In the present work, a computer model was developed to simulate random packing of aggregates. For the sake of simplicity, two dimensional situation was considered and all of the aggregates in concrete were assumed as ...In the present work, a computer model was developed to simulate random packing of aggregates. For the sake of simplicity, two dimensional situation was considered and all of the aggregates in concrete were assumed as ellipse. 2D elliptical models of random packing were firstly demonstrated in periodic boundary condition. In addition, the ellipse random packing model was employed for the influence of aspect ratios on the packing fraction of ellipses. The modeling results demonstrate that the packing fraction of ellipses firstly increases then drops down with increasing aspect ratio. The maximal random packing fraction is 0.66 when aspect ratio is 1.04 in the periodic boundary condition.展开更多
Random packings of spherical particles have attracted attention for many years.An algorithm based on compression is developed to generate random packings of spherical particles in this paper.This method is different f...Random packings of spherical particles have attracted attention for many years.An algorithm based on compression is developed to generate random packings of spherical particles in this paper.This method is different from previous compression-based algorithm.In order to increase the packing density,a process of shaking is applied during packing process.The algorithm is mainly composed of three procedures:generating initial packing configuration by using random sequential adsorption(RSA),compressing packing domain,and shaking.The packing structure is characterized by packing density and coordinate number.The packing density increases with iteration number and a stable packing configuration is obtained after the iteration number is more than 34 000.The packing density is 0.85 and the average coordinate number is 3.7 in a stable packing configuration.展开更多
The random packing of tetrahedral particles is studied by applying the discrete element method （DEM）, which simulates the effects of friction, height ratio, and eccentricity. The model predictions are ana- lyzed in ...The random packing of tetrahedral particles is studied by applying the discrete element method （DEM）, which simulates the effects of friction, height ratio, and eccentricity. The model predictions are ana- lyzed in terms of packing density and coordination number （CN）. It is demonstrated that friction has the maximal effect on packing density and mean CN among the three parameters. The packing den- sity of the regular tetrahedron is 0.71 when extrapolated to a zero friction effect. The shape effects of height ratio and eccentricity show that the regular tetrahedron has the highest packing density in the family of tetrahedra, which is consistent with what has been reported in the literature. Compared with geometry-based packing algorithms, the DEM packing density is much lower. This demonstrates that the inter-particle mechanical forces have a considerable effect on packing. The DEM results agree with the published experimental results, indicating that the polyhedral DEM model is suitable for simulating the random packing of tetrahedral particles.展开更多
Many studies on random packed beds have been dedicated to local porosity(void fraction)or orientation distribution of particles.However,despite the random nature of the considered packings,very little attention has be...Many studies on random packed beds have been dedicated to local porosity(void fraction)or orientation distribution of particles.However,despite the random nature of the considered packings,very little attention has been devoted to examination whether the number of particles used in experiments/simulations is sufficiently large to get reproducible results.The reproducibility of the key packing parameters depends on the size of the population of particles(sample size)and ordering effects induced by the confining walls.This work investigates quantitatively the influence of the sample size on the statistical variation of the packed bed characteristics.Packed beds of Raschig rings were generated with a sequential algorithm and three column diameters were considered.It has been found that in the case of the orientation distribution the results depend strongly on the sample size,especially for slender columns,while the porosity profiles are well-reproducible characteristics even for relatively small packings of rings.Some complementary results for full cylinders are also included.展开更多
Random loose packing is the minimum-density granular packing which can maintain mechanical stability. In this study, x-ray tomography is used to investigate the internal structure of an isotropically prepared random l...Random loose packing is the minimum-density granular packing which can maintain mechanical stability. In this study, x-ray tomography is used to investigate the internal structure of an isotropically prepared random loose packing through a special apparatus to minimize the effect of gravity. It is found that the minimum packing density is around 0.587. The microscopic structural analysis of the packing is also carried out.展开更多
The three-dimensional random packing of particles has attracted physicists, chemists, sedimentologists, materials scientists and mathematicians for more than a century. The study focuses on the packing density, porosi...The three-dimensional random packing of particles has attracted physicists, chemists, sedimentologists, materials scientists and mathematicians for more than a century. The study focuses on the packing density, porosity, the packing concentration, coordination number and the effect of the particle’s shape, density on the packing etc. For the metals and crystallized rocks with equigranular texture without porosity, there exists the"triple-point junction" with an angle of 120掳 in two dimensions. Every particle is adjacent to another six particles. To explain this texture, scientists proposed the definition of"Voronoi polygon". J. A. Dodds tried to demonstrate this conclusion by展开更多
1 Introduction Since the last century, a lot of scholars ifi mathematics, physics, chemistry, mineralogy and materials science have been interested in the problem of particles packing, as it is very important in the s...1 Introduction Since the last century, a lot of scholars ifi mathematics, physics, chemistry, mineralogy and materials science have been interested in the problem of particles packing, as it is very important in the study of crystal structure, liquid structure, materials science and engineering technology. Actually, there are three types of particles random packing, i. e. the loosest random packing, the dense random packing simultaneous with or without the mechanical movement, such as the tapping, jolting or vibrating. They can be defined as the loosest, medium and densest random packing, respectively. The same type of particles展开更多
Micro structures of equal sphere packing （ranging from loose to dense packing） generated numerically by discrete element method under different vibration conditions are characterized using Voronoi/Delaunay tessellat...Micro structures of equal sphere packing （ranging from loose to dense packing） generated numerically by discrete element method under different vibration conditions are characterized using Voronoi/Delaunay tessellation, which is applied on a wide range of packing densities. The analysis on micro properties such as the total perimeter, surface area, and the face number distribution of each Voronoi polyhedron, and the pore size distribution in each Voronoi/Delaunay subunit is systematically carried out. The results show that with the increasing density of sphere packing, the Voronoi//Delaunay pore size distribution is narrowed. That indicates large pores to be gradually substituted by small uniformed ones during densification. Meanwhile, the distributions of face number, total per/meter, and surface area of Voronoi polyhedra at high packing densities tend to be narrower and higher, which is in good agreement with those in random loose packing.展开更多
In this paper we have found a general subordinator, X, whose range up to time 1, X([0,1)), has similar structure as random re orderings of the Cantor set K(ω).X([0,1)) and K(ω) have the same exact Hausdorff measure...In this paper we have found a general subordinator, X, whose range up to time 1, X([0,1)), has similar structure as random re orderings of the Cantor set K(ω).X([0,1)) and K(ω) have the same exact Hausdorff measure function and the integal test of packing measure.展开更多
Suppose {Xn} is a random walk in time-random environment with state space Z^d, ｜Xn｜ approaches infinity, then under some reasonable conditions of stability, the upper bound of the discrete Packing dimension of the r...Suppose {Xn} is a random walk in time-random environment with state space Z^d, ｜Xn｜ approaches infinity, then under some reasonable conditions of stability, the upper bound of the discrete Packing dimension of the range of {Xn} is any stability index α. Moreover, if the environment is stationary, a similar result for the lower bound of the discrete Hausdorff dimension is derived. Thus, the range is a fractal set for almost every environment.展开更多
基金Funded by the National Natural Science Foundation of China (No.50708018)the Chinese Ministry of Education Project ( No.20070286018)the Ministry of Science and Technology of China "973 Project"(No.2009CB623203)
文摘In the present work, a computer model was developed to simulate random packing of aggregates. For the sake of simplicity, two dimensional situation was considered and all of the aggregates in concrete were assumed as ellipse. 2D elliptical models of random packing were firstly demonstrated in periodic boundary condition. In addition, the ellipse random packing model was employed for the influence of aspect ratios on the packing fraction of ellipses. The modeling results demonstrate that the packing fraction of ellipses firstly increases then drops down with increasing aspect ratio. The maximal random packing fraction is 0.66 when aspect ratio is 1.04 in the periodic boundary condition.
基金National Key Basic Research and Developing Project,China(973 program) (No. 2005CB623902)A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions,China
文摘Random packings of spherical particles have attracted attention for many years.An algorithm based on compression is developed to generate random packings of spherical particles in this paper.This method is different from previous compression-based algorithm.In order to increase the packing density,a process of shaking is applied during packing process.The algorithm is mainly composed of three procedures:generating initial packing configuration by using random sequential adsorption(RSA),compressing packing domain,and shaking.The packing structure is characterized by packing density and coordinate number.The packing density increases with iteration number and a stable packing configuration is obtained after the iteration number is more than 34 000.The packing density is 0.85 and the average coordinate number is 3.7 in a stable packing configuration.
文摘The random packing of tetrahedral particles is studied by applying the discrete element method （DEM）, which simulates the effects of friction, height ratio, and eccentricity. The model predictions are ana- lyzed in terms of packing density and coordination number （CN）. It is demonstrated that friction has the maximal effect on packing density and mean CN among the three parameters. The packing den- sity of the regular tetrahedron is 0.71 when extrapolated to a zero friction effect. The shape effects of height ratio and eccentricity show that the regular tetrahedron has the highest packing density in the family of tetrahedra, which is consistent with what has been reported in the literature. Compared with geometry-based packing algorithms, the DEM packing density is much lower. This demonstrates that the inter-particle mechanical forces have a considerable effect on packing. The DEM results agree with the published experimental results, indicating that the polyhedral DEM model is suitable for simulating the random packing of tetrahedral particles.
基金The investigation was supported by National Science Centre(Poland)under the Grant No.UMO-2018/31/D/ST8/00199Ministry of Science and Higher Education(Poland)is gratefully acknowledged for providing the scholarship for young outstanding scientists No.STYP/15/0246/E-358/2020 to dr PawełNiegodajew.
文摘Many studies on random packed beds have been dedicated to local porosity(void fraction)or orientation distribution of particles.However,despite the random nature of the considered packings,very little attention has been devoted to examination whether the number of particles used in experiments/simulations is sufficiently large to get reproducible results.The reproducibility of the key packing parameters depends on the size of the population of particles(sample size)and ordering effects induced by the confining walls.This work investigates quantitatively the influence of the sample size on the statistical variation of the packed bed characteristics.Packed beds of Raschig rings were generated with a sequential algorithm and three column diameters were considered.It has been found that in the case of the orientation distribution the results depend strongly on the sample size,especially for slender columns,while the porosity profiles are well-reproducible characteristics even for relatively small packings of rings.Some complementary results for full cylinders are also included.
基金supported by the Thirteenth Shanghai Jiao Tong University Students Innovation Practice Plan,China(Grant No.IPP13086)the National Natural Science Foundation of China(Grant Nos.11175121,11675110,and U1432111)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20110073120073)
文摘Random loose packing is the minimum-density granular packing which can maintain mechanical stability. In this study, x-ray tomography is used to investigate the internal structure of an isotropically prepared random loose packing through a special apparatus to minimize the effect of gravity. It is found that the minimum packing density is around 0.587. The microscopic structural analysis of the packing is also carried out.
基金Project supported by the National Natural Science Foundation of China.
文摘The three-dimensional random packing of particles has attracted physicists, chemists, sedimentologists, materials scientists and mathematicians for more than a century. The study focuses on the packing density, porosity, the packing concentration, coordination number and the effect of the particle’s shape, density on the packing etc. For the metals and crystallized rocks with equigranular texture without porosity, there exists the"triple-point junction" with an angle of 120掳 in two dimensions. Every particle is adjacent to another six particles. To explain this texture, scientists proposed the definition of"Voronoi polygon". J. A. Dodds tried to demonstrate this conclusion by
基金Project supported by the National Natural Science Foundation of China.
文摘1 Introduction Since the last century, a lot of scholars ifi mathematics, physics, chemistry, mineralogy and materials science have been interested in the problem of particles packing, as it is very important in the study of crystal structure, liquid structure, materials science and engineering technology. Actually, there are three types of particles random packing, i. e. the loosest random packing, the dense random packing simultaneous with or without the mechanical movement, such as the tapping, jolting or vibrating. They can be defined as the loosest, medium and densest random packing, respectively. The same type of particles
文摘Micro structures of equal sphere packing （ranging from loose to dense packing） generated numerically by discrete element method under different vibration conditions are characterized using Voronoi/Delaunay tessellation, which is applied on a wide range of packing densities. The analysis on micro properties such as the total perimeter, surface area, and the face number distribution of each Voronoi polyhedron, and the pore size distribution in each Voronoi/Delaunay subunit is systematically carried out. The results show that with the increasing density of sphere packing, the Voronoi//Delaunay pore size distribution is narrowed. That indicates large pores to be gradually substituted by small uniformed ones during densification. Meanwhile, the distributions of face number, total per/meter, and surface area of Voronoi polyhedra at high packing densities tend to be narrower and higher, which is in good agreement with those in random loose packing.
文摘In this paper we have found a general subordinator, X, whose range up to time 1, X([0,1)), has similar structure as random re orderings of the Cantor set K(ω).X([0,1)) and K(ω) have the same exact Hausdorff measure function and the integal test of packing measure.
基金Project supported by NNSF of China (10371092)Foundation of Wuhan University
文摘Suppose {Xn} is a random walk in time-random environment with state space Z^d, ｜Xn｜ approaches infinity, then under some reasonable conditions of stability, the upper bound of the discrete Packing dimension of the range of {Xn} is any stability index α. Moreover, if the environment is stationary, a similar result for the lower bound of the discrete Hausdorff dimension is derived. Thus, the range is a fractal set for almost every environment.
