二维正交各向异性结构弹塑性问题的边界元分析

给出了二维正交各向异性结构弹塑性问题的边界元分析方法, 包括相应边界积分方程、内点应力公式、边界元求解格式以及弹塑性应力计算方法。在弹塑性分析中, 引入了Hill-Tsai 屈服准则, 采用初应力法和切向预测径向返回法确定实际应力状态。通过具体算例分析了二维正交各向异性结构的弹塑性应力和塑性区分布情况, 部分数值结果与已有结果进行了比较, 两者基本吻合。结果表明, 本文中给出的边界元法可以有效地用于求解二维正交各向异性结构的弹塑性问题。      

正交各向异性孔板的材料参数识别

结合优化技术和边界元分析,针对正交各向异性孔板进行了材料参数的识别。材料参数识别的问题转化为极小化目标函数的问题,其中目标函数定义为测量位移与边界元计算相应的位移之差的平方和。采用Levenberg-Marquardt方法解极小化目标函数的问题,其中灵敏度的计算是基于离散的边界元代数矩阵方程对识别材料参数的求导。数值算例中,首先把边界元计算正交各向异性圆孔方板位移的结果与解析解进行比较,两者符合良好;然后采用本文提出的方法识别正交各向异性圆孔方板的材料参数。数值算例表明本文提出的方法是有效的。     

正交各向异性薄板振动响应的波函数法

提出了适用于正交各向异性薄板弯曲振动响应预测的波函数法,基于Kirchhoff正交各向异性薄板振动控制方程,推导了体现各主轴物理量且精确满足其控制方程的复合结构波函数。通过傅里叶变换,在波数域对响应函数进行角积分,得到处于外部激励下的无限正交各向异性板振动响应。结合正交各向异性薄板的物理边界,运用加权余量法求得各正交各向异性结构波函数的系数,得到薄板的弯曲振动响应。建立矩形正交各向异性板的波函数响应模型,通过双级数解法验证了方法的正确性,与有限元法的对比结果说明,波函数法对正交各向异性薄板在中频范围的振动响应预测有着更高的计算效率。     

边界元法在环境声学中的应用

边界元法是边界积分方程的数值解法 ,是随着计算机技术的发展而出现的。建立声学边界积分方程分两种方法 :直接法与间接法。本文介绍了边界元法在环境声学中的应用 ,如声屏障和不同情况下道路周围的声场分布、复杂气象条件对声传播的影响的问题等。由于边界元法是半解析半数值解法。在解边界积分方程时会遇到解的存在与唯一性问题。     

正交各向异性复合柱圆弧型循环对称界面裂纹

讨论反平面载荷作用下空心复合柱的循环对称圆弧型裂纹问题。复合柱由两极正交各向异性功能梯度弹性层粘接而成。采用分离变量将这个混合边值问题转化为Cauchy核奇异积分方程,并用Lobatto-Chebyshev求积法对积分方程进行数值求解,得到了应力强度因子的数值解。分析了梯度非均匀参数,几何与材料参数变动等对应力强度因子的影响。     

用边界元法求双参数地基上正交异性板的动力响应

本文利用功的互等定理导出了双参数地基上正交异性板动力弯曲的边界积分方程，通过拉普拉斯变换，将问题转换到拉 普拉斯空间中求解，然后利用拉普拉斯数值逆变换得到在自然空间中的解。     

正交各向异性板动力响应的边界元方法

本文讨论了正交各向异性板动力响应的边界元方法,发展了一种新的求近似基本解的方法,由该方法得到的基本解,给出了弹性薄板诸问题近似基本解的统一形式。应用这个基本解,得到了正交各向异性板和弹性地基板稳态强迫振动的边界元方程。文中的算例表明,本文的方法具有相当高的精度。     

薄壁杆件翘曲剪应力的边界元精确积分解法

用非连续边界元对薄壁杆件的约束扭转进行了分析,推导出了求解边界点二次翘曲函数值的边界积分方程,给出了边界积分方程数值求解时积分计算的精确表达式。数值算例表明:利用边界积分方程方法分析薄壁杆件的约束扭转问题时效率和精度高,同时采用精确积分可以有效的处理"边界层效应"问题。     

美式期权价格的积分表示及其数值方法

本文利用Laplace变换方法得到带连续红利的美式看涨期权价格的积分表示,以及最优执行边界满足的一个非线性的第二类Volterra积分方程.然后用数值积分公式给出了积分方程的数值解,从而得到了带连续红利的美式看涨期权价格及其执行边界的数值解.     

叠层复合材料厚板壳分析的边界元法

本文首先利用平面波分解和Ｈｏｒｍａｎｄｅｒ算子法提出了计入剪切变形的叠层复合材料厚板壳的基本解，然后利用加权残数法建立了边界积分方程和边界元法，利用文中提出的方法，分析了一些算例并与解析解作了比较。     

Single edge-cracked orthotropic strip under three-point load

The problem of an orthotropic strip having a crack of unit length normal to one edge and subjected to a bending moment resulting from three-point loading is solved using integral transform method. The mixed boundary conditions lead to dual integral equations which are ultimately reduced to a Fredholm integral equation of second kind. The integral equation thus obtained is solved by the method developed by Fox and Goodwin. Numerical solutions for a fibre-reinforced composite material have been carried out to determine the stress intensity factor of an orthotropic medium. The same has been compared with the isotropic case.     

Analysis of functionally graded plates by meshless method: A purely analytical formulation

Functionally graded plates under static and dynamic loads are investigated by the local integral equation method (LIEM) in this paper. Plate bending problem is described by the Reissner moderate thick plate theory. The governing equations for the functionally graded material with respect to the neutral plane are presented in the Laplace transform domain and therefore the in-plane and bending problems are uncoupled. Both isotropic and orthotropic material properties are considered. The local integral equation method is developed with the locally supported radial basis function (RBF) interpolation. As the closed forms of the local boundary integrals are obtained, there are no domain or boundary integrals to be calculated numerically in this approach. The solutions of the nodal values for the entire plate are obtained by solving a set of linear algebraic equation system with certain boundary conditions. Details of numerical procedures are presented and the accuracy and convergence characteristics of the method are examined. Several examples are presented for the functionally graded plates under static and dynamic loads and the accuracy for proposed method has been observed compared with 3D analytical solutions.     

A general integral equation formulatin for homogeneous orthotropic potential problems

In this paper an integral equation formulation is proposed for the analysis of orthotropic potential problems. The two primary integral equations of the method are derived from the original governing differential equation firstly by rewriting it in a slightly different form and then applying the direct boundary element method formulation. The solution procedure is based on the use of the fundamental solutions for the isotropic potential case and special attention is given to the differentiation of a singular integral which yields an additional term as well as to the evaluation of the resulting Cauchy principal value integral. A simple discretization for the boundary and its interior domain is adopted in order to express the primary integral equations of the method in matrix form. Three examples are presented, the results of which illustrate the satisfactory accuracy of the method. The main feature of the proposed formulation is its generality, which makes possible its direct extension to solve such as heat conduction or subsurface flow in anisotropic media and, foremost, to orthotropic and anisotropic elasticity or elastoplasticity.     

Elasto-plastic Analysis of Two-dimensional Orthotropic Bodies with the Boundary Element Method

The Boundary Element Method (BEM) is introduced to analyze the elasto-plastic problems of 2-D orthotropic bodies. With the help of known boundary integral equations and fundamental solutions, a numerical scheme for elasto-plastic analysis of 2-D orthotropic problems with the BEM is developed. The Hill orthotropic yield criterion is adopted in the plastic analysis. The initial stress method and tangent predictor-radial return algorithm are used to determine the stress state in solving the nonlinear equation with the incremental iteration method. Finally, numerical examples show that the BEM is effective and reliable in analyzing elasto-plastic problems of orthotropic bodies.     

Analysis of orthotropic thick plates by meshless local Petrov–Galerkin (MLPG) method

A meshless local Petrov–Galerkin (MLPG) method is applied to solve static and dynamic problems of orthotropic plates described by the Reissner–Mindlin theory. Analysis of a thick orthotropic plate resting on the Winkler elastic foundation is given too. A weak formulation for the set of governing equations in the Reissner–Mindlin theory with a unit test function is transformed into local integral equations on local subdomains in the mean surface of the plate. Nodal points are randomly spread on the surface of the plate and each node is surrounded by a circular subdomain to which local integral equations are applied. The meshless approximation based on the Moving Least–Squares (MLS) method is employed in the numerical implementation. The present computational method is applicable also to plates with varying thickness. Numerical results for simply supported and clamped plates are presented. Copyright © 2006 John Wiley & Sons, Ltd.     

Initial strain effects in multilayer composite laminates

A boundary integral formulation for the analysis of stress fields induced in composite laminates by initial strains, such as may be due to temperature changes and moisture absorption is presented. The study is formulated on the basis of the theory of generalized orthotropic thermo-elasticity and the governing integral equations are directly deduced through the generalized reciprocity theorem. A suitable expression of the problem fundamental solutions is given for use in computations. The resulting linear system of algebraic equations is obtained by the boundary element method and stress interlaminar distributions in the boundary-layer are calculated by using a boundary only discretization. The approach is general and it does not require a priori assumptions. Numerical results are presented to show the potential of the proposed approach.     

On the boundary integral equations approach to a semi-infinite strip investigation

Summary An orthotropic semi-infinite strip under arbitrary boundary conditions is considered. By means of Fourier transforms, boundary integral relations of special type with moving and motionless singularities of the Cauchy type are obtained. These relations lead to a system of singular integral equations corresponding to the various mixed boundary value problem. The power of singularities at the corner points, stresses and stress intensity factors are calculated for different loads and various material properties.     

固支三维弹性矩形厚板的精确解

采用有限积分变换和状态空间理论相结合的方法推导出了固支三维弹性矩形厚板的精确解.在分析过程中摒弃以往薄板和中厚板理论中有关应力和位移函数的各种人为假定,完全从三维弹性力学基本方程出发,经过变量代换将关于应力和位移分量的六阶偏微分方程组化为2 个彼此独立的四阶、二阶矩阵微分方程,再利用有限积分变换的方法得到空间状态方程,并由Cayley-Hamilton定理求得应力和位移分量沿板厚度z 方向的传递矩阵,最后利用边界条件定解出待定常数,经过有限积分逆变换解得了固支三维厚板的精确解.通过计算实例验证了该文方法的正确性.     

A new method for the determination of the flexural rigidity of an orthotropic plate

In this paper a new method for the determination of flexural rigidities in orthotropic plate bending problems is presented. Boundary integral equations are established for the curvatures and the deflections inside the domain. By a simple discretization of the boundary and the inside plate, the elimination of curvatures is possible. If the fundamental solution of isotropic plates is chosen, then a linear system of n equations with three unknowns is obtained. These equations are provided by the knowledge of the deflections inside the plates, and the unknowns are the flexural rigidities. By using the least square method, the computation of these rigidities becomes easy.     

Shape design sensitivity analysis for non-linear anisotropic heat conducting solids and shape optimization by the BEM

Shape design sensitivity analysis (SDSA) expressions have been derived for non-linear anisotropic heat conducting solid bodies by following the material derivative concept and adjoint variable method of optimal shape design given in the literature. The variation of a general integral functional has been described in terms of primary and adjoint quantities evaluated at the varying boundaries. As an example problem in shape optimization, optimal outer boundary profiles of an orthotropic solid body are obtained by the boundary element method (BEM), after reformulating the SDSA equations in a form which is most suitable for the BEM.