Computer-aided spillway design using the boundary element method and non-linear programming

The general context of this paper is to support the design of spillways by a direct mathematical approach instead of trial-and-error methods. First, a two-dimensional model is formulated to determine the free surface and the discharge for a stationary, incompressible, homogeneous, non-viscous and irrotational flow over a fixed spillway. The flow satisfies the Laplace equation and the Bernoulli equation (potential flow). An important feature of the model is that it can be extended to design the spillway structure when the spillway is not fixed but the pressure on the spillway is described by a cavitation criterion. Next, the continuous model is discretized by the boundary element method (BEM). We use a non-linear programming algorithm to calculate the pressures and the shape of the spillway. A computer-aided design package is developed on a PC using the equations describing the free surface, the BEM and standard optimization techniques. The input and output of the model are realized using graphical routines. Finally, we discuss the convergence and the computation time of the algorithms.     

Die design by a boundary element method

A simple technique to design extrusion dies for three dimensional profiles based on Boundary Element Methods is reported. The technique is applied to design a few dies for triangular and square Newtonian extrudates. The results obtained compare well with the available data on common design practice.     

A boundary element formulation using the simple method

A new boundary element method is described for calculation of the steady incompressible laminar flows. The method is based on the well-known SIMPLE algorithm. The new boundary element method allows one to find the fields of the pressure and velocity corrections without inner iterations, thus reducing the computational time drastically. This makes it different from the method developed by Patankar and Spalding.³² However, the new method demands a much larger computer strorage. The boundary integral equations are discretized with the help of constant boundary elements and constant cells. The values of the integrals along the boundary elements and the cells for the two-dimensional domain are found analytically. To preserve the stability in the iteration process, under-relaxation for the convection terms is used. This paper gives the results of calculations of the flows between two plane parallel plates at Re = 20 and Re = 200, the flows in a square cavity with a moving upper lid at Re = 1 and Re = 100 and the flow in a plane channel with sudden symmetric expansion at Re =46·6.     

Lifting aerofoil calculation using the boundary element method

The bbundary integral formulation and boundary element method are extended to include lifting flow problems. This involves inclusion of a branch cut in the flow field and imposition of a Kutta condition to determine the circulation, Γ Additional boundary integral contributions arise from the cut surface. Techniques for calculating Γ are developed and we treat, in particular, a superposition procedure which permits very efficient computation. Numerical results are presented for an NACA0012 aerofoil at several angles of attack.     

Loading-carrying welds joints analysis using boundary element method

The behavior of loading-carrying welds joints has been studied extensively using boundary element method. The symmetric boundary element method for multiple cracks problem is derived using Betti’s reciprocal theorem. The analysis can be performed effectively in single domain. High order element is proposed to solve the double integrals. The stress intensity factors are calculated for weld root and weld toe and the critical value for class F2 and W are obtained. Formulation for the critical value is obtained for the engineering design. The results are compared with those obtained by dual boundary element method and derived from the code of practice. Finally, the theoretical fatigue life of such joints is estimated.     

SOLVING THE FREE BOUNDARY PROBLEM IN CONTINUOUS CASTING BY USING BOUNDARY ELEMENT METHOD

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A structural shape optimization system using the two-dimensional boundary contour method

Summary The research recently conducted has demonstrated that the Boundary Contour Method (BCM) is very competitive with the Boundary Element Method (BEM) in linear elasticity Design Sensitivity Analysis (DSA). Design Sensitivity Coefficients (DSCs), required by numerical optimization methods, can be efficiently and accurately obtained by two different approaches using the two-dimensional (2-D) BCM as presented in Refs. [1] and [2]. These approaches originate from the Boundary Integral Equation (BIE). As discussed in [2], the DSCs given by both BIE-based DSA approaches are identical, and thus the users can choose either of them in their applications. In order to show the advantages of this class of DSA in structural shape optimization, an efficient system is developed in which the BCM as well as a BIE-based DSA approach are coupled with a mathematical programming algorithm to solve optimal shape design problems. Numerical examples are presented. Received 20 July 1998; accepted for publication 7 December 1998     

Numerical simulation of the ground effect using the boundary element method

As is well known, the lift of a wing passing over the ground becomes larger than that of a wing in a finite air field because of the ground effect. Owing to its special aerodynamic characteristics and applications, the problem of the ground effect has become increasingly common. In this paper some investigations were conducted to calculate the unsteady aerodynamic forces for long and short ground plates by means of boundary element techniques. In order to calculate the pressure variation on a long ground plate, the steady boundary element method was used. However, when using a short ground plate, the boundary element method was modified to treat the unsteady aerodynamic phenomena. Experimental studies were also made for both ground plates to confirm the validity of the numerical results. At low angles of attack the qualitative behaviour of the unsteady aerodynamic pressure on both ground plates was well predicted by the boundary element methods and qualitative agreement is found between the calculated and measured results. © 1997 John Wiley & Sons, Ltd.     

Numerical solution of axisymmetric cavity flows using the boundary element method

This paper presents a formulation of the boundary element method (BEM) for solution of axisymmetric cavity flow problems. The governing equation is written in terms of Stokes' stream function, requiring a new fundamental solution to be found. The iterative procedure for adjusting the free-surface position is similar to that used for planar cavity flows. Numerical results are compared with finite difference and finite element solutions, showing the robustness of the BEM model.     

Boundary element method applied to topology optimization using the level set method and an alternative velocity regularization

Meccanica - The topology optimization (TO) is a valuable tool in the early stages of structural engineering design. It enables the determination of the structural layout accounting for the required...     

pFFT快速边界元方法模拟三维声散射

研究了用pFFT快速边界元方法模拟声散射问题的关键技术。采用Burton—Miller方程消除了声学边界元方法中外问题解的不唯一现象。为此,文中研究了采用常量元时该方程中超奇异积分的计算方法。最后,通过对平面声波的刚性圆球声散射的数值模拟,验证了建立的声学pFFT快速边界元方法。     

NUMERICAL SIMULATION OF 2D FIBER-REINFORCED COMPOSITES USING BOUNDARY ELEMENT METHOD

Introduction Withthedevelopmentofmodernindustry,compositesareincreasinglybeingappliedto agreatnumberofimportantstructures.Todeterminethemacroscopicaleffective characteristicsofcompositesisanessentialprobleminmanyengineeringapplications.The macroscopicalef…     

Free vibration analyses by boundary element method using component mode synthesis

The boundary element method for dynamic analysis of two dimensional structures was developed by Nardini and Brebbia in 1983. Free vibration analysis of structures by BEM results in a generalized eigenproblem with coefficient matrices nonsymmetric and full. So, it costs a lot of CPU time to solve the eigenproblem. In order to reduce the cost the improved free interface coupling method has been adopted. By aid of lower eigenvectors and residual modes the degrees of freedom of substructure equaion of dynamic equilibrium can be reduced. By assembling the reduced substructure equations, the system of equations for the whole structure will be obtained. By using the traction and displacement compatibility conditions on the interface, the second transformation matrix has been developed for further reduction of system equations. The technique has been applied to some specific examples which give the evidence that the method is satisfactory and efficient.     

Transient heat conduction analysis using the NURBS-enhanced scaled boundary finite element method and modified precise integration method

The Non-uniform rational B-spline(NURBS)enhanced scaled boundary finite element method in combination with the modified precise integration method is proposed for the transient heat conduction problems in this paper.The scaled boundary finite element method is a semi-analytical technique,which weakens the governing differential equations along the circumferential direction and solves those analytically in the radial direction.In this method,only the boundary is discretized in the finite element sense leading to a reduction of the spatial dimension by one with no fundamental solution required.Nevertheless,in case of the complex geometry,a huge number of elements are generally required to properly approximate the exact shape of the domain and distorted meshes are often unavoidable in the conventional finite element approach,which leads to huge computational efforts and loss of accuracy.NURBS are the most popular mathematical tool in CAD industry due to its flexibility to fit any free-form shape.In the proposed methodology,the arbitrary curved boundary of problem domain is exactly represented with NURBS basis functions,while the straight part of the boundary is discretized by the conventional Lagrange shape functions.Both the concepts of isogeometric analysis and scaled boundary finite element method are combined to form the governing equations of transient heat conduction analysis and the solution is obtained using the modified precise integration method.The stiffness matrix is obtained from a standard quadratic eigenvalue problem and the mass matrix is determined from the low-frequency expansion.Finally the governing equations become a system of first-order ordinary differential equations and the time domain response is solved numerically by the modified precise integration method.The accuracy and stability of the proposed method to deal with the transient heat conduction problems are demonstrated by numerical examples.     

Potential flow around obstacles using the scaled boundary finite‐element method

The scaled boundary finite‐element method is a novel semi‐analytical technique, combining the advantages of the finite element and the boundary element methods with unique properties of its own. The method works by weakening the governing differential equations in one co‐ordinate direction through the introduction of shape functions, then solving the weakened equations analytically in the other (radial) co‐ordinate direction. These co‐ordinate directions are defined by the geometry of the domain and a scaling centre. The method can be employed for both bounded and unbounded domains. This paper applies the method to problems of potential flow around streamlined and bluff obstacles in an infinite domain. The method is derived using a weighted residual approach and extended to include the necessary velocity boundary conditions at infinity. The ability of the method to model unbounded problems is demonstrated, together with its ability to model singular points in the near field in the case of bluff obstacles. Flow fields around circular and square cylinders are computed, graphically illustrating the accuracy of the technique, and two further practical examples are also presented. Comparisons are made with boundary element and finite difference solutions. Copyright © 2003 John Wiley & Sons, Ltd.     

形状记忆合金结构拓扑优化设计方法研究

形状记忆合金由于其优良的力学特性得到了广泛关注,并形成了一系列具有变革性的创新应用.为了充分提升形状记忆合金结构的力学性能,提出了一种基于实体各向同性材料惩罚模型SIMP (Solid Isotropic Materi-al with Penalization)的形状记忆合金结构拓扑优化方法.基于ZM宏观唯象本构模型,考虑形状记忆合金材料特性,对拓扑优化过程中引入的中间密度材料的奥氏体和马氏体弹性模量以及相变转变应力进行插值.同时,考虑形状记忆合金本身的材料非线性和结构在大变形下的几何非线性效应,以获得准确的力学响应.采用三密度场法来避免最终设计结果出现的棋盘格现象、网格依赖性和大量中间密度单元.利用超单元法来改善由于低密度单元引起的非线性有限元分析过程的数值不稳定问题.利用伴随法对优化模型中的响应函数进行灵敏度分析.最后,通过二维和三维的数值算例验证了本文的优化设计方法,结果表明本文提出的拓扑优化框架能够对预期性能的形状记忆合金结构方案进行求解.     

Stochastic boundary element method in elasticity

The stochastic boundary element method is developed to analyze elasticity problems with random material and/or geometrical parameters and randomly perturbed boundaries. Based on the first-order Taylor series expansion, the boundary integration equations concerning the mean and deviation of the displacements are derived, respectively. It is found that the randomness of material parameters is equivalent to a random body force, so the mean and covariance matrices of unknown boundary displacements and tractions can be obtained. Furthermore, the mean and covariance of displacements and stresses at inner points can also be obtained. Numerical examples show that the proposed stochastic boundary element method gives satisfactory solutions, as compared with those obtained by theoretical analysis or other numerical methods. The project supported by the National Natural Science Foundation of China and the State Education Commission Foundation of China     

Damage analysis by boundary element method

The response of cracked bodies subjected to loading was investigated by the boundary element method in this paper. The two-law elastic-cohesive-softening model was used for crack propagation analysis. The interface conditions for uncracked, craze, open crack, adhesive crack and slid crack parts were discussed and the corresponding incremental iteration algorithm was given. A simplified damage propagation model was presented. The technique has been applied to some specific examples which give the evidence that the method is satisfactory and efficient.     

A symmetrical nonsingular boundary element method

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