Continuum-based discrete element method(CDEM)is an explicit numerical method used for simulation of progressive failure of geological body.To improve the efficiency of contact detection and simplify the calculation st...Continuum-based discrete element method(CDEM)is an explicit numerical method used for simulation of progressive failure of geological body.To improve the efficiency of contact detection and simplify the calculation steps for contact forces,semi-spring and semi-edge are introduced in calculation.Semispring is derived from block vertex,and formed by indenting the block vertex into each face(24semisprings for a hexahedral element).The formation process of semi-edge is the same as that of semi-spring(24semi-edges for a hexahedral element).Based on the semi-springs and semi-edges,a new type of combined contact model is presented.According to this model,six contact types could be reduced to two,i.e.the semi-spring target face contact and semi-edge target edge contact.By the combined model,the contact force could be calculated directly(the information of contact type is not necessary),and the failure judgment could be executed in a straightforward way(each semi-spring and semi-edge own their characteristic areas).The algorithm has been successfully programmed in C++program.Some simple numerical cases are presented to show the validity and accuracy of this model.Finally,the failure mode,sliding distance and critical friction angle of Jiweishan landslide are studied with the combined model.展开更多
Numerical analyses of earthquake effects on the deformation, stability, and load transfer of a slope covered by deposits are traditionally based on the assumption that the slope is a continuum. It would be problem...Numerical analyses of earthquake effects on the deformation, stability, and load transfer of a slope covered by deposits are traditionally based on the assumption that the slope is a continuum. It would be problematic, however, to extend these approaches to the simulation of the slide, collapse and disintegration of the deposits under seismic loading. Contrary to this, a discrete element method （DEM） provides a means to consider large displacement and rotation of the non-continuum. To take the advantages of both methods of continuum and non- continuum analyses, seismic responses of a slope covered by deposits are studied by coupling a twodimensional （a-D） finite difference method and a 2-D DEM, with the bedrock being modelled by the finite difference grids and the deposits being represented by disks. A smooth transition across the boundaries of the continuous/discontinuous domains is obtained by imposing the compatibility condition and equilibrium condition along their interfaces. In the course of computation, the same time-step value is chosen for both continuous and discontinuous domains. The free-field boundaries are adopted for lateral grids of bedrock domain to eliminate the radiation damping effect. When the static equilibrium under gravity load is obtained, dynamic calculation begins under excitation of the seismic wave input from the continuum model bottom. In this way, responses to the earthquake of a slope covered by deposits are analyzed dynamically. Combined with field monitoring data, deformation and stability of the slope are discussed. The effects of the relevant parameters of spectrum characteristic, duration, andpeak acceleration of seismic waves are further investigated and explained from the simulations.展开更多
This study addresses a critical challenge in CFD-DEM simulations:the accurate assignment of drag force to fluid mesh cells when the cell size exceeds particle sizes.Traditional particle centroid method(PCM)approaches ...This study addresses a critical challenge in CFD-DEM simulations:the accurate assignment of drag force to fluid mesh cells when the cell size exceeds particle sizes.Traditional particle centroid method(PCM)approaches often lead to abrupt drag force variations as particles cross cell boundaries due to their discrete nature.To overcome this limitation,we propose a novel algorithm that computes an analytical solution for the effective projected area(EPA)of particles within computational cells,aligned with the relative velocity direction.The drag force is then proportionally scaled according to this EPA calculation.The paper presents a specific implementation case of our algorithm,focusing on scenarios where a cell vertex resides within a particle boundary.For EPA determination,we introduce an innovative classification approach based on face-windward surface relations.Extensive validation involved 100,000 test cases with varying cell-particle relative positions(all constrained by the vertex-in-particle condition),systematically classified into 18 types using our scheme.Results demonstrate that all computed EPA values remain within theoretical bounds,confirming the classification's comprehensiveness.Through 5 classic particle movement simulations,we show that our method maintains continuous EPA variation across time steps-a marked improvement over PCM's characteristic discontinuities.Implementation within the CFD-DEM framework for single-particle sedimentation yields terminal velocities that closely match experimental data while ensuring smooth drag force transitions between fluid cells.Compared to PCM,the present method reduces the relative error in terminal settling velocity by approximately 43%.Moreover,comparative studies of dual-particle sedimentation demonstrate our algorithm's superior performance relative to conventional PCM approaches.For Particle 1,the terminal vertical velocity predicted by the present method reduces the relative error by approximately 17%compared to PCM.These advances significantly enhance simulation fidelity for particle-fluid interaction problems where cell-particle size ratios challenge traditional methods.展开更多
A discrete element method(DEM)-computa-tional fluid dynamics(CFD)two-way coupling method was employed to simulate the hydrodynamics in a two-dimensional spouted bed with draft plates.The motion of particles was modele...A discrete element method(DEM)-computa-tional fluid dynamics(CFD)two-way coupling method was employed to simulate the hydrodynamics in a two-dimensional spouted bed with draft plates.The motion of particles was modeled by the DEM and the gas flow was modeled by the Navier-Stokes equation.The interactions between gas and particles were considered using a two-way coupling method.The motion of particles in the spouted bed with complex geometry was solved by com-bining DEM and boundary element method(BEM).The minimal spouted velocity was obtained by the BEM-DEM-CFD simulation and the variation of the flow pat-tern in the bed with different superficial gas velocity was studied.The relationship between the pressure drop of the spouted bed and the superficial gas velocity was achieved from the simulations.The radial profile of the averaged vertical velocities of particles and the profile of the aver-aged void fraction in the spout and the annulus were stat-istically analyzed.The flow characteristics of the gas-solid system in the two-dimensional spouted bed were clearly described by the simulation results.展开更多
Pneumatic conveying of coarse coal particles with various pipeline configurations and swirling intensities was investigated using a coupled computational fluid dynamics and discrete element method. A particle cluster ...Pneumatic conveying of coarse coal particles with various pipeline configurations and swirling intensities was investigated using a coupled computational fluid dynamics and discrete element method. A particle cluster agglomerated by the parallel-bond method was modeled to analyze the breakage of coarse coal particles. The numerical parameters, simulation conditions, and simulation results were experimentally validated. On analyzing total energy variation in the agglomerate during the breakage process, the results showed that downward fluctuation of the total particle energy was correlated with particle and wall col- lisions, and particle breakage showed a positive correlation with the energy difference. The correlation between the total energy variation of a particle cluster and particle breakage was also analyzed. Parti- cle integrity presented a fluctuating upward trend with pipe bend radius and increased with swirling number for most bend radii. The degree of particle breakage differed with pipeline bending direction and swirling intensity： in a horizontal bend, the bend radius and swirling intensity dominated the total energy variations： these effects were not observed in a vertical bend. The total energy of the particle cluster exiting a bend was generally positively correlated with the bend radius for all conditions and was independent of bending direction.展开更多
基金the National Basic Research Program of the Ministry of Science and Technology of China (Grant No. 2010CB731506)the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (Grant No. 2012BAK10B01)the Youth Science Fund of National Natural Science Foundation of China (Grant No. 11302230)
文摘Continuum-based discrete element method(CDEM)is an explicit numerical method used for simulation of progressive failure of geological body.To improve the efficiency of contact detection and simplify the calculation steps for contact forces,semi-spring and semi-edge are introduced in calculation.Semispring is derived from block vertex,and formed by indenting the block vertex into each face(24semisprings for a hexahedral element).The formation process of semi-edge is the same as that of semi-spring(24semi-edges for a hexahedral element).Based on the semi-springs and semi-edges,a new type of combined contact model is presented.According to this model,six contact types could be reduced to two,i.e.the semi-spring target face contact and semi-edge target edge contact.By the combined model,the contact force could be calculated directly(the information of contact type is not necessary),and the failure judgment could be executed in a straightforward way(each semi-spring and semi-edge own their characteristic areas).The algorithm has been successfully programmed in C++program.Some simple numerical cases are presented to show the validity and accuracy of this model.Finally,the failure mode,sliding distance and critical friction angle of Jiweishan landslide are studied with the combined model.
基金the National Basic Research Program of China (Grant No. 2008CB425802)
文摘Numerical analyses of earthquake effects on the deformation, stability, and load transfer of a slope covered by deposits are traditionally based on the assumption that the slope is a continuum. It would be problematic, however, to extend these approaches to the simulation of the slide, collapse and disintegration of the deposits under seismic loading. Contrary to this, a discrete element method （DEM） provides a means to consider large displacement and rotation of the non-continuum. To take the advantages of both methods of continuum and non- continuum analyses, seismic responses of a slope covered by deposits are studied by coupling a twodimensional （a-D） finite difference method and a 2-D DEM, with the bedrock being modelled by the finite difference grids and the deposits being represented by disks. A smooth transition across the boundaries of the continuous/discontinuous domains is obtained by imposing the compatibility condition and equilibrium condition along their interfaces. In the course of computation, the same time-step value is chosen for both continuous and discontinuous domains. The free-field boundaries are adopted for lateral grids of bedrock domain to eliminate the radiation damping effect. When the static equilibrium under gravity load is obtained, dynamic calculation begins under excitation of the seismic wave input from the continuum model bottom. In this way, responses to the earthquake of a slope covered by deposits are analyzed dynamically. Combined with field monitoring data, deformation and stability of the slope are discussed. The effects of the relevant parameters of spectrum characteristic, duration, andpeak acceleration of seismic waves are further investigated and explained from the simulations.
基金the National Science and Technology Major Project(2011ZX06901-003)。
文摘This study addresses a critical challenge in CFD-DEM simulations:the accurate assignment of drag force to fluid mesh cells when the cell size exceeds particle sizes.Traditional particle centroid method(PCM)approaches often lead to abrupt drag force variations as particles cross cell boundaries due to their discrete nature.To overcome this limitation,we propose a novel algorithm that computes an analytical solution for the effective projected area(EPA)of particles within computational cells,aligned with the relative velocity direction.The drag force is then proportionally scaled according to this EPA calculation.The paper presents a specific implementation case of our algorithm,focusing on scenarios where a cell vertex resides within a particle boundary.For EPA determination,we introduce an innovative classification approach based on face-windward surface relations.Extensive validation involved 100,000 test cases with varying cell-particle relative positions(all constrained by the vertex-in-particle condition),systematically classified into 18 types using our scheme.Results demonstrate that all computed EPA values remain within theoretical bounds,confirming the classification's comprehensiveness.Through 5 classic particle movement simulations,we show that our method maintains continuous EPA variation across time steps-a marked improvement over PCM's characteristic discontinuities.Implementation within the CFD-DEM framework for single-particle sedimentation yields terminal velocities that closely match experimental data while ensuring smooth drag force transitions between fluid cells.Compared to PCM,the present method reduces the relative error in terminal settling velocity by approximately 43%.Moreover,comparative studies of dual-particle sedimentation demonstrate our algorithm's superior performance relative to conventional PCM approaches.For Particle 1,the terminal vertical velocity predicted by the present method reduces the relative error by approximately 17%compared to PCM.These advances significantly enhance simulation fidelity for particle-fluid interaction problems where cell-particle size ratios challenge traditional methods.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.20306012)the China Postdoctoral Science Foundation(2005038061).
文摘A discrete element method(DEM)-computa-tional fluid dynamics(CFD)two-way coupling method was employed to simulate the hydrodynamics in a two-dimensional spouted bed with draft plates.The motion of particles was modeled by the DEM and the gas flow was modeled by the Navier-Stokes equation.The interactions between gas and particles were considered using a two-way coupling method.The motion of particles in the spouted bed with complex geometry was solved by com-bining DEM and boundary element method(BEM).The minimal spouted velocity was obtained by the BEM-DEM-CFD simulation and the variation of the flow pat-tern in the bed with different superficial gas velocity was studied.The relationship between the pressure drop of the spouted bed and the superficial gas velocity was achieved from the simulations.The radial profile of the averaged vertical velocities of particles and the profile of the aver-aged void fraction in the spout and the annulus were stat-istically analyzed.The flow characteristics of the gas-solid system in the two-dimensional spouted bed were clearly described by the simulation results.
文摘Pneumatic conveying of coarse coal particles with various pipeline configurations and swirling intensities was investigated using a coupled computational fluid dynamics and discrete element method. A particle cluster agglomerated by the parallel-bond method was modeled to analyze the breakage of coarse coal particles. The numerical parameters, simulation conditions, and simulation results were experimentally validated. On analyzing total energy variation in the agglomerate during the breakage process, the results showed that downward fluctuation of the total particle energy was correlated with particle and wall col- lisions, and particle breakage showed a positive correlation with the energy difference. The correlation between the total energy variation of a particle cluster and particle breakage was also analyzed. Parti- cle integrity presented a fluctuating upward trend with pipe bend radius and increased with swirling number for most bend radii. The degree of particle breakage differed with pipeline bending direction and swirling intensity： in a horizontal bend, the bend radius and swirling intensity dominated the total energy variations： these effects were not observed in a vertical bend. The total energy of the particle cluster exiting a bend was generally positively correlated with the bend radius for all conditions and was independent of bending direction.
