| In the real world, there are granular materials everywhere, such as food particles in agricultural production and agricultural processing, gravel materials in the course of construction gravel materials, medicine and fertilizer granular material in the field of medicine and chemical industry. The nature of granular materials is between solid and fluid, it has a complex physical properties. Research on granular materials with traditional continuous media mechanics method, only put granular materials as a whole and can't analyze motion of granular materials.In 1971, Cundall proposed discrete element method to analyze the mechanical properties of granular materials. The basic idea of discrete element method is to abstract granular materials as a group of particles with a certain kind of shape and mass, endue the particle-particle and particle-boundary various physical parameters, analyze the movement of particles and the various physical effects of particles-particle and particles- boundary. The calculation process of discrete element method is divided into a number of time steps, using the dynamic relaxation method, Newton's second law to calculate force conditions, velocity and displacement of each particle at each time step. In addition to analyze motion characteristics of granular materials, the discrete element method can analyze to the flow of chemical reactions and heat transfer process. At present, the discrete element method has become the common methods to research mechanical properties of granular materials and is widely used in geotechnical engineering and equipment, mining engineering and equipment, chemical process and equipment, pharmaceutical engineering and equipment, food and agricultural engineering and equipment research fields.Currently, the task group has developed a set of design and performance analysis in one, universal, digital design and analysis software. The software put the model of the boundary with CAD, set up a meta based two-dimensional boundary element method for discrete analysis model, process contact inspections of particle-particle and particle-boundary with neighbor search and geometric and numerical methods. Now the two-dimensional discrete element analysis software can simulation several kind of particle with high accuracy.It is a key issue of how to put the model of particle in discrete element method. It is necessary to model highly accurate in order to accurately simulated the movement of granular materials. Home and abroad, mostly discrete element simulation software use circular particle modeling, it is very simple in contact detection and the calculation of composite volume of round particle, but the circular particle is much different from the actual object, make low accuracy of simulation, the simulation result is quite different from actual result. Currently, the model of particle with complex shape use combination particle model, which the particle consist of with several round with different radius. It calculates the force of combination particle by calculating the force of the round which the combination particle is consists. The combination particle model has high accurate and high quantity of computation. The research on new particle model is important to the development of discrete element analysis method.Super-quadratics equation is the expansion of elliptic equations in two-dimensional, according to statistics, 80% of the natural world plane image circle equation can be expressed by super-quadratics equation. This feature of super-quadratics equation makes put model of complex shape particle using super-quadratics equation possible. In this paper put model of complex shape particle with super-quadratics equation, use the geometric potential method to process contact inspections of particle- particles and particle-boundary.The calculation of the value of the composition oval-shaped particles and particles with boundaries using the geometric potential can be summarized as solving a constrained optimization problem. As the complexity of the super-quadratics equation, there is various problems when solve the constrained optimization problem with commonly used optimization method, such as the Newton method, quasi-Newton method, conjugate gradient method and the multiplier method. these algorithms are high demanding of the initial point, and demand the first-order partial differential equations of the target function, the computational complexity is high, and the local convergence of these algorithms are the algorithm is not guaranteed to get the global optimal solution. Discrete element analysis method with high precision requires the use of high-precision global convergence algorithm to solve this problem.In this article, we use genetic algorithm for solving this optimization problem. The main work in this article is the following:1. The calculation of the value of the composition oval-shaped particles and particles with boundaries using the geometric potential can be summarized as solving a constrained optimization problem. As the complexity of the super-quadratics equation, it can't solve this problem effectively with commonly used optimization method. So we solve this problem with genetic algorithm in this article. This article also introduces the basic principles of genetic algorithms and the basic structure of genetic algorithms, and the method improving the efficiency of genetic algorithm.2. This article describe the principle and algorithm of complex shape particle of discrete element method analysis method, use super-quadratics equations put the DEM analyses model of complex shape particles, process contact inspections and compute the value of the composition using geometric potential and genetic algorithms, the contact inspections of particle-boundary is same to the contact inspections of particle-particle, compute the number of point of intersection between the line and the particle to process contact inspections between the particle and line.3. This article accomplish the two-dimensional super-quadratics particle discrete element simulation software using VC + + and integrate it into the project team two-dimensional discrete element analysis software developed by task group.4. Introduced the basic principles of software testing methods, and test the two-dimensional super-quadratics particle discrete element method simulation software. We test the overlap calculation process of particle- particle and particle–boundary by white-box testing, test the accuracy and reliability of software using black-box testing. The results show that the two-dimensional super-quadratics particle discrete element simulation software has realized the expected function.The work in this article has a certain sense to perfect the two-dimensional digital design and analysis software developed by our team, and to expand the usage of the software. |
PDF Full Text Request