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1.
h—层状自适应边界元方法的算法   总被引:1,自引:0,他引:1  
汪新  邢延 《计算力学学报》2000,17(2):201-206222
给出了h-层状自适应边界元方法的基本算法,并介绍了应用这一算法编写求平面弹性静力学问题的计算机程序Elquahhbe。这处程序中包含一些新的内容:它的自适应细分过程通过一个新型的左指示因子加以驱动;整个细分过程的信息都压缩到两组“指针”数组中,对“指针”数组进行简单运算即可得到生成离散网格和装配系统矩阵所需的信息,因此较好地解决了数据管理中存储与导出的矛盾。数值算例证明这些方法是行之有效的。  相似文献   

2.
改进的Z~2应力恢复过程与h型自适应有限元分析   总被引:1,自引:0,他引:1  
建议了一种较为精确的边界应力求解方法,并用于改进Zienkiewicz-Zhu(Z2)应力恢复过程。改进过程增加的计算量不大,但可有效地改善后验误差估计精度。h型自适应有限元分析结果表明,改进过程更有利于最优网格寻求工作  相似文献   

3.
改进的Z^2应力恢复过程与h型自适应有限元分析   总被引:2,自引:0,他引:2  
建议了一种较为精确的边界应力求解方法,并用于改进Zienkiewicz-Zhu(Z^2)应力恢复过程。改进过程增加的计算量不大,但可有效地改善后验误估计精度。h型自适应有限元分析结果表明,改进过程更有利于最优网格寻求工作。  相似文献   

4.
基于协调三角形剖分算法、分子表数据结构和Zienkiewicz-Zhu误差估计方法,本文研制出适用于自适应多重网格有限元的网格生成器。该网格生成器可对复杂的区域进行自适应加密。当荷载作用边界随时间变化及在动力荷载作用下,网格生成器可退化与再加密网格。  相似文献   

5.
利用非连续元离散边界积分方程,有效地解决了“角点效应”问题,对影响非连续元精度和分析效率的几个问题从数值计算的角度进行了讨论,将非连续边界元用于自适应边界元分析,给出了自适应边界元误差指示确定的一种方法,通过对具体实例分析表明了给所方法的可行性,。》  相似文献   

6.
全自动自适应网格细化   总被引:1,自引:0,他引:1  
本文利用弹塑性误差估计模型,预示出金属成形数值模拟过程中网格细化时新网格尺寸,提出补角法修正锻件边界构形并利用三次B样条统一表达边界构形,实现了对边界细化并进而产生自适应细化网格。  相似文献   

7.
本文提供了一种可作为弹性接触问题有限元分析后处理过程的误差估计方法.这种方法是应用应力平滑过程,通过能量模的形式而建立的.在这种误差估计方法的基础上,实现了有限元网格的自适应局部加密.数值分析实例表明,借助于这种最优离散化过程,可使计算误差平均分配于各个单元,并使总体计算误差降低.  相似文献   

8.
Taylor展开多极边界元法有效的提高了边界元法的求解效率,使之可用于大规模问题的计算。然而,由于计算中对基本解进行了Taylor级数展开,与传统边界元方法相比计算精度有所下降。本文主要针对三维弹性问题Taylor展开多极边界元法的计算精度和误差进行研究。文中对两种方法的计算精度进行了比较;研究了核函数的Taylor展开性质;推导了三维弹性问题基本解的误差估计公式;给出了Taylor展开多极边界元法中远近场的划分原则。通过具体的算例,证明了该方法的正确性和误差估计公式的有效性,说明了影响Taylor展开多极边界元法求解精度的因素。  相似文献   

9.
结构动力分析自适应有限元方法综述   总被引:1,自引:0,他引:1  
龚国庆  刘寒冰 《力学进展》2000,30(3):332-342
结构动力分析自适应有限元方法主要研究有限元动力分析的误差估计理论,建立适用于复杂结构动力分析的有限元网格自适应过程.介绍了结构动力问题自适应有限元方法的重要发展,包括固有振动和动响应分析的误差估计及相应的自适应策略;且简要介绍了几种现有的网格生成技术及其特点.最后指出这种方法存在的问题和今后的研究方向.  相似文献   

10.
提出一种改进的声学边界元法(M-BEM)用于准确计算水下航行体发动机振动引起的近场辐射噪声。分别采用奇异分解技术和自适应边界元积分算法解决了Helmholtz积分方程在求解近场声压时出现的超奇异积分和奇异积分问题。采用一脉动球源的声辐射算例对方法进行验证,数值解与精确解误差小于1.5dB。结合有限元方法并考虑流固耦合作...  相似文献   

11.
In this paper, we present an approach of dynamic mesh adaptation for simulating complex 3‐dimensional incompressible moving‐boundary flows by immersed boundary methods. Tetrahedral meshes are adapted by a hierarchical refining/coarsening algorithm. Regular refinement is accomplished by dividing 1 tetrahedron into 8 subcells, and irregular refinement is only for eliminating the hanging points. Merging the 8 subcells obtained by regular refinement, the mesh is coarsened. With hierarchical refining/coarsening, mesh adaptivity can be achieved by adjusting the mesh only 1 time for each adaptation period. The level difference between 2 neighboring cells never exceeds 1, and the geometrical quality of mesh does not degrade as the level of adaptive mesh increases. A predictor‐corrector scheme is introduced to eliminate the phase lag between adapted mesh and unsteady solution. The error caused by each solution transferring from the old mesh to the new adapted one is small because most of the nodes on the 2 meshes are coincident. An immersed boundary method named local domain‐free discretization is employed to solve the flow equations. Several numerical experiments have been conducted for 3‐dimensional incompressible moving‐boundary flows. By using the present approach, the number of mesh nodes is reduced greatly while the accuracy of solution can be preserved.  相似文献   

12.
仲健  江涛  章青 《计算力学学报》2011,28(Z1):10-14
自然单元法(NEM)是一种新兴的无网格数值计算方法,具有前处理简单和易于准确施加本质边界条件等优点.本文基于Z-Z后验误差估计方法,给出了一种自然单元法的误差估计因子和自适应分析细化方案.采用结点处的光滑应变计算相应的恢复应力,并用于构造全域上的恢复应力场.通过结点Voronoi单胞内的能量范数相对误差指示需要进行结点...  相似文献   

13.
In this work we present a numerical method for solving the incompressible Navier–Stokes equations in an environmental fluid mechanics context. The method is designed for the study of environmental flows that are multiscale, incompressible, variable‐density, and within arbitrarily complex and possibly anisotropic domains. The method is new because in this context we couple the embedded‐boundary (or cut‐cell) method for complex geometry with block‐structured adaptive mesh refinement (AMR) while maintaining conservation and second‐order accuracy. The accurate simulation of variable‐density fluids necessitates special care in formulating projection methods. This variable‐density formulation is well known for incompressible flows in unit‐aspect ratio domains, without AMR, and without complex geometry, but here we carefully present a new method that addresses the intersection of these issues. The methodology is based on a second‐order‐accurate projection method with high‐order‐accurate Godunov finite‐differencing, including slope limiting and a stable differencing of the nonlinear convection terms. The finite‐volume AMR discretizations are based on two‐way flux matching at refinement boundaries to obtain a conservative method that is second‐order accurate in solution error. The control volumes are formed by the intersection of the irregular embedded boundary with Cartesian grid cells. Unlike typical discretization methods, these control volumes naturally fit within parallelizable, disjoint‐block data structures, and permit dynamic AMR coarsening and refinement as the simulation progresses. We present two‐ and three‐dimensional numerical examples to illustrate the accuracy of the method. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

14.
In FE based global digital image correlation (DIC) a finite element mesh is used to describe the deformation of the region of interest (ROI). However, the identification of an optimal mesh is a difficult problem and is often obtained by using “mechanical” pre-knowledge of the solution. In Finite Element Analysis (FEA) an optimal mesh can be found without any pre-knowledge of the solution by using mesh adaptivity, where an initial (non optimal) mesh is refined until the optimal solution is obtained. Refinement of the mesh can be based on error and/or convergence estimators. Despite the fundamental differences between FEA and DIC, in the present article the convergence procedure is successfully used in a recently published global FE based DIC method. In the used global DIC method elements can receive higher order shape functions, also known as p-elements. Using the aforementioned algorithm, also called p-DIC, refinement to a non-uniform higher order mesh is possible. Using the non-uniform mesh, an optimal mesh can be obtained for each section of the ROI. The presented study shows that a convergence scheme can be used to automatically control the mesh refinement in a global DIC approach. The convergence boundary, in percentage, is a more intuitive boundary than the absolute error boundary used in the original p-DIC approach. The procedure is validated using numerical examples and the robustness to experimental variables is investigated. Finally, the complete procedure is tested against a wide range of practical examples.  相似文献   

15.
自适应一致性高阶无单元伽辽金法   总被引:5,自引:4,他引:1  
近来提出的一致性高阶无单元伽辽金法通过导数修正技术大幅度减少了所需积分点数目,并能够精确地通过线性和二次分片试验,显著改善标准无单元伽辽金法的计算效率、精度和收敛性.本文在此基础之上,充分利用无单元法易于在局部区域添加节点的优势,发展了一致性高阶无单元伽辽金法的h型自适应分析方法.根据应变能密度梯度该方法自适应地确定需节点加密的区域,基于背景积分网格的局部多层细化要求生成新的计算节点,同时考虑了节点分布由密到疏渐进过渡的情形.采用相邻两次计算的应变能的相对误差作为自适应过程的停止准则,将所发展自适应无网格法应用于由几何外形、边界外载和体力等因素造成的应力集中问题的计算分析.数值结果表明,所发展方法能够自适应地对高应力梯度区域进行节点加密,自动给出合理的计算节点分布.与已有的标准无网格法的自适应分析相比,所发展方法在计算效率、精度和应力场光滑性等方面均展现出显著优势.与采用节点均匀分布的一致性高阶无单元伽辽金法相比,它大幅度地减少了计算节点数目,有效提高了一致性高阶无单元伽辽金法在分析应力集中等存在局部高梯度问题时的计算效率和求解精度.  相似文献   

16.
基于滤波方法和卡门尺度对原始剪切应力输运(shear stress transport, SST)湍流模型进行了改进,提出了一种卡门尺度修正的滤波SST 方法. 湍流多尺度效应必须在分离流场模拟中给予反映,该方法减弱了雷诺平均(Reynolds averaged Navier-Stokes, RANS)方法时间平均特性对于流场脉动量的压迫作用,在流场中引入了大涡模拟(large eddy simulation, LES)方法的亚格子模型,形成一种新型的脱体涡模拟方法(detached eddy simulation,DES)方法;同时,为了降低原始DES方法在网格加密过程中产生网格诱发的雷诺应力损耗,利用卡门尺度对滤波因子进行修正. 平板边界层算例中,卡门尺度对于RANS方法的跟随性远远强于DES方法,在边界层内的速度型和RANS方法吻合很好,而DES方法在加密过程中速度型的鲁棒性较差,说明卡门尺度在有效地保护了边界层内使用RANS求解,降低速度型偏离对数率现象的产生;HGR-01翼型算例证明BY-SST方法可以有效的避免网格诱导分离现象的产生;证明BY-SST方法在分离流动中的精度高于DES方法.  相似文献   

17.
Adaptive mesh refinement (AMR) shows attractive properties in automatically refining the flow region of interest, and with AMR, better prediction can be obtained with much less labor work and cost compared to manually remeshing or the global mesh refinement. Cartesian AMR is well established; however, AMR on hybrid unstructured mesh, which is heavily used in the high‐Reynolds number flow simulation, is less matured and existing methods may result in degraded mesh quality, which mostly happens in the boundary layer or near the sharp geometric features. User intervention or additional constraints, such as freezing all boundary layer elements or refining the whole boundary layer, are required to assist the refinement process. In this work, a novel AMR strategy is developed to handle existing difficulties. In the new method, high‐order unstructured elements are first generated based on the baseline mesh; then the refinement is conducted in the parametric space; at last, the mesh suitable for the solver is output. Generating refined elements in the parametric space with high‐order elements is the key of this method and this helps to guarantee both the accuracy and robustness. With the current method, 3‐dimensional hybrid unstructured mesh of huge size and complex geometry can be automatically refined, without user intervention nor additional constraints. With test cases including the 2‐dimensional airfoil and 3‐dimensional full aircraft, the current AMR method proves to be accurate, simple, and robust.  相似文献   

18.
In this study,we present adaptive moving boundary computation technique with parallel implementation on a distributed memory multi-processor system for large scale thermo-fluid and interfacial flow computations.The solver utilizes Eulerian-Lagrangian method to track moving(Lagrangian) interfaces explicitly on the stationary(Eulerian) Cartesian grid where the flow fields are computed.We address the domain decomposition strategies of Eulerian-Lagrangian method by illustrating its intricate complexity of the computation involved on two different spaces interactively and consequently,and then propose a trade-off approach aiming for parallel scalability.Spatial domain decomposition is adopted for both Eulerian and Lagrangian domain due to easy load balancing and data locality for minimum communication between processors.In addition,parallel cell-based unstructured adaptive mesh refinement(AMR) technique is implemented for the flexible local refinement and even-distributed computational workload among processors.Selected cases are presented to highlight the computational capabilities,including Faraday type interfacial waves with capillary and gravitational forcing,flows around varied geometric configurations and induced by boundary conditions and/or body forces,and thermo-fluid dynamics with phase change.With the aid of the present techniques,large scale challenging moving boundary problems can be effectively addressed.  相似文献   

19.
Highly nonlinear, turbulent, dynamic, fluid-structure interaction problems characterized by large structural displacements and deformations, as well as self-contact and topological changes, are encountered in many applications. For such problems, the Eulerian computational framework, which is often equipped with an embedded (or immersed) boundary method for computational fluid dynamics, is often the most appropriate framework. In many circumstances, it requires the computation of the time-dependent distance from each active mesh vertex of the embedding mesh to the nearest embedded discrete surface. Such circumstances include, for example, modeling turbulence using the Spalart-Allmaras or detached eddy simulation turbulence models and performing adaptive mesh refinement in order to track the boundary layer. Evaluating at each time step the distance to the wall is computationally prohibitive, particularly in the context of explicit-explicit fluid-structure time-integration schemes. Hence, this paper presents two complementary approaches for reducing this computational cost. The first one recognizes that many quantities depending on the wall distance are relatively insensitive to its inaccurate evaluation in the far field. Therefore, it simplifies a state-of-the-art algorithm for computing the wall distance accordingly. The second approach relies on an effective wall distance error estimator to update the evaluation of the wall distance function only when otherwise, a quantity of interest that depends on it would become tainted by an unacceptable level of error. The potential of combining both approaches for dramatically accelerating the computation of the wall distance is demonstrated with the Eulerian simulation of the inflation of a disk-gap-band parachute system in a supersonic airstream.  相似文献   

20.
黏弹性人工边界等效荷载计算的改进方法   总被引:3,自引:0,他引:3  
黏弹性人工边界在场地地震反应和结构-地基动力相互作用等问题的计算中已得到了广泛的应用.地震波在黏弹性人工边界中的输入是通过将地震波转化为作用于人工边界处的等效载荷来实现的.计算等效节点载荷的常规方法默认边界节点对应区域内的应力为均布力,但实际上该节点对应区域内的应力分布通常是不均匀的.本文在有限元方法结合黏弹性局部人工边界的显式时域波动方法的基础上,建立了无限域散射问题地震波等效载荷计算的一种改进方法.该方法采用细化网格与应力积分相结合的方法计算人工边界等效节点力,有效地降低了人工边界上等效节点力的计算误差.以不同角度入射地震波的二维算例为例,算例给出的波场位移云图和节点位移时程曲线验证了本文方法的有效性,其计算精度与网格尺寸和地震波入射角度密切相关,且网格越小、入射角度越小,计算精度越高.对于相同的网格尺寸,本文采用方法的计算精度明显高于常规方法,尤其是对于斜入射问题优势更为明显.  相似文献   

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