A Boundary Integral Formulation for Poroelastic Materials

Wave propagation in porous media is an important topic, e.g. in geomechanics or the oil-industry. We formulate a linear system of coupled partial differential equations based on Biot's theory with the solid displacements and the pore pressure as the primary unknowns. To solve this system of coupled partial differential equations in a semi-infinite homogeneous domain the BEM (Boundary element method) is especially suitable. Starting from a representation formula a system of two boundary integral equations is derived. These boundary integral equations are used to solve related boundary value problems via a direct approach. Coercivity of the resulting bilinear form is shown, from which unique solvability of the variational formulation follows from injectivity. Using these results we derive the unique solvability of the related boundary integral equations. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Boundary Integral Equation Solution of Non-linear Plane Potential Problems

This paper presents the boundary integral equation (BIE) formulation,and numerical solution procedure for two-dimensional problemsgoverned by Laplac's equation and subject to non-linear boundaryconditions. The introduction of non-linear terms constitutesa fundamental extension of the BIE method, as previous applicationshave been restricted entirely to linear problems. Furthermore,non-linearities necessitate the use of iterative solution techniqueswhich present the conceptual disadvantage that a solution isnot guaranteed. However, such difficulties were not encounteredwith the Newton—Raphson method employed in this study.The various features of the BIE technique are illustrated bythe application to a physical problem which is of significancein heat exchanger design.     

Integral Equation Formulation of Oseen Flow Problems

An integral equation approach to the problem of Oseen flow pastobstacles is presented and an approximate solution of the appropriateintegral equations is obtained for low Reynolds numbers. Bothobstacles in bounded and unbounded media are examined.     

Laplace方程边值问题的边界积分方程法

§ 1.　Introduction　　Inengineeringandtechnology ,theproblemofstaticelectricfieldscanbeattributedtotheboundaryproblemofLaplaceequationofstaticeletricpotentialfunction .Themethodsofclassi calmathematicalphysicscanbeonlyusedtosolveboundaryproblemofverysimpledomainandspecialboundarycondition .Althoughthemethodsoflimitedelementscanbeusedtosolvetheproblemsonarbitrarydomain ,butitneedstopartitionthewholedomainandtocalculateverycomplex .Theapproachofboundaryintegralequationistosolverelatedproblemsb…     

二维多项式本征应变边界积分方程及其数值验证

针对弹性介质中的椭圆形异质体,给出了低阶多项式分布的二维本征应变边界积分方程和相应的Eshelby张量的定义．以边界元分域法为参照,利用含有单个异质体的弹性介质对提出的计算模型和算法进行了数值验证．结果表明该算法取得较大的改进,其计算效率高于传统的边界元法,计算精度则高于采用常数本征应变的计算模型．     

共振条件下二阶积分边值问题解的存在性（英文）

利用上下解方法和带参数的紧向量场解集的连通性质研究了共振条件下一类二阶微分方程积分边值问题{u′′（t）=f（t,u（t））,t∈（0,1）,u（0）=∫10u（s）dα（s）,u（1）=∫10u（s）dβ（s）解的存在性.     

弹性摩擦接触问题的边界元—线性互补解法

本文对Coulomb摩擦的弹性接触问题给出了边界元一线性互补解法.这是对固体力学中自由边界问题进行边界元数学规划求解的新尝试,文中附有算例     

半无穷区间二阶半正积分边值问题的多解性

通过构造一个特殊锥,结合平移变换的方法得到了一类半无穷区间半正积分边值问题至少存在三个正解的充分条件,并举例阐述了主要结果.     

分数阶微分方程积分边值问题解的存在性

研究了带有积分边值条件的分数阶微分方程的边值问题,利用Banach压缩映像原理和Krasnoselskii不动点定理,得到了分数阶微分方程边值问题解的存在性、唯一性和至少存在一个解的充分条件.     

Boundary Integral Equation Method in the Steady State Oscillation Problems for Anisotropic Bodies

The three-dimensional steady state oscillation problems of the elasticity theory for homogeneous anisotropic bodies are studied. By means of the limiting absortion principle the fundamental matrices maximally decaying at infinity are constructed and the generalized Sommerfeld–Kupradze type radiation conditions are formulated. Special functional spaces are introduced in which the basic and mixed exterior boundary value problems of the steady state oscillation theory have unique solutions for arbitrary values of the oscillation parameter. Existence theorems are proved by reduction of the original boundary value problems to equivalent boundary integral (pseudodifferential) equations. © 1997 by B.G. Teubner Stuttgart-John Wiley & Sons, Ltd.     

Quasi-Newton Methods for Discretized Non-linear Boundary Problems

The discretization of non-linear boundary problems generallyleads to a finite system of non-linear algebraic equations,and it is to be expected that this latter has special structurearising both from the boundary problem and the method of discretizationused. The numerical solution of the algebraic system representsa serious numerical problem, and it is the point of this paperto indicate that, in certain important cases, special purposequasi-Newton methods can be constructed. We illustrate by consideringa single nonlinear differential equation discretized by collocationand present experimental results which indicate that an improvementin performance can be expected from the special methods.     

Boundary Hypersingular Integral Delay Equation for Nonstationary Problems of Scattering by Perfectly Conducting Bodies

Differential Equations - We consider the application of the method of boundary integral equations to the problem of scattering of an electromagnetic field obeying the nonstationary Maxwell...     

A Unified Integral Equation Scheme for Doubly Periodic Laplace and Stokes Boundary Value Problems in Two Dimensions

We present a spectrally accurate scheme to turn a boundary integral formulation for an elliptic PDE on a single unit cell geometry into one for the fully periodic problem. The basic idea is to use a small least squares solve to enforce periodic boundary conditions without ever handling periodic Green's functions. We describe fast solvers for the two‐dimensional (2D) doubly periodic conduction problem and Stokes nonslip fluid flow problem, where the unit cell contains many inclusions with smooth boundaries. Applications include computing the effective bulk properties of composite media (homogenization) and microfluidic chip design. We split the infinite sum over the lattice of images into a directly summed “near” part plus a small number of auxiliary sources that represent the (smooth) remaining “far” contribution. Applying physical boundary conditions on the unit cell walls gives an expanded linear system, which, after a rank‐1 or rank‐3 correction and a Schur complement, leaves a well‐conditioned square system that can be solved iteratively using fast multipole acceleration plus a low‐rank term. We are rather explicit about the consistency and nullspaces of both the continuous and discretized problems. The scheme is simple (no lattice sums, Ewald methods, or particle meshes are required), allows adaptivity, and is essentially dimension‐ and PDE‐independent, so it generalizes without fuss to 3D and to other elliptic problems. In order to handle close‐to‐touching geometries accurately we incorporate recently developed spectral quadratures. We include eight numerical examples and a software implementation. We validate against high‐accuracy results for the square array of discs in Laplace and Stokes cases (improving upon the latter), and show linear scaling for up to 10⁴ randomly located inclusions per unit cell. © 2018 Wiley Periodicals, Inc.     

带Riemann-Stieltjes积分条件的三阶边值问题的单调正解

研究了一类带Riemann-Stieltjes积分条件的非线性三阶非局部边值问题,将边值问题正解存在性的研究转化为扰动Hammerstein积分方程的研究,通过构造Green(格林)函数及讨论其性质,运用推广的Leggett-Williams型不动点定理,得到了至少存在3个和2n-1个正解的存在性准则, 所得结果推广和改进了最近文献中的结果,并充分反映了非线性项含导数对正解存在性研究的影响.主要结果由实例加以阐述.     

边界条件带导数的积分边值问题的正解

研究如下二阶积分边值问题的正解:■其中f∈C([0,1]×R~+,R~+).在先验估计的基础上,利用不动点指数理论建立了正解的存在性和多重正解的存在性.     

A Functional Equation Of J.A. Baker Involving Integral Means

The functional equation $$f(x)={1\over 2}\int^{x+1}_{x-1}f(t)\ dt\ \ \ {\rm for}\ \ \ x\ \in\ {\rm R}$$ has the linear functions ?(x) = a + bx (a, b ∈ ?) as trivial solutions. It is shown that there are two kinds of nontrivial solutions, (i) ?(x) = eλ_i ^x (i = 1, 2, …), where the λ_i∈ ? are the fixed points of the map z ? sinh z, and (ii) C^∞-solutions ? for which the values in the interval [?1,1] can be prescribed arbitrarily, but with the provision that ?^(j)(? 1) = ?^(j)(0) = ?^(j)(1) = 0 for all j = 0, 1, 2 …     

改进的无奇异局部边界积分方程方法

在局部边界积分方程方法中,当源节点位于分析域的整体边界上时,局部边界积分将出现奇异积分问题,这些奇异积分需要做特别的处理．为此,提出了对域内节点采用局部积分方程,而对边界节点直接采用移动最小二乘近似函数引入边界条件来解决奇异积分问题,这同时也解决了对积分边界进行插值引入近似误差的问题．作为应用和数值实验,对Laplace方程和Helmholtz方程问题进行了分析,取得了很好的数值结果．进而,在Helmholtz方程求解中,采用了含波解信息的修正基函数来代替单项式基函数进行近似．数值结果显示,这样处理是简单高效的,在高波数声传播问题的求解中非常具有前景．     

On a Conformally Invariant Integral Equation Involving Poisson Kernel

We study a prescribing functions problem of a conformally invariant integral equation involving Poisson kernel on the unit ball. This integral equation is not the dual of any standard type of PDE. As in Nirenberg problem, there exists a Kazdan–Warner type obstruction to existence of solutions. We prove existence in the antipodal symmetry functions class.