Coupling of assumed stress finite element and boundary element methods with stress-traction equilibrium

In this study, the stress based finite element method is coupled with the boundary element method in two different ways. In the first one, the ordinary distribution matrix is used for coupling. In the second one, the stress traction equilibrium is used at the interface line of both regions as a new coupling process. This new coupling procedure is presented without a distribution matrix. Several case studies are solved for the validation of the developed coupling procedure. The results of case studies are compared with the distribution matrix coupling, displacement based finite element method, assumed stress finite element method, boundary element method, ANSYS and analytical results whenever possible. It is shown that the coupling of the stress traction equilibrium with assumed stress finite elements gives as accurate results as those by the distribution matrix coupling.     

A Petrov–Galerkin finite element model for one‐dimensional fully non‐linear and weakly dispersive wave propagation

A new finite element method is presented to solve one‐dimensional depth‐integrated equations for fully non‐linear and weakly dispersive waves. For spatial integration, the Petrov–Galerkin weighted residual method is used. The weak forms of the governing equations are arranged in such a way that the shape functions can be piecewise linear, while the weighting functions are piecewise cubic with C²‐continuity. For the time integration an implicit predictor–corrector iterative scheme is employed. Within the framework of linear theory, the accuracy of the scheme is discussed by considering the truncation error at a node. The leading truncation error is fourth‐order in terms of element size. Numerical stability of the scheme is also investigated. If the Courant number is less than 0.5, the scheme is unconditionally stable. By increasing the number of iterations and/or decreasing the element size, the stability characteristics are improved significantly. Both Dirichlet boundary condition (for incident waves) and Neumann boundary condition (for a reflecting wall) are implemented. Several examples are presented to demonstrate the range of applicabilities and the accuracy of the model. Copyright © 2001 John Wiley & Sons, Ltd.     

Hybrid investigation on residual stresses induced by self-drilling screw on polycarbonate plates

The residual stresses induced by using self-drilling screws on polycarbonate plates were investigated by the hybrid method which incorporates the digital photoelastic method and finite element method (FEM). Different types of screws lead to different photoelastic fringe patterns, which provide the boundary conditions needed in the numerical simulation. By changing the two main parameters (pressure and temperature), the FEM results can be matched well with the experimental results for drilling at 0° tilt angle. For drilling at other tilt angles, the photoelastic fringe patterns provide useful information for failure analysis.     

DIGITAL ANALYSIS TECHNOLOGY FOR MORPHOLOGY OF POLYMER CHAIN COILS IN FLOW FIELDS

Polymer chain coils with entanglement is a crucial scale of structures in polymer materials since their relaxation times are matching practical processing times. Based on the phenomenological model of polymer chain coils and a new finite element approach, we have designed a computer software including solver, pre- and post-processing modules, and developed a digital analysis technology for the morphology of polymer chain coils in flow fields (DAMPC). Using this technology we may simulate the morphology development of chain coils in various flow fields, such as simple shear flow, elongational flow,and any complex flow at transient or steady state. The appli cations made up to now show that the software predictions arecomparable with experimental results.     

激光辐照下充压圆筒变形的相似律问题

 以充压圆筒在强激光辐照下的变形与破坏响应为研究目标，首先利用相似分析方法，主要采用了方程分析法和量纲分析法，确定了相似准则。然后利用ANSYS有限元程序，模拟了三组几何和物理相似的大小模型。通过对计算结果的分析表明，满足相似准则的大小模型，在相应的时间和空间，相对的物理参量是一致的。     

Parallel structural optimization applied to bone remodeling on distributed memory machines

In this paper, we investigate parallel structural optimization methods on distributed memory MIMD machines. We have restricted ourselves to the case of minimizing a multivariate non-linear function subject to bounds on the independent variables, when the objective function is expensive to evaluate as compared to the linear algebra portion of the optimization. This is the case in structural applications, when a large three-dimensional finite element mesh is used to model the structure.This paper demonstrates how parallelism can be exploited during the function and gradient computation as well as the optimization iterations. For the finite element analysis, a torus wrap skyline solver is used. The reflective Newton method, which attempts to reduce the number of iterations at the expense of more linear algebra per iteration, is compared with the more conventional active set method. All code is developed for an Intel iPSC/860, but can be ported to other distributed memory machines.The methods developed are applied to problems in bone remodeling. In the area of biomechanics, optimization models can be used to predict changes in the distribution of material properties in bone due to the presence of an artificial implant. The model we have used minimizes a linear combination of the mass and strain energy in the entire domain subject to bounds on the densities in each finite element.Early results show that the reflective Newton method can outperform active set methods when few variables are active at the minimum.     

Elasto-plastic analysis of Reissner-Mindlin plates by the use of hybrid stress FEM with layered model

Based on a _mR -type variational formulation featuring a cross-depth layered model in conjunction with a mechanical sub-element for simulating the material constitution, the cross-depth plasticity development of the Reissner-Mindlin plate is investigated by following the loading process. A 4-node quadrilateral hybrid-stressc ⁰-continuous plate-bending element HPT-9 is formulated. Numerical examinations demonstrate its remarkable characteristic behavior in being free from spurious kinematic mode, capable of alleviating locking difficulties as the thin plate limit is approached and providing numerical results with remarkable accuracy and computational efficiency over Spilker's counterpart LH₄. An elasto-plastic analysis of Reissner-Mindlin plates has justified the validity and effectiveness of the present scheme in depicting the cross-depth plasticity development following the loading process.The Project is Supported by National Natural Science Foundation of China.     

Comparison of body‐fitted,embedded and immersed solutions of low Reynolds‐number 3‐D incompressible flows

The solutions obtained for low Reynolds‐number incompressible flows using the same flow solver and solution technique on body‐fitted, embedded surface and immersed body grids of similar size are compared. The cases considered are a sphere at Re = 100 and an idealized stented aneurysm. It is found that the solutions using all these techniques converge to the same grid‐independent solution. On coarser grids, the effect of higher‐order boundary conditions is noticeable. Therefore, if the manual labor required to set up a body‐fitted domain is excessive (as is often the case for patient‐specific geometries with medical devices), and/or computing resources are plentiful, the embedded surface and immersed body approaches become very attractive options. Copyright © 2007 John Wiley & Sons, Ltd.     

退火诱导机械合金化Fe42.5 A142.5 Ti5 B1o合金的结构演变与晶粒生长动力学

利用XRD和TEM方法研究Fe42.5 Al42.5 Ti5B10合金在机械合金化及等温热处理过程中的结构演变及品粒生长动力学,讨沦了机械合金化合成机理和热处理过程巾的晶粒生长机理.结果表明,球磨过程中Al,Ti,B原子向Fe晶格中扩散,形成re(Al,Ti,B)固溶体.机械合金化合成Fe(A1,Ti,B)遵循连续扩散混合机理.球磨50 h后,金属Fe,Al,Ti,B已完全合金化,球磨终产物为纳米晶Fe(Al,Ti,B).球磨50h的粉体在热处理过程中除了发牛晶体缺陷和应力释放等过程以外,Fe(Al,Ti,B)分解形成纳米晶B2一FeAI及TiB2组成相.根据晶粒生长动力学理论计算纳米晶FeAI的晶粒牛长激活能为525.6 kJ/mol.     

A mixed hybrid formulation based on oscillated finite element polynomials for solving Helmholtz problems

A mixed-hybrid-type formulation is proposed for solving Helmholtz problems. This method is based on (a) a local approximation of the solution by oscillated finite element polynomials and (b) the use of Lagrange multipliers to “weakly” enforce the continuity across element boundaries. The computational complexity of the proposed discretization method is determined mainly by the total number of Lagrange multiplier degrees of freedom introduced at the interior edges of the finite element mesh, and the sparsity pattern of the corresponding system matrix. Preliminary numerical results are reported to illustrate the potential of the proposed solution methodology for solving efficiently Helmholtz problems in the mid- and high-frequency regimes.