A tangential force-displacement model for elastic frictional contact between particles in triaxial test simulations

A tangential contact model for three-dimensional discrete element simulations is proposed and used in the micro-mechanical simulation of a drained triaxial test. In this model, the dependence of the tangential contact force on the contact loading history is accounted for. A representative volume element with spherical discrete elements and periodic boundary conditions is used in the simulations to reduce the computation costs. Numerical results of a triaxial test obtained with a linear and the proposed tangential contact model are compared. The results for both contact models are qualitatively in agreement with theory. The linear contact model needs calibration as the used parameters lack physical meaning, while the proposed contact model only uses physical properties of the particles

Simulation of clay soil de-compaction by subsoiling process using discrete element method

High pressures on the soil surface by action of heavy machinery and tillage process cause soil compaction and hardpan layers formation. De-compaction is a energy demanding operation applied to break deeply compacted soil for agricultural uses. Three dimensional simulations of soil decompaction are presented based on a soil-tool interaction model implemented in DEMeter software. Formulation of soil-soil and soil-tool interaction are combined into an elastic-plastic particle based model for soil deformation and evaluated in different tension states among soil particles; The macromechanical input parameters include: adhesion, friction, Young’s modulus, Poisson’s coefficient, elastic limit, plastic limit and soil density. Compression triaxial tests and shear box tests were carried out in order to obtain the required mechanical properties for a tropical clay soil. Simulations of unconfined compression tests using different particle sizes and inter-particle tension were used to calibrate the model to experimental stress-strain curves. The performance of complex tillage tools geometries is tested with 3D simulations and evaluated based on the reaction force on the tool as a function of time and displacement. The results show qualitative and quantitative adjusts of real patter of soil behaviour

Solving microscopic flow problems using Stokes equations in SPH

International audienceStarting from the Smoothed Particle Hydrodynamics method (SPH), we propose an alternative way to solve flow problems at a very low Reynolds number. The method is based on an explicit drop out of the inertial terms in the normal SPH equations, and solves the coupled system to find the velocities of the particles using the conjugate gradient method. The method will be called NSPH which refers to the noninertial character of the equations. Whereas the time-step in standard SPH formulations for low Reynolds numbers is linearly restricted by the inverse of the viscosity and quadratically by the particle resolution, the stability of the NSPH solution benefits from a higher viscosity and is independent of the particle resolution. Since this method allows for a much higher time-step, it solves creeping flow problems with a high resolution and a long timescale up to three orders of magnitude faster than SPH. In this paper, we compare the accuracy and capabilities of the new NSPH method to canonical SPH solutions considering a number of standard problems in fluid dynamics. In addition, we show that NSPH is capable of modeling more complex physical phenomena such as the motion of a red blood cell in plasm

Discrete element modelling for process simulation in agriculture

This paper presents an overview of discrete element modelling (DEM) as a modelling technique for granular assemblies. It focusses on DEM for agricultural products and processes and discusses important algorithmic and physical issues connected to this domain. Existing applications in the literature are reviewed and an overview of ongoing DEM applications in the Laboratory for Agro-Machinery and Processing is presented. (C) 2003 Elsevier Ltd. All rights reserved.status: publishe

Discrete element simulations of the influence of fertiliser physical properties on the spread pattern from spinning disc spreaders

This paper describes a sensitivity study of the flow of granular fertiliser particles on a spinning disc using a discrete element model. The aim was to get a qualitative insight in the influences of individual physical properties of the particles (such as friction coefficient, restitution, and shape) as well as their bulk behaviour on the resulting spread pattern. The results show that certain particle properties, particularly friction coefficients, have a large influence on the spread pattern, and hence should examined carefully in the process of producing granular fertilisers, perhaps by particle coating, or taken into account when applying the fertiliser in the field. Other properties, such as particle stiffness hardly affect the results. Furthermore, it was shown that the friction coefficient and shape of a particle strongly interfere in their particular influence on the spread pattern. Overall, the discrete element model could provide a powerful instrument for the manufacturers in the development of new kinds of spreaders and fertilisers. © 2009 IAgrE.status: publishe

A tangential force-displacement model for elastic frictional contact between particles in triaxial test simulations

A tangential contact model for three-dimensional discrete element simulations is proposed and used in the micro-mechanical simulation of a drained triaxial test. In this model, the dependence of the tangential contact force on the contact loading history is accounted for. A representative volume element with spherical discrete elements and periodic boundary conditions is used in the simulations to reduce the computation costs. Numerical results of a triaxial test obtained with a linear and the proposed tangential contact model are compared. The results for both contact models are qualitatively in agreement with theory. The linear contact model needs calibration as the used parameters lack physical meaning, while the proposed contact model only uses physical properties of the particles

Zn-Pb mineralisatie in het Tatestown prospect, (Ierland)

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