Dynamic fracture mechanics analysis for composite material with material non-homogeneity in thickness direction

The problem considered here is the response of a non-homogeneous composite material containing some cracks subjected to dynamic loading. It is assumed that the composite material is orthotropic and all the material properties depend only on the coordinatey (along the thickness direction). In the analysis, the elastic region is divided into a number of plies of infinite length. The material properties are taken to be constants for each ply. By utilizing the Laplace transform and Fourier transform technique, the general solutions for plies are derived. The singular integral equations of the entire elastic region are obtained and solved by the virtual displacement principle. Attention is focused on the time-dependent full field solutions of stress intensity factor(SIF) and strain energy release rate. As a numerical illustration, the dynamic stress intensity factor of a substrate/functionally graded film structure with two cracks under suddenly applied forces on cracks face are presented for various material non-homogeneity parameters.     

两个参数的三项非齐次递推式的计算公式

讨论两个参数的三项非齐次递推式的解计算公式。其结果,使得象规格为2~m2m个元的r-重复排列的个数之类的定解问题,皆可以直接解出。     

一类非齐次复微分方程解的增长性

研究了一类线性非齐次微分方程f(k)+ak-1f(k-1)+…+a1f-′(eQ(z)-a0)f=eQ(z)+F(z)解的增长性,其中aj(j=0,1,…,k-1)为常数,Q(z)为非常数多项式,F(z)为级小于deg Q的整函数.     

An application of non-singularity BEM to plate bending, buckling and natural vibration problems

In this paper the fundamental solution of the singular governing equation of plate static bending is taken as the Green's function, which can satisfy the governing equation precisely in the plate region. Based on the principle of superposition, let the function values on the plate boundary, induced by a set of the Green's function sources (including the known sources in the plate region and the unknown sources in the fictitious region), satisfy the prescribed conditions on specially chosen boundary matching points, and the corresponding semi-analytical and semi-numerical solution can be obtained, which is free from the restraint of boundary forms and boundary conditions. The more matching points there are on the boundary, the better the accuracy of results is. Finally, in static bending problems a set of linear algebraic equations has to be computed; in buckling problems the minimum value of buckling eigenvalue equation has to be found; in natural vibration problems the eigenvalues of the frequency equation have to be calculated. Numerical examples are given and the results are compared with those by the analytical method and other methods. It can be seen that they are very close to each other.     

Structure Functions in Complex Flows

The turbulence in the ocean and atmosphere is most of the time non-homogeneous in nature. These spatial changes could affect the structure of the turbulence. In this work a classification is proposed to determine the intermittency and mixing ability. The variation of the structure functions and the scaling exponent in decaying non-homogeneous turbulence produced by a grid and by a jet is measured with a sonic velocimeter SONTEK3-D. We use Extended Self Similarity (ESS) to obtain better estimates of the scaling exponents of the structure functions of order up to the 6th. We study the variation of the absolute scaling exponents _p and relative scaling exponents ¯_p as a function of distance from the source of turbulence. In most cases, the absolute scaling exponent ₃ is shown to vary as function of the separation distance l. On the other hand the relative scaling exponents ¯_p depend on the location of the flow and in most cases the deviations from the Kolmogorov 1941 scaling are related to the intermittency.     

利用齐次化原理求解常系数非齐次线性方程初值问题

文章给出利用齐次化原理求解n阶常系数非齐次线性方程初值问题的方法.通过基本问题可得到原方程的解,避免了利用常数变易法求解的诸多不便,同时也将非齐次项的形式拓展到了所有可积函数.     

A Posteriori Error Estimators and Adaptivity for Finite Element Approximation of the Non-Homogeneous Dirichlet Problem

Techniques are developed for a posteriori error analysis of the non-homogeneous Dirichlet problem for the Laplacian giving computable error bounds for the error measured in the energy norm. The techniques are based on the equilibrated residual method that has proved to be reliable and accurate for the treatment of problems with homogeneous Dirichlet data. It is shown how the equilibrated residual method must be modified to include the practically important case of non-homogeneous Dirichlet data. Explicit and implicit a posteriori error estimators are derived and shown to be efficient and reliable. Numerical examples are provided illustrating the theory.     

SOME PROPERTIES OF GALTON-WATSON BRANCHING PROCESSES IN VARYING ENVIRONMENTS

This article deals with some properties of Galton-Watson branching processes in varying environments. A necessary and suffcient condition for relative recurrent state is presented, and a series of ratio limit properties of the transition probabilities are showed.     

关于常系数非齐次线性微分方程通解的注释

给出了二、三阶常系数非齐次线性微分方程的通解的表达式,并且对于任意阶常系数非齐次线性微分方程的某些类别也给出了通解的表达式.     

A STABILITY RESULT ON SOLUTIONS TO CERTAIN FOURTH ORDER NON-HOMOGENEOUS DIFFERENTIAL EQUATIONS

In this paper,we study the fourth order non-homogeneous differential equations x(4) + f1()+ f2() + f3(■) + f4(x) = p(t,x,■,,x),and obtain suffcient conditions,under which the solutions to the system tend to zero as t →∞.