The objective of this work is to model the microstructure of asphalt mixture and build virtual test for asphalt mixture by using Particle Flow Code in three dimensions(PFC^(3D))based on three-dimensional discrete elem...The objective of this work is to model the microstructure of asphalt mixture and build virtual test for asphalt mixture by using Particle Flow Code in three dimensions(PFC^(3D))based on three-dimensional discrete element method.A randomly generating algorithm was proposed to capture the three-dimensional irregular shape of coarse aggregate.And then,modeling algorithm and method for graded aggregates were built.Based on the combination of modeling of coarse aggregates,asphalt mastic and air voids,three-dimensional virtual sample of asphalt mixture was modeled by using PFC^(3D).Virtual tests for penetration test of aggregate and uniaxial creep test of asphalt mixture were built and conducted by using PFC^(3D).By comparison of the testing results between virtual tests and actual laboratory tests,the validity of the microstructure modeling and virtual test built in this study was verified.Additionally,compared with laboratory test,the virtual test is easier to conduct and has less variability.It is proved that microstructure modeling and virtual test based on three-dimensional discrete element method is a promising way to conduct research of asphalt mixture.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
This study presents the first step of a research project that aims at using a three-dimensional （3D） hybridfinite-discrete element method （FDEM） to investigate the development of an excavation damaged zone（EDZ） ...This study presents the first step of a research project that aims at using a three-dimensional （3D） hybridfinite-discrete element method （FDEM） to investigate the development of an excavation damaged zone（EDZ） around tunnels in a clay shale formation known as Opalinus Clay. The 3D FDEM was first calibratedagainst standard laboratory experiments, including Brazilian disc test and uniaxial compression test. Theeffect of increasing confining pressure on the mechanical response and fracture propagation of the rockwas quantified under triaxial compression tests. Polyaxial （or true triaxial） simulations highlighted theeffect of the intermediate principal stress （s2） on fracture directions in the model： as the intermediateprincipal stress increased, fractures tended to align in the direction parallel to the plane defined by themajor and intermediate principal stresses. The peak strength was also shown to vary with changing s2. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.展开更多
We simulated three-dimensional heat transfer inside a horizontal rotating drum using the discrete element method and a thermal conduction model.The aim was to determine the effect of end-wall heating on thermal behavi...We simulated three-dimensional heat transfer inside a horizontal rotating drum using the discrete element method and a thermal conduction model.The aim was to determine the effect of end-wall heating on thermal behavior of a granular bed.The simulation showed that the end-wall heating significantly affects the axial temperature profile of the bed,particularly when the length-to-diameter ratio is low.Particles near the wall heated faster and became more thermally uniform than those in the center of the drum.The region affected by the end heating gradually increased over time.Increasing the rotation speed enhanced the heat conduction rate,and increasing the fill level reduced the mean temperature and thermal uniformity of the granular bed.Heat transfer was also simulated for drums with different length-to-diameter ratios.展开更多
We calculate the multicomponent responses of surface-hole transient electromagnetic method. The methods and models are unsuitable as geoelectric models of conductive surrounding rocks because they are based on regular...We calculate the multicomponent responses of surface-hole transient electromagnetic method. The methods and models are unsuitable as geoelectric models of conductive surrounding rocks because they are based on regular local targets. We also propose a calculation and analysis scheme based on numerical simulations of the subsurface transient electromagnetic fields. In the modeling of the electromagnetic fields, the forward modeling simulations are performed by using the finite-difference time-domain method and the discrete image method, which combines the Gaver–Stehfest inverse Laplace transform with the Prony method to solve the initial electromagnetic fields. The precision in the iterative computations is ensured by using the transmission boundary conditions. For the response analysis, we customize geoelectric models consisting of near-borehole targets and conductive wall rocks and implement forward modeling simulations. The observed electric fields are converted into induced electromotive force responses using multicomponent observation devices. By comparing the transient electric fields and multicomponent responses under different conditions, we suggest that the multicomponent-induced electromotive force responses are related to the horizontal and vertical gradient variations of the transient electric field at different times. The characteristics of the response are determined by the varying the subsurface transient electromagnetic fields, i.e., diffusion, attenuation and distortion, under different conditions as well as the electromagnetic fields at the observation positions. The calculation and analysis scheme of the response consider the surrounding rocks and the anomalous field of the local targets. It therefore can account for the geological data better than conventional transient field response analysis of local targets.展开更多
Three-dimensional discrete element face-to-face contact model with fissure water pressure is established in this paper and the model is used to simulate three-stage process of landslide under fissure water pressure in...Three-dimensional discrete element face-to-face contact model with fissure water pressure is established in this paper and the model is used to simulate three-stage process of landslide under fissure water pressure in the opencast mine,according to the actual state of landslide in Panluo iron mine where landslide happened in 1990 and was fathered in 1999.The calculation results show that fissure water pressure on the sliding surface is the main reason causing landslide and the local soft interlayer weakens the stability of slope.If the discrete element method adopts the same assumption as the limit equilibrium method,the results of two methods are in good agreement;while if the assumption is not adopted in the discrete element method,the criticalφnumerically calculated is less than the one calculated by use of the limit equilibrium method for the sameC.Thus,from an engineering point of view,the result from the discrete element model simulation is safer and has more widely application since the discrete element model takes into account the effect of rock mass structures.展开更多
To address the problem that granular compound fertilizer is prone to agglomeration during mechanized direct seeding of oilseed rape in the middle and lower reaches of the Yangtze River,which causes clogging of the fer...To address the problem that granular compound fertilizer is prone to agglomeration during mechanized direct seeding of oilseed rape in the middle and lower reaches of the Yangtze River,which causes clogging of the fertilizer discharger and leads to a reduction in the uniformity and stability of fertilizer discharge,research on the crushing mechanism of caking compound fertilizer was performed.Considering that it is difficult to measure the bonding force between caking fertilizer particles directly,a simulation model of caking composite fertilizer was established with the bonding model in EDEM discrete element software.To decrease error between the simulation and physical test results,the normal contact stiffness,tangential contact stiffness,critical normal stress,critical tangential stress,bonding radius,and other parameters of the bonding model of caking composite fertilizer were calibrated.The three-dimensional structure of the caking composite fertilizer was obtained via three-dimensional scanning,the critical crushing displacement and critical crushing force of the caking composite fertilizer were measured via compression testing with a mass spectrometer,and the optimal parameter combination of the bonding model was determined via EDEM discrete element simulation of the Plackett-Burman test,steepest ascent test,and Box-Behnken test.The results of the simulated compression tests under the optimal parameter combination show that the relative errors of the critical crushing displacement and critical crushing force with respect to the physical test results were 0.296%and 0.343%,respectively.Using the crushing rate of caking compound fertilizer as an evaluation index,the feasibility of the calibrated parameters was verified for a four-head spiral two-row fertilizer discharger installed in a direct seeding machine for oilseed rape.The results show that the relative errors of the caking fertilizer crushing rates from the simulation relative to those of the bench and field tests were 5.81%and 5.06%,respectively,indicating that the calibration parameters of the discrete element model were accurate and could be used for parameter analysis of caking fertilizer with a discrete element model.These results can provide a reference for the structural optimization of fertilizer discharger crushing of caking fertilizer of direct seeding machine for oilseed rape.展开更多
This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex cragk propagation in quasi-brittle materials in a relatively easy and efficient manner. The ...This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex cragk propagation in quasi-brittle materials in a relatively easy and efficient manner. The cohesive elements with softening traction-separation relations and damage initiation and evolution laws are embedded between solid elements in regions of interest in the initial mesh to model potential cracks. The initial mesh can consist of tetrahedrons, wedges, bricks or a mixture of these elements. Neither remeshing nor objective crack propagation criteria are needed. Four examples of concrete specimens, including a wedgesplitting test, a notched beam under torsion, a pull-out test of an anchored cylinder and a notched beam under impact, were modelled and analysed. The simulated crack propagation processes and load-displacement curves agreed well with test results or other numerical simulations for all the examples using initial meshes with reasonable densities. Making use of Abaqus＇s rich pre/post- processing functionalities and powerful standard/explicit solvers, the developed method offers a practical tool for engineering analysts to model complex 3D fracture problems.展开更多
The karst cave serves as the primary storage space in carbonate reservoirs.Simultaneously connecting multiple karst caves through hydraulic fracturing is key to the efficient development of carbonate reservoirs.Howeve...The karst cave serves as the primary storage space in carbonate reservoirs.Simultaneously connecting multiple karst caves through hydraulic fracturing is key to the efficient development of carbonate reservoirs.However,there is lack of systematic research on the mechanisms and influencing factors of fracture propagation in car-bonate rocks.This paper established models including karst cave models,single natural fracture-cave models,and multiple natural fracture-cave models based on the discrete lattice method.It thoroughly studied how geological and operational factors affect the fracture propagation and the connectivity of karst caves.The final step involved establishing a prototype well model and optimizing operation parameters.The research indicates that an increase in the Young's modulus and pore pressure of karst cave could facilitate hydraulic fracture connecting with caves.When the pore pressure is lower than that in the matrix,it will generate a repulsive effect on hydraulic fractures.The natural fracture along the hydraulic fracture path significantly facilitates the connection with caves.When the wellbore azimuth is less than 60℃,the fracture's diversion radius is small,and hydraulic fractures primarily connect with karst cave through natural fractures.When the wellbore azimuth exceeds 60℃,the fracture's diversion radius increases.Under the combined action of hydraulic fractures and natural fractures,the stimulated volume of the karst cave noticeably increases.Under the same liquid volume,increasing the injection rate could enhance the cave stimulated volume.Combining the findings from numerical simulation studies resulted in the development of a diagram that depicts the connectivity of karst caves,providing valuable insight for hydraulic fracturing operations in carbonate reservoirs.展开更多
基金Project(51378006) supported by National Natural Science Foundation of ChinaProject(141076) supported by Huoyingdong Foundation of the Ministry of Education of China+1 种基金Project(2242015R30027) supported by Excellent Young Teacher Program of Southeast University,ChinaProject(BK20140109) supported by the Natural Science Foundation of Jiangsu Province,China
文摘The objective of this work is to model the microstructure of asphalt mixture and build virtual test for asphalt mixture by using Particle Flow Code in three dimensions(PFC^(3D))based on three-dimensional discrete element method.A randomly generating algorithm was proposed to capture the three-dimensional irregular shape of coarse aggregate.And then,modeling algorithm and method for graded aggregates were built.Based on the combination of modeling of coarse aggregates,asphalt mastic and air voids,three-dimensional virtual sample of asphalt mixture was modeled by using PFC^(3D).Virtual tests for penetration test of aggregate and uniaxial creep test of asphalt mixture were built and conducted by using PFC^(3D).By comparison of the testing results between virtual tests and actual laboratory tests,the validity of the microstructure modeling and virtual test built in this study was verified.Additionally,compared with laboratory test,the virtual test is easier to conduct and has less variability.It is proved that microstructure modeling and virtual test based on three-dimensional discrete element method is a promising way to conduct research of asphalt mixture.
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This study presents the first step of a research project that aims at using a three-dimensional （3D） hybridfinite-discrete element method （FDEM） to investigate the development of an excavation damaged zone（EDZ） around tunnels in a clay shale formation known as Opalinus Clay. The 3D FDEM was first calibratedagainst standard laboratory experiments, including Brazilian disc test and uniaxial compression test. Theeffect of increasing confining pressure on the mechanical response and fracture propagation of the rockwas quantified under triaxial compression tests. Polyaxial （or true triaxial） simulations highlighted theeffect of the intermediate principal stress （s2） on fracture directions in the model： as the intermediateprincipal stress increased, fractures tended to align in the direction parallel to the plane defined by themajor and intermediate principal stresses. The peak strength was also shown to vary with changing s2. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.
文摘We simulated three-dimensional heat transfer inside a horizontal rotating drum using the discrete element method and a thermal conduction model.The aim was to determine the effect of end-wall heating on thermal behavior of a granular bed.The simulation showed that the end-wall heating significantly affects the axial temperature profile of the bed,particularly when the length-to-diameter ratio is low.Particles near the wall heated faster and became more thermally uniform than those in the center of the drum.The region affected by the end heating gradually increased over time.Increasing the rotation speed enhanced the heat conduction rate,and increasing the fill level reduced the mean temperature and thermal uniformity of the granular bed.Heat transfer was also simulated for drums with different length-to-diameter ratios.
基金supported by the Young Scientists Fund of the National Natural Science Foundation of China(No.41304082)the China Postdoctoral Science Foundation(No.2016M590731)+2 种基金the Young Scientists Fund of the Natural Science Foundation of Hebei Province(No.D2014403011)the Program for Young Excellent Talents of Higher Education Institutions of Hebei Province(No.BJ2016046)the Geological survey project of China Geological Survey(No.1212011121197)
文摘We calculate the multicomponent responses of surface-hole transient electromagnetic method. The methods and models are unsuitable as geoelectric models of conductive surrounding rocks because they are based on regular local targets. We also propose a calculation and analysis scheme based on numerical simulations of the subsurface transient electromagnetic fields. In the modeling of the electromagnetic fields, the forward modeling simulations are performed by using the finite-difference time-domain method and the discrete image method, which combines the Gaver–Stehfest inverse Laplace transform with the Prony method to solve the initial electromagnetic fields. The precision in the iterative computations is ensured by using the transmission boundary conditions. For the response analysis, we customize geoelectric models consisting of near-borehole targets and conductive wall rocks and implement forward modeling simulations. The observed electric fields are converted into induced electromotive force responses using multicomponent observation devices. By comparing the transient electric fields and multicomponent responses under different conditions, we suggest that the multicomponent-induced electromotive force responses are related to the horizontal and vertical gradient variations of the transient electric field at different times. The characteristics of the response are determined by the varying the subsurface transient electromagnetic fields, i.e., diffusion, attenuation and distortion, under different conditions as well as the electromagnetic fields at the observation positions. The calculation and analysis scheme of the response consider the surrounding rocks and the anomalous field of the local targets. It therefore can account for the geological data better than conventional transient field response analysis of local targets.
基金supported by the National 973 Project(Grant No.2002CB412703)the Important AspecProject of the Chinese Academy of Sciences(Grant No.KJCX2_SW_L1).
文摘Three-dimensional discrete element face-to-face contact model with fissure water pressure is established in this paper and the model is used to simulate three-stage process of landslide under fissure water pressure in the opencast mine,according to the actual state of landslide in Panluo iron mine where landslide happened in 1990 and was fathered in 1999.The calculation results show that fissure water pressure on the sliding surface is the main reason causing landslide and the local soft interlayer weakens the stability of slope.If the discrete element method adopts the same assumption as the limit equilibrium method,the results of two methods are in good agreement;while if the assumption is not adopted in the discrete element method,the criticalφnumerically calculated is less than the one calculated by use of the limit equilibrium method for the sameC.Thus,from an engineering point of view,the result from the discrete element model simulation is safer and has more widely application since the discrete element model takes into account the effect of rock mass structures.
基金supported by the China Agricultural Research System of MOF and MARA(NO:CARS-12).
文摘To address the problem that granular compound fertilizer is prone to agglomeration during mechanized direct seeding of oilseed rape in the middle and lower reaches of the Yangtze River,which causes clogging of the fertilizer discharger and leads to a reduction in the uniformity and stability of fertilizer discharge,research on the crushing mechanism of caking compound fertilizer was performed.Considering that it is difficult to measure the bonding force between caking fertilizer particles directly,a simulation model of caking composite fertilizer was established with the bonding model in EDEM discrete element software.To decrease error between the simulation and physical test results,the normal contact stiffness,tangential contact stiffness,critical normal stress,critical tangential stress,bonding radius,and other parameters of the bonding model of caking composite fertilizer were calibrated.The three-dimensional structure of the caking composite fertilizer was obtained via three-dimensional scanning,the critical crushing displacement and critical crushing force of the caking composite fertilizer were measured via compression testing with a mass spectrometer,and the optimal parameter combination of the bonding model was determined via EDEM discrete element simulation of the Plackett-Burman test,steepest ascent test,and Box-Behnken test.The results of the simulated compression tests under the optimal parameter combination show that the relative errors of the critical crushing displacement and critical crushing force with respect to the physical test results were 0.296%and 0.343%,respectively.Using the crushing rate of caking compound fertilizer as an evaluation index,the feasibility of the calibrated parameters was verified for a four-head spiral two-row fertilizer discharger installed in a direct seeding machine for oilseed rape.The results show that the relative errors of the caking fertilizer crushing rates from the simulation relative to those of the bench and field tests were 5.81%and 5.06%,respectively,indicating that the calibration parameters of the discrete element model were accurate and could be used for parameter analysis of caking fertilizer with a discrete element model.These results can provide a reference for the structural optimization of fertilizer discharger crushing of caking fertilizer of direct seeding machine for oilseed rape.
基金supported by EPSRC UK(No.EP/F00656X/1)Xiangting Su's one-year visit to the University of Liverpoosupported by the China Scholarship Council and the National Natural Science Foundation of China(No.50579081).
文摘This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex cragk propagation in quasi-brittle materials in a relatively easy and efficient manner. The cohesive elements with softening traction-separation relations and damage initiation and evolution laws are embedded between solid elements in regions of interest in the initial mesh to model potential cracks. The initial mesh can consist of tetrahedrons, wedges, bricks or a mixture of these elements. Neither remeshing nor objective crack propagation criteria are needed. Four examples of concrete specimens, including a wedgesplitting test, a notched beam under torsion, a pull-out test of an anchored cylinder and a notched beam under impact, were modelled and analysed. The simulated crack propagation processes and load-displacement curves agreed well with test results or other numerical simulations for all the examples using initial meshes with reasonable densities. Making use of Abaqus＇s rich pre/post- processing functionalities and powerful standard/explicit solvers, the developed method offers a practical tool for engineering analysts to model complex 3D fracture problems.
基金supported by the Natural Science Foundation of China(Grant No.52074332).
文摘The karst cave serves as the primary storage space in carbonate reservoirs.Simultaneously connecting multiple karst caves through hydraulic fracturing is key to the efficient development of carbonate reservoirs.However,there is lack of systematic research on the mechanisms and influencing factors of fracture propagation in car-bonate rocks.This paper established models including karst cave models,single natural fracture-cave models,and multiple natural fracture-cave models based on the discrete lattice method.It thoroughly studied how geological and operational factors affect the fracture propagation and the connectivity of karst caves.The final step involved establishing a prototype well model and optimizing operation parameters.The research indicates that an increase in the Young's modulus and pore pressure of karst cave could facilitate hydraulic fracture connecting with caves.When the pore pressure is lower than that in the matrix,it will generate a repulsive effect on hydraulic fractures.The natural fracture along the hydraulic fracture path significantly facilitates the connection with caves.When the wellbore azimuth is less than 60℃,the fracture's diversion radius is small,and hydraulic fractures primarily connect with karst cave through natural fractures.When the wellbore azimuth exceeds 60℃,the fracture's diversion radius increases.Under the combined action of hydraulic fractures and natural fractures,the stimulated volume of the karst cave noticeably increases.Under the same liquid volume,increasing the injection rate could enhance the cave stimulated volume.Combining the findings from numerical simulation studies resulted in the development of a diagram that depicts the connectivity of karst caves,providing valuable insight for hydraulic fracturing operations in carbonate reservoirs.
