Semicoarsening smoothers for the simulation of a flat plate at yaw

This paper presents a full multigrid solver for the simulation of flow over a yawed flat plate. The two problems associated with this simulation; boundary layers and entering flows with non-aligned characteristics, have been successfully overcome through the combination of a plane-implicit solver and semicoarsening. In fact, this multigrid algorithm exhibits a textbook multigrid convergence rate, i.e., the solution of the discrete system of equations is obtained in a fixed amount of computational work, independently of the grid size, grid stretching factor and non-alignment parameter. Also, a parallel variant of the smoother based on a four-color ordering of planes is investigated.     

非结构网格的并行多重网格解算器

多重网格方法作为非结构网格的高效解算器,其串行与并行实现在时空上都具有优良特性.以控制方程离散过程为切入点,说明非结构网格在并行数值模拟的流程,指出多重网格方法主要用于求解时间推进格式产生的大规模代数系统方程,简述了算法实现的基本结构,分析了其高效性原理;其次,综述性地概括了几何多重网格与代数多种网格研究动态,并对其并行化的热点问题进行重点论述.同时,针对非结构网格的实际应用,总结了多重网格解算器采用的光滑算子;随后列举了非结构网格应用的部分开源项目软件,并简要说明了其应用功能;最后,指出并行多重网格解算器在非结构网格应用中的若干关键问题和未来的研究方向.     

基于内流动力学的海洋输油柔性立管鲁棒边界控制

海洋输油柔性立管的振动是引起立管疲劳破坏的主要原因,对其研究边界控制是消除振动疲劳、减少断裂的有效方法.本文引入内流动力学,完善了立管原始无穷维分布参数模型,更好地表达了柔性立管的动力学响应.为抑制柔性立管在内外流激励下的振动奠下基础,本文用Lyapunov直接法对柔性立管系统的稳定性和状态一致有界性进行了证明,设计了边界控制器调节柔性立管的振动,其中控制器使用了符号函数来消除不确定性环境扰动对振动控制效果的影响,提高了系统的鲁棒性.仿真实验表明本文所设计的控制算法有效地减少了柔性立管的振动偏移量.     

用CFX软件仿真料仓通风系统

在某塑料厂高压聚乙烯料仓安全隐患研究及治理项目中,利用CFX仿真模拟软件对料仓通风系统进行仿真分析,找出了原料仓通风系统存在的缺陷,提出几种改造设计方案,并对设计方案进行了优化筛选,通过现场实施效果良好。     

稳健模糊C-均值聚类算法在图像分割中的应用研究

模糊C-均值聚类是模式识别中的重要算法之一,很早就被应用到图像分割中。由于原始的模糊C-均值聚类算法没有考虑图像的空间信息,算法对图像中的噪音点十分敏感。针对这个问题,很多稳健模糊C-均值聚类算法被提出。通常的做法是在原来模糊C-均值聚类的目标函数中加入空间信息惩罚项。本文讨论这类方法,具体分析不同算法的空间信息加入方式,并指出其优缺点。     

基本矩阵的鲁棒贪心估计算法

分析了基于随机抽样检验思想的现有鲁棒算法在基本矩阵的求解问题中存在的不足,提出一种获得基本矩阵最优解的算法.利用各种鲁棒技术获得内点集,以点到极线的距离作为最优量度标准,采用贪心策略在内点集中寻找最优子集,并利用最优子集来计算基本矩阵.合成数据与真实图像的实验结果表明,该算法在基本矩阵的求解精度、抗噪声能力、对极点的稳定性等方面优于现有的鲁棒方法.     

Shared-Memory Parallel Vector Implementation of the Immersed Boundary Method for the Computation of Blood Flow in the Beating Mammalian Heart

This paper describes the parallel implementation of the immersed boundary method on a shared-memory machine such as the Cray C-90 computer. In this implementation, outer loops are parallelized and inner loops are vectorized. The sustained computation rates achieved are 0.258 Gflops with a single processor, 1.89 Gflops with 8 processors, and 2.50 Gflops with 16 processors. An application to the computer simulation of blood flow in the heart is presented.     

On the robustness of a multigrid method for anisotropic reaction-diffusion problems

In this paper, we consider a reaction-diffusion boundary value problem in a three-dimensional thin domain. The very different length scales in the geometry result in an anisotropy effect. Our study is motivated by a parabolic heat conduction problem in a thin foil leading to such anisotropic reaction-diffusion problems in each time step of an implicit time integration method [7]. The reaction-diffusion problem contains two important parameters, namely ε >0 which parameterizes the thickness of the domain and μ >0 denoting the measure for the size of the reaction term relative to that of the diffusion term. In this paper we analyze the convergence of a multigrid method with a robust (line) smoother. Both, for the W- and the V-cycle method we derive contraction number bounds smaller than one uniform with respect to the mesh size and the parameters ε and μ.      

动态过程辨识的一种BP鲁棒算法

针对ＢＰ算法在进行系统辨识时存在着速度慢、非平滑内插、受噪声影响很大、逼近精度不高，特别是对强干扰不具有鲁棒性等问题，提出一种ＢＰ网络的鲁棒算法，该算法直接利用样本点对样本点的分布特征进行估计，并采用带有损失因子的与误差分布有关的二次型能量函数，并用于动态系统辨识。仿真结果表明了算法不仅对白噪声具有鲁棒性，而且对强干扰也具有鲁棒性。     

利用字符特征快速实现汽车牌照定位算法

本文针对快速识别汽车牌照提出了一个实用的算法．主要在预处理开始就充分考虑如何突出车牌的字符特征,并在实际定位过程中充分利用这些特征．从而达到快速以识别并定位汽车牌照的目的．     

基于车牌识别的二值化算法研究

二值化算法在车牌识别系统中的车牌定位方面有着很重要的作用,但是光照条件的影响,使得二值化算法中的阈值T确定较为困难。该文提出了一种灰度值拉升的改进算法,可以降低二值化算法过程中的阈值的确定难度,并通过实例证明了这种算法的可行性。     

Modeling and Simulation of Vehicles Carrying Liquid Cargo

A method for modeling and simulation of the dynamics ofvehicles subject to liquid slosh loads is presented. The vehiclecomponents are modeled as a multibody system, the sloshing liquiddynamics is determined from solving the instationary, incompressibleNavier–Stokes equations under consideration of free surfaces. Toanalyze the overall system dynamics, the concept of modular simulationis applied decomposing the dynamic system into subsystems. The rigidbody and fluid subsystems are modeled by separate software codes whichare coupled by the transfer of in- and output variables duringsimulation runtime.To account for the vehicle motions, thefluid equations of motion are transformed into a moving frame ofreference, inputs and outputs of the fluid subsystem are derived. Forsolving the incompressible Navier–Stokes equations, efficient methodshave to be applied. The system of equations resulting from a FiniteVolume discretization is solved by a multigrid method, the location offree surfaces is determined by a Volume-of-Fluid approach. To validatethe methods for modeling fluid dynamics, benchmark calculations of theflow around a cylinder and the collapse of a water column are presented.The proposed method for modeling the interaction of sloshingliquids and vehicle motions is used to determine the brakingcharacteristics of partially liquid-filled tank vehicles. It is shownthat a loss of directional control due to wheel lock-up is more likelyfor tank vehicles with sloshing liquid cargo than for vehicles loadedwith equivalent rigid cargo because of the dynamic liquid load shift.     

递推鲁棒频域辨识算法误差界计算的改进*

文［１］研究了带未建模动态系统的频域辨识问题，辨识的结果为传递函数在单位圆上的有限个点估计及其误差界。本文指出文［１］定理的错误，并对其进行了更正，数字仿真表明，更正的误差界比文［１］中的误差界更精确。     

Vorton dynamics: a case study of developing a fluid dynamics model for a vector processor

The raw performance of vector processors such as the CDC CYBER-205 has been well documented. The ability to apply this raw power to ever more complex algebraic algorithms has been reported in [9]. The final step in making computers of this class truly the revolutionary tools they are claimed to be is to develop whole applications that perform at a significant fraction of the raw power. This involves two distinct subclasses of problems. On the one hand, there are those pre-existing applications that must be mapped onto vector processors in such a way that not only is performance maintained, but also a (sometimes vague) set of computational boundary conditions of the user community is satisfied. On the other hand, there are those models which are developed ab initio with machines such as the CYBER-205 in mind. The development of solutions to problems in the former class involves psychology and politics as well as mathematics and computer science. We limit ourselves here to reporting on an example of the latter class, viz. a model to study a particular fluid-dynamic phenomenon, that was specifically designed with the CYBER-205 in mind.     

基于非结构滑移网格技术的旋翼型无人机空气动力学并行数值模拟方法

在现代飞行器设计中,数值模拟方法以低成本、高效率和高灵活性等优点成为研究飞行器空气动力学的重要方法.在旋翼型无人机流场模拟中,由于旋翼与机身存在相互作用,为获得精确模拟结果需要对整个无人机的流场进行模拟,因此,有效地模拟旋翼与机身的相对运动是实现成功模拟的关键步骤,这使得此类模拟问题极具挑战性.文章设计了一套求解旋翼型无人机空气动力学数值模拟问题的基于非结构滑移网格技术的高可扩展并行计算方法.该方法对控制方程的离散,在空间方向采用非结构移动网格有限元方法,时间推进采用全隐式二阶向后差分格式,最后采用一种并行Newton-Krylov-Schwarz方法求解离散后的非线性方程组.作为应用,文章对一个真实旋翼型无人机模型在悬停状态下的外流场进行了数值模拟,获得了一些非常详细的流场信息.数值结果显示,算法在天河2号上使用4 096个处理器核时仍具有接近线性的并行加速比,这为下一步开展旋翼型无人机的高保真度快速模拟奠定了良好的基础.     

CFD并行计算中的多区结构网格二次剖分方法与实现

在多区结构网格计算流体动力学(computational fluid dynamics,CFD)并行模拟中,为了与并行计算资源相适应,经常需要对原始流场网格进行二次剖分与区块分组.在对区块分组和网格二次剖分进行了总结综述的基础上,重点提出针对多区结构网格二次剖分的两种策略:几何剖分和嵌套二分.基于这两种策略完成了剖分软件工具TH-MeshSplit,可实现初级方式、专业方式和专家方式3种运行方式,为用户在自动化与灵活性方面提供了多样化选择.数值实验结果表明,两种剖分策略及其实现软件可在较短时间内完成复杂的剖分,剖分后的网格在负载平衡性、计算通信比等方面具有更优的性能,从而为后续CFD流场的高效并行加速求解奠定了基础.     

Robust stabilizers for an implicit dynamical delay system of the neutral type

A feedback stabilization problem is investigated for a class of imperfectly known implicit systems with discrete and distributed delays. The imperfections acting on the systems, which may be time‐, state‐, delayed state‐, and/or input‐dependent, are modelled as additive nonlinear perturbations influencing a known set of nonlinear functional differential equations of the neutral type. Sufficient conditions, which include a delay‐dependent matrix inequality and a delay‐dependent stability criterion involving some bounding parameters for the uncertainty in the system, are presented and a class of robust feedback stabilizers, including both memoryless and those with memory, are designed to guarantee a prescribed stability property for the class of implicit systems. Copyright © 2005 John Wiley & Sons, Ltd.     

Robust correlation coefficients as the initial data for the solution of problems of confluent analysis

A technology for the solution of problems of confluent analysis of noisy technological processes is developed based on the technologies used in calculation of the variance of interference, the degree of robustness of estimators of the auto-and cross-correlation functions, robust correlation matrices, and balance algorithms for the relative errors of their elements.     

一类不确定非线性系统的变结构鲁棒控制及应用

针对一类具有不确定性的非线性系统，在假定系统模型不确定性界已知的情况下，提出一个变结构鲁棒控制算法。以船舶减摇鳍非线性控制系统为例，进行变结构鲁棒自适应控制器的设计，经仿真研究表明，它可以使控制系统具有较强的鲁棒性。     

基于栅格划分构建平面点集凸壳的算法研究

提出了一个构建平面点集凸壳的新算法。该算法用栅格阵列将待处理点集划分成若干个子集,这样凸壳可以由部分位于点集边缘的子集确定;然后按逆时针顺序逐步处理这些子集,得到一个包含待处理点集的简单多边形,删除凹顶点后就得到待处理点集的凸壳。由于只对点集边缘的点进行局部处理,从而提高了构建凸壳的效率。在最坏情况下该算法的时间复杂度为O(NlogN)。