【作者】 柳有权；

【导师】 吴恩华；

【作者基本信息】 中国科学院研究生院（软件研究所） ， 计算机应用技术， 2005， 博士

【摘要】 基于物理的计算机动画一直是计算机图形学领域的一个热点研究方向,尤其是电影特效的发展以及电子游戏的强力需求推动着这一方向的研究。人们不仅需要形象的真实感,也需要运动的真实感。而真实世界蕴涵着复杂的运动规律,其复杂度往往使得人们难以用一些简单过程来表述。如何发现这些规律并通过计算机计算重现真实世界的运动成为基于物理的计算机动画的关键技术。然而一方面人们对真实世界的许多现象的内在本质仍处在探索中,在计算机图形领域中对于这些现象缺乏对其物理模型本身比较合适的描述和建模,另一方面物理计算的复杂性往往带来性能的严重损失,满足不了许多对时间要求较高的图形学应用领域的需求,因此如何在视觉误差范围内对其计算处理进行加速就显得尤为重要。本文以基于物理的计算机动画作为研究目标,并试图在物理模拟的真实感和效率之间寻求一个良好的平衡点,从而满足众多应用领域的需求。 本文对这一课题的研究着重集中在以下三个方面:第一,对于基于物理的树木动画,寻求新的方法以模拟和加速枝条自然的变形计算;第二,试图利用图形卡的最新进展,以新的图形硬件(GPU)的可编程性和一定程度的并行性加速通用代数运算,实现基于物理的计算机动画的加速;第三,研究基于物理的流体模拟,着重研究流体与物体表面的作用以及流体计算的加速。 本文算法的主要贡献和创新点在于如下工作: □第一次在计算机图形学领域将表面流体的运动和表面形态的湿度变化结合起来,以模拟流体流经不同介质表层所产生的复杂真实效果。对于潮湿的表面采用物体表面对水的实际吸收量作为控制因子来表现其不同程度的湿润情形。同时模拟了整个表层污物的输运以及侵蚀和沉积过程。 □利用GPU求解纳维-斯托克斯流体运动方程组,实现了烟雾等流体在复杂环境中实时自然流动。求解过程中采用半拉格朗日方法求解对流项,结合隐式迭代以获得绝对稳定的格式,从而满足大的时间步长。由于整个计算映射到GPU上,从而利用GPU的并行性获得充分的加速,使得整个计算和绘制达到实时效果,另外,为了能灵活地处理复杂边界,创造性地引入修正因子和偏移两幅纹理,通过修正因子纹理来设计各类边界,而通过偏更多还原

【Abstract】 Physically based computer animation is always a hot topic in computer graphics especially in the special effects industry for films and games. Only physics makes more realistic. However, the complexity of the physical computation often leads to serious performance degradation, so it is necessary to investigate on the acceleration techniques. This paper aims to solve the problem by seeking for a tradeoff between the realistic effects and real time performance, to meet the needs from various applications.This paper focuses on the study in three aspects, including physically based tree animation with new method to accelerate the calculation of tree’s branch deformation; general purpose computation on GPU (Graphics Processing Unit) which takes advantages of the parallelism and the programmability of graphics hardware to accelerate the calculation; physically based fluid simulation by GPU to accelerate the computation of Navier-Stokes equations, and simulate the on-surface flow in real-time.The main contributions of this thesis are mainly in the following aspects:□ First ever attempt on coupling the on-surface flow with water absorption which to control the rendering of wetting effects. And stains transportation, erosion and deposition are also incorporated into the on-surface flow.□ Based on the Navier-Stokes equations, we use GPU as a co-processor with CPU to simulate the smoke flowing with complex obstacles in 2D and 3D domains. To make sure stability with large time-step, the semi-Lagrangian method is used to compute the advection term and the implicit iteration method is used to compute the pressure-Poisson equation and the diffusion term. To process the complex obstacles, we introduce the modification texture which is used to embody various boundary conditions and the offset texture which is used to indicate the right directions to the obstacles.□ Accelerate the algebra operations with GPU. To utilize the full potential of GPU, we take advantages of the four channels and the whole pipelines to reduce the number of rendering pass.□ Use FEM (Finite Element Method) to compute the deformation of tree in wind. To accelerate the simulation, this paper takes a hybrid FEM way to alleviate the computation burden with different strategies for different kinds of branches. For those non-end branches with small swing, static analysis is enough to get their deformation; while for those non-end branches, we use step-by-step Newmark integration to calculate their vibration. Furthermore, we use shadow mapping technique based on GPU to achieve a realistic appearance.更多还原