Techniques And Implementation Of Granular DEM Simulation For Mechanical Product Design

Discrete Element Method (DEM) is an effective numerical method for solving the dynamical problems of granular media and block systems under movable boundary conditions. DEM simulation has been widely applied to the fields of mechanical design for the particle preparation and processing equipment, and has achieved a serial of valuable research conclusions. Compared to its application in other engineering fields, the DEM simulation in the mechanical product design should specially consider the following problems and how to solve the problems.Firstly, the boundary model usually represents a movable machine component in the DEM simulation. The boundary model occupies a spatial volume with a certain surface geometry, and moves as a rigid body in the prescribed manner. Although the regular boundary can be exactly described by using the elementary geometries, such as cuboids, tetrahedrons and cylinders, this representation method is not convenient enough to describe those boundary surface which have more complex shapes.Generally, the velocity combination principle of the rigid body can specify the most motion patterns of boundary models. However, for those boundary models which have to continuously move along the predefined paths, the expression of this motion is not suitable due to the instantaneous variation of the kinematical parameters of the boundary models.The surface wear caused by the highly frequent collisions between the particles and the boundary facets is an important problem in the fatigue failure analysis of components. The objective to predict the surface wear in the DEM simulation is that the volume removed due to the impacting and attrition during a collision should be quantitatively computed by statistics and data analysis from the results of the simulation, and the profile of the worn surfaces of the components should be visually demonstrated. However, these problems have been received limited attention in currently reported literature.Secondly, most problems in mechanical engineering involve complex mechanics environment where a large number of particles impact the components rapidly and frequently and the directions of kinematic parameters and the collision forces of particles change in a very short time. A contact detection algorithm should accurately capture all kinds of collisions between particles and complex boundary models; meanwhile, a contact detection algorithm needs to have a lower time complexity in order to reduce the whole time consumption of the DEM simulation.Thirdly, all the related implementation of the DEM simulation techniques should be delicately deployed in a simulation software. A well-designed DEM simulation software enables researchers to concentrate on designing numerical experiments, understanding and interpreting the simulation results, rather than struggling with the heavy programming work. The DEM simulation system should provide a serial of straightforward pre-processing functions and the integral data visualization tools for different problems in the mechanical product design and analysis. However, there is few reported literature to express the implementation of such simulation software.This dissertation addresses the above three kinds of problems, and the research work mainly focus on the following five aspects.(1) By studying various DEM application cases, three main problems on the DEM simulation applied in the course of design and analysis of the related mechanical products have been pointed out.(2) The triangulated mesh is used here to represent the surface geometry of the boundary models. A trajectory planning method has been then completed to express the motion along with the paths, and this method is verified as an effective representation for this kind of motion pattern by a numerical experiment of excavating. At last, a novel wear prediction method based on the triangular mesh boundary has been established, by which the removed volume of the surface material is related to the impact energy, and the profile of the worn component can be reasonably predicted.(3) A novel contact detection algorithm to find the contacts between spherical particles and triangulated mesh boundaries has been proposed. This algorithm uses the fixed grid subdivision method to search space neighbors for a particle element, and takes less check steps to clarify the contact information than the currently published the intersection check methods. Through simulation cases, the effectiveness and robustness of this algorithm has been verified.(4) A suit of3D DEM simulation system has been developed and implemented. From the architecture aspect, the entire simulation system is divided into three functional modules. Then, the three modules have been implemented based on the object-oriented programming and the design patterns, respectively. The numerical case for a screw conveyor has been conducted to validate this simulation system. (5) The above mentioned methods are employed in the DEM simulation application for tumbling ball mills. The numerical experiments have been conducted to analysis the motion pattern of the grinding media in a mill, to measure the power draw, the impact energy spectrum and the collision distribution, and to predict the profile of the worn liner. The results indicate that it is of benefit for the application of the DEM simulation to the related mechanical product design.