两点边值问题的一种精细求解方法

将求解域均匀离散,由状态参量在相邻结点间的精细积分关系式,确定一组代数方程;并将其写成矩阵形式,代入边界条件后,代数方程组的系数矩阵可化为块三对角形式。针对这一特性,给出了一种高效的递推消元算法。由于没有离散误差,该方法具有较高的精度,不仅适用于任意边界的常规两点边值问题,还适用于奇异摄动边值问题。数值算例充分证明了本文方法的精度和效率。     

Asymptotic finite element method for boundary value problems

The Asymptotic Finite Element method for improvement of standard finite element solutions of perturbation equations by the addition of asymptotic corrections to the right hand side terms is presented. It is applied here to 1-D and 2-D diffusion–convection equations and to non-linear similarity equations. Excellent results were obtained without the a priori use of special trial and test functions. Theoretical expectations were confirmed.     

Laplace transform method in boundary value problems for the Helmholtz equation

The purpose of this present note is to obtain boundary integral equation formulations of boundary value problems for the two-dimensional Helmholtz equation. The intergral equations are derived using the Laplace transform method.     

两点边值问题的小波配点法

根据多分辨分析,提出用任意连续的尺度函数构造区间上的插值基函数,形成以尺度函数为基础的求解两点边值问题的小波配点法.该方法中,尺度函数不受紧支撑、插值等性质的限制,计算复杂度小,数值解收敛性由多分辨分析理论保证.同时,给出边值条件的积分处理方法,能够方便地处理任意边界条件,当尺度函数不具有高阶导数时,该方法也能有效使用.数值算例表明,该方法是一个高效、高精度的算法.     

一种新的求解对流扩散边值问题的无网格方法

基于配点法和楔形基函数,提出了一种新的求解对流扩散边值问题的无网格方法。通过一维和二维的问题验证了该数值方法的可行性;并根据数值算例和分析,可以看到该数值方法能达到满意的收敛效果。该数值方法的隐格式形式能够有效地消除对流占优问题的数值振荡现象,是一种真正的无网格方法。     

A hybrid immersed boundary and material point method for simulating 3D fluid–structure interaction problems

A numerical method is developed for solving the 3D, unsteady, incompressible Navier–Stokes equations in curvilinear coordinates containing immersed boundaries (IBs) of arbitrary geometrical complexity moving and deforming under forces acting on the body. Since simulations of flow in complex geometries with deformable surfaces require special treatment, the present approach combines a hybrid immersed boundary method (HIBM) for handling complex moving boundaries and a material point method (MPM) for resolving structural stresses and movement. This combined HIBM & MPM approach is presented as an effective approach for solving fluid–structure interaction (FSI) problems. In the HIBM, a curvilinear grid is defined and the variable values at grid points adjacent to a boundary are forced or interpolated to satisfy the boundary conditions. The MPM is used for solving the equations of solid structure and communicates with the fluid through appropriate interface‐boundary conditions. The governing flow equations are discretized on a non‐staggered grid layout using second‐order accurate finite‐difference formulas. The discrete equations are integrated in time via a second‐order accurate dual time stepping, artificial compressibility scheme. Unstructured, triangular meshes are employed to discretize the complex surface of the IBs. The nodes of the surface mesh constitute a set of Lagrangian control points used for tracking the motion of the flexible body. The equations of the solid body are integrated in time via the MPM. At every instant in time, the influence of the body on the flow is accounted for by applying boundary conditions at stationary curvilinear grid nodes located in the exterior but in the immediate vicinity of the body by reconstructing the solution along the local normal to the body surface. The influence of the fluid on the body is defined through pressure and shear stresses acting on the surface of the body. The HIBM & MPM approach is validated for FSI problems by solving for a falling rigid and flexible sphere in a fluid‐filled channel. The behavior of a capsule in a shear flow was also examined. Agreement with the published results is excellent. Copyright © 2007 John Wiley & Sons, Ltd.     

A simultaneous space-time wavelet method for nonlinear initial boundary value problems

A high-precision and space-time fully decoupled numerical method is developed for a class of nonlinear initial boundary value problems. It is established based on a proposed Coiflet-based approximation scheme with an adjustable high order for the functions over a bounded interval, which allows the expansion coefficients to be explicitly expressed by the function values at a series of single points. When the solution method is used, the nonlinear initial boundary value problems are first spatially discretized into a series of nonlinear initial value problems by combining the proposed wavelet approximation and the conventional Galerkin method, and a novel high-order step-by-step time integrating approach is then developed for the resulting nonlinear initial value problems with the same function approximation scheme based on the wavelet theory. The solution method is shown to have the N th-order accuracy, as long as the Coiflet with [0, 3 N-1]compact support is adopted, where N can be any positive even number. Typical examples in mechanics are considered to justify the accuracy and efficiency of the method.     

Precise integration method for a class of singular two-point boundary value problems

In this paper we present a precise integration method based on high order multiple perturbation method and reduction method for solving a class of singular twopoint boundary value problems.Firstly,by employing the method of variable coefficient dimensional expanding,the non-homogeneous ordinary differential equations(ODEs) are transformed into homogeneous ODEs.Then the interval is divided evenly,and the transfer matrix in every subinterval is worked out using the high order multiple perturbation method,and a set of algebraic equations is given in the form of matrix by the precise integration relation for each segment,which is worked out by the reduction method.Finally numerical examples are elaboratedd to validate the present method.     

Non-linear boundary value problems for the circular membrane

Existence and uniqueness theorems are proved for two boundary value problems for the axisymmetric deformation of a circular membrane subjected to normal pressure. The nonlinear Föppl membrane theory is employed. The shooting method is used to establish these results. It is also shown that if the edge is free to move in the plane of the membrane then a necessary and sufficient condition for the existence of a unique solution is that the pressure is self-equilibrating.     

解两点边值问题的精细循环约化方法

将精细积分技术与循环约化方法相结合,提出两点边值问题的一种高精度、高效率求解方法。将求解域均匀离散,利用相邻两点间的传递关系式建立区段代数方程,将各区段的代数方程集成代数方程组,并利用循环约化方法对其求解。由于离散过程中几乎没有引入离散误差,并且在循环约化过程中采用了大量、小量分离技术,因此本方法具有极高的精度;同时循环约化过程充分利用2N算法的特点,使计算效率高、存储量小。研究结果表明,相对于已有的求解两点边值问题的精细积分法,本文方法适用范围更广,效率更高。例如对两端固支、受均布横向荷载作用下梁的非齐次方程计算,本文方法的精度可达到小数点后十三位,已经非常精确。     

Non-element method of solving 2D boundary problems defined on polygonal domains modeled by Navier equation

The paper presents a non-element method of solving boundary problems defined on polygonal domains modeled by corner points. To solve these problems a parametric integral equation system (PIES) is used. The system is characterized by a separation of the approximation of boundary geometry from the approximation of boundary functions. This feature makes it possible to effectively investigate the convergence of the obtained solutions with no need of performing the approximation of boundary geometry. The testing examples included confirm high accuracy of the solutions.     

A method for solving boundary value problems and two-dimensional theories without ad hoc assumptions

A method is proposed with which certain three-dimensional problems may be solved and also approximate two-dimensional theories can be deduced from three-dimensional equations of the theory of elasticity without ad hoc assumptions. To illustrate the method, the axially symmetric problem of hollow cylinders of any length is treated herein. The method, however, can be applied to nonaxisymmetric deformation of cylinders, spheres, plates, and other problems.     

Wavelet multiresolution interpolation Galerkin method for nonlinear boundary value problems with localized steep gradients

The wavelet multiresolution interpolation for continuous functions defined on a finite interval is developed in this study by using a simple alternative of transformation matrix. The wavelet multiresolution interpolation Galerkin method that applies this interpolation to represent the unknown function and nonlinear terms independently is proposed to solve the boundary value problems with the mixed Dirichlet-Robin boundary conditions and various nonlinearities, including transcendental ones, in which the discretization process is as simple as that in solving linear problems, and only common two-term connection coefficients are needed. All matrices are independent of unknown node values and lead to high efficiency in the calculation of the residual and Jacobian matrices needed in Newton’s method, which does not require numerical integration in the resulting nonlinear discrete system. The validity of the proposed method is examined through several nonlinear problems with interior or boundary layers. The results demonstrate that the proposed wavelet method shows excellent accuracy and stability against nonuniform grids, and high resolution of localized steep gradients can be achieved by using local refined multiresolution grids. In addition, Newton’s method converges rapidly in solving the nonlinear discrete system created by the proposed wavelet method, including the initial guess far from real solutions.

     

A micro-polar theory for binary media with application to phase-transitional flow of fiber suspensions

A phase-transitional flow takes place during the filling stage by injection molding of short-fiber reinforced thermoplastics. The mechanical properties of the final product are highly dependent on the flow-induced distribution and orientation of particles. Therefore, modelling of the flow which allows to predict the formation of fiber microstructure is of particular importance for analysis and design of load bearing components. The aim of this paper is a discussion of existing models which characterize the behavior of fiber suspensions as well as the derivation of a model which treats the filling process as a phase-transitional flow of a binary medium consisting of fluid particles (liquid constituent) and immersed particles-fibers (solid-liquid constituent). The particle density and the mass density are considered as independent functions in order to account for the phenomenon of sticking of fluid particles to fibers. The liquid constituent is treated as a non-polar viscous fluid, but with a non-symmetric stress tensor. The state of the solid-liquid constituent is described by the antisymmetric stress tensor and the antisymmetric moment stress tensor. The forces of viscous friction between the constituents are taken into account. The equations of motion are formulated for open physical systems in order to consider the phenomenon of sticking. The chemical potential is introduced based on the reduced energy balance equation. The second law of thermodynamics is formulated by means of two inequalities under the assumption that the constituents may have different temperatures. In order to take into account the phase transitions of the liquid-solid type which take place during the flow process a model of compressible fluid and a constitutive equation for the pressure are proposed. Finally, the set of governing equations which should be solved numerically in order to simulate the filling process are summarized. The special cases of these equations are discussed by introduction of restricting assumptions.Received: 6 May 2002, Accepted: 16 December 2002, Published online: 29 July 2003PACS: 83.10.Ff, 83.70.Hg, 83.50.Cz Correspondence to: H. Altenbach     

Existence of solutions for nonlinear elliptic boundary value problems

IntroductionInRef.[1 ]KannanandLockergivetheexistenceofatleastonesolutionofTy-h(t,y ,… ,y(n- 1) )y=f(t,y ,… ,y(n- 1) )　　 (a相似文献   

Variational approach to non-linear boundary value problems for elasto-plastic incompressible bending plate

Non-linear boundary value problems for inelastic isotropic homogeneous incompressible bending plate, within the range of J₂-deformation theory, are considered. An existence of the weak solution of the non-linear problem with clamped boundary condition is obtained in H²(Ω) by using monotone operator theory and Browder-Minty theorem. For linearization of the non-linear problem a monotone iteration scheme is constructed. It is shown that the sequence of potentials obtained from the sequence of approximate solutions (i.e. iterations), is a monotone decreasing one. Convergence of the iteration process in H²-norm is proved by using the convexity argument. Numerical solutions, based on finite-difference scheme, are given for linear bending problems with rigid clamped as well as simply supported boundary conditions. Further numerical examples are presented to illustrate the convergence of approximate solutions and monotonicity of the potentials as applied to the non-linear problems.     

求解位势问题的虚边界元法

本文提出了求解位势问题的虚边界元法，建立了位势问题的虚边界元的离散方程式，推导了离散化求系数的积分解析式。该方法与传统边界元法相比具有不存在奇异积分和边界附近精度较高等优点，可用来计算真空静电场、稳定温度场、流体绕流、介质中的渗流等各类位势问题。大量算例均获得了满意的结果。