International Journal for Numerical and Analytical Methods in Geomechanics, 2003
The evolution of the microstructure of an assembly of cohesionless granular materials with associ... more The evolution of the microstructure of an assembly of cohesionless granular materials with associated pores, which carry the overall applied stresses through frictional contacts is a complex phenomenon. The macroscopic flow of such materials take place by the virtue of the relative rolling and sliding of the grains on the micro-scale. A new discrete element method for biaxial compression simulations of random assemblies of oval particles with mixed sizes is introduced. During the course of deformation, the new positions of the grains are determined by employing the static equilibrium equations. A key aspect of the method is that, it is formulated for ellipse cross-sectional particles, hence desirable inherent anisotropies are possible. A robust algorithm for the determination of the contact points between neighbouring grains is given. Employing the present methodology, many aspects of the behaviour of two-dimensional assemblies of oval cross-sectional rods have been successfully addressed. The effects of initial void ratio, interparticle friction angle, aspect ratio, and bedding angle on the rolling and sliding contacts are examined. The distribution of normals to the rolling and sliding contacts have different patterns and are concentrated along directions, which are approximately perpendicular to one another. On the other hand, the distribution of all contact normals (combined rolling and sliding) are close to that of rolling contacts, which confirm that rolling is the dominant mechanism. This phenomenon becomes more pronounced for higher intergranular friction angle. Characteristics of the rolling and sliding contacts are also discussed in the context of the force angle, which is the inclination of contact force with respect to the contact normal.
International Journal for Numerical and Analytical Methods in Geomechanics, 2006
With the increasing demand for discrete element simulations with larger number of particles and m... more With the increasing demand for discrete element simulations with larger number of particles and more realistic particle geometries, the need for efficient contact detection algorithms is more evident. To date, the class of common plane (CP) methods is among the most effective and widely used contact detection algorithms in discrete element simulations of polygonal and polyhedral particles. This paper introduces a new approach to obtain the CP by employing a newly introduced concept of shortest link. Among all the possible line segments that connect any point on the surface of particle A to any point on the surface of particle B, the one with the shortest length defines the shortest link between the two particles. The perpendicular bisector plane of the shortest link fulfils all the conditions of a CP, suggesting that CP can be obtained by seeking the shortest link. A new algorithm, called shortest link method (SLM), is proposed to obtain the shortest link and subsequently the CP between any two polyhedral particles. Comparison of the analysis time between SLM and previously introduced algorithms demonstrate that SLM results in a substantial speed up for polyhedral particles contact detection.
International Journal for Numerical and Analytical Methods in Geomechanics, 2003
The evolution of the microstructure of an assembly of cohesionless granular materials with associ... more The evolution of the microstructure of an assembly of cohesionless granular materials with associated pores, which carry the overall applied stresses through frictional contacts is a complex phenomenon. The macroscopic flow of such materials take place by the virtue of the relative rolling and sliding of the grains on the micro-scale. A new discrete element method for biaxial compression simulations of random assemblies of oval particles with mixed sizes is introduced. During the course of deformation, the new positions of the grains are determined by employing the static equilibrium equations. A key aspect of the method is that, it is formulated for ellipse cross-sectional particles, hence desirable inherent anisotropies are possible. A robust algorithm for the determination of the contact points between neighbouring grains is given. Employing the present methodology, many aspects of the behaviour of two-dimensional assemblies of oval cross-sectional rods have been successfully addressed. The effects of initial void ratio, interparticle friction angle, aspect ratio, and bedding angle on the rolling and sliding contacts are examined. The distribution of normals to the rolling and sliding contacts have different patterns and are concentrated along directions, which are approximately perpendicular to one another. On the other hand, the distribution of all contact normals (combined rolling and sliding) are close to that of rolling contacts, which confirm that rolling is the dominant mechanism. This phenomenon becomes more pronounced for higher intergranular friction angle. Characteristics of the rolling and sliding contacts are also discussed in the context of the force angle, which is the inclination of contact force with respect to the contact normal.
International Journal for Numerical and Analytical Methods in Geomechanics, 2006
With the increasing demand for discrete element simulations with larger number of particles and m... more With the increasing demand for discrete element simulations with larger number of particles and more realistic particle geometries, the need for efficient contact detection algorithms is more evident. To date, the class of common plane (CP) methods is among the most effective and widely used contact detection algorithms in discrete element simulations of polygonal and polyhedral particles. This paper introduces a new approach to obtain the CP by employing a newly introduced concept of shortest link. Among all the possible line segments that connect any point on the surface of particle A to any point on the surface of particle B, the one with the shortest length defines the shortest link between the two particles. The perpendicular bisector plane of the shortest link fulfils all the conditions of a CP, suggesting that CP can be obtained by seeking the shortest link. A new algorithm, called shortest link method (SLM), is proposed to obtain the shortest link and subsequently the CP between any two polyhedral particles. Comparison of the analysis time between SLM and previously introduced algorithms demonstrate that SLM results in a substantial speed up for polyhedral particles contact detection.
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Papers by Erfan Nezami