Discretizing Three-dimensional Pulsating Wind Field For Falling Snow Simulation Based On D3q7 Lattice

The simulation of snow in the natural landscape could greatly enhance the realistic effect of the virtual scene. The features, such as the irregular shape of snowflakes, the uncertain movement of the snow and the interaction with the environmental factors, determined that the approach of snow modeling and the description of the snow movement were very complicated. The premise of simulating the realistic falling snow scene is to make the snow particles immersed into the wind field. Therefore, this paper focused on the following areas.Firstly, the characteristics of the fluctuating wind are identified according to the existing literature about aerodynamics. The D3Q7 lattice is used to improve the model of wind field. For the LBM, the description of stochastic movement of wind was just introducing one or several external force in the motion equation of wind particle to simulate random characteristic of wind particle's movement, which had great difference with the trajectory of wind. The D3Q7 descripts random characteristic of the wind coming from every directions more authentic, thus the wind's movement is more realistic, furthermore, force analysis of snow particle immersed in the wind field could be helpful for enhancing the realistic effect of the simulated falling snow scene.Secondly, since force analysis of the snow particle has been completed, the locomotion of snow particle along the grid line can be obtained. But the calculated locations of the snow particles were not exactly corresponded to the three-dimensional lattice nodes, this problem could be solved by the probability analysis approach. This method makes sure that the average position of the snow particles changes with the expected speed flow, while the movement is along the lattice lines. Finally, we not only ensure the randomness of the falling snow, but also guarantee the physical accuracy of the falling snow particles in macro level.Thirdly, the method of fractal and draw-line is adopted to construct three-dimensional snow. The snow model constructed in the falling snow scene before was two-dimensional, in that case, the simulation effect of the snow's rotation in the natural landscape could not be satisfied. The method mentioned in this paper can not only ensure the rendering speed of snow in falling snow scene but also satisfy the requirment of rotation simulation.Finally, a falling snow simulation system was designed and realized to validate the effectiveness of this method for falling snow simulation.