一种具有边界自适应能力的蒙皮网格生成算法

根据图像生成网格是骨骼蒙皮动画生成的关键步骤，网格质量直接影响动画效果，但网格优化工作量大且严重依赖制作者本身技能。对此，本文提出一种能够自适应图像边界的蒙皮网格生成算法。首先，利用图像轮廓的法向量变换计算得到包围图像的均匀近似多边形；接着使用信息熵作为衡量图形内部灵活性的权重，结合改进的重心Voronoi算法对图形内部采样，获得按权重分布均匀的内部采样点；最后，结合边界多边形顶点与内部点进行带边界约束的Delaunay三角剖分，得到可用于骨骼蒙皮动画的三角网格。实验结果表明本文所提出的算法可生成高质量网格，且高度匹配原图像边界，可用于骨骼蒙皮动画制作。     

可控性的双层粒子刚体脆性破裂模拟动画

提出一种可控性的双层粒子模型的刚体脆性破裂动画的模拟框架。首先,使用接触力学分析撞击时固体内部产生的弹性位移并采用光滑粒子流体动力学进行离散求解,在此基础上建立一个可控性的内力分析模型。其次,提出一种双层粒子模型来对刚体进行建模,在保证内力计算精度的同时提高了刚体动力学中碰撞检测的效率。最后实现了多个刚体脆性模型场景的动画。该算法可适用于刚体脆性破裂模拟的动画应用。     

多精度混合弹性变形及其交互模拟

固体的弹性变形模拟作为计算机物理动画领域的重要内容,如何在保证模拟真实感的同时尽可能地提高计算效率以满足交互应用,一直是其研究难点.为此,提出一种多精度混合弹性变形模型来高效地模拟固体的弹性变形及其交互.该模型通过对物体计算空间进行物理和几何区域的用户自定义比例划分,并混合处理交界面处计算结点,实现2种变形区域的稳定耦合;利用虚拟顶点算法对物理变形区域进行稳定和光滑的虚拟切割模拟;提出自适应边界粒子采样的固流耦合算法模拟固流交互.实验结果表明,文中模型通过调整2种区域计算结点的比例,控制和调整弹性变形模拟的效率和精度,可以满足虚实交互和固流交互模拟中稳定和高效的性能需求.     

C动画程序设计

本文介绍了用Turbo C进行动画程序设计的几种方法并用简单实例进行了演示。利用人的视觉暂留特点,在屏幕上制作动画,是目前热门的话题,动画技术是计算机图形学中一个重要内容,它可用于游戏娱乐、广告、软件、包装画面、辅助教学、科学实验模拟、论证、仿真等计算机辅助设计(CAD)。Turbo C提供的一些图形处理函数可用于动画设计。总结起来,动画可用下述的一些方法实现。 1.利用开辟动态图视口方法 Turbo C中可用setviewport()设置图视口,此后的画图操作则均在该设置的图视口中进行。当用该函数在屏幕不同位置设置图视口,使各图视口窗口大小不变,而其位置在动态变化。     

基于MATLAB GUI的火炮调炮动态特性评估系统设计

火炮调炮性能在一定程度上影响着火炮作战性能的发挥,尤其对机动性和准确性有着重要影响。为了能方便、及时地检测评估调炮性能,开发了一种基于MATLAB GUI的火炮调炮动态特性评估系统。系统主要包含曲线绘制、图形窗口数显、性能指标计算和动画演示模块。曲线绘制模块能够利用实时测量并采集到的火炮调炮动态姿态数据,绘制多达8组参数曲线;每个图形窗口均具备数显功能,便于对比分析曲线变化。性能指标计算模块可针对调炮过程曲线,完成多个动态性能指标参数的计算,可用于定量分析调炮过程。动画演示模块能够利用采集到的高低、方向调炮数据及采样时间,对调炮过程进行多角度、重复性演示,便于使用人员整体观察调炮全过程。使用人员能够通过曲线显示、数据显示功能、性能指标计算和动画演示等模块,对火炮调炮动态特性进行有效评估。该系统操作简单,通用性强。     

利用Ulead COOL 3D巧做几何变形动画

在教学中，往往需要利用动画来模拟事物的变化过程，说明科学原理以及事物之间的相互关系，利用计算机动画来表现事物甚至比电影的效果更好，尤其是三维动画。因此，较完善的多媒体教学软件都应配有动画以加强教学效果。     

基于完全拉格朗日粒子方法的物理动画模拟

自然界中不同类型物体和行为的真实感模拟是物理动画的重要内容,但实现基于统一数值方法的模拟仍是研究难点。基于光滑粒子动力学方法和连续介质力学物理模型,提出一种基于完全拉格朗日粒子方法的物理动画模拟算法,模拟刚性物体、弹性物体和不可压缩流体的动力学行为。此外,结合固体表面粒子的自适应采样方案和相对贡献计算方案,提出一种稳定的固流交互算法。实验结果表明,该方法适合于虚拟环境中不同类型物体运动和交互的统一建模和模拟。     

二维数据随机延拓成三维水域动画方法研究

提出一种简单有效的、节约计算开销的方法,用于制作实现三维场景中水域动画效果。该方法的实现过程为利用二维模拟水流或波浪数据延拓到三维空间中,实现水沿其主导传播方向产生波动动画,其中利用了基于物理方程和粒子系统的方法。在动画过程中,这些二维水流帧画面被随机地沿横向方向取样,在动画时间和由用户自定义噪声的参数设置下取得的切片(称为时间片)结构中进行。在重构三维水流画面中,使用了带平滑滤波器的几何技术,以弥补因取样所造成的切片损伤。使用随机布朗运动噪声数据补偿三维画面数据,逼真地显示了涟漪波和怒涛波的动画。     

利用Ulead COOL 3D巧做几何变形动画

在教学中,往往需要利用动画来模拟事物的变化过程,说明科学原理以及事物之间的相互关系,利用计算机动画来表现事物甚至比电影的效果更好,尤其是三维动画.因此,较完善的多媒体教学软件都应配有动画以加强教学效果.     

基于渐进式聚类的局部光与材质设计技术

文中提出一种基于图形处理器(GPU,graphics processing unit)的重光照技术,可以在局部点光源,表面反射属性和视点的同时变化中,以交互式的帧率计算全局光照.为了支持这些变化,选择在运行时刻模拟光能的物理传播过程.尽管这种模拟往往由于计算代价过于昂贵而难以被交互式系统采用,但是文中通过引入一个被称为传播树的层次性结构来大大降低模拟计算的开销.在误差允许的范围内,传播树将近似的发光面片进行聚类,然后便可以使用聚类的代表面片来近似整个场景.另外,还挖掘出了光能分布场在空间上和时间上的连续性,并以此为基础对聚类进行渐进式调整,以避免在每一帧中都得从头计算聚类划分,这就叫渐进式聚类.由于采样点之间的可见性可以预计算,把本来很复杂的间接光照计算问题化解成了简单的累加和少量的合并与分裂操作,即聚类代表所发射出的光能的累加以及聚类的合并与分裂.而累加、合并和分裂都是可以直接在图形硬件上并行执行的.在材质动画和场景装修等实际应用中,使用文中技术能够以交互式的速度生成带有多次反射效果的全局光照.     

Numerical analysis of anisotropic ductile continuum damage

The paper deals with the numerical analysis of large elastic–plastic deformation behavior of anisotropically damaged ductile solids based on a generalized macroscopic theory within the framework of nonlinear continuum damage mechanics. Estimates of the stress and strain histories are obtained from a straightforward numerical integration algorithm based on operator split methodology which employs an inelastic (damage–plastic) predictor followed by an elastic corrector step. The finite element method is used to approximate the linearized variational problem. Furthermore, identification of material parameters is discussed. Numerical simulation of the elastic–plastic deformation behavior of damaged tension specimens demonstrate the efficiency of the formulation.     

Topology optimization based on finite strain plasticity

In this paper infinitesimal elasto-plastic based topology optimization is extended to finite strains. The employed model is based on rate-independent isotropic hardening plasticity and to separate the elastic deformation from the plastic deformation, use is made of the multiplicative split of the deformation gradient. The mechanical balance laws are solved using an implicit total Lagrangian formulation. The optimization problem is solved using the method of moving asymptotes and the sensitivity required to form convex separable approximations is derived using a path-dependent adjoint strategy. The optimization problem is regularized using a PDE-type filter. A simple boundary value problem where the plastic work is maximized is used to demonstrate the capability of the presented model. The numerical examples reveal that finite strain plasticity successfully can be combined with topology optimization.     

A real-time multigrid finite hexahedra method for elasticity simulation using CUDA

We present a multigrid approach for simulating elastic deformable objects in real time on recent NVIDIA GPU architectures. To accurately simulate large deformations we consider the co-rotated strain formulation. Our method is based on a finite element discretization of the deformable object using hexahedra. It draws upon recent work on multigrid schemes for the efficient numerical solution of partial differential equations on such discretizations. Due to the regular shape of the numerical stencil induced by the hexahedral regime, and since we use matrix-free formulations of all multigrid steps, computations and data layout can be restructured to avoid execution divergence of parallel running threads and to enable coalescing of memory accesses into single memory transactions. This enables to effectively exploit the GPU’s parallel processing units and high memory bandwidth via the CUDA parallel programming API. We demonstrate performance gains of up to a factor of 27 and 4 compared to a highly optimized CPU implementation on a single CPU core and 8 CPU cores, respectively. For hexahedral models consisting of as many as 269,000 elements our approach achieves physics-based simulation at 11 time steps per second.     

Chain Shape Matching for Simulating Complex Hairstyles

Animations of hair dynamics greatly enrich the visual attractiveness of human characters. Traditional simulation techniques handle hair as clumps or continuum for efficiency; however, the visual quality is limited because they cannot represent the fine‐scale motion of individual hair strands. Although a recent mass‐spring approach tackled the problem of simulating the dynamics of every strand of hair, it required a complicated setting of springs and suffered from high computational cost. In this paper, we base the animation of hair on such a fine‐scale on Lattice Shape Matching (LSM), which has been successfully used for simulating deformable objects. Our method regards each strand of hair as a chain of particles, and computes geometrically derived forces for the chain based on shape matching. Each chain of particles is simulated as an individual strand of hair. Our method can easily handle complex hairstyles such as curly or afro styles in a numerically stable way. While our method is not physically based, our GPU‐based simulator achieves visually plausible animations consisting of several tens of thousands of hair strands at interactive rates.     

Interactive thin elastic materials

Despite great strides in past years are being made to generate motions of elastic materials such as cloth and biological skin in virtual world, unfortunately, the computational cost of realistic high‐resolution simulations currently precludes their use in interactive applications. Thin elastic materials such as cloth and biological skin often exhibit complex nonlinear elastic behaviors. However, modeling elastic nonlinearity can be computationally expensive and numerically unstable, imposing significant challenges for their use in interactive applications. This paper presents a novel simulation framework for simulating realistic material behaviors with interactive frame rate. Central to the framework is the use of a constraint‐based multi‐resolution solver for efficient and robust modeling of the material nonlinearity. We extend a strain‐limiting method to work on deformation gradients of triangulated surface models in three‐dimensional space with a novel data structure. The simulation framework utilizes an iterative nonlinear Gauss–Seidel procedure and a multilevel hierarchy structure to achieve computational speedups. As material nonlinearity are generated by enforcing strain‐limiting constraints at a multilevel hierarchy, our simulation system can rapidly accelerate the convergence of the large constraint system with simultaneous enforcement of boundary conditions. The simplicity and efficiency of the framework makes simulations of highly realistic thin elastic materials substantially fast and is applicable of simulations for interactive applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Real‐Time Subspace Integration for Example‐Based Elastic Material

Example‐based material allows simulating complex material behaviors in an art‐directed way. This paper presents a method for fast subspace integration for example‐based elastic material, which is suitable for real‐time simulation in computer graphics. At the core of the method is the formulation of a new potential using example‐based Green strain tensors. By using this potential, the deformation can be attracted towards the example‐based deformation feature space, the example weights can be explicitly obtained and the internal force can be decomposed into the conventional one and an additional one induced by the examples. The real‐time subspace integration is then developed with subspace integration costs independent of geometric complexity, and both the reduced conventional internal force and additional one being cubic polynomials in reduced coordinates. Experiments demonstrate that our method can achieve real‐time simulation while providing comparable quality with the prior art.     

基于OpenGVS战场火焰烟雾的模拟

战场特效有助于虚拟战场环境气氛的烘托,其模拟质量直接影响着整个战场仿真的质量.对于战场上的烟雾、火焰等不规则物体,不能采用传统的几何方法建模,而只能采用粒子系统等复杂的数学模型进行模拟.但在战场环境模拟时,同一场景中常常会出现多处火焰、烟雾的情况,这时巨大的计算量势必大大影响场景仿真的实时性.文章对基于OpenGVS的特效实现方法进行了研究,提出一种基于OpenGVS开发平台,将粒子系统模型与二维纹理动画模拟相结合的实现方式,明显减少了模拟所需计算量.将此方法运用到某型高炮训练仿真器的场景模拟中,实际应用表明,保证实时性的同时使战场特效得到了高质量的模拟.     

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。     

Interaction model between elastic objects for haptic feedback considering collisions of soft tissue

The simulation of organ–organ interaction is indispensable for practical and advanced medical VR simulator such as open surgery and indirect palpation. This paper describes a method to represent real-time interaction between elastic objects for accurate force feedback in medical VR simulation. The proposed model defines boundary deformation of colliding elements based on temporary surface forces calculated by temporary deformation. The model produces accurate deformation and force feedback considering collisions of objects as well as prevents unrealistic overlap of objects. A prototype simulator of rectal palpation is constructed on general desktop PC with a haptic device, PHANToM. The system allows users to feel different stiffness of a rear elastic object located behind another elastic object. The results of experiments confirmed the method expresses organ–organ interaction in real-time and produces realistic and perceivable force feedback.     

Nonlinear inelastic uniform torsion of composite bars by BEM

In this paper the elastic–plastic uniform torsion analysis of composite cylindrical bars of arbitrary cross-section consisting of materials in contact, each of which can surround a finite number of inclusions, taking into account the effect of geometric nonlinearity is presented employing the boundary element method. The stress–strain relationships for the materials are assumed to be elastic–plastic–strain hardening. The incremental torque–rotation relationship is computed based on the finite displacement (finite rotation) theory, that is the transverse displacement components are expressed so as to be valid for large rotations and the longitudinal normal strain includes the second-order geometric nonlinear term often described as the “Wagner strain”. The proposed formulation does not stand on the assumption of a thin-walled structure and therefore the cross-section’s torsional rigidity is evaluated exactly without using the so-called Saint Venant’s torsional constant. The torsional rigidity of the cross-section is evaluated directly employing the primary warping function of the cross-section depending on both its shape and the progress of the plastic region. A boundary value problem with respect to the aforementioned function is formulated and solved employing a BEM approach. The influence of the second Piola–Kirchhoff normal stress component to the plastic/elastic moment ratio in uniform inelastic torsion is demonstrated.