固体入水的边界压力处理及表面粒子位置的修正

基于传统光滑粒子流体动力学(SPH)方法的边界力法、虚粒子法或耦合力法处理固体入水时,流 体与固体交互界面的粒子密度不连续、压力不稳定、固体边界处会发生部分流体粒子穿透或分离等现象,而流 体表面因为受到力的作用,表面破碎后,液面较粗糙。针对上述问题,结合边界力和虚粒子的优点,对耦合力 法进行改进,处理运动固体边界,阻止流体粒子穿透固体边界;改进交互界面的压力计算方法,提高计算精度, 稳定交互界面压力场;对流体表面的粒子位置进行校正,提升流体表面自由流动液面边界的模拟效果。通过经 典的二维固体入水实验,对该方法进行了验证,实验结果表明,本文方法在流体粒子与固体粒子交互后,交互 界面压力稳定,界面分离清晰无穿透,表面流体粒子分布均匀,流场的运动真实自然。     

弱可压缩流体边界处理算法

针对流体与固体边界的交互模拟问题,提出一种基于弱可压缩光滑粒子流体动力学(SPH)的边界处理算法.首先,引入一种新的体积权重函数,解决固体边界非均匀采样区域流体密度的计算误差问题;然后,提出一种新的边界力计算模型,避免校正流体粒子位置信息,保证固体边界不可穿透;最后,提出一种改进的流体压力计算模型,保证流体的弱可压缩性.实验结果表明,所提算法可以有效地解决基于位置校正的边界处理方法在模拟弱可压缩流体与非均匀采样固体边界交互时存在的稳定性问题,且仅需边界粒子的位置信息,在节约内存的同时避免了位置校正所带来的额外计算开销.     

SPH 流固耦合模拟自适应采样固壁虚粒子边界处理方法

固壁虚粒子边界处理方法是流体模拟中一种主要边界处理方法,但其不能确保流 体粒子不穿透固体边界,并且计算量较大。为防止流体粒子穿透边界,在边界附近设置一个阻 尼区,阻尼区内的流体粒子被边界施加一个弹性力和一个和流体粒子运动速度方向相反的阻尼 力,使得边界附近流体粒子更加稳定。为减少计算量,提出两种边界粒子自适应采样法：一种 是依据边界周围粒子数目的不同,边界粒子自适应地采样质量不同的大小粒子;另一种是依据 边界周围粒子数目的不同,边界粒子自适应的采样不同层数的相同质量粒子。与传统的固体边 界粒子采样方法相比,该方法减少了边界粒子数目,加快了模拟速度,节省了计算机内存,基 于GPU 加速技术实现的三维流体模拟,能够进行实时交互。     

SPH体积映射流固交互的稳定性及细节提升方法

针对现有的光滑粒子流体动力学(SPH)流固交互方法中存在的稳定性以及流体细节表现不佳的问题,提出一种改进的体积映射流固交互方法.首先采用无散度SPH方法对流体进行建模,保证流体的不可压缩性;然后引入体积映射方法处理固体边界,以隐式函数的形式表示边界而无需使用粒子,解决粒子采样的固体表面不平滑的问题;再引入移动最小二乘法对固体边界上的压强进行插值,避免压强镜像带来的误差,提升体积映射方法中压强和压强梯度计算的精确性,提高系统的稳定性;最后引入粒子重采样方法进行流体表面细化,充分表现流体表面区域的不同粒子特征,增强流固交互后的流体细节,提高真实感.在斯坦福大学公开的基本三维模型上的实验结果表明,所提方法能够真实、稳定地表现不可压缩流体与固体的交互现象,处理多个静态或动态固体的复杂场景,并且能够有效地刻画流体细节.     

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。     

一种基于SPH流体模拟的固液边界改进算法

光滑粒子流体动力学(SPH)法是一种无网格的流体模拟方法,固液边界处理是SPH法模拟流体行为的重点和难点。本文提出一种单层加密粒子法进行固液边界处理。与虚拟粒子法将边界假设为静止的流体粒子不同,本文将边界假设为具有一定密度的固体粒子,依靠物理约束进行流体计算。这种方法能够有效降低模拟中穿越边界的粒子数量,使得流体边界处的模拟更加符合真实情况。本文采用仿真流体数据对提出的算法进行验证,并对其有效性进行分析讨论。     

流-固交互及可变形体破裂的真实感模拟

为了模拟流体与动态环境的相互作用,提出一种流-固交互及可变形体破裂的真实感建模与绘制的算法.该算法使用光滑粒子流体动力学(SPH)与有限单元法(FEM)分别对流体与变形固体进行建模;再根据流-固交互作用的特点,给出一种快速分离液体表面粒子与固体表面网格的交互方法,并采用虚节点的流-固耦合模型模拟了液-固相互作用力.文中算法可用于多个流-固交互破裂的现象,如水管崩裂、水冲堤坝等.     

SPH扩展方法实现液体与固体交互实时模拟

为解决模拟液体和固体交互时速度缓慢与效果不真实的问题,对传统SPH(Smoothed Particle Hydrodynamics)方法进行扩展.首先,将液体和固体均视为粒子的集合,使用SPH扩展方法模拟液体的流动,固体粒子作为液体粒子的一部分与液体交互,同时保持固体自身的形状,减少了计算量;其次,为了加快搜索液固交互时相互作用粒子的速度,解决SPH中搜索最近相邻粒子速度较慢的问题,提出链表搜索方法搜索相互作用的粒子;最后,运用Marching Cubes体绘制算法重建液体表面,实现液固交互的真实模拟.实验表明:5000粒子规模以下、光滑半径为0.01时,液固交互的绘制帧率达到14-74帧/秒;同时,液体的飞溅及漩涡表现更加真实.     

面向非牛顿流体仿真的边界处理方法

针对现有的光滑粒子流体动力学(SPH)非牛顿流体仿真方法的边界条件不合理问题,提出一种适用于非牛顿流体仿真的边界处理方法.首先使用Cross模型实现牛顿流体和非牛顿流体的统一建模;然后通过对固体边界粒子进行加权计算,为边界处的流体粒子设定边界力的法向量;最后采用Coulomb摩擦力边界条件对边界处流体粒子的速度进行迭代更新,并将其融合到预测-校正算法框架中.实验结果表明,文中方法能够根据用户的需要调节流固边界处的摩擦系数;与自由滑移边界下的仿真相比,该方法下非牛顿流体黏度随速度的降低而增大,并表现出固体形态的物理特性.     

复杂场景流固耦合的高效模拟

大规模复杂流体场景的高效交互模拟技术在灾难仿真、虚拟现实和影视特效制作等领域都有重要的应用价值.针对现有基于物理的流体算法大多只适于尺度较小的场景,难以有效地模拟复杂流体大场景中流固耦合时的固体破碎效果的问题,提出一种复杂场景的固液耦合高效模拟方法.首先提出一种基于流体隐式粒子法和散度为零的SPH法相混合的计算框架,在确保流体物理属性的同时充分利用细粒度的隐式粒子来丰富流体运动细节,提高场景模拟的真实感;然后采用一种多维度的流固耦合分合计算策略来进一步提高流固耦合效率;为实现流体冲击下的固体破碎效果,采用一种物理与几何相混合的破碎方法:以基于断裂力学中的应变能密度模型来确定固体破碎时碎片的分布,采用基于几何的质心Voronoi方法快速生成碎片,最终实现百万量级粒子参与的复杂流体场景的交互模拟,以及高速流体冲击下的固体破碎效果的高效模拟.     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

基于QTE的蒙古文显示机制研究与实现

蒙古语言是中国蒙古族使用的通用语言,由于蒙古文区别于其他文字的书写方式和其自身变形机制等特点,在很多通用的文字处理引擎中都不被支持。在嵌入式产品开发与应用领域中Linux加QTE已经成为流行方式。该文给出了一种在QTE环境上实现基于标准Unicode的蒙古文点阵显示和变形算法, 并自定义了支持蒙古文的QTE组件,扩展了QTE功能,为在Linux加QTE方式的嵌入式体系结构中处理蒙古文提供了一种解决方法。