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发表于 2005-8-17 12:53:24
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[求助]选择模拟颗粒运动的方法
呵呵我只知道点皮毛.
今天GOOGLE发现我见过的方法类似DEM, 可能在处理CONTACT时有些不同. 用什么语言没关系吧. 你应用背景是什么?
The numerical model based on Distinct Element Method (DEM) was introduced by Cundall and Strack (1979). In the DEM, the interaction between the particles was regarded as a dynamic process that achieves a static equilibrium when the internal forces were balanced. The contact forces and displacements of a stressed assembly of particles are found by tracing the movements of the individual particles. Movements result from the propagation through the particle system of disturbances caused by specified wall and particle motion or body forces. This was a dynamic process in which the speed of propagation depends on the physical properties of the discrete system. The dynamic behavior was represented numerically by a time stepping algorithm. The solution scheme was identical to that used by the explicit Finite Difference Method for continuum analysis. The formal procedure of the DEM takes advantage of the idea to select and define the duration of a time step in such a way that during a single time step, the disturbances in the state of equilibrium can spread only from the regarded particle to its direct
neighbors (Itasca 1999; Markus 2000). The particle-flow model had the following assumptions:
a) the particles are treated as rigid bodies;
b) the contacts occur over a vanishingly small area;
c) behavior at the contacts use a soft-contact approach where the rigid particles were
allowed to overlap one another at contact points;
d) the magnitude of the overlap is related to the contact force via the force-displacement
law, and the overlaps are small in relation to particle sizes;
e) bonds can exist at contacts between particles; and
f) all the particles are spherical, however the clump logic supports the creation of superparticles of arbitrary shape. Each clump consists of a set of overlapping particles that acts as a rigid body with a deformable boundary.
The calculations performed in the DEM exchange between the application of Newton’s second law to the particles and a force-displacement law at the contacts. The calculation cycle in
the software was a time stepping algorithm that required the repeated application of the law of motion to each particle, a force-displacement law to each contact, and a constant updating of wall positions. During the course of simulation, contacts existed between two balls or between a ball and a wall were formed and broken automatically. The calculation cycle is depicted in Fig. 41. At the beginning, the set of contacts is updated from the known particle and wall positions. Then, the force-displacement law was applied to each contact to update the contact forces based on the relative motion between two entities at the contact and the contact constitutive model.
Then, the law of motion applies to each particle to update its velocity and position based on the resultant force and moment arising from the contact forces and any body forces acting on the particle. The wall positions are also updated based on the specified wall velocities (Itasca 1999).
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