基于物理模型的火苗动画

本文提出了一种基于物理模型的火苗数值模拟方法。真实感和实时性是计算机图形学追求的两个目标。传统的动画技术生成的物体运动是虚拟的,并不能完全反映物体的真实运动。与传统的动画技术相比,基于物理的动画更能表现运动的真实性。本文在用非粘性不可压欧拉方程表示火苗物理模型的基础上,利用破开算予法将其分解成外力项、对流项和投影项分别进行求解,每一步都稳定,因而整个求解也就稳定。求解过程的稳定性保证了模拟可以用大时间步长,也就保证了模拟的实时性。与传统的方法相比,能同时满足计算机图形学的真实感和实时性要求。     

实时稳定的二维烟雾模拟

烟雾模拟是计算机动画模拟的重要组成部分.在模拟过程中保证实时性和稳定性是烟雾动画模拟的一个重要方面.该文的目的是在计算机上模拟出真实感的烟雾.文中采用无粘不可压欧拉方程作为烟雾的基本物理模型,对这种简化的流体方程求解可以加快计算的速度,使模拟的速度加快.数值上,引入了CIP方法的一种改进形式USCIP方法来求解N-S方程的对流项,该方法是无条件稳定的.求解方法的稳定实现了大时间步长模拟,保证了模拟实时性和稳定性,最后模拟得到二维的烟雾效果.实验证明本方法能实时稳定地模拟出具有真实感的二维烟雾效果.     

基于物理的流体运动模拟方法研究

提出了一种基于物理的流体运动模拟方法,同传统的模拟技术相比,基于物理的模拟更能表现真实感运动。选用的物理模型是完整的Navier-Stokes方程组,针对完整的Navier-Stokes方程组,利用破开算子法将模型分解成外力、对流、扩散和投影项分别进行计算。因为每一步都稳定,所以整个求解过程也稳定。因此可以用大时间步长来模拟流体运动。Navier-Stokes方程组保证了真实感,而此求解方法保证了效率。     

基于模态分析法的变形动画技术

运动物体碰撞变形动画在电脑动画领域中有着重要作用。模拟物体的碰撞变形方法主要有基于几何模型法和基于物理模型法。随着多媒体和电脑动画技术的发展,对于物体变形动画模拟的真实性要求越来越高,采用物理模型法能得到更加逼真的模拟效果。针对运动物体的碰撞变形动画,采用模态分析法将复杂的非线性系统转换为能单独求解的线型方程组,从而提高了变形动画模拟的求解速度。结果表明,所述方法能获得变形动画模拟的实时性和视觉效果的逼真性。     

基于物理模型的三维火焰实时渲染

火焰等无规则物体的模拟近年来成为计算机图形学中的一个研究热点。传统的基于粒子和纹理技术生成的火焰,并不能真实地反映物体的运动过程,生成的火焰效果图具有随机和生硬的特点。为了解决火焰模拟过程中难以实现的实时性和真实感的问题,文中采用一种基于物理模型的火焰实时渲染方法,应用有限差分法求解Navier-Stokes方程,采用半拉格朗日法求解平流项,扩散方程则利用隐式迭代方法进行求解,利用GPU强大的并行计算能力对求解过程进行加速,利用光线投射算法对火焰进行渲染,最后生成了逼真的火焰图像。实验结果表明该方法实现简单,渲染速度快,显示的效果真实。     

基于物理模型的烟雾动画模拟

本文结合计算流体力学和计算机图形学,实现了烟雾的模拟动画。文章首先给出了烟雾的物理模型方程,并采用N-S方程和半拉格朗日方法来求解烟雾的物理模型方程,从而得到了烟雾的三维密度场数据,最后用体绘制方法中的光线投射法实现了动画模拟。     

基于OSG的实时烟雾模拟的研究与应用

为了模拟出具有实时性和真实感的烟雾效果,分析了传统烟雾的模拟方法,提出了一种基于OSG平台下的实时烟雾模拟方法。该方法采用流体力学纳维-斯托克斯方程组作为基本物理模型,通过添加漩涡约束力来达到真实性的要求。由于NS方程求解的复杂性和CPU计算的限制性,在方程解算上,提出一种基于GPU的采用半拉格朗日方法、雅克比迭代法等稳定的求解方法,并结合体绘制技术来实现实时烟雾的模拟。实验结果表明,该方法能快速模拟出实时、逼真的烟雾效果。     

一种烟雾实时模拟的新方法

介绍了一种基于流体力学方程的多尺度流体模型,通过Helmholtz-Hodge算子将模型分解为对流、扩散、外力、投影等项分别进行求解,每一步都稳定,因而整个求解也就稳定。同时利用“涡流限制”的技术提高模拟的真实性。与传统方法相比,该方法能实时高效地模拟具有真实感的二维烟雾效果。     

基于物理的烟雾动画设计与实现

在计算机图象学的算法研究中,烟雾、水流和火焰等流体的模拟是一个即困难又吸引人的问题.结合计算流体力学和计算机图形学,实现了烟雾的模拟动画.本文给出烟雾的物理模型方程,并采用N-S方程和半拉格朗日方法来求解烟雾的物理模型方程,从而得到烟雾的密度场数据.最后用体绘制方法实现了三维密度场转换成屏幕上的图像.     

三维烟雾的实时模拟

提出了一种基于流体力学方程并采取欧拉法实时模拟三维真实感烟雾的算法。通过Navier-Stokes方程建立烟雾流场的物理模型,以保证视觉的真实感。为了保证运算的实时性,烟雾流场划分为三维网格空间,并将烟雾速度场的分布定义于每个立方网格单元的中心点;通过线性插值获取整幅图像中每个像素的烟雾浓度。将烟雾模拟技术用于图像的显示特技中,以产生图像消散成烟雾的视觉效果,得到了比较满意的模拟效果。     

大规模流体场景的真实感与实时模拟

目的 基于物理的流体动画模拟是计算机图形学领域中的研究热点,针对实际应用中仍难以实现大规模流体场景的真实感与实时模拟,提出了基于shallow water方程的物理模拟方法。方法 首先,给出shallow water方程的稳定欧拉数值求解方法,解决模拟过程中存在的毛刺、陡坡水滴斑点等数值求解的不稳定性问题;其次,提出刚体和粒子系统与流体高度场的稳定耦合模型,实现双向固流耦合和流体表面细节的真实感模拟;最后,设计高度场的多精度网格算法以及粒子的隔点采样方法,加速大规模流体的物理模拟计算。结果 实验结果表明,本文方法解决了传统欧拉方法求解shallow water方程的流体模拟过程中存在的不稳定和计算复杂等问题,在300×300网格分辨率和2.2×10⁴粒子数的规模下,达到了20帧/s的实时模拟速度。结论 本文算法具有良好的高效性和稳定性,适用于电子游戏和视景仿真等实时应用领域中的大规模流体场景的真实感模拟。     

Markov-type velocity field for efficiently animating water stream

In computer graphics, one of the most challenging tasks is continuously varying phenomena such as waving, swaying, and flowing motions. In this paper, we present a novel hybrid model (physical-stochastic) to create an endless animation in which offline simulation is used to produce an infinitely varying real-time animated result. In this particular case, a water stream model is proposed. Most fully 3D physically based simulation methods for depicting fluid flows are very time and memory consuming. Thus, these methods are still reserved for offline simulations and small-domain real-time simulations, especially in the case of fluid flows with irregularly repeating patterns. The proposed model is based on the tracer particle technique, uses a non-static velocity field, and consists of two main phases. In the first phase, we construct the stochastic velocity field by using the physically based method. The second phase is the main part, in which we create real-time endless animation. Here, we introduce a new type of velocity field which we refer to as a Markov-type velocity field (MTVF). MTVF allows us to animate a water stream endlessly in real-time by avoiding the time-consuming process of solving the corresponding equations for every simulation step.     

具有真实感的三维人脸动画

具有真实感的三维人脸模型的构造和动画是计算机图形学领域中一个重要的研究课题.如何在三维人脸模型上实时地模拟人脸的运动,产生具有真实感的人脸表情和动作,是其中的一个难点.提出一种实时的三维人脸动画方法,该方法将人脸模型划分成若干个运动相对独立的功能区,然后使用提出的基于加权狄里克利自由变形DFFD(Dirichlet free-form deformation)和刚体运动模拟的混合技术模拟功能区的运动.同时,通过交叉的运动控制点模拟功能区之间运动的相互影响.在该方法中,人脸模型的运动通过移动控制点来驱动.为了简化人脸模型的驱动,提出了基于MPEG-4中脸部动画参数FAP(facial animation parameters)流和基于肌肉模型的两种高层驱动方法.这两种方法不但具有较高的真实感,而且具有良好的计算性能,能实时模拟真实人脸的表情和动作.     

Efficient Smoke Simulation on Curvilinear Grids

We present an efficient approach for performing smoke simulation on curvilinear grids. Our technique is based on a fast unconditionally‐stable advection algorithm and on a new and efficient solution to enforce mass conservation. It uses a staggered‐grid variable arrangement, and has linear cost on the number of grid cells. Our method naturally integrates itself with overlapping‐grid techniques, lending to an efficient way of producing highly‐realistic animations of dynamic scenes. Compared to approaches based on regular grids traditionally used in computer graphics, our method allows for better representation of boundary conditions, with just a small increment in computational cost. Thus, it can be used to evaluate aerodynamic properties, possibly enabling unexplored applications in computer graphics, such as interactive computation of lifting forces on complex objects. We demonstrate the effectiveness of our approach, both in 2‐D and 3‐D, through a variety of high‐quality smoke animations.     

织物动态仿真中改进的粒子模型

针对三维织物动态仿真中存在的超弹性现象,考虑到织物的高度非线性材料性能,提出了一种改进的粒子模型。该模型内力表达式中不仅考虑了材料线性刚度的作用,而且增加了非线性项作用,使所建立的模型更加符合织物的物理特性。在外力计算方面,考虑了实际风力作用下粒子间存在的遮挡情况,并给出了相应的风力计算算法。仿真研究表明,该改进模型能较好地反映织物的力学性能,所获得模拟结果也更加真实。     

Physically‐based forehead animation including wrinkles

Physically‐based animation techniques enable more realistic and accurate animation to be created. We present a fully physically‐based approach for efficiently producing realistic‐looking animations of facial movement, including animation of expressive wrinkles. This involves simulation of detailed voxel‐based models using a graphics processing unit‐based total Lagrangian explicit dynamic finite element solver with an anatomical muscle contraction model, and advanced boundary conditions that can model the sliding of soft tissue over the skull. The flexibility of our approach enables detailed animations of gross and fine‐scale soft‐tissue movement to be easily produced with different muscle structures and material parameters, for example, to animate different aged skins. Although we focus on the forehead, our approach can be used to animate any multi‐layered soft body. © 2014 The Authors. Computer Animation and Virtual Worlds published by John Wiley & Sons, Ltd.     

Multi‐layer Lattice Model for Real‐Time Dynamic Character Deformation

Due to the recent advancement of computer graphics hardware and software algorithms, deformable characters have become more and more popular in real‐time applications such as computer games. While there are mature techniques to generate primary deformation from skeletal movement, simulating realistic and stable secondary deformation such as jiggling of fats remains challenging. On one hand, traditional volumetric approaches such as the finite element method require higher computational cost and are infeasible for limited hardware such as game consoles. On the other hand, while shape matching based simulations can produce plausible deformation in real‐time, they suffer from a stiffness problem in which particles either show unrealistic deformation due to high gains, or cannot catch up with the body movement. In this paper, we propose a unified multi‐layer lattice model to simulate the primary and secondary deformation of skeleton‐driven characters. The core idea is to voxelize the input character mesh into multiple anatomical layers including the bone, muscle, fat and skin. Primary deformation is applied on the bone voxels with lattice‐based skinning. The movement of these voxels is propagated to other voxel layers using lattice shape matching simulation, creating a natural secondary deformation. Our multi‐layer lattice framework can produce simulation quality comparable to those from other volumetric approaches with a significantly smaller computational cost. It is best to be applied in real‐time applications such as console games or interactive animation creation.     

真实感固流交互动画的统一物质点法模拟

固流交互模拟是基于物理的流体模拟技术的重要研究内容,其中如何解决非穿透 和滑移接触是难点。为此,提出一种真实感固流交互动画的统一物质点法模拟方法。首先,给 出一种基于物质点法的快速微可压缩流体模拟方法,并在统一背景欧拉网格上对固体和流体动 量方程进行求解;其次,检测固流接触区域并在其上构建局部多重背景网格,给出一种动量守 恒保持的速度修正方法对固体和流体各自网格结点进行速度修正,从而实现固流交互的非穿透 和滑移接触效果模拟。实验结果表明,该方法可以模拟稳定、真实的固流交互动画,适用于计 算机图形学和虚拟现实领域中的真实感模拟应用。