To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fract...To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fractures,this study considered the combined impact of geological-engineering factors on conductivity.Using reservoir production parameters and the discrete elementmethod,multispherical proppants were constructed.Additionally,a 3D fracture model,based on the specified conditions of the L block,employed coupled(Computational Fluid Dynamics)CFD-DEM(Discrete ElementMethod)for joint simulations to quantitatively analyze the transport and placement patterns of multispherical proppants in intersecting fractures.Results indicate that turbulent kinetic energy is an intrinsic factor affecting proppant transport.Moreover,the efficiency of placement and migration distance of low-sphericity quartz sand constructed by the DEM in the main fracture are significantly reduced compared to spherical ceramic proppants,with a 27.7%decrease in the volume fraction of the fracture surface,subsequently affecting the placement concentration and damaging fracture conductivity.Compared to small-angle fractures,controlling artificial and natural fractures to expand at angles of 45°to 60°increases the effective support length by approximately 20.6%.During hydraulic fracturing of gas wells,ensuring the fracture support area and post-closure conductivity can be achieved by controlling the sphericity of proppants and adjusting the perforation direction to control the direction of artificial fractures.展开更多
Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is sti...Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is still limited understanding of the propagation and extension of fractures around the wellbore during the fracturing process of horizontal wells in hydrate reservoirs,as well as the stress interference patterns between fractures.This study simulates hydraulic fracturing processes in hydrate reservoirs using a fluidsolid coupling discrete element method(DEM),and analyzes the impacts of hydrate saturation and geological and engineering factors on fracture extension and stress disturbance.The results show that hydraulic fracturing is more effective when hydrate saturation exceeds 30%and that fracture pressure increases with saturation.The increase in horizontal stress differential enhances the directionality of fracture propagation and reduces stress disturbance.The distribution uniformity index(DUI)reveals that injection pressure is directly proportional to the number of main fractures and inversely proportional to fracturing time,with fracturing efficiency depending on the spacing between injection points and the distance between wells.This work may provide reference for the commercial exploitation of natural gas hydrates.展开更多
Nonuniform track support and differential settlements are commonly observed in bridge approaches where the ballast layer can develop gaps at crosstie-ballast interfaces often referred to as a hanging crosstie conditio...Nonuniform track support and differential settlements are commonly observed in bridge approaches where the ballast layer can develop gaps at crosstie-ballast interfaces often referred to as a hanging crosstie condition.Hanging crossties usually yield unfavorable dynamic effects such as higher wheel loads,which negatively impact the serviceability and safety of railway operations.Hence,a better understanding of the mechanisms that cause hanging crossties and their effects on the ballast layer load-deformation characteristics is necessary.Since the ballast layer is a particulate medium,the discrete element method(DEM),which simulates ballast particle interactions individually,is ideal to explore the interparticle contact forces and ballast movements under dynamic wheel loading.Accurate representations of the dynamic loads from the train and track superstructure are needed for high-fidelity DEM modeling.This paper introduces an integrated modeling approach,which couples a single-crosstie DEM ballast model with a train–track–bridge(TTB)model using a proportional–integral–derivative control loop.The TTB–DEM model was validated with field measurements,and the coupled model calculates similar crosstie displacements as the TTB model.The TTB–DEM provided new insights into the ballast particle-scale behavior,which the TTB model alone cannot explore.The TTB–DEM coupling approach identified detrimental effects of hanging crossties on adjacent crossties,which were found to experience drastic vibrations and large ballast contact force concentrations.展开更多
The homogeneity of aggregate blend has a significant influence on the performance of asphalt mixture.The composition of aggregate blend,including the size combination and the mass ratio between each size particles(MRE...The homogeneity of aggregate blend has a significant influence on the performance of asphalt mixture.The composition of aggregate blend,including the size combination and the mass ratio between each size particles(MRESP),is an important factor affecting the homogeneity.This study investigated the influence of the size combination and MRESP on the distribution homogeneity of particles in aggregate blend using discrete element method(DEM).An indicator quantifying the distribution homogeneity was established according to the coefficient of variation(CV)for particle number.Two-size,three-size,and four-size aggregate blends with various compositions were designed.Laboratory tests show the DEM simulation is feasible.The particle distribution homogeneity in various blends was analyzed.The results showed the distribution homogeneity of each size particles in a blend is closely related to their mass fraction.The higher the mass fraction of the particles,the more homogeneous the distribution of them.The MRESP has no significant influence on the homogeneity of the blend composed of only coarse aggregates.However,the homogeneity of the blend composed of coarse and fine aggregates improves gradually with the increase of the mass fraction of fine aggregates.The smaller the maximum particle size in a blend,the better the homogeneity.It is suggested that the mass fraction of fine aggregates should be between 33%and 50%for achieving good homogeneity of aggregate blends.The research results can provide a reference for gradation design of asphalt mixture.展开更多
Gas storage in abandoned mines is one way to reuse waste space resources.The surrounding rock of gas storage reservoirs in underground roadways undergoes damage and deformation under the cyclic loading of gas charging...Gas storage in abandoned mines is one way to reuse waste space resources.The surrounding rock of gas storage reservoirs in underground roadways undergoes damage and deformation under the cyclic loading of gas charging and discharging,which can pose a risk to the safety of the reservoirs.This study establishes a true triaxial numerical model of rock mass with the discrete element method(DEM)and explores the crack evolution of surrounding rock of underground gas storage during cyclic loading and unloading.Also,a damage evolution model in numerical analysis considering residual deformation is developed to explain the experimental results.As was revealed,cyclic loading and unloading resulted in fatigue damage in the specimen and caused strength deterioration of the specimen.During the loading process,the uniformly distributed force chains of the rock mass redistributed,evolving gradually to mostly transverse force chains.This contributed to the appearance of blank areas in the force chains when through cracks appear.The ratio of tensile cracks to shear cracks gradually decreases and finally stabilizes at 7:1.The damage evolution model considering residual strain can be mutually verified with the numerical simulation results.Based on the DEM model,it was found that there was a certain threshold of confining pressure.When the confining pressure exceeded 30 MPa,the deformation to ductility of sandstone samples began to accelerate,with a greater residual strength.This study provides a theoretical basis for analyzing the long-term mechanical behavior of surrounding rock of gas storage in abandoned mines.展开更多
The glutenite reservoir is strongly heterogeneous due to the random distribution of gravels, making it challenging to perform hydraulic fracturing effectively. To solve this issue, it is essential to study interaction...The glutenite reservoir is strongly heterogeneous due to the random distribution of gravels, making it challenging to perform hydraulic fracturing effectively. To solve this issue, it is essential to study interaction behavior between hydraulic fractures(HFs) and gravels. A coupled hydro-mechanical model is proposed for HF propagation in glutenite using a grain-based discrete element method. This paper first investigates the dynamic evolution of HFs in glutenite, then analyzes the influences of various factors such as horizontal stress difference(Δσ), minimum horizontal stress(σh), gravel content(Vg), gravel size(dg), and stiffness ratio of gravel to matrix(Rs) on HF propagation geometries. Results show that penetrating the gravel is the primary HF-gravel interaction behavior, which follows sequential and staggered initiation modes. Bypassing the gravel is the secondary behavior, which obeys the sequential initiation mode and occurs when the orientation of the gravel boundary is inclined to the maximum horizontal stress(σH). An offset along the gravel boundary is usually formed while penetrating gravels, and the offsets may cause fracture widths to decrease by 37.8%-84.4%. Even if stress dominates the direction of HF propagation, HFs still tend to deflect within gravels. The deviation angle from σH decreases with rising Δσand increases with the increase of dgand Rs. Additionally, intra-gravel shear HFs(IGS-HFs) are prone to be generated in coarse-grained glutenite under high Δσ, while more gravel-bypassing shear HFs(GBSHFs) tend to be created in argillaceous glutenite with high Rsthan in sandy glutenite with low Rs. The findings above prompt the emergence of a novel HF propagation pattern in glutenite, which helps to understand the real HF geometries and to provide theoretical guidance for treatments in the field.展开更多
Ceramic spheres,typically with a particle diameter of less than 0.8 mm,are frequently utilized as a critical proppant material in hydraulic fracturing for petroleum and natural gas extraction.Porous ceramic spheres wi...Ceramic spheres,typically with a particle diameter of less than 0.8 mm,are frequently utilized as a critical proppant material in hydraulic fracturing for petroleum and natural gas extraction.Porous ceramic spheres with artificial inherent pores are an important type of lightweight proppant,enabling their transport to distant fracture extremities and enhancing fracture conductivity.However,the focus frequently gravitates towards the low-density advantage,often overlooking the pore geometry impacts on compressive strength by traditional strength evaluation.This paper numerically bypasses such limitations by using a combined finite and discrete element method(FDEM)considering experimental results.The mesh size of the model undergoes validation,followed by the calibration of cohesive element parameters via the single particle compression test.The stimulation elucidates that proppants with a smaller pore size(40μm)manifest crack propagation evolution at a more rapid pace in comparison to their larger-pore counterparts,though the influence of pore diameter on overall strength is subtle.The inception of pores not only alters the trajectory of crack progression but also,with an increase in porosity,leads to a discernible decline in proppant compressive strength.Intriguingly,upon crossing a porosity threshold of 10%,the decrement in strength becomes more gradual.A denser congregation of pores accelerates crack propagation,undermining proppant robustness,suggesting that under analogous conditions,hollow proppants might not match the strength of their porous counterparts.This exploration elucidates the underlying mechanisms of proppant failure from a microstructural perspective,furnishing pivotal insights that may guide future refinements in the architectural design of porous proppant.展开更多
Aiming to analyze the damage mechanism of UTAO from the perspective of meso-mechanical mechanism using discrete element method(DEM),we conducted study of diseases problems of UTAO in several provinces in China,and fou...Aiming to analyze the damage mechanism of UTAO from the perspective of meso-mechanical mechanism using discrete element method(DEM),we conducted study of diseases problems of UTAO in several provinces in China,and found that aggregate spalling was one of the main disease types of UTAO.A discrete element model of UTAO pavement structure was constructed to explore the meso-mechanical mechanism of UTAO damage under the influence of layer thickness,gradation,and bonding modulus.The experimental results show that,as the thickness of UTAO decreasing,the maximum value and the mean value of the contact force between all aggregate particles gradually increase,which leads to aggregates more prone to spalling.Compared with OGFC-5 UTAO,AC-5 UTAO presents smaller maximum and average values of all contact forces,and the loading pressure in AC-5 UTAO is fully diffused in the lateral direction.In addition,the increment of pavement modulus strengthens the overall force of aggregate particles inside UTAO,resulting in aggregate particles peeling off more easily.The increase of bonding modulus changes the position where the maximum value of the tangential force appears,whereas has no effect on the normal force.展开更多
Previous studies on the hollow cylinder torsional shear test(HCTST)have mainly focused on the macroscopic behavior,while the micromechanical responses in soil specimens with shaped particles have rarely been investiga...Previous studies on the hollow cylinder torsional shear test(HCTST)have mainly focused on the macroscopic behavior,while the micromechanical responses in soil specimens with shaped particles have rarely been investigated.This paper develops a numerical model of the HCTST using the discrete element method(DEM).The method of bonded spheres in a hexagonal arrangement is proposed to generate flexible boundaries that can achieve real-time adjustment of the internal and external cell pressures and capture the inhomogeneous deformation in the radial direction during shearing.Representative angular particles are selected from Toyoura sand and reproduced in this model to approximate real sand particles.The model is then validated by comparing numerical and experimental results of HCTSTs on Toyoura sand with different major principal stress directions.Next,a series of HCTSTs with different combinations of major principal stress direction(a)and intermediate principal stress ratio(b)is simulated to quantitatively characterize the sand behavior under different shear conditions.The results show that the shaped particles are horizontally distributed before shearing,and the initial anisotropic packing structure further results in different stressestrain curves in cases with different a and b values.The distribution of force chains is affected by both a and b during the shear process,together with the formation of the shear bands in different patterns.The contact normal anisotropy and contact force anisotropy show different evolution patterns when either a or b varies,resulting in the differences in the non-coaxiality and other macroscopic responses.This study improves the understanding of the macroscopic response of sand from a microscopic perspective and provides valuable insights for the constitutive modeling of sand.展开更多
Expanded polystyrene(EPS)particle-based lightweight soil,which is a type of lightweight filler,is mainly used in road engineering.The stability of subgrades under dynamic loading is attracting increased research atten...Expanded polystyrene(EPS)particle-based lightweight soil,which is a type of lightweight filler,is mainly used in road engineering.The stability of subgrades under dynamic loading is attracting increased research attention.The traditional method for studying the dynamic strength characteristics of soils is dynamic triaxial testing,and the discrete element simulation of lightweight soils under cyclic load has rarely been considered.To study the meso-mechanisms of the dynamic failure processes of EPS particle lightweight soils,a discrete element numerical model is established using the particle flow code(PFC)software.The contact force,displacement field,and velocity field of lightweight soil under different cumulative compressive strains are studied.The results show that the hysteresis curves of lightweight soil present characteristics of strain accumulation,which reflect the cyclic effects of the dynamic load.When the confining pressure increases,the contact force of the particles also increases.The confining pressure can restrain the motion of the particle system and increase the dynamic strength of the sample.When the confining pressure is held constant,an increase in compressive strain causes minimal change in the contact force between soil particles.However,the contact force between the EPS particles decreases,and their displacement direction points vertically toward the center of the sample.Under an increase in compressive strain,the velocity direction of the particle system changes from a random distribution and points vertically toward the center of the sample.When the compressive strain is 5%,the number of particles deflected in the particle velocity direction increases significantly,and the cumulative rate of deformation in the lightweight soil accelerates.Therefore,it is feasible to use 5%compressive strain as the dynamic strength standard for lightweight soil.Discrete element methods provide a new approach toward the dynamic performance evaluation of lightweight soil subgrades.展开更多
In this study,a common-node DEM-SPH coupling model based on the shared node method is proposed,and a fluid–structure coupling method using the common-node discrete element method-smoothed particle hydrodynamics(DS-SP...In this study,a common-node DEM-SPH coupling model based on the shared node method is proposed,and a fluid–structure coupling method using the common-node discrete element method-smoothed particle hydrodynamics(DS-SPH)method is developed using LS-DYNA software.The DEM and SPH are established on the same node to create common-node DEM-SPH particles,allowing for fluid–structure interactions.Numerical simulations of various scenarios,including water entry of a rigid sphere,dam-break propagation over wet beds,impact on an ice plate floating on water and ice accumulation on offshore structures,are conducted.The interaction between DS particles and SPH fluid and the crack generation mechanism and expansion characteristics of the ice plate under the interaction of structure and fluid are also studied.The results are compared with available data to verify the proposed coupling method.Notably,the simulation results demonstrated that controlling the cutoff pressure of internal SPH particles could effectively control particle splashing during ice crushing failure.展开更多
This research introduces a novel approach to enhancing bucket elevator design and operation through the integration of discrete element method(DEM)simulation,design of experiments(DOE),and metaheuristic optimization a...This research introduces a novel approach to enhancing bucket elevator design and operation through the integration of discrete element method(DEM)simulation,design of experiments(DOE),and metaheuristic optimization algorithms.Specifically,the study employs the firefly algorithm(FA),a metaheuristic optimization technique,to optimize bucket elevator parameters for maximizing transport mass and mass flow rate discharge of granular materials under specified working conditions.The experimental methodology involves several key steps:screening experiments to identify significant factors affecting bucket elevator operation,central composite design(CCD)experiments to further explore these factors,and response surface methodology(RSM)to create predictive models for transport mass and mass flow rate discharge.The FA algorithm is then applied to optimize these models,and the results are validated through simulation and empirical experiments.The study validates the optimized parameters through simulation and empirical experiments,comparing results with DEM simulation.The outcomes demonstrate the effectiveness of the FA algorithm in identifying optimal bucket parameters,showcasing less than 10%and 15%deviation for transport mass and mass flow rate discharge,respectively,between predicted and actual values.Overall,this research provides insights into the critical factors influencing bucket elevator operation and offers a systematic methodology for optimizing bucket parameters,contributing to more efficient material handling in various industrial applications.展开更多
In order to investigate the permanent deformation behavior of asphalt mixtures from discontinuity, the virtual rutting test of asphalt mixtures is developed by the discrete element method （DEM）. A digital specimen g...In order to investigate the permanent deformation behavior of asphalt mixtures from discontinuity, the virtual rutting test of asphalt mixtures is developed by the discrete element method （DEM）. A digital specimen generation procedure considering aggregate gradation and irregular shape is developed based on the probability theory and the Monte Carlo method. The virtual rutting test is then conducted based on the generated digital specimen. In addition, on the basis of the time-temperature superposition （TTS） principle, a calculation method is used to reduce the computation time of the virtual rutting test. The simulation results are compared with the laboratory measurements. The results show that the calculation method based on the TFS principle in the discrete element （DE） viscoelastic model can significantly reduce the computation time. The deformation law of asphalt mixtures in the virtual rutting test is similar to the laboratory measurements, and the deformation and the dynamic stability of the virtual rutting test are slightly greater than the laboratory measurements. The two-dimensional virtual rutting test can predict the permanent deformation performance of asphalt mixtures.展开更多
COREX process is one of the earliest industrialized smelting reduction ironmaking technology.A numerical simulation model based on discrete element method ( DEM ) has been developed to analyze the burden distribution ...COREX process is one of the earliest industrialized smelting reduction ironmaking technology.A numerical simulation model based on discrete element method ( DEM ) has been developed to analyze the burden distribution in the melter gasifier of COREX process.The DEM considering the collisions between particles can directly reproduce the charging process.The burden trajectory , the location and the burden surface profile are analyzed in melter gasifier with a mixing charging of coal and direct reduction iron ( DRI ) at the same time.Considering the porosity of packed bed has an important effect on the gas flow distribution of melter gasifier , a method to calculate porosity has been proposed.The distribution of DRI and coal and the porosity in the radial direction are given under different charging patterns , which is necessary to judge the gas flow distribution and provide base data for further researching the melter gasifier for the next work in the future.The research results can be used to guide the operation of adjusting charging and provide important basis for optimizing the charging patterns in order to obtain the reasonable gas distribution.展开更多
Many rock avalanches were triggered by the Wenchuan earthquake on May 12, 2008 in southwest China. Protection galleries covered with a single soil layer are usually used to protect against rockfall. Since one-layer pr...Many rock avalanches were triggered by the Wenchuan earthquake on May 12, 2008 in southwest China. Protection galleries covered with a single soil layer are usually used to protect against rockfall. Since one-layer protection galleries do not have sufficient buffer capacity, a two-layered absorbing system has been designed. This study aims to find whether an expanded poly-styrol （EPS） cushion, which is used in the soil-covered protection galleries for shock absorption, could be positioned under dynamic loadings. The dynamic impacts of the two-layered absorbing system under the conditions of rock avalanches are numerically simulated through a 2D discrete dement method. By selecting reasonable parameters, a series of numerical experiments were conducted to find the best combination for the two- layered absorbing system. The values of the EPS layer area as a percentage of the total area were set as 0% （Sl）, 22~ （S2）, and 70% （$3）. 22~ of the area of the EPS layer was found to be a reasonable value, and experiments were conducted to find the best position of the EPS layer in the two-layered absorbing system. The numerical results yield useful conclusions regarding the interaction between the impacting avalanches and the two-layered absorbing system. The soil layer can absorb the shock energy effectively and S2 （0.4-m thick EPS cushion covered with soil layer） is the most efficient combination, which can reduce the impact force, compared with the other combinations.展开更多
With the development of high-speed and heavy-haul railway in China, problems like insufficient thickness of ballast bed and overlarge track stiffness are obvious. Ballast may break into small particles and their conta...With the development of high-speed and heavy-haul railway in China, problems like insufficient thickness of ballast bed and overlarge track stiffness are obvious. Ballast may break into small particles and their contact status will deteriorate under cyclic loading, resulting in ballast degradation. Discrete element method(DEM) was used to research improved performance of ballast bed using elastic sleeper. Clusters were generated by bonding spheres to model real ballasts, while broken bonds were utilized to distinguish breakage. Two kinds of ballast beds with elastic sleeper and conventional sleeper were established, respectively. After applying cyclic loading to the models, differences of mechanical properties between two models were analyzed by contrasting their dynamic behavior indexes, such as particle contact force, sleeper settlement, vibration velocity and acceleration, breakage characteristic. The results illustrate that compared with conventional sleeper, elastic sleeper increases sleeper settlement, while reduces ballast vibration and contact force between particles, which could depress ballast breakage.展开更多
The past decade has witnessed the substantial growth in research interests and progress on the subject of coupled hydro-mechanical processes in rocks and soils,driven mainly by the surge of research in unconventional ...The past decade has witnessed the substantial growth in research interests and progress on the subject of coupled hydro-mechanical processes in rocks and soils,driven mainly by the surge of research in unconventional hydrocarbon reservoirs and associated hazards.Many coupling techniques have been developed to include the effects of fluid flow in the discrete element method(DEM),and the techniques have been applied to a variety of geomechanical problems.Although these coupling methods have been successfully applied in various engineering fields,no single fluid/DEM coupling method is universal due to the complexity of engineering problems and the limitations of the numerical methods.For researchers and engineers,the key to solve a specific problem is to select the most appropriate fluid/DEM coupling method among these modeling technologies.The purpose of this paper is to give a comprehensive review of fluid flow/DEM coupling methods and relevant research.Given their importance,the availability or unavailability of best practice guidelines is outlined.The theoretical background and current status of DEM are introduced first,and the principles,applications,and advantages and disadvantages of different fluid flow/DEM coupling methods are discussed.Finally,a summary with speculation on future development trends is given.展开更多
The particulate discrete element method(DEM) can be employed to capture the response of rock,provided that appropriate bonding models are used to cement the particles to each other.Simulations of laboratory tests are ...The particulate discrete element method(DEM) can be employed to capture the response of rock,provided that appropriate bonding models are used to cement the particles to each other.Simulations of laboratory tests are important to establish the extent to which those models can capture realistic rock behaviors.Hitherto the focus in such comparison studies has either been on homogeneous specimens or use of two-dimensional(2D) models.In situ rock formations are often heterogeneous,thus exploring the ability of this type of models to capture heterogeneous material behavior is important to facilitate their use in design analysis.In situ stress states are basically three-dimensional(3D),and therefore it is important to develop 3D models for this purpose.This paper revisits an earlier experimental study on heterogeneous specimens,of which the relative proportions of weaker material(siltstone) and stronger,harder material(sandstone) were varied in a controlled manner.Using a 3D DEM model with the parallel bond model,virtual heterogeneous specimens were created.The overall responses in terms of variations in strength and stiffness with different percentages of weaker material(siltstone) were shown to agree with the experimental observations.There was also a good qualitative agreement in the failure patterns observed in the experiments and the simulations,suggesting that the DEM data enabled analysis of the initiation of localizations and micro fractures in the specimens.展开更多
A three-dimensional discrete element model of the connective type is presented. Moreover,a three-dimensional numerical analysis code,which can carry out the transitional pro- cess from connective model(for continuum)t...A three-dimensional discrete element model of the connective type is presented. Moreover,a three-dimensional numerical analysis code,which can carry out the transitional pro- cess from connective model(for continuum)to contact model(for non-continuum),is developed for simulating the mechanical process from continuum to non-continuum.The wave propagation process in a concrete block(as continuum)made of cement grout under impact loading is numer- ically simulated with this code.By comparing its numerical results with those by LS-DYNA,the calculation accuracy of the model and algorithm is proved.Furthermore,the failure process of the concrete block under quasi-static loading is demonstrated,showing the basic dynamic tran- sitional process from continuum to non-continuum.The results of calculation can be displayed by animation.The damage modes are similar to the experimental results.The two numerical examples above prove that our model and its code are powerful and efficient in simulating the dynamic failure problems accompanying the transition from continuum to non-continuum.It also shows that the discrete element method(DEM)will have broad prospects for development and application.展开更多
Discrete element method(DEM)has been intensively used to study the constitutive behaviour of granular materials.However,to what extent a real granular material can be reproduced by virtual DEM simulations remains uncl...Discrete element method(DEM)has been intensively used to study the constitutive behaviour of granular materials.However,to what extent a real granular material can be reproduced by virtual DEM simulations remains unclear.This study attempts to answer this question by comparing DEM simulations with typical features of experimental granular materials.Three groups of models with spherical and clumped particles are investigated from four perspectives:(i)deviatoric stress and volumetric behaviour;(ii)critical state behaviour;(iii)stress-dilatancy relationship;and(iv)the evolution of principal stress ratio against axial strain.The results demonstrate that DEM with spherical or clumped particles is capable of qualitatively describing macroscopic deviatoric stress responses,volumetric behaviour,and critical state behaviour observed in experiments for granular materials.On the other hand,some qualitative deviations between experiments and the investigated DEM simulations are also observed,in terms of the stress-dilatancy behaviour and principal stress ratio against axial strain,which are proven to be critical for constitutive modelling.The results demonstrate that DEM with spherical or clumped particles may not necessarily fully capture experimental features of granular materials even from a qualitative perspective.It is thus encouraged to thoroughly validate DEM with experiments when developing constitutive models based on DEM observations.展开更多
基金funded by the project of the Major Scientific and Technological Projects of CNOOC in the 14th Five-Year Plan(No.KJGG2022-0701)the CNOOC Research Institute(No.2020PFS-03).
文摘To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fractures,this study considered the combined impact of geological-engineering factors on conductivity.Using reservoir production parameters and the discrete elementmethod,multispherical proppants were constructed.Additionally,a 3D fracture model,based on the specified conditions of the L block,employed coupled(Computational Fluid Dynamics)CFD-DEM(Discrete ElementMethod)for joint simulations to quantitatively analyze the transport and placement patterns of multispherical proppants in intersecting fractures.Results indicate that turbulent kinetic energy is an intrinsic factor affecting proppant transport.Moreover,the efficiency of placement and migration distance of low-sphericity quartz sand constructed by the DEM in the main fracture are significantly reduced compared to spherical ceramic proppants,with a 27.7%decrease in the volume fraction of the fracture surface,subsequently affecting the placement concentration and damaging fracture conductivity.Compared to small-angle fractures,controlling artificial and natural fractures to expand at angles of 45°to 60°increases the effective support length by approximately 20.6%.During hydraulic fracturing of gas wells,ensuring the fracture support area and post-closure conductivity can be achieved by controlling the sphericity of proppants and adjusting the perforation direction to control the direction of artificial fractures.
基金financially supported by the National Key Research and Development Plan(2023YFC2811001)the National Natural Science Foundation of China(42206233)the Taishan Scholars Program(tsqn202312280,tsqn202306297)。
文摘Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is still limited understanding of the propagation and extension of fractures around the wellbore during the fracturing process of horizontal wells in hydrate reservoirs,as well as the stress interference patterns between fractures.This study simulates hydraulic fracturing processes in hydrate reservoirs using a fluidsolid coupling discrete element method(DEM),and analyzes the impacts of hydrate saturation and geological and engineering factors on fracture extension and stress disturbance.The results show that hydraulic fracturing is more effective when hydrate saturation exceeds 30%and that fracture pressure increases with saturation.The increase in horizontal stress differential enhances the directionality of fracture propagation and reduces stress disturbance.The distribution uniformity index(DUI)reveals that injection pressure is directly proportional to the number of main fractures and inversely proportional to fracturing time,with fracturing efficiency depending on the spacing between injection points and the distance between wells.This work may provide reference for the commercial exploitation of natural gas hydrates.
基金a U.S. Federal Railroad Administration (FRA)BAA project,titled “Mitigation of Differential Movement at Railway Transitions for High-Speed Passenger Rail and Joint Passenger/Freight Corridors”the financial support provided by the China Scholarship Council (CSC),which funded Zhongyi Liu’s and Wenjing Li’s time and research efforts for this study
文摘Nonuniform track support and differential settlements are commonly observed in bridge approaches where the ballast layer can develop gaps at crosstie-ballast interfaces often referred to as a hanging crosstie condition.Hanging crossties usually yield unfavorable dynamic effects such as higher wheel loads,which negatively impact the serviceability and safety of railway operations.Hence,a better understanding of the mechanisms that cause hanging crossties and their effects on the ballast layer load-deformation characteristics is necessary.Since the ballast layer is a particulate medium,the discrete element method(DEM),which simulates ballast particle interactions individually,is ideal to explore the interparticle contact forces and ballast movements under dynamic wheel loading.Accurate representations of the dynamic loads from the train and track superstructure are needed for high-fidelity DEM modeling.This paper introduces an integrated modeling approach,which couples a single-crosstie DEM ballast model with a train–track–bridge(TTB)model using a proportional–integral–derivative control loop.The TTB–DEM model was validated with field measurements,and the coupled model calculates similar crosstie displacements as the TTB model.The TTB–DEM provided new insights into the ballast particle-scale behavior,which the TTB model alone cannot explore.The TTB–DEM coupling approach identified detrimental effects of hanging crossties on adjacent crossties,which were found to experience drastic vibrations and large ballast contact force concentrations.
基金funded by the National Natural Science Foundation of China(No.51978048).
文摘The homogeneity of aggregate blend has a significant influence on the performance of asphalt mixture.The composition of aggregate blend,including the size combination and the mass ratio between each size particles(MRESP),is an important factor affecting the homogeneity.This study investigated the influence of the size combination and MRESP on the distribution homogeneity of particles in aggregate blend using discrete element method(DEM).An indicator quantifying the distribution homogeneity was established according to the coefficient of variation(CV)for particle number.Two-size,three-size,and four-size aggregate blends with various compositions were designed.Laboratory tests show the DEM simulation is feasible.The particle distribution homogeneity in various blends was analyzed.The results showed the distribution homogeneity of each size particles in a blend is closely related to their mass fraction.The higher the mass fraction of the particles,the more homogeneous the distribution of them.The MRESP has no significant influence on the homogeneity of the blend composed of only coarse aggregates.However,the homogeneity of the blend composed of coarse and fine aggregates improves gradually with the increase of the mass fraction of fine aggregates.The smaller the maximum particle size in a blend,the better the homogeneity.It is suggested that the mass fraction of fine aggregates should be between 33%and 50%for achieving good homogeneity of aggregate blends.The research results can provide a reference for gradation design of asphalt mixture.
基金National Natural Science Foundation of China,Grant/Award Numbers:U22A20598,52104107National Key Research and Development Program of China,Grant/Award Numbers:2023YFC2907300,2019YFE0118500,2019YFC1904304Natural Science Foundation of Jiangsu Province,Grant/Award Number:BK20200634。
文摘Gas storage in abandoned mines is one way to reuse waste space resources.The surrounding rock of gas storage reservoirs in underground roadways undergoes damage and deformation under the cyclic loading of gas charging and discharging,which can pose a risk to the safety of the reservoirs.This study establishes a true triaxial numerical model of rock mass with the discrete element method(DEM)and explores the crack evolution of surrounding rock of underground gas storage during cyclic loading and unloading.Also,a damage evolution model in numerical analysis considering residual deformation is developed to explain the experimental results.As was revealed,cyclic loading and unloading resulted in fatigue damage in the specimen and caused strength deterioration of the specimen.During the loading process,the uniformly distributed force chains of the rock mass redistributed,evolving gradually to mostly transverse force chains.This contributed to the appearance of blank areas in the force chains when through cracks appear.The ratio of tensile cracks to shear cracks gradually decreases and finally stabilizes at 7:1.The damage evolution model considering residual strain can be mutually verified with the numerical simulation results.Based on the DEM model,it was found that there was a certain threshold of confining pressure.When the confining pressure exceeded 30 MPa,the deformation to ductility of sandstone samples began to accelerate,with a greater residual strength.This study provides a theoretical basis for analyzing the long-term mechanical behavior of surrounding rock of gas storage in abandoned mines.
基金supported by the National Natural Science Foundation of China(Grant No.52304003)the Natural Science Foundation of Sichuan Province(Grant No.2024NSFSC0961)the Postdoctoral Fellowship Program of CPSF(Grant No.GZB20230090).
文摘The glutenite reservoir is strongly heterogeneous due to the random distribution of gravels, making it challenging to perform hydraulic fracturing effectively. To solve this issue, it is essential to study interaction behavior between hydraulic fractures(HFs) and gravels. A coupled hydro-mechanical model is proposed for HF propagation in glutenite using a grain-based discrete element method. This paper first investigates the dynamic evolution of HFs in glutenite, then analyzes the influences of various factors such as horizontal stress difference(Δσ), minimum horizontal stress(σh), gravel content(Vg), gravel size(dg), and stiffness ratio of gravel to matrix(Rs) on HF propagation geometries. Results show that penetrating the gravel is the primary HF-gravel interaction behavior, which follows sequential and staggered initiation modes. Bypassing the gravel is the secondary behavior, which obeys the sequential initiation mode and occurs when the orientation of the gravel boundary is inclined to the maximum horizontal stress(σH). An offset along the gravel boundary is usually formed while penetrating gravels, and the offsets may cause fracture widths to decrease by 37.8%-84.4%. Even if stress dominates the direction of HF propagation, HFs still tend to deflect within gravels. The deviation angle from σH decreases with rising Δσand increases with the increase of dgand Rs. Additionally, intra-gravel shear HFs(IGS-HFs) are prone to be generated in coarse-grained glutenite under high Δσ, while more gravel-bypassing shear HFs(GBSHFs) tend to be created in argillaceous glutenite with high Rsthan in sandy glutenite with low Rs. The findings above prompt the emergence of a novel HF propagation pattern in glutenite, which helps to understand the real HF geometries and to provide theoretical guidance for treatments in the field.
基金the financial support provided by Tianfu Yongxing Laboratory Organized Research Project Funding(No.2023CXXM01)the ARC linkage program(No.LP200100420).
文摘Ceramic spheres,typically with a particle diameter of less than 0.8 mm,are frequently utilized as a critical proppant material in hydraulic fracturing for petroleum and natural gas extraction.Porous ceramic spheres with artificial inherent pores are an important type of lightweight proppant,enabling their transport to distant fracture extremities and enhancing fracture conductivity.However,the focus frequently gravitates towards the low-density advantage,often overlooking the pore geometry impacts on compressive strength by traditional strength evaluation.This paper numerically bypasses such limitations by using a combined finite and discrete element method(FDEM)considering experimental results.The mesh size of the model undergoes validation,followed by the calibration of cohesive element parameters via the single particle compression test.The stimulation elucidates that proppants with a smaller pore size(40μm)manifest crack propagation evolution at a more rapid pace in comparison to their larger-pore counterparts,though the influence of pore diameter on overall strength is subtle.The inception of pores not only alters the trajectory of crack progression but also,with an increase in porosity,leads to a discernible decline in proppant compressive strength.Intriguingly,upon crossing a porosity threshold of 10%,the decrement in strength becomes more gradual.A denser congregation of pores accelerates crack propagation,undermining proppant robustness,suggesting that under analogous conditions,hollow proppants might not match the strength of their porous counterparts.This exploration elucidates the underlying mechanisms of proppant failure from a microstructural perspective,furnishing pivotal insights that may guide future refinements in the architectural design of porous proppant.
文摘Aiming to analyze the damage mechanism of UTAO from the perspective of meso-mechanical mechanism using discrete element method(DEM),we conducted study of diseases problems of UTAO in several provinces in China,and found that aggregate spalling was one of the main disease types of UTAO.A discrete element model of UTAO pavement structure was constructed to explore the meso-mechanical mechanism of UTAO damage under the influence of layer thickness,gradation,and bonding modulus.The experimental results show that,as the thickness of UTAO decreasing,the maximum value and the mean value of the contact force between all aggregate particles gradually increase,which leads to aggregates more prone to spalling.Compared with OGFC-5 UTAO,AC-5 UTAO presents smaller maximum and average values of all contact forces,and the loading pressure in AC-5 UTAO is fully diffused in the lateral direction.In addition,the increment of pavement modulus strengthens the overall force of aggregate particles inside UTAO,resulting in aggregate particles peeling off more easily.The increase of bonding modulus changes the position where the maximum value of the tangential force appears,whereas has no effect on the normal force.
基金supports from the National Key R&D Program of China(Grant No.2023YFC3009400)Research Grants Council of Hong Kong(Grant Nos.15220221 and 15229223).
文摘Previous studies on the hollow cylinder torsional shear test(HCTST)have mainly focused on the macroscopic behavior,while the micromechanical responses in soil specimens with shaped particles have rarely been investigated.This paper develops a numerical model of the HCTST using the discrete element method(DEM).The method of bonded spheres in a hexagonal arrangement is proposed to generate flexible boundaries that can achieve real-time adjustment of the internal and external cell pressures and capture the inhomogeneous deformation in the radial direction during shearing.Representative angular particles are selected from Toyoura sand and reproduced in this model to approximate real sand particles.The model is then validated by comparing numerical and experimental results of HCTSTs on Toyoura sand with different major principal stress directions.Next,a series of HCTSTs with different combinations of major principal stress direction(a)and intermediate principal stress ratio(b)is simulated to quantitatively characterize the sand behavior under different shear conditions.The results show that the shaped particles are horizontally distributed before shearing,and the initial anisotropic packing structure further results in different stressestrain curves in cases with different a and b values.The distribution of force chains is affected by both a and b during the shear process,together with the formation of the shear bands in different patterns.The contact normal anisotropy and contact force anisotropy show different evolution patterns when either a or b varies,resulting in the differences in the non-coaxiality and other macroscopic responses.This study improves the understanding of the macroscopic response of sand from a microscopic perspective and provides valuable insights for the constitutive modeling of sand.
基金supported by the National Natural Science Foundation of China (No. 51509211)the China Postdoctoral Science Foundation (No. 2016M602863)+5 种基金the Natural Science Foundation of Shaanxi Province (Nos. 2024JC-YBMS-354 and 2021JLM-51)the Excellent Science and Technology Activities Foundation for Returned Overseas Teachers of Shaanxi Province (No. 2018031)the Social Development Foundation of Shaanxi Province (No. 2015SF260)the Postdoctoral Science Foundation of Shaanxi Province (No. 2017BSHYDZZ50)Shaanxi Key Laboratory of Safety and Durability of Concrete Structures, Xijing University (No. SZ02306)Xi’an Key Laboratory of Geotechnical and Underground Engineering, Xi’an University of Science and Technology (No. XKLGUEKF21-02)
文摘Expanded polystyrene(EPS)particle-based lightweight soil,which is a type of lightweight filler,is mainly used in road engineering.The stability of subgrades under dynamic loading is attracting increased research attention.The traditional method for studying the dynamic strength characteristics of soils is dynamic triaxial testing,and the discrete element simulation of lightweight soils under cyclic load has rarely been considered.To study the meso-mechanisms of the dynamic failure processes of EPS particle lightweight soils,a discrete element numerical model is established using the particle flow code(PFC)software.The contact force,displacement field,and velocity field of lightweight soil under different cumulative compressive strains are studied.The results show that the hysteresis curves of lightweight soil present characteristics of strain accumulation,which reflect the cyclic effects of the dynamic load.When the confining pressure increases,the contact force of the particles also increases.The confining pressure can restrain the motion of the particle system and increase the dynamic strength of the sample.When the confining pressure is held constant,an increase in compressive strain causes minimal change in the contact force between soil particles.However,the contact force between the EPS particles decreases,and their displacement direction points vertically toward the center of the sample.Under an increase in compressive strain,the velocity direction of the particle system changes from a random distribution and points vertically toward the center of the sample.When the compressive strain is 5%,the number of particles deflected in the particle velocity direction increases significantly,and the cumulative rate of deformation in the lightweight soil accelerates.Therefore,it is feasible to use 5%compressive strain as the dynamic strength standard for lightweight soil.Discrete element methods provide a new approach toward the dynamic performance evaluation of lightweight soil subgrades.
基金supported by the National Natural Science Foundation of China(Grant No.52201323).
文摘In this study,a common-node DEM-SPH coupling model based on the shared node method is proposed,and a fluid–structure coupling method using the common-node discrete element method-smoothed particle hydrodynamics(DS-SPH)method is developed using LS-DYNA software.The DEM and SPH are established on the same node to create common-node DEM-SPH particles,allowing for fluid–structure interactions.Numerical simulations of various scenarios,including water entry of a rigid sphere,dam-break propagation over wet beds,impact on an ice plate floating on water and ice accumulation on offshore structures,are conducted.The interaction between DS particles and SPH fluid and the crack generation mechanism and expansion characteristics of the ice plate under the interaction of structure and fluid are also studied.The results are compared with available data to verify the proposed coupling method.Notably,the simulation results demonstrated that controlling the cutoff pressure of internal SPH particles could effectively control particle splashing during ice crushing failure.
基金This research was funded by the Faculty of Engineering,King Mongkut’s University of Technology North Bangkok.Contract No.ENG-NEW-66-39.
文摘This research introduces a novel approach to enhancing bucket elevator design and operation through the integration of discrete element method(DEM)simulation,design of experiments(DOE),and metaheuristic optimization algorithms.Specifically,the study employs the firefly algorithm(FA),a metaheuristic optimization technique,to optimize bucket elevator parameters for maximizing transport mass and mass flow rate discharge of granular materials under specified working conditions.The experimental methodology involves several key steps:screening experiments to identify significant factors affecting bucket elevator operation,central composite design(CCD)experiments to further explore these factors,and response surface methodology(RSM)to create predictive models for transport mass and mass flow rate discharge.The FA algorithm is then applied to optimize these models,and the results are validated through simulation and empirical experiments.The study validates the optimized parameters through simulation and empirical experiments,comparing results with DEM simulation.The outcomes demonstrate the effectiveness of the FA algorithm in identifying optimal bucket parameters,showcasing less than 10%and 15%deviation for transport mass and mass flow rate discharge,respectively,between predicted and actual values.Overall,this research provides insights into the critical factors influencing bucket elevator operation and offers a systematic methodology for optimizing bucket parameters,contributing to more efficient material handling in various industrial applications.
基金The National Natural Science Foundation of China(No.51108081)
文摘In order to investigate the permanent deformation behavior of asphalt mixtures from discontinuity, the virtual rutting test of asphalt mixtures is developed by the discrete element method （DEM）. A digital specimen generation procedure considering aggregate gradation and irregular shape is developed based on the probability theory and the Monte Carlo method. The virtual rutting test is then conducted based on the generated digital specimen. In addition, on the basis of the time-temperature superposition （TTS） principle, a calculation method is used to reduce the computation time of the virtual rutting test. The simulation results are compared with the laboratory measurements. The results show that the calculation method based on the TFS principle in the discrete element （DE） viscoelastic model can significantly reduce the computation time. The deformation law of asphalt mixtures in the virtual rutting test is similar to the laboratory measurements, and the deformation and the dynamic stability of the virtual rutting test are slightly greater than the laboratory measurements. The two-dimensional virtual rutting test can predict the permanent deformation performance of asphalt mixtures.
基金Item Sponsored by Fundamental Research Funds for Central Universities of China ( N090402021 )
文摘COREX process is one of the earliest industrialized smelting reduction ironmaking technology.A numerical simulation model based on discrete element method ( DEM ) has been developed to analyze the burden distribution in the melter gasifier of COREX process.The DEM considering the collisions between particles can directly reproduce the charging process.The burden trajectory , the location and the burden surface profile are analyzed in melter gasifier with a mixing charging of coal and direct reduction iron ( DRI ) at the same time.Considering the porosity of packed bed has an important effect on the gas flow distribution of melter gasifier , a method to calculate porosity has been proposed.The distribution of DRI and coal and the porosity in the radial direction are given under different charging patterns , which is necessary to judge the gas flow distribution and provide base data for further researching the melter gasifier for the next work in the future.The research results can be used to guide the operation of adjusting charging and provide important basis for optimizing the charging patterns in order to obtain the reasonable gas distribution.
基金financial support from the Project of National Science Foundation of China(Grant No.41272346)the National Outstanding Youth Funds(Grant No.41225011)+2 种基金financial support from the Science & Technology Research Plan of China Railway Eryuan Engineering Group CO.LTD (Grant No.13164196(13-15))the Project of National Science Foundation of China(Grant Nos. 41472293,91430105)"hundred talents" program of CAS
文摘Many rock avalanches were triggered by the Wenchuan earthquake on May 12, 2008 in southwest China. Protection galleries covered with a single soil layer are usually used to protect against rockfall. Since one-layer protection galleries do not have sufficient buffer capacity, a two-layered absorbing system has been designed. This study aims to find whether an expanded poly-styrol （EPS） cushion, which is used in the soil-covered protection galleries for shock absorption, could be positioned under dynamic loadings. The dynamic impacts of the two-layered absorbing system under the conditions of rock avalanches are numerically simulated through a 2D discrete dement method. By selecting reasonable parameters, a series of numerical experiments were conducted to find the best combination for the two- layered absorbing system. The values of the EPS layer area as a percentage of the total area were set as 0% （Sl）, 22~ （S2）, and 70% （$3）. 22~ of the area of the EPS layer was found to be a reasonable value, and experiments were conducted to find the best position of the EPS layer in the two-layered absorbing system. The numerical results yield useful conclusions regarding the interaction between the impacting avalanches and the two-layered absorbing system. The soil layer can absorb the shock energy effectively and S2 （0.4-m thick EPS cushion covered with soil layer） is the most efficient combination, which can reduce the impact force, compared with the other combinations.
基金Project(U1234211)supported by the National Natural Science Foundation of ChinaProject(2013G009-B)supported by China Railway Corporation
文摘With the development of high-speed and heavy-haul railway in China, problems like insufficient thickness of ballast bed and overlarge track stiffness are obvious. Ballast may break into small particles and their contact status will deteriorate under cyclic loading, resulting in ballast degradation. Discrete element method(DEM) was used to research improved performance of ballast bed using elastic sleeper. Clusters were generated by bonding spheres to model real ballasts, while broken bonds were utilized to distinguish breakage. Two kinds of ballast beds with elastic sleeper and conventional sleeper were established, respectively. After applying cyclic loading to the models, differences of mechanical properties between two models were analyzed by contrasting their dynamic behavior indexes, such as particle contact force, sleeper settlement, vibration velocity and acceleration, breakage characteristic. The results illustrate that compared with conventional sleeper, elastic sleeper increases sleeper settlement, while reduces ballast vibration and contact force between particles, which could depress ballast breakage.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41772286 and 42077247)the Fundamental Research Funds for the Central Universities, China
文摘The past decade has witnessed the substantial growth in research interests and progress on the subject of coupled hydro-mechanical processes in rocks and soils,driven mainly by the surge of research in unconventional hydrocarbon reservoirs and associated hazards.Many coupling techniques have been developed to include the effects of fluid flow in the discrete element method(DEM),and the techniques have been applied to a variety of geomechanical problems.Although these coupling methods have been successfully applied in various engineering fields,no single fluid/DEM coupling method is universal due to the complexity of engineering problems and the limitations of the numerical methods.For researchers and engineers,the key to solve a specific problem is to select the most appropriate fluid/DEM coupling method among these modeling technologies.The purpose of this paper is to give a comprehensive review of fluid flow/DEM coupling methods and relevant research.Given their importance,the availability or unavailability of best practice guidelines is outlined.The theoretical background and current status of DEM are introduced first,and the principles,applications,and advantages and disadvantages of different fluid flow/DEM coupling methods are discussed.Finally,a summary with speculation on future development trends is given.
文摘The particulate discrete element method(DEM) can be employed to capture the response of rock,provided that appropriate bonding models are used to cement the particles to each other.Simulations of laboratory tests are important to establish the extent to which those models can capture realistic rock behaviors.Hitherto the focus in such comparison studies has either been on homogeneous specimens or use of two-dimensional(2D) models.In situ rock formations are often heterogeneous,thus exploring the ability of this type of models to capture heterogeneous material behavior is important to facilitate their use in design analysis.In situ stress states are basically three-dimensional(3D),and therefore it is important to develop 3D models for this purpose.This paper revisits an earlier experimental study on heterogeneous specimens,of which the relative proportions of weaker material(siltstone) and stronger,harder material(sandstone) were varied in a controlled manner.Using a 3D DEM model with the parallel bond model,virtual heterogeneous specimens were created.The overall responses in terms of variations in strength and stiffness with different percentages of weaker material(siltstone) were shown to agree with the experimental observations.There was also a good qualitative agreement in the failure patterns observed in the experiments and the simulations,suggesting that the DEM data enabled analysis of the initiation of localizations and micro fractures in the specimens.
基金Project supported by the National Natural Science Foundation of China(Nos.59978005 and 10232024)the National Distinguished Youth Fund of China(No.10025212).
文摘A three-dimensional discrete element model of the connective type is presented. Moreover,a three-dimensional numerical analysis code,which can carry out the transitional pro- cess from connective model(for continuum)to contact model(for non-continuum),is developed for simulating the mechanical process from continuum to non-continuum.The wave propagation process in a concrete block(as continuum)made of cement grout under impact loading is numer- ically simulated with this code.By comparing its numerical results with those by LS-DYNA,the calculation accuracy of the model and algorithm is proved.Furthermore,the failure process of the concrete block under quasi-static loading is demonstrated,showing the basic dynamic tran- sitional process from continuum to non-continuum.The results of calculation can be displayed by animation.The damage modes are similar to the experimental results.The two numerical examples above prove that our model and its code are powerful and efficient in simulating the dynamic failure problems accompanying the transition from continuum to non-continuum.It also shows that the discrete element method(DEM)will have broad prospects for development and application.
文摘Discrete element method(DEM)has been intensively used to study the constitutive behaviour of granular materials.However,to what extent a real granular material can be reproduced by virtual DEM simulations remains unclear.This study attempts to answer this question by comparing DEM simulations with typical features of experimental granular materials.Three groups of models with spherical and clumped particles are investigated from four perspectives:(i)deviatoric stress and volumetric behaviour;(ii)critical state behaviour;(iii)stress-dilatancy relationship;and(iv)the evolution of principal stress ratio against axial strain.The results demonstrate that DEM with spherical or clumped particles is capable of qualitatively describing macroscopic deviatoric stress responses,volumetric behaviour,and critical state behaviour observed in experiments for granular materials.On the other hand,some qualitative deviations between experiments and the investigated DEM simulations are also observed,in terms of the stress-dilatancy behaviour and principal stress ratio against axial strain,which are proven to be critical for constitutive modelling.The results demonstrate that DEM with spherical or clumped particles may not necessarily fully capture experimental features of granular materials even from a qualitative perspective.It is thus encouraged to thoroughly validate DEM with experiments when developing constitutive models based on DEM observations.
