薄板弯曲自由振动问题的高精度近似解析解及改进研究

对于薄板弯曲自由振动问题,已有如下方法:在Hamilton(哈密顿)体系下基于分离变量法得到挠度的解析形式,并建立自振频率联立方程组,给出求解振动频率和振型函数的方法.笔者指出该方法中所用挠度函数的解析式实际上是一种满足位移边界条件的高精度近似解,基于Rayleigh-Ritz(瑞利-里茨)法再次求近似频率后发现,原方法的近似解的精度很高.另外,对于含有固支、简支等不同的边界形式,恰当地选取不同位置作为坐标系的原点,得到含有频率的方程组的统一形式,且较为简洁.这些形式可基于四边固支、四边简支等边界条件的矩形板研究,依照板变形的对称性可验证频率方程组形式的正确性,并得到不同边界条件下频率方程形式之间的联系与转化.     

解任意四边形板弯曲问题的样条有限元法

关于用样条函数解板的弯曲问题,[1]在1979年讨论了矩形板和菱形板的弯曲;[2]在1981年对简支边界条件的矩形板,用振动梁函数和B样条函数组合作为插值函数,得到了效率更高的算式;[3]在1984年对[2]作了补充,采用拉格朗日乘子法,得到了在各种边界条件下平板弯曲的近似解,但所讨论的仍然是矩形板.     

三阶线性非齐次微分方程的Hyers-Ulam稳定性

讨论了三阶线性非齐次微分方程y′′′+p(x)y″+q(x)y′+r(x)y+f(x)=0的Hyers-Ulam稳定性,即若函数f是它的一个近似解,则该方程一定存在与f是任意接近的精确解,并给出了简单实例.     

一类随机最优控制问题的单调控制解

讨论了一类可允许控制策略满足单调非降条件的随机最优控制问题,给出了值函数v(t,x,y,)满足一类受梯度限制的Hamilton-Jacobi-Bellman(HJB)方程:max{Lv(t,x,y), v(t,x,y)/ y}=0,其中Lv(t,x,y)= v/ t b(t,x,y,) v/ x 1/2σ2(t,x,y) 2v/ x2 f(t,x,y).借助粘性解的思想,定义了该类HJB方程的粘性解并在此意义下证明了v(t,x,y)是唯一粘性解,这类方程在随机控制,金融数学等领域内有重要应用.     

基于样条的高阶矩阵微分方程近似解

矩阵微分方程经常出现在许多物理模型和工程技术模型中.利用矩阵样条构造形如{y(p)(x)=Ap-1(x)y(p-1)(x)+Ap-2(x)y(p-2)(x)+…+A1(x)y(1)(x)+A0(x)y(x)+B0(x),y(a)=ya,…,y(p-1)(a)=y(p-1)a,x∈[a,b];Ai(x),B0(x)∈C4[a,b],0≤i≤p-烅烄烆1的高阶矩阵线性微分方程初值问题的数值解.给出实现算法和数值解的近似误差估计以及数值实例.先将高阶矩阵微分方程转化为一阶矩阵微分方程,然后利用三次矩阵样条求出一阶矩阵线性微分方程的数值解,从而解决高阶微分方程问题.     

矩形薄板弯曲的近似解法——康托洛维奇-伽辽金法

本文从广义梁微分方程出发,推导出三次样条梁函数。由于采用了广义函数,在集中荷载,集中弯矩等得到截断多项式的解。弹性薄板偏微分方程荷载项采用了广义函数(δ函数及σ函数),无论是集中荷载、集中弯矩、均布荷载,小方块荷载都可表示成为x、y两个方向的截断多项式变形曲线。利用康托洛维奇法将偏微分方程转换成为常微分方程,再用伽辽金法可得良好的近似解。文内算例较为丰富,包括各种边界弹性薄板,各种荷载、变截面薄板以及悬臂板等。     

Hammerstein非线性积分方程组的非平凡解及应用

该文利用拓扑方法和锥理论研究下列Hammerstein非线性积分方程组u(x)=∫_G k(x,y)f(y,u(y),v(y)) dy,v(x)=∫_Gk(x,y)g(y,u(y),v(y)) dy.在适当的条件下,证明了上述方程组非平解的存在性,并把所得结果应用于研究非线性二阶常微分方程组边值问题的非平凡解的存在性.     

二阶模糊线性微分方程边值问题的模糊近似解

讨论了二阶模糊线性微分方程边值问题{y"+p(t)y'+q(t)y=g(t),t∈[a,b],t∈[a,b]y(a)=(a),y(b)=(β),(α),(β)∈E1的模糊近似解,即利用配置法将微分方程转化为函数线性方程组,针对其系数函数的符号的不同,通过计算函数线性方程组获得了原模糊微分方程的模糊近似解.     

变厚度正交各向异性矩形板非线性非对称弯曲问题的基本方程

在不计体力,考虑了薄膜力引起在z方向的分力,导出了厚度线性变化的正交各向异性矩形板非线性非对称弯曲问题的本构方程;在引进无量纲变量和引入三个小参数的条件下,给出了挠度函数W(x,y)和应力函数Φ(x,y)的无量纲化的支配方程形式．     

功能梯度板的柱面弯曲弹性力学解

在推广后的England-Spencer功能梯度板理论基础上,研究了功能梯度板在不同荷载作用下的柱面弯曲问题.采用该理论中的位移展开公式,并且材料参数沿板厚方向可以任意连续变化,并将材料由各向同性推广到正交各向异性.假设板在y方向无限长,最终建立了一个从弹性力学理论出发的正交各向异性功能梯度板在横向分布荷载作用下柱面弯曲问题的板理论.通过算例分析,讨论了边界条件、材料梯度及板厚跨比等因素对功能梯度板静力响应的影响.     

锥壳的位移解及应用*

本文提出求锥壳方程通解的另一种方法——位移法.文中根据文献[1]给出的壳体基本关系,导出锥壳一般弯曲问题的位移方程组,然后通过引入一个位移函数U(s,θ)(在极限情况下,就变为对于圆柱壳所引入的位移函数),从而将锥壳基本方程组化成关于位移函数U(s,θ)的8阶可解偏微分方程(控制微分方程).对于一般弯曲问题,该方程的一般解以广义超几何函数给出;对于轴对称弯曲问题,用Bessel函数给出其一般解.作为锥壳位移解法的应用,讨论了Winkler地基模式上的锥壳的轴对称弯曲问题,给出数值结果.     

矩形片筏基础的挠度分析

工程上对片筏的力学分析，通常采用温克勒地基模型，且假定床基系数是常量。本则认为床基系数是坐标的函数，考虑了具有线性变化床基系数的地基上的片筏，利用伽辽金法求得周边固支片筏在均布荷载作用下的挠度。所得结果颇具一般性且实用价值更高。     

纯扭各向异性复合材料板断裂分析的复变函数方法

对受纯扭载荷作用的线弹性各向异性纤维复合材料板裂纹尖端附近的应力场进行探讨.选取带复参数的挠度函数,利用复变函数方法和待定系数法,借助边界条件,确定复参数,从而推出了裂纹尖端附近的弯矩、扭矩、应力和位移计算公式.所得到的公式在有关的断裂分析中有一定的实用价值和参考作用,最后给出了数值算例.     

纯扭正交异性复合材料板的断裂分析

对受纯扭载荷作用的线弹性正交异性复合材料板裂纹尖端附近的断裂性态进行探讨。利用复变函数方法，通过求解偏微分方程的边值问题，推出了裂纹尖端附近的弯矩、扭矩、应力和位移的表达式，最后给出了数值算例。     

A recursive methodology for the solution of semi-analytical rectangular anisotropic thin plates in linear bending

A new recursive methodology is introduced to solve anisotropic thin plates bending problems, which is based on three concepts: (a) the plate differential operator additively decomposed obeying a material constitutive hierarchy; (b) the plate displacement field expanded into an infinite series and (c) an homotopy-like scheme applied to determine each term of the series. The pb-2 Rayleigh–Ritz Method is adopted to construct the solution space. Convergence conditions are presented and related to the differential operator decomposition and material’s anisotropy degree. Different cases of geometry, loading and boundary conditions were studied using the methodology and excellent agreement with available solutions was found.     

Levy-type solution for buckling analysis of thick functionally graded rectangular plates based on the higher-order shear deformation plate theory

In this article, an analytical approach for buckling analysis of thick functionally graded rectangular plates is presented. The equilibrium and stability equations are derived according to the higher-order shear deformation plate theory. Introducing an analytical method, the coupled governing stability equations of functionally graded plate are converted into two uncoupled partial differential equations in terms of transverse displacement and a new function, called boundary layer function. Using Levy-type solution these equations are solved for the functionally graded rectangular plate with two opposite edges simply supported under different types of loading conditions. The excellent accuracy of the present analytical solution is confirmed by making some comparisons of the present results with those available in the literature. Furthermore, the effects of power of functionally graded material, plate thickness, aspect ratio, loading types and boundary conditions on the critical buckling load of the functionally graded rectangular plate are studied and discussed in details. The critical buckling loads of thick functionally graded rectangular plates with various boundary conditions are reported for the first time and can be used as benchmark.     

3D elasticity analytical solution for bending of FG micro/nanoplates resting on elastic foundation using modified couple stress theory

This paper addresses a 3D elasticity analytical solution for static deformation of a simply-supported rectangular micro/nanoplate made of both homogeneous and functionally graded (FG) material within the framework of modified couple stress theory. The plate is assumed to be resting on a Winkler–Pasternak elastic foundation, and its modulus of elasticity is assumed to vary exponentially along thickness. By expanding displacement components in double Fourier series along in-plane coordinates and imposing relevant boundary conditions, the boundary value problem (BVP) of plate system, including its governing partial differential equations (PDEs) of equilibrium are reduced to BVP consisting only ordinary ones (ODEs). Parametric studies are conducted among displacement and stress components developed in the plate and FG material gradient index, length scale parameter, and foundation stiffnesses. From the numerical results, it is concluded that the out-of-plane shear stresses are not necessarily zero at the top and bottom surfaces of plate. The results of this investigation may serve as a benchmark to verify further bending analyses of either homogeneous or FG micro/nanoplates on elastic foundation.     

弹性基上锥壳一般弯曲问题的精确解

本文应用Donnell的简化假定,从弹性基上锥壳位移型微分方程组出发,通过引入一个位移函数U(s,θ)(在极限情况下就退化成V.S.Vlasov对于圆柱壳所引的位移函数[5]),将基本微分方程组化成为一个八阶可解偏微分方程.这个方程的一般解用级数形式给出.对于在实际中有广泛应用价值的Winkler弹性基上锥壳的轴对称弯曲问题,本文给出了详细的数值结果,并求出了边缘荷载作用下的影响系数,这对计算弹性基上锥壳组合结构有着重要的意义.     

Symmetry and regularity of solutions to a system with three-component integral equations

Consider the system with three-component integral equations u(x) = Rn |x y|α nw(y)rv(y)q dy,v(x) = Rn |x y|α nu(y)pw(y)rdy,w(x) = Rn |x y|α nv(y)q u(y)pdy,where 0 < α < n,n is a positive constant,p,q and r satisfy some suitable conditions.It is shown that every positive regular solution(u(x),v(x),w(x)) is radially symmetric and monotonic about some point by developing the moving plane method in an integral form.In addition,the regularity of the solutions is also proved by the contraction mapping principle.The conformal invariant property of the system is also investigated.     

Two theorems on boundary properties of minimal surfaces in nonparametric form

Let D be a region with rectifiable Jordan boundary , and let z=f(x, y) be a minimal surface defined over D. This paper establishes that: 1) function z=f(x, y) almost everywhere on has finite or infinite angular boundary values; 2) if region D is the exterior of a circle then, almost everywhere on boundary , function z=f(x, y) can be continued by continuity.Translated from Matematicheskie Zametki, Vol. 21, No. 4, pp. 551–556, April, 1977.