求二维非定常流数值解的主从网格方法

0．前言二维非定常流的拉格朗日型数值方法,是计算多种介质问题的常用的数值方法．最早是建立在随流体运动的四边形网格上的有限差分方法[1,2]．这种方法的优点显著,缺点是网格容易相交重复（两个网格同时占用一份空间）,致使计算不能进行,因此出现了三角网格方法[3]和邻域可变的任意多边形网格方法[4]．三角网格方法基本上不出现网格相交,但是人为粘性和边角的朝向可能引起大的误差．任意多边形网格的邻域关系确定不好也会引起很大的误差甚至错的计算结果．因此使用最广泛的还是建立在固定邻域的四边形网格上的拉格朗日方法．为了避…     

近组分模型中主变量的选取问题研究

近组分模型有两种主变量选取方法,分别是选取自然变量作为主变量的方法和选取总属性变量作为主变量的方法。比较了这两种方法在数学模型和数值求解流程方面的差异,分析了在计算精度和计算效率方面产生的异同。二氧化碳驱概念模型的模拟结果表明,油气两相都存在时,虽然两种方法在一维驱替和二维驱替中的计算精度是一样的,但是选取自然变量作为主变量的方法不仅允许的最大时间步长更大,而且在相同时间步下运行速度更快。在相同时间步下,选取自然变量作为主变量的方法在二维驱替中提速效果有所降低。     

数值求解中网格自适应加密和合并技术的研究

在计算流体力学(CFD)领域,几乎所有的方法都离不开网格,网格是各种数值方法的基础,网格质量的好坏直接影响数值结果的精度,甚至影响到数值计算的成败,随着计算流体力学解决的问题越来越复杂,对网格质量的要求也越来越高,传统的统一网格技术已不能适应这一不断发展的需求,为此CFD工作者发展了许多方法,如迭合网格、贴体网格和非     

非结构网格上解二维Hamilton-Jacobi方程的一种有限体积方法

本文利用最小二乘插值的思想,发展了一类在非结构网格上解Hamilton-Jacobi方程的方法．此方法通过确定超定线性方程组来得到所求单元上的二次插值多项式,并利用极值原理的思想,保证其数值解的导数不出现新的极值．典型算例表明此方法计算速度快,对间断有很好的分辨能力．     

一种二维数值网格的构造方法

１．引言二维数值网格构造是一种二维区域上的自动网格生成技术．是为了适应数值求解任意形状二维区域上的偏微分方程而发展起来的．它产生以后,对于一些不规则区域上对边值敏感问题以及非定常二维流动问题等的数值计算起了重要的作用．从本世纪六十年代开始,有许多欧美和前苏联等学者在网格构造方面做了许多开拓的和内容较为丰富的工作．人们也越来越认识到网格构造无论是在差分法还是有限元的数值计算中都具有重要的地位．在求解非定常问题时,可以不管物理区域如何变化,始终保证计算在同一规则的参数区域中．特别在流体力学计算中,由…     

弹性网格变形方法及其应用

1.引言 网格生成是数值计算中的基础问题.在微分方程数值方法的实现过程中,一个合适的计算网格可以提高计算精度,大大降低计算复杂性.近年来,人们所关注的数值求解微分方程自适应方法也包含了网格自动生成的研究.目前,国内外在这方面的研究工作很多.以网格类型而言,有结     

后台阶流动的非均匀格子Boltzmann方法模拟

使用非均匀格子Boltzmann方法对后台阶流动进行了数值模拟.将流体流动区域划分为不同的子区域:对于每个子区域内部,分布函数使用均匀网格计算;对于区域边界,分布函数采用嵌套网格方法进行处理.数值计算结果与其它实验、数值结果相吻合.     

映射技术在液-液混合中的应用

本文给出了描述非周期液-液混合流的映射方法．根据非周期混合流的特点,对周期映射方法进行了改进．针对不同时刻的映射矩阵,建立了计算该矩阵非零分量的优化算法．为减小网格单元重叠所导致的单元信息传递误差,用最初网格代替变形网格,提出了重构映射矩阵的概念用以传递映射过程中的相关变量．对不同雷诺数背景流体中单液滴和双液滴混合初始阶段的流变特征进行了模拟．数值实验表明:用偏析强度表征的混合质量随时间呈指数增长;较高的背景流体雷诺数,有利于混合质量的提高;多液滴之间的相互交融对混合过程存在较大影响．     

多群粒子输运问题在多核集群系统上的混合并行计算

本文分析了非结构网格多群粒子输运Sn方程求解的并行性,拟合多核机群系统的特点,设计了MPI/OpenMP混合程序,针对空间网格点采用区域分解划分,计算结点间基于消息传递MPI编程,每个MPI计算进程在计算过程中碰到关于能群的计算,就生成多个OpenMP线程,计算结点内针对能群进行多线程并行计算。数值测试结果表明,非结构网格上的粒子输运问题的混合并行计算能较好地匹配多核机群系统的硬件结构,具有良好的可扩展性,可以扩展到1024个CPU核。     

基于非结构网格的飞行器多体分离数值模拟

针对基于非结构网格方法的飞行器多体分离数值模拟中的局部网格重构问题,提出了一种基于单元相邻关系的重构区域构造方法。首先,根据单元半径比检查网格质量并标记重构单元;其次,通过网格单元的相邻关系对重构区域进行扩展;最后,通过标记非二边流形边的周围单元保证重构区域边界定义满足二边流形准则。基于该方法的某分离物投放数值实验中,成功进行了16次网格局部重构操作,重构后总体网格单元半径比的平均值达到0.71以上。计算结果和风洞实验数据的比较分析表明,数值实验精确地计算出分离物的运动轨迹和运动姿态,验证了非结构动网格重构过程的有效性。     

地铁车站开挖过程中的变形监测及仿真分析

为研究地铁车站开挖过程对地下连续墙、管线、墙顶和周边建筑的影响,采用ANSYS有限元方法建模计算,并与实测数据进行对比,验证了模型的可靠度,其最大误差为7.45%。利用该模型计算各部位的沉降,得出:随着开挖过程的进行,第一道支撑轴力从644.8 kN变化到3610 kN,增长460%;墙顶在第10天的沉降位移为0.82 mm;管线在第10天的沉降位移为0.35 mm;考虑地下水位变化时,周边5 m处的建筑会产生0.79 mm的沉降位移。根据力学平衡方程从理论上分析了地下连续墙的变形曲线。结合模拟结果,对不同因素引起的位移变化进行分析并提出解决方案,为今后绿色安全施工提供指导方法。     

On predicting abrupt contraction flows with differential and algebraic viscoelastic models

The numerical simulation of flows through a planar contraction at low Reynolds number is considered for Newtonian and for viscoelastic fluids. The recently proposed algebraic extra-stress model (AESM) derived from the differential constitutive equation for an Oldroyd-B fluid is extended to a Phan-Thien–Tanner fluid. The approach is based on the exact polynomial representation using a three-term tensor basis. It is also shown that the algebraic formulation reproduces exactly the extra-stress tensor components for pure shear and for pure elongation flow. A parameter based on the strain rate and the rotation rate tensors is presented to identify the regions of the flow where the AESM model produces exact results. A second-order numerical scheme accurate in time and space, based on the finite volume method using a staggered grid has been applied to solve the conservation and constitutive equations for the Newtonian and viscoelastic flows. The numerical simulations for the viscoelastic fluids have been done using the classical constitutive equations in a differential form and the algebraic extra-stress model. Excellent agreement between the extra-stress values is obtained with the two different approaches, showing the viability of AESM.     

肺泡显微切片的三维重建

本文讨论了对肺泡类软组织切片图象进行三维重建的方法，重点分析了显微切片图象各类噪声的去除方法及灰度校正、几何位置校正、形态校正的方法．其中几何位置技正一直是序列显微切片重建的难点．本文提出的金字塔异或指数自动配难方法大大缩短了几何位置技正时间．从利用体无绘制技术重建的肺泡组织的三维形态来看，该配难方法具有较高的精度．实验证明该重建方法也适用于其他空腔组织、软组织的重建．     

Indoor Positioning System Using Axis Alignment and Complementary IMUs for Robot Localization

An indoor positioning method for robots is presented to improve the precision of displacement measurement using only low-cost inertial measurement units(IMUs).Firstly,a high-fidelity displacement estimation for linear motion is proposed.A new robot motion model is designed as well as an axis alignment that only uses a single axis of the accelerometer.The integral error of velocity is eliminated by a new subsection calculation method.Two complementary IMUs are combined by assigning them different weights to obtain high accuracy displacement results.Secondly,an orientation estimation based on a fusion filter for the steering motion is proposed.Experiments show that the proposed method significantly improves the accuracy of linear motion measurement and is effective for the indoor positioning of a robot.     

Evolutionary topology optimization of continuum structures with a global displacement control

The conventional compliance minimization of load-carrying structures does not directly deal with displacements that are of practical importance. In this paper, a global displacement control is realized through topology optimization with a global constraint that sets a displacement limit on the whole structure or certain sub-domains. A volume minimization problem is solved by an extended evolutionary topology optimization approach. The local displacement sensitivities are derived following a power-law penalization material model. The global control of displacement is realized through multiple local displacement constraints on dynamically located critical nodes. Algorithms are proposed to secure the stability and convergence of the optimization process. Through numerical examples and by comparing with conventional stiffness designs, it is demonstrated that the proposed approach is capable of effectively finding optimal solutions which satisfy the global displacement control. Such solutions are of particular importance for structural designs whose deformed shapes must comply with functioning requirements such as aerodynamic performances.     

通过PVDF阵列测量体积位移的实验研究

针对目前PVDF体积位移传感器的研究主要集中在经典边界条件(如简支、固定、自由等)、需要预知精确的边界条件等不足,提出通过伪逆方法结合Tikhonov正则化方法设计振动梁在任意未知边界条件下的压电式体积位移传感器的通用设计模型。以一未知边界条件的振动梁为例,用一组PVDF阵列测量其体积位移。在该梁表面均匀粘贴一组相同形状的矩形PVDF薄膜,然后通过所提出的新方法设计这组PVDF输出信号的加权系数,从而得到体积位移。实验结果表明这种传感器设计方法是可行的,并且不需要预知振动梁的边界条件或模态信息。     

A novel displacement constrained optimization approach for black and white structural topology designs under multiple load cases

The gray problem of displacement constrained topology volume minimization under multiple load cases still is an opening topic of research. A series of topologies with clear profiles generated from an optimization process are very beneficial to method engineering applications. In this paper, a novel displacement constrained optimization approach for black and white structural topology designs under multiple load cases, is proposed to obtain a series of topologies with clear profiles. Firstly, a distribution feature of constraint displacement derivatives is investigated. Secondly, an adaptive adjusting approach of design variable bounds is proposed, and an improved approximate model with varied constraint limits and a volume penalty objective function are constructed. Thirdly, an improved density-based optimization method is proposed for the displacement constrained topology volume minimization under multiple load cases. Finally, several examples are given to demonstrate that the results obtained by the proposed method provide a series of topologies with clear profiles during an optimization process. It is concluded from examples that the proposed method is effective and robust for generating an optimal topology.     

Lennard－Jones流体化学位的Monte Carlo分子模拟

提出了用于计算体系化学位的ＭｏｎｔｅＣａｒｌｏ逐级取样分子模拟方法。这一方法克服了通常试验粒子方法在高密度或复杂分子体系中所存在的取样困难。应用这一方法对Ｌｅｎｎａｒｄ－Ｊｏｎｅｓ流体在密度ρσ３＝０．６５，０．７０，０．８０，０．９０时的化学位进行模拟的结果是令人满意的，表明该方法能有效地模拟高密度流体的化学位。     

Design,modeling and test of a novel compliant orthogonal displacement amplification mechanism for the compact micro-grasping system

In the compact micro-grasping system, the combination of precisely orthogonal movement transformation, displacement amplification and simple structure is important. The typical solution of the combination issue requires bidirectional symmetric input forces/displacements. However, under a certain driving condition, numerous actuators used in micro-manipulation only supply unidirectional input froce/displacement for the driven mechanism, which makes the typical solution infeasible. In this study, a novel compliant orthogonal displacement amplification mechanism (DAM) is proposed to solve the combination issue for numerous actuators used in micro-grasping. The proposed mechanism is a triangulation amplification-based mechanism with undetermined structural parameters. The number of the undetermined parameters and the solution principle are analyzed. The design process is presented. Finite element analysis (FEA) is used to verify the design method. The FEA results show that, for the design examples, the errors evaluating the orthogonal movement transformation are smaller than 0.56 % and 0.15 % respectively, and the displacement amplification ratios are larger than 4.6. The orthogonal displacement amplification is realized. A precise model of the displacement amplification ratio is derived. The dynamic performances of the proposed orthogonal DAM are modeled and FEA verified. Furthermore, a microgripper utilizing the proposed mechanism is presented. The performances of the gripper, including the displacement amplification and the parallel movement of the jaws, are verified by FEA and experiments.

     

Image Registration for Digital Subtraction Angiography

In clinical practice, Digital Subtraction Angiography (DSA) is a powerful technique for the visualization of blood vessels in the human body. The diagnostic relevance of the images is often reduced by artifacts which arise from the misalignment of successive images in the sequence, due to patient motion. In order to improve the quality of the subtraction images, several registration techniques have been proposed. However, because of the required computation times, it has never led to algorithms that are fast enough so as to be acceptable for integration in clinical applications. In this paper, a new approach to the registration of digital angiographic images is proposed. It involves an edge-based selection of control points for which the displacement is computed by means of template matching, and from which the complete displacement vector field is constructed by means of interpolation. The final warping of the images according to the calculated displacement vector field is performed real-time by graphics hardware. Experimental results with several clinical data sets show that the proposed algorithm is both effective and very fast.