Simulation Study Of Particle With Greater Differences In Ratio Of Length To Diameter Based On Multigrid Method

Particles or granular substances are widely used in agricultural production,ore,transportation,pharmaceuticals and so on.therefore,it is very important to study the movement of particulate matter.With the continuous development of science and technology,the research in this field has been deepened.However,because of the fluidity and discreteness of particles,it is not suitable to use the traditional continuum mechanics method to study,so there are still many unsolved problems.Discrete element method(DEM)is a numerical simulation method,which is mainly used to calculate a large number of particles under specific conditions.It is considered as an important tool for particle simulation research.This method optimizes the structure and reduces the development cycle by modeling and simulating the physical prototype.Contact calculation is the most time-consuming part of discrete element method.At present,grid method,neighbor list method and other search methods are commonly used to determine the particle neighbors to be detected to improve the efficiency of calculation.However,in the agricultural production,there are many particles with different shapes and sizes,such as wheat and maize.When using the discrete element method,because of the large size of the grid searched by the neighbors,the number of neighbor particles are increased,resulting in a significant increase in the complexity of contact calculation.After many years of research,the simulation calculation based on discrete element method has been deeply studied,and a simulation calculation software possesses integrating design,calculation,simulation demonstration and performance analysis has been developed.In this paper,the existing discrete element simulation software Agri DEM is used to study the problems in the contact calculation of particles with large aspect ratio in production.A neighbor search algorithm for particles with large aspect ratio based on multi-grid is added.At the same time,two boundary types,force threshold boundary and elastic boundary are added,which adds new choices for the design and simulation analysis of complex machinery.Firstly,the multi-grid method is analyzed and studied in this paper.First,the whole computational domain is divided into multiple grids with different sizes.In the simulation calculation,it can be mapped to the corresponding hierarchical grids according to the central coordinates and sizes of the particles to be detected,and then the neighbor elements can be determined by the grid number and grid layer number of the particles to be detected.Next,the same-level search and cross-level search are carried out.The neighbor metadata and the particles to be detected are contacted to determine the contact situation between the particles,and the design of the multi-grid method is realized.Secondly,referring to the design of non-spherical particles in the research group,the model of large aspect ratio particles is established by means of multi-sphere combination.At the same time,the particles with large aspect ratio are virtual discretized into particles with small aspect ratio,and then the discrete particles are mixed with other particles to search for neighbors by multi-grid method,which provides a new idea for the contact calculation of particles with large aspect ratio in discrete element method.Next,the force threshold boundary and elastic boundary modules are designed.When particles are in contact with mechanical components,the boundary will change in different ways,such as static,translational,rotational and deformation,due to given threshold,error coefficient,boundary type and boundary material.The study of force threshold boundary and elastic boundary provides more choices for complex boundary(mechanical components)modeling.Finally,the above contents are designed and the test results are analyzed.The function was verified by the selection of different size particles,grid layers and grid size.At the same time,the wheat plant particles after harvest were used to test the universality of the program.The test results show that the accuracy of the above functions also verifies the stability of the software architecture,and the test meets the requirements of the simulation.