Discrete Element Method Modeling Based On Expanding Multi-Concave Particle

Classical discrete element method is based on the ideal spherical particle unit in most cases.However,many real particles in nature and engineering applications are not ideal spheres.There are obvious differences between the non-spherical particles and the spherical particles in the common particle flow behavior,such as plane and shear.The shape effect of non-spherical particles cannot be simulated by changing the parameters of spherical particles.It is necessary to develop a discrete element method based on concave particle unit to study the physical and mechanical behavior of concave particles(e.g.corn,cell)in the production life,since most non-spherical particle construction methods cannot be used directly to construct concave particles.Aiming at the limitation of the few simulation methods and high computational cost of the discrete element model of concave particles,a discrete element method based on the expansion of multi-concave particle unit is proposed in this paper..The multi-concave particle unit is constructed based on multi-ball subtraction Boolean operation,and the positions and sizes of concave are controlled by means of normal and random distribution.The method of extend the concave is proposed to smooth particle surface to avoid the singularity of edge contact.Seven contact forms of convex,concave,and plane are given,and the algorithm of particle-particle and particle-boundary contact algorithm is established.The calculation consumption of contact judgment is greatly reduced by using GPU parallel over computation.The calculation model of multi-concave particle contact force is given and the motion of particle is calculated by momentum theorem and quaternion algorithm.The validity of the discrete element method of expanding multi-concave particle is verified by the particle heap problem.The results show that there is a significant difference between the static pile angle of the multi-concave particle and the ideal spherical particle.Pile angle of concave particles is inversely proportional to the size and number of pit in the particle surface.The blockage effect of multi-concave particle and ideal spherical particle can be found during the unloading process of the square hopper,the spherical particles are more obvious.