【作者】 王娟；

【导师】 吕梦雅；

【作者基本信息】 燕山大学 ， 计算机应用技术， 2010， 硕士

【摘要】 自然景物的模拟一直是计算机图形学中最具挑战性的问题之一。自然景观中飘雪的模拟,可以大大提高虚拟场景的逼真效果。雪花形态的不规则性、运动的无规律性以及受环境因素影响大的特点,决定了其建模方式和运动描述方法更为困难。真实感的飘雪模拟是要让雪花粒子真正的浸入到风场中。为此,本文着重从以下几方面进行研究和探讨。首先,用D3bQ15晶格改进风场模型。用LBM建立风场模型时,如果所用笛卡尔晶格的离散速度数少,则风场模型的数值精确度低;反之,则会导致系统的计算效率低。而D3bQ15晶格更好的各向同性及特定空间较少的采样数,调和了由离散速度数决定的风场模型的精确度和计算效率之间的矛盾,更好的满足了飘雪场景模拟中真实性和实时性的要求。其次,规划雪花粒子的运动。基于D3bQ15晶格建立风场模拟飘雪场景时,雪花粒子必须沿晶格线运动,但下一时刻雪花粒子的位置不一定正好对应于三维空间的晶格节点。用基于概率的方法处理,保证了雪花粒子的平均位置随预期速度流变化的同时,沿着晶格线运动。这样既模拟了雪花飘动的随机性,又保证了雪花粒子的飘动在宏观上是准确的。最后,为验证基于D3bQ15晶格离散三维风场模拟飘雪场景的有效性,设计并实现了飘雪模拟系统。实验证明:用D3bQ15晶格建立风场模型模拟飘雪场景,能更好的满足飘雪场景真实性和实时性的要求。更多还原

【Abstract】 The simulation of the natural phenomena has always been one of the most challenging problems. The simulation of snow in the natural landscape could greatly enhance the realistic effect of the virtual scene. The irregular shape of snowflakes, the uncertain movement and the regularity of the snow by the environmental factors determined that its modeling approach and the description of its movement was more difficult. To make snow particles immersed into the wind field is the premise of simulating the realistic falling snow scene. Therefore, this paper focused on the following areas.Firstly, the D3bQ15 lattice to improve the model of wind field was used. For the LBM, the numerical accuracy of the wind field was lower when the quantity of the discrete velocity was fewer, but the computational efficiency was slower when the quantity of the discrete velocity was more. A new method was developed. The D3bQ15 of Body-Centre Cubic lattice was used to discrete three-dimensional wind field in view of the limitations of the Cartesian lattice. D3bQ15 lattice has better isotropic and the fewer samples in specific space. It can reconcile the contradictions between the accuracy and the efficiency caused by the quantity of discrete velocity. The new developed method can better meet the demand in the authenticity and the real-time for the falling snow scene than the Cartesian lattice.Secondly, the movement of the snow particles was analyzed. For the movement of the snow particles must be along the lattice lines when based on the lattice of D3bQ15 in simulating the falling snow scene. But the locations of the snow particles in the next time were not exactly corresponded to the three -dimensional lattice nodes. We solve this problem with the approach based on the probability. This method makes sure that the average position of the snow particles change with the expected speed flow, while movement along the lattice lines. In this way, we not only simulate the randomness of falling snow, but also guarantee the macro level of physical accuracy of the falling snow particles.Finally, to validate the effectiveness of the D3bQ15, a falling snow simulation system was designed and realized. The results in the experiments indicated that the new developed method can better meet the demand in the authenticity and the real-time for the falling snow scene than the Cartesian lattice. This study is a useful exploration for falling snow simulation.更多还原