experimental and simulation research on rupture behavior of coal-based solid waste material backfilling column under non-uniformly distributed load with different loading ratios

Artificial construction backfilling columns underground based on coal-based solid waste materials is an important method to slow down surface subsidence and reduce the environmental pollution caused by coal gangue hills and fly ash. Taking the Xinyang coal mine as an example, based on a self-developed non-uniform load application device, acoustic emission (AE) and digital image correlation (DIC) monitoring technology, the evolution law of rupture behavior of coal-based solid waste material backfilling columns under different loading ratios was revealed. When the loading ratios are 1, 1.1319, 1.3585, 1.6371, and 2.0631, the average compression strength with the same material ratio is 3.96 MPa, 4.05 MPa, 4.22 MPa, 4.57 MPa, and 3.94 MPa, respectively. It is indicated that an increase in the loading ratio within the critical range is beneficial for stimulating the collaborative bearing of different parts inside the backfilling columns. From the perspective of the internal rupture behavior of the backfilling columns, the increase in loading ratio promotes a significant increase in the proportion of shear cracks, which has increased from 17.07% to 37.02%, resulting in the shear failure of backfilling columns. Meanwhile, as the loading ratio increases, the crack initiation position gathers from the left and right sides to the middle, and the final crack shape gradually transitions from two inclined and parallel main cracks to an inverted "V" shaped intersecting main cracks. The research is of great significance for improving the understanding of the failure law of backfilling columns and the safety evaluation of engineering-bearing structures under non-uniform loads.

The influence of pulse frequency on the energy evolution law and rock-breaking effect of pulsed abrasive water jet

Compared to continuous abrasive jet and high-pressure water jet, pulsed abrasive water jet can intermittently generate high water hammer pressure and is commonly used in applications such as coal mining and petroleum engineering for rock-breaking purposes. Pulse frequency is one of the key factors affecting the evolution of abrasive acceleration and jet impact energy, thereby influencing the system's energy transfer efficiency and cutting ability. The equation of motion for abrasive acceleration is established based on the two-phase flow theory, and the variation law of abrasive velocity with pulse frequency is solved. Fluent-EDEM (Extended Discrete Element Method) was used to simulate the abrasive water jet flow field structure and abrasive acceleration process under different pulse frequency conditions, and the intrinsic influence mechanism of pulse frequency on impact energy was clarified. Combined with rock-breaking experiments using pulsed abrasive water jets, the following conclusions are drawn: as the pulse frequency increases, the inertia of the abrasive makes it unable to respond in a timely manner to the high pulsation frequency of water, resulting in a reduction in the exchange rate of intermittent energy and a gradual decrease in the maximum velocity of the abrasive. This trend is more pronounced at a higher pulse frequency. Within the same time period, the cumulative impact energy of the pulsed abrasive water jet decreases first and then increases with the increase in pulse frequency, indicating the existence of an optimal impact frequency that maximizes the cumulative impact energy of the pulsed abrasive water jet. Under fixed jet pressure conditions and the same erosion time, the pulsed abrasive water jet with a frequency of 30 Hz exhibits the best rock-breaking capability.

Investigating Small Disturbance Stability in Wind Farm Grid-Connected Systems: A Data-Driven Approach

The presence of unknown synchronization characteristics, unclear instability mechanism, and various fault mode evolution laws, lacking corresponding theoretical support and analysis methods and instability criteria, are defined with clear physical concepts. It is still impossible to systematically understand the transient synchronization mechanism of the wind power grid-connected system from the perspective of the whole fault stage. Therefore, this study uniformly reveals its temporary synchronous stability problem and proposes a large/small disturbance adaptive synchronous stability control method, which improves the dynamic characteristics of the wind turbine through the control of the inverter itself to improve the system stability—using different scenarios, such as single doubly-fed wind turbines. The experimental results show that the small disturbance on the AC side significantly impacts the system characteristics, followed by a bit of annoyance on the DC side. The DC side fault will cause a change in system frequency characteristics, especially at the receiving end. However, compared with the Voltage Source Converters-High Voltage Direct Current (VSC-HVDC)system, Modular Multilevel Converters-High Voltage Direct Current (MMC-HVDC) systems operate at a much higher frequency and produce less low-frequency harmonics. This makes them less likely to induce subsynchronous oscillations in the system.

A simple gradation-state-dependent model for granular materials

This paper proposes a gradation-state-dependent constitutive model to capture the granular materials' mechanical behaviours considering the granular crushing's influence. Firstly, a gradation evolution law is developed to reflect the change in grain size distribution (GSD) with the growth of stress levels, and then, based on the evolution law, the elastic compliance matrix is modified to reflect the effects of particle breakage. Secondly, as the critical state line (CSL) exhibits gradation dependence, a novel method is developed to describe the family of CSLs under different fixed gradations. Subsequently, by combining the gradation evolution law with the CSL equation, the paper explains the steepening of the slope of the critical state line when the crushing is activated. With the improvement of CSL, the material's shear dilatancy and contraction properties are better reflected, assisting in establishing a plastic compliance matrix. Employing the derived elastic and plastic compliance matrix, the elastic–plastic model reflecting the influence of gradation and state effects is established and verified with a series of experimental and discrete element method (DEM) simulation results.

Data-driven discovery of stochastic dynamical systems with [formula omitted]-stable Lévy noise based on residual networks

Identifying evolution laws of complex systems from massive data has been a challenging issue in the cross field of stochastic dynamics and data science with greater and greater concern in recent years. So far, significant progress has been made in dealing with cases where differential equations are driven by Gaussian noise, yet work for non-Gaussian cases remains great room for growth. In this paper, a data-driven approach based on deep residual networks (ResNets) is proposed to extract governing laws of stochastic dynamical systems perturbed by non-Gaussian α-stable Lévy noise. Specifically, we firstly separate the non-Gaussian noise from drift term for subsequent extraction according to the fundamental theory of differential equations. For the noise part, the Lévy jump measure and noise intensity are estimated via some properties of α-stable distribution. Next the residual network is employed to identify drift. Numerical results of systems of 1 to 3 dimensions are given to demonstrate the feasibility of this method. It is necessary to emphasize here that the contribution of this method is mainly manifested in its effective resolution of the identification for complex non-Gaussian stochastic dynamical systems via cutting-edge machine learning techniques.