| Discrete element method is a kind of numerical calculation method used to analyze the mechanical behavior of granular materials and the ruler of their sport, is put forward by Dr. Peter Cundall in the turn of the last century. The main idea of discrete element method takes the whole consisting of many discrete units, according to the contact between two discrete units, establishing mechanical model. The motion state of each discrete element is obtained by Newton's second law, through introducing the time step, recursively computing granular materials movement process, and gaining behavior of the whole granular materials. Initially, the method is mainly used study of rock mechanics, but because of the limitations of the finite element method and the advantage of discrete element method, discrete element method has been continuously inherited and developed, After nearly three decades, through numerous experts, scholars and research institutions, discrete element method has been gradually developed, currently, in the studying of mining, agriculture, water conservancy and hydropower, it has widely used.From space discrete element method can be divided into two-dimensional and three-dimensional. Commonly, oval, disc and polygon is used to simulate granular materials by two-dimensional discrete element method. Although the two-dimensional discrete element method is simple, efficient and etc, it becomes more mature day by day, however, establishing and analyzing mechanical model is limited to flat, so two-dimensional discrete element method, the scope of application still has its limitations. In recent years, three-dimensional discrete element method made discrete element method further developed. Granular material is commonly modeled used sphere unit, ellipsoid unit and block by three-dimensional discrete element method. Not only fully inheriting the advantages of two-dimensional discrete element method, but also greatly improving the accuracy of the calculation and simulation, it works well.In the past, a new mechanical part must be designed, and then tested and improved, and be redesigned, retested and so on, it is a complex process which costs much. In order to solve this problem, our group develops digital software which can design component, simulate and analyze how the component works. After further development based the Pro / Engineer, it can analyze and optimize mechanical component. It cuts cost when design new component.3D Software is designed according to three-dimensional discrete element method, although the three-dimensional discrete element method compared with two-dimensional discrete element method only increases one dimension, but the complexity of modeling, analysis and simulation multiples which makes developing and testing software more difficult. Prominent issues are many, for example: calculation is slow and inefficient, simulation is not realistic compared to Pro / Engineer, part of function is unachieved and etc. In this paper, I study issues above further based summing up and inheriting the experience of developing three-dimensional software.Simulation of soil particle usually requires a large swatch, the software can't generate enough particles if we take time step method. During generating these particles will move as a result of collisions, so it can't achieve a similar stationary state as the soil. In order to meet need that generating large-scale particles and simulating soil, this paper uses the method that generates particles in a hexahedron or cylinder, all particles will be generated at one time by the method above, and in the subsequent time step, enlarging particles according to factor set by the user and the time when particles begin being enlarged. Particles will move because of collision while they are being enlarged, ultimately, they achieve steady-state uniform mixing. At the same time, this paper has also established the method that generating particles while feed port is moving. When feed port is moving, three-dimensional software computes out the position of the feed port by formula, and generates particles.In order to improve the performance of three-dimensional software, in this paper, I established the algorithm of determining contact that spherical particle with disc and spherical surface. First, the border is converted to the local coordinate system which center is same to center of border, and then determining contact of particle with border in the local coordinate system, finally, convert the result to the global coordinate system according to Cramer's rule, computation number is reduced with this method in determining contact, to a certain extent can improve the performance of three-dimensional software. At the same time, this paper also details the OpenMP technique in three-dimensional software configuration and application, OpenMP technology is verified by testing and it is important and useful. Always, the physical properties is different between particle and border In the industry and agriculture, the model of generating multi-attribute particle and the model of determining contact of multi-attribute particle with multi-attribute border is established in this paper to meet the actual demand. The correction formula is used in the calculation to correct parameters in the mechanics model, and differentiate particles with color through OpenGL.Although the three-dimensional software already has a sound theoretical basis, but there are still many function not been realized yet, affecting the process of testing and application, to make three-dimensional software more applicably, the following functions are added in this paper: switch simulation and display, switch display of numbering particle, switch display of partial's location, check parameter, make statistics of particle flow, make statistics of particles'mass and store time step.The way by which original three-dimensional software extract data is correct and it fit for simulation, but it is worse than Pro / Engineer software. In this paper, on the basis of long-term research and test, VDA-3DS entity-plan can be displayed. With this method, the plan drawn by Pro / Engineer software is saved as VDA format and be converted to 3DS format. A 3DS file read module is added in the three-dimensional software to get information of 3DS files and displays them, and these entity-plans can be translate and rotated, improving fidelity of simulation.In this paper, introduction of virtual reality technology in three-dimensional software is an innovation, how to introduce virtual reality technology in face of three-dimensional software's structure, function and etc is made a particular description, and through the sky-box building systems, the terrain generation system and user roaming model to create three-dimensional virtual environment, it makes a way for introducing virtual reality technology to three-dimensional software.In the VC++6.0, fulfill all the above-mentioned algorithms and functions, and test developed software with software engineering method, proof relevant coding and building method correct. |
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