Overburden fracture evolution laws and water-controlling technologies in mining very thick coal seam under water-rich roof

Considering the danger of water inrush in mining very thick coal seam under water-rich roof in Majialiang Coal Mine,the universal discrete element(UDEC)software was used to simulate the overburden fracture evolution laws when mining 4#coal seam.Besides,this study researched on the influence of face advancing length,speed and mining height on the height of the water flowing fractured zones(HWFFZ),and analyzed the correlation of face advancing length and change rules of aquifer water levels and goaf water inflow.Based on those mentioned above,this research proposed the following water-controlling technologies:draining the roof water before mining,draining goaf water,reasonable advancing speed and mining thickness.These water-controlling technologies were successfully used in the feld,thus ensured safely mining the very thick coal seam under water-rich roof.

Strength evolution law of cracked rock based on localized progressive damage model

In the light of the localized progressive damage model,the evolution law of cohesive and frictional strength with irreversible strains was determined.Then,the location and the extent of the excavation disturbed zone in one deep rock engineering were predicted by using the strength evolution law.The theoretical result is close to the result of in-situ test.The strength evolution law excels the elastic-perfectly plastic model and elasto-brittle plastic model in which the cohesive and frictional strength are mobilized simultaneously.The results obtained indicate that the essential failure mechanism of the cracked rock can be described by the cohesion weakening and friction strengthening evolution law.

A Study on Dual-Load-Zone Model of Overlying Strata andEvolution Law of Mining Stress

The changeable structure and movement law of overlying strata are the maincontributor to the change of mining stress.Starting from the relevant theory of keystratum and particularly based on the theory of mine ground pressure and strata control,this research proposed a new solution to mining stress problems by establishing adual-load-zone stratum structural model.Elastic foundation beam theory was used tosolve the stress of overlying strata of the dual-load-zones with superposition method,which revised the traditional calculation method of mining stress.The abnormal increaseof lead abutment pressure in the mining area was explained effectively,through which theevolution law of mining stress in the case of hard rock was obtained.The results indicatethat mining stress experiences a drastic change within the range of 50 m ahead of the coalwall due to the collapse of main roof;under the influence of main key stratum andinferior key strata,the influence range of lead abutment pressure is extended up toapproximately 120 m in the working face;this remarkable increase can be attributed tothe excessive length of sagging zone.Results from both the dual-load-zone modelexperiment and field measurement demonstrate high consistency.The model can predictthe influence range of abutment pressure effectively and thus guide the safety productionof mining.

Route strategy of satellite network in GNSS based on topology evolution law

As each type of satellite network has different link features, its data transmission must be designed based on its link features to improve the efficiency of data transferring. The transmission of navigation integrated services information （NISI） in a global navigation satellite system （GNSS） with inter-satellite links （ISLs） is studied by taking the real situation of inter-satellite communication links into account. An on-demand computing and buffering centralized route strategy is proposed based on dynamic grouping and the topology evolution law of the GNSS network within which the satellite nodes are operated in the manner of dynamic grouping. Dynamic grouping is based on satellites spatial relationships and the group role of the satellite node changes by turns due to its spatial relationships. The route strategy provides significant advantages of high efficiency, low complexity, and flexi- ble configuration, by which the established GNSS can possess the features and capabilities of feasible deployment, efficient transmission, convenient management, structural invulnerability and flexible expansion.

Stress field evolution law of mining environment reconstructing structure with change of filling height

For improving global stability of mining environment reconstructing structure,the stress field evolution law of the structure with the filling height change of low-grade backfill was studied by ADINA finite element analysis code.Three kinds of filling schemes were designed and calculated,in which the filling heights were 2,4,and 7 m,separately.The results show that there are some rules in the stress field with the increase of the filling height as follows:(1) the maximum value of tension stress of the roof decreases gradually,and stress conditions are improved gradually;(2) the tension stress status in the vertical pillar is transformed into the compressive stress status,and the carrying capacity is improved gradually;however,when the filling height is beyond 2.8 m,the carrying capacity of the vertical pillar grows very slowly,so,there is little significance to continue to fill the low-grade backfill;(3) the bottom pillar suffers the squeezing action from the vertical pillars at first and then the gravity action of the low-grade backfill,and the maximum value of tension stress of the bottom pillar firstly increases and then decreases.Considering the economic factor,security and other factors,the low-grade backfill has the most reasonable height(2.8 m) in the scope of all filling height.

Time evolution law of a two-mode squeezed light field passing through twin diffusion channels

We explore the time evolution law of a two-mode squeezed light field(pure state)passing through twin diffusion channels,and we find that the final state is a squeezed chaotic light field(mixed state)with entanglement,which shows that even though the two channels are independent of each other,since the two modes of the initial state are entangled with each other,the final state remains entangled.Nevertheless,although the squeezing(entanglement)between the two modes is weakened after the diffusion,it is not completely removed.We also highlight the law of photon number evolution.In the calculation process used in this paper,we make full use of the summation method within the ordered product of operators and the generating function formula for two-variable Hermite polynomials.

New approach for obtaining the time-evolution law of a chaotic light field in a damping gaining-process

A new approach for studying the time-evolution law of a chaotic light field in a damping-gaining coexisting process is presented. The new differential equation for determining the parameter of the density operator p（t） is derived and the solution of f for the damping and gaining processes are studied separately. Our approach is direct and the result is concise since it is not necessary for us to know the Kraus operators in advance.

Simulation Test for Evolution Laws of Tensile Fractures in a Coal Mining Area

In order to study evolution laws of tensile fractures in a coal mining area, based on the classification of the fractures formed by mining, a physical simulation test was carried out to simulate the dynamic evolution process of tensile fractures in coal mining areas. The results showed that after the coal in the mining area was mined, the mining area underwent obvious movement and deformation and forms tensile fractures. As the min-ing working face was advanced, the tensile fractures underwent the dynamic process of generation, development and closure. The changing curves of density of tensile fractures with the increase of mining length of the working face liked a ladder （it increased slowly and then rapidly） and then had two peaks （the second peak was higher than the first peak）.

Evolution laws of strength parameters of soft rock at the post-peak considering stiffness degradation

To evaluate the strength attenuation law of soft rock in the western mining area of China, we established an evolution model for the strength parameters of soft mudstone at the post-peak stage by employing a tri-linear strain softening model. In the model, a stiffness degradation coefficient co and a softening modulus coefficient a were introduced to take into account the stiff- ness degradation, and the subsequent yield surfaces at post-peak stage were all assumed to meet the Molar-Coulomb yield criterion. Furthermore, attenuation laws of stiffness and strength parameters of soft mudstone were analyzed according to an engineering case. Finally, the model＇s accuracy was verified by comparison of results from numerical calculation and tri-axial compression tests. Results showed that the attenuation of the friction angle was dominated mainly by the instantaneous stress states and damage features, while the attenuation law of cohesion was also related to the plastic behavior. The degradation rates of strength param- eters decreased with increasing confining pressure and the friction angle tended towards its initial value. Residual strengths were also enhanced with increasing confming pressure. The results indicate that the evolution model can accurately describe the strain softening behavior of soft rock.

Geometric Evolution Laws for Thin Crystalline Films: Modeling and Numerics

Geometrical evolution laws are widely used in continuum modeling of surface and interface motion in materials science.In this article,we first give a brief review of various kinds of geometrical evolution laws and their variational derivations,with an emphasis on strong anisotropy.We then survey some of the finite element based numerical methods for simulating the motion of interfaces focusing on the field of thin film growth.We discuss the finite element method applied to front-tracking,phase-field and level-set methods.We describe various applications of these geometrical evolution laws to materials science problems,and in particular,the growth and morphologies of thin crystalline films.

A Robust and Efficient Adaptive Multigrid Solver for the Optimal Control of Phase Field Formulations of Geometric Evolution Laws

We propose and investigate a novel solution strategy to efficiently and accurately compute approximate solutions to semilinear optimal control problems,focusing on the optimal control of phase field formulations of geometric evolution laws.The optimal control of geometric evolution laws arises in a number of applications in fields including material science,image processing,tumour growth and cell motility.Despite this,many open problems remain in the analysis and approximation of such problems.In the current work we focus on a phase field formulation of the optimal control problem,hence exploiting the well developed mathematical theory for the optimal control of semilinear parabolic partial differential equations.Approximation of the resulting optimal control problemis computationally challenging,requiring massive amounts of computational time and memory storage.The main focus of this work is to propose,derive,implement and test an efficient solution method for such problems.The solver for the discretised partial differential equations is based upon a geometric multigrid method incorporating advanced techniques to deal with the nonlinearities in the problem and utilising adaptive mesh refinement.An in-house twogrid solution strategy for the forward and adjoint problems,that significantly reduces memory requirements and CPU time,is proposed and investigated computationally.Furthermore,parallelisation as well as an adaptive-step gradient update for the control are employed to further improve efficiency.Along with a detailed description of our proposed solution method together with its implementation we present a number of computational results that demonstrate and evaluate our algorithms with respect to accuracy and efficiency.A highlight of the present work is simulation results on the optimal control of phase field formulations of geometric evolution laws in 3-D which would be computationally infeasible without the solution strategies proposed in the present work.

Generation and Evolution of Cavitation Bubbles in Volume Alternate Cavitation(VAC)

Cavitation generation methods have been used in multifarious directions because of their diversity,and numerous studies and discussions have been conducted on cavitation generation methods.This study aims to explore the generating mechanism and evolution law of volume alternate cavitation(VAC).In the VAC,liquid water is placed in an airtight container with a variable volume.As the volume alternately changes,the liquid water inside the container continues to cavitate.Then,the mixture turbulence model and in-cylinder dynamic grid model are adopted to conduct computational fluid dynamics simulation of volume alternate cavitation.In the simulation,the cloud images at seven heights on the central axis are monitored,and the phenomenon and mechanism of height and eccentricity are analyzed in detail.By employing the cavitation flow visualization method,the generating mechanism and evolution law of cavitation are revealed.The synergistic effects of experiments and high-speed camera capturing confirm the correctness of the simulation results.In the experiment,the volume change stroke of the airtight container is set to 20 mm,the volume change frequency is 18 Hz,and the shooting frequency of the high-speed camera is set to 10000 FPS.The experimental results indicate that the position of the cavitation phenomenon has a reasonable law during the whole evolution cycle of the cavitation cloud.Also,the volume alternation cycle corresponds to the generation,development,and collapse stages of cavitation bubbles.

Geographical Names as Cultural Symbols:The Law of Naming System’s Evolution in Southwest China

In this paper,the geographic name in Southwest China is regarded as a symbolic representation of human beings,and the dynamic social and historical process behind the place names is restored from the perspective of the symbolic anthropology.There are three paths in the construction and evolution of geographic names in Southwest China—Ethnic information,sacred systems,and local representation,which have been rewritten,masked,and reconstructed over the years.As a result,the system of geographical names is gradually formed and integrated into local memory through space building,culture filling,and so on,affecting and influencing local group identity and cognitive concept.

Regulating Effect of Substrate Temperature on Sputteringgrown Ge/Si QDs under Low Ge Deposition

The effect of deposition temperature on the morphology and optoelectronic performance of Ge/Si QDs grown by magnetron sputtering under low Ge deposition(~4 nm)was investigated by atomic force microscopy,Raman spectroscopy,and photoluminescence(PL)tests.The experimental results indicate that temperatures higher than 750℃effectively increase the crystallization rate and surface smoothness of the Si buffer layer,and temperatures higher than 600℃significantly enhance the migration ability of Ge atoms,thus increasing the probability of Ge atoms meeting and nucleating to form QDs on Si buffer layer,but an excessively high temperature will cause the QDs to undergo an Ostwald ripening process and thus develop into super large islands.In addition,some PL peaks were observed in samples containing small-sized,high-density Ge QDs,the photoelectric properties reflected by these peaks were in good agreement with the corresponding structural characteristics of the grown QDs.Our results demonstrate the viability of preparing high-quality QDs by magnetron sputtering at high deposition rate,and the temperature effect is expected to work in conjunction with other controllable factors to further regulate QD growth,which paves an effective way for the industrial production of QDs that can be used in future devices.

Surrounding Rock Failure Mechanism and Control Technology of Gob-Side Entry with Triangle Coal Pillar at Island Longwall Panel in 15 m Extra-Thick Coal Seams

Taking the return air roadway of Tashan 8204 isolated island working face as the background, the evolution law of the stress field in the surrounding rock of the widened coal pillar area roadway during the mining period of the isolated island working face is obtained through numerical simulation. The hazardous area of strong mine pressure under different coal pillar widths is determined. Through simulation, it is known that when the width of the coal pillar is less than 20 m, there is large bearing capacity on the coal side of the roadway entity. The force on the side of the coal pillar is relatively small. When the width of the coal pillar ranges from 25 m to 45 m, the vertical stress on the roadway and surrounding areas is relatively high. Pressure relief measures need to be taken during mining to reduce surrounding rock stress. When the width of the coal pillar is greater than 45 m, the peak stress of the coal pillar is located in the deep part of the surrounding rock, but it still has a certain impact on the roadway. It is necessary to take pressure relief measures to transfer the stress to a deeper depth to ensure the stability of the triangular coal pillar during the safe mining period of the working face. This provides guidance for ensuring the stability of the triangular coal pillar during the safe mining period of the working face.

Time evolution of a squeezed chaotic field in an amplitude damping channel when used as a generating field for a squeezed number state

We investigate how an optical squeezed chaotic field（SCF） evolves in an amplitude dissipation channel. We have used the integration within ordered product of operators technique to derive its evolution law. We also show that the density operator of SCF can be viewed as a generating field of the squeezed number state.

Fractal characterization for the mining crack evolution process of overlying strata based on microseismic monitoring technology

In order to study the evolution laws during the development process of the coal face overburden rock mining-induced fissure,we studied the process of evolution of overburden rock mining-induced fissures and dynamically quantitatively described its fractal laws,based on the high-precision microseismic monitoring method and the nonlinear Fractal Geometry Theory.The results show that:the overburden rock mining-induced fissure fractal dimension experiences two periodic change processes with the coal face advance,namely a Small→ Big→ Small process,which tends to be stable;the functional relationship between the extraction step distance and the overburden rock mining-induced fissure fractal dimension is a cubic curve.The results suggest that the fractal dimension reflects the evolution characteristics of the overburden rock mining-induced fissure,which can be used as an evaluation index of the stability of the overburden rock strata,and it provides theoretical guidance for stability analysis of the overburden rock strata,goaf roof control and the support movements in the mining face.

Effects of Strain Rate and Fiber Content on the Dynamic Mechanical Properties of Sisal Fiber Cement-Based Composites

In this paper,a split Hopkinson pressure bar(SHPB)was used to investigate the dynamic impact mechanical behavior of sisal fiber-reinforced cement-based composites(SFRCCs),and the microscopic damage evolution of the composites was analyzed by scanning electron microscopy(SEM)and energy-dispersive X-ray spectrome-try(EDS).The results show that the addition of sisal fibers improves the impact resistance of cement-based composite materials.Compared with ordinary cement-based composites(OCCs),the SFRCCs demonstrate higher post-peak strength,ductility,and energy absorption capacity with higher fiber content.Moreover,the SFRCCs are strain rate sensitive materials,and their peak stress,ultimate strain,and energy integrals all increase with increasing strain rate.From the perspective of fracture failure characteristics,the failure of OCCs is dominated by the brittle failure of crystal cleavage.In contrast,the failure mode of the SFRCCs changes to microscale matrix cracks,multi-scale pull-out interface debonding of fibers(fine filaments and bundles),and mechanical interlock.This research provides an experimental basis for the engineering application of high-performance and green cement-based composites.

Creep damage evolution process of asphalt binder based on viscoelastic characteristics

The creep damage evolution of asphalt binder plays a significant role in investigating the formation mechanism of rutting.The rutting is the common distress at high temperatures for asphalt pavements.However,the reliability of existing creep damage parameters is under questioned,and these parameters cannot accurately illustrate the change of intrinsic microstructure for asphalt binder.In this paper,a new test protocol was given access to study the evolution of viscoelastic parameters during creep damage.It was completed by inserting the frequency sweep during creep test.The frequency sweep curve clusters were fitted by the generalized Kelvin-Voigt model for obtaining the change law of model parameters.Based on the change law and sensitivity analysis of model parameters,(E_(2)+E_(3))/2 was proposed as the creep damage variable.According to the curve of(E_(2)+E_(3))/2 versus loading time,two stages during the creep test could be identified:an approximate constant value in phase I and a linear decrease in phase II.Intrinsic differences about creep property of binders could be determined by this new proposed parameter.Above results not only ensure better understanding of the creep damage mechanism of binders,but also lay the theoretical foundation on predicting the anti-rutting performance of binders.

Physical and mechanical properties of sandstone containing a single fissure after exposure to high temperatures

In order to investigate the physical and mechanical properties of sandstone containing fissures after exposure to high temperatures,fissures with different angles α were prefabricated in the plate sandstone samples,and the processed samples were then heated at 5 different temperatures.Indoor uniaxial compression was conducted to analyze the change rules of physical properties of sandstone after exposure to high temperature,and the deformation,strength and failure characteristics of sandstone containing fissures.The results show that,with increasing temperature,the volume of sandstone increases gradually while the quality and density decrease gradually,and the color of sandstone remains basically unchanged while the brightness increases markedly when the temperature is higher than 585 ℃;the peak strength of sandstone containing fissures first decreases then increases when the temperature is between 25℃and 400℃.The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature,and the mechanical properties of sandstone show obvious deterioration after 400 ℃.The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature;with increasing angle αof the fissure,the evolution characteristics of the macro-mechanical parameters of sandstone are closely related to the their own mechanical properties.When the temperature is 800 ℃,the correlation between the peak strength and average modulus of sandstone and the angle α of the fissure is obviously weakened.The failure modes of sandstone containing fissures after high temperature exposure are of three different kinds including:tensile crack failure,tensile and shear cracks mixed failure,and shear crack failure.Tensile and shear crack mixed failure occur mainly at low temperatures and small angles;tensile crack failure occurs at high temperatures and large angles.