Real-time Rendering Of Gas Phenomena In 3D Virtual Urban Environment

The rendering of gas phenomena in three-dimension scene based on computational fluid has broad applications, such as virtual reality and environment protection. Recently, with the development of computer hardware and the advancement of real-time fluid simulation, rendering of gas phenomena in complex environment becomes possible. However, because of the complexity of the turbulent wind in local area in gas diffusion model, render gas phenomena in complex environment still has many difficulties and challenges.Combining the real-time rendering techniques in computer graphics with the theory of gas diffusion, the dissertation develop a method to simulate and render gas phenomena in city environment, paying more attention to the large eddy model for local turbulent wind field, the application of A.Fick classic diffusion equation, and the fluid simulation for large scale with buildings.Based on the requirement of real-time fluid simulation, gas phenomena in small scale and ideal environment can by rendered by semi-Lagrange method and three-dimension grid. The Poisson equation in gas diffuse function can be solved by super block loosen method. For large scales, instead of a large three-dimension grid, a sequence consists of two-dimension grids is used to decrease the complexity in space and time. So gas phenomena in large space can be rendered in recent computer hardware environment.The dissertation use texture mapping to render the whole fluid, in which the texture map is constructed based on the particles density. Based on the radiate transform theory, one can form the function of alpha value for gas particles by combining the diaphaneity and the particles density. And based on the sky-lighting-multiple-particle scatter theory, the light intensity of texture map can be set to add the detail to the rendering.The dissertation also use the large eddy model around a single building to simulate the effect of building to the wind filed in small scale. The eddy model will be simplified so that it can be used in semi-Lagrange algorithm, and also decrease the complexity of time. Mirror reflection can used to simulate the alternation between fluid and buildings. Based on the position of buildings, subgrids are divided in large space to simulate the local turbulent wind field. After the development of rendering method in city environment, one can simulate the detail of fluid around buildings.