弹性地基上正交各向异性变厚度圆薄板的大挠度问题

本文推出了均布载荷下弹性基地上的正交各向异性变厚度圆薄板大挠度问题的基本方程。利用修正迭代法获得了该问题的二阶近似解。     

A Decomposition Method for Some Biharmonic Problems

In this paper we consider two biharmonic problems [13] which will be conventionally indicated as "simply supported" and "clamped plate" problem. We construct a decomposition method [16], [19] related to the partition of the plate in two, or more, subdomains. We carry on the numerical treatment of the method first decoupling these fourth order problems into two second order problems, then discretizing these problems by mixed linear finite element and obtaining an algebraic system. Moreover, we present an iterative block algorithm for solving the foregoing system, which can be efficiently developed on parallel computers.In the end, we extend the method to the respective biharmonic variational inequalities [10].     

Asymptotic Expansions and Numerical Methods for Compressible and Low Mach Number Fluid Flow

The results of a formal asymptotic low Mach number analysis [5, 6] of the Euler equations of gas dynamics are used to extend the validity of a numerical method from the simulation of compressible inviscid flow fields to the low Mach number regime. Although, different strategies are applicable [7, 8, 5, 9] in this context we focus our view to a preconditioning technique recently proposed by Guillard and Viozat [16]. We present a finite volume approximation of the governing equations using a Lax‐Friedrichs scheme whereby a preconditioning of the incorporated numerical dissipation is employed. A discrete asymptotic analysis proves the validity of the scheme in the low Mach number regime.     

SADDLEPOINT APPROXIMATIONS TO THETWO-SAMPLE PERMUTATION TESTS

1.IntroductionPermutationtestisapowerfultoolinstatisticalinference.However,itsapplicationishinderedbythecomputationalintensity.Onewaytoovercomethisdifficultyistouseasymptoticapproximations.EdgeworthexpansionshavebeenobtainedbyAlbers,BickelandVanZ..tti]jBickelandVanZwet[ZItRobinsonlg]tJohnandR.bi....[lo]tandthesegivegoodapproximationsinmostcases.However,theseEdgeworthexpansionssometimescangiveveryinaccurateresultsinthetailsofthedistribution,withwhichwearemostconcernedforinferenceandforcon…     

Waves in an inhomogeneous fluid in the presence of a dock : PMM vol. 39, n 6, 1975, pp. 1140–1142

We investigate the propagation of waves generated by oscillations of a section of the bottom of a tank through a two-layer fluid, in the presence of a dock. Wave motions in an inhomogeneous fluid generated by displacement of a section of the bottom of a tank were studied in [1] where the upper surface of the fluid was assumed either to be completely free, or completely covered with ice. In the present paper we use the method given in [2] to investigate a similar problem under the assumption that the fluid surface is partly covered with an immovable rigid plate. The expressions obtained for the velocity potential are used to determine the form of the free surface and of the interface. We show that when the fluid is inhomogeneous, the wave amplitude on the free surface increases, while the presence of a plate reduces the amplitude of the surface waves, as well as of the internal waves in the region between the plate and the oscillating section of the bottom.     

流体层流运动稳定性中的Ляпунов方法

本文是[1]的继续.在本文中,利用[1]的结果我们证明了,对于流体的层流运动稳定性而言,在线性化问题中,按特征值定义与按扰动能量定义二者是完全等价的,从外,借助于Ляпунов方法,我们又证明了,如果线性化问题是渐近稳定的,当考虑非线性影响时,只要扰动能量足够小,则仍然是渐近稳定的.     

A dual graph-norm refinement indicator for finite volume approximations of the Euler equations

Summary. We generalise and apply a refinement indicator of the type originally designed by Mackenzie, Süli and Warnecke in [15] and [16] for linear Friedrichs systems to the Euler equations of inviscid, compressible fluid flow. The Euler equations are symmetrized by means of entropy variables and locally linearized about a constant state to obtain a symmetric hyperbolic system to which an a posteriori error analysis of the type introduced in [15] can be applied. We discuss the details of the implementation of the refinement indicator into the DLR--Code which is based on a finite volume method of box type on an unstructured grid and present numerical results. Received May 15, 1995 / Revised version received April 17, 1996     

On time-dependent behavior of cross-ply laminated strips with viscoelastic interfaces

The two-dimensional problem of a simply supported laminated orthotropic strip with viscoelastic interfaces under static loading is studied. State-space formulations are developed based on the exact elasticity equations governing orthotropic media and the Kelvin–Voigt constitutive relation of interfaces. Since the response of the strip is time-dependent, the power series expansion technique is adopted to model the variations of elastic fields with time. Results show that the response of the laminated strip with viscoelastic interfaces changes remarkably with time, which is also significantly different from that of a plate with perfect interfaces or with viscous interfaces. Note that from the present analysis, the response for a laminated plate with spring-like interfaces or with viscous interfaces can be easily obtained because they are just two particular cases of the present Kelvin–Voigt model.     

The existence of minimal surfaces of given topological structure under prescribed boundary conditions

The purpose of the present paper is the solution of the boundary value problems for minimal surfaces when the boundaries are not, or not entirely-fixed Jordan curves but are free to move on prescribed manifolds. At the same time I shall present modifications and simplifications of my previous solution of the Plateau' and Douglas' problem for fixed boundary curves and prescribed topological structure and incidentally discuss certain features of the problem in order to clarify its relation to the theory of conformal mapping. Though based on previous publications, the paper may, except for some references, be read independently. Nos. [9], [10], [11], [12], [13], [14] of the bibliography at the end of the paper. References to this list are made in square brackets throughout this paper.     

Multinomial convolution polynomials

In [9] Knuth shows how to derive the convolution formulas of Hagen, Rothe and Abel from Vandermonde's convolution and the binomial theorem for integer exponents. In the present paper, we shall first present a short and elementary proof of the multi-extension of the above convolution formulas, due to Raney and Mohanty. In the second part we shall present a multi-version of Knuth's approach to convolution polynomials and derive another short proof of the above formulas.     

Refined stability theory for sandwich shells with transversally stiff core. 3. Simplest one-dimensional problems

The applicability and accuracy of stability equations of the refined theory for sandwich shells with a transversally stiff core proposed in [1] are investigated. The model problem of calculating the critical loads and stress fields in the core at mixed forms of the loss of stability is solved for an infinitely wide sandwich plate with an orthotropic core and composite load-carrying layers subjected to in-plane edge loads. The case of pure bending of the plate is considered in detail. The results obtained by variation of the physical-mechanical parameters are compared with the solutions of the three-dimensional theory for the core [2]. It is shown that the version of the refined theory [1] is more accurate than the other two-dimensional theories.For Pt. 2 see [1].Center for Study of Dynamics and Stability, Tupolev Kazan State Technical University, Kazan, Tatarstan, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 1, pp. 57–65, January–Feburary, 1998.     

Boundary value problems for rotationally symmetric mean curvature flows

The motion of surfaces by their mean curvature has been studied by several authors from different points of view. K. A. Brake studied this problem from the geometric measure theory point of view, the parametric problem was studied by G. Huisken [5]. Nonparametric mean curavture flow with boundary conditions was studied in [6] and [7]. Rotationally symmetric mean curvature flows have been treated by G. Dziuk, B. Kawohl [3], but also by S. Altschuler, S. B. Angenent and Y. Giga [2]. In this paper we consider the case in which the initial surface has rotational symmetry and we shall generalize the results in [3] in the sense that we shall give more general boundary conditions which enforce the formation of a singularity in finite time. The proofs rely entirely on parabolic maximum principles. Received: 6 September 2006     

A simplified formulation of a plate/shell element for geometrically nonlinear analysis of moderately large deflections with small rotations

This paper presents a total Lagrangian formulation of a plate/shell element for geometrically nonlinear analysis with the assumption of moderately large deflections but small rotations. Mallet and Marcal's nonlinear stiffness matrices [N₁] and [N₂] are derived explicitly by the procedure suggested by Rajasekaran and Murray for a four-node parallelogram isoparametric element with bilinear interpolation functions and an orthotropic constitutive relationship. The performance of the element based on this simplified formulation has been tested through a number of examples. It is concluded that this element offers potential for geometrically nonlinear analysis of large-scale practical structures.     

Mutual subordination of multivariate stationary processes over any locally compact abelian group

Summary Our purpose is to extend Kolmogorov's theorem [5, Th. 10] on mutual subordination for univariate weakly stationary stochastic processes over the (discrete) group of integers to multivariate processes over any (Hausdorff) locally compact abelian (lca) group. This extension is given in Theorems (1.12) and (3.4) below. We shall lean heavily on the joint paper [10] on the decomposition of matricial measures, to which the present paper may be regarded as a sequel.In Section 1 of the paper we shall define and prove theorems on the concept of E-subordination, where E is a projection-valued measure. In Section 2 we shall examine the structure of stationary processes over an lca group. In Section 3 we shall consider the concept of subordination of stationary processes. Finally in Section 4, we shall apply our subordination theorems to deduce that matrixvalued functions in L ₂ on the unit circle having no negative frequencies have a constant rank a.e. (Lebesgue) (4.2), a theorem of F. and M. Riesz (4.3), and a theorem on wandering subspaces due to Robertson [9] (4.4).The author is grateful to Prof. P. R. Masani for his generous help in formulating this paper.     

Explicit Buckling Analysis and Design Equations for Composite Plates under Compression with Free Reinforced Edges

In the present contribution, the buckling problem of compressively loaded symmetrically laminated orthotropic composite plates with free reinforced edges is studied [1]. Starting from the exact transcendental elasticity solution of the problem, a straightforward criterion for the determination of the minimum bending stiffness EI_min of the edge stiffeners is presented that allows for the determination of EI such that no global buckling of the plate and flange occurs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The heat conductivity problem in a thin plate with contrasting fiber inclusions

Based on the asymptotic analysis of an elliptic boundary value problem in a thin domain, a homogenized model of the heat distribution in a composite plate of small relative thickness h ∈ (0,1] is constructed under the assumption that thermal conductivity of the fiber and that of the filler contrast very much. Namely, the plate is assumed to contain several periodic families of fibers, the diameters of the fibers and the distances between the fibers being of the same order h. Fibers in each family have the same thermal conductivity; the values of thermal conductivity of fibers in different families may vary, but should be of the same order in h. Thermal conductivity of the filler is one order smaller in h. The asymptotics is constructed by means of matching the classical asymptotic ansatz for thin plates and fibers. The periodic structure of the composite is crucially used to construct the asymptotic expansion which consists of terms of the following two types: a periodic solution of the three-dimensional problems in the periodicity cell and a solution to a two-dimensional homogenized problem in the longitudinal cross-section of the plate. The asymptotic procedure provides a simple algorithm to compute coefficients in the homogenized second-order differential operator. The asymptotics obtained is justified using the weighted Friedrichs inequality and the error estimates are asymptotically sharp.     

On global transonic shocks for the steady supersonic Euler flows past sharp 2-D wedges

In this paper, under certain downstream pressure condition at infinity, we study the globally stable transonic shock problem for the perturbed steady supersonic Euler flow past an infinitely long 2-D wedge with a sharp angle. As described in the book of Courant and Friedrichs [R. Courant, K.O. Friedrichs, Supersonic Flow and Shock Waves, Interscience, New York, 1948] (pages 317-318): when a supersonic flow hits a sharp wedge, it follows from the Rankine-Hugoniot conditions and the entropy condition that there will appear a weak shock or a strong shock attached at the edge of the sharp wedge in terms of the different pressure states in the downstream region, which correspond to the supersonic shock and the transonic shock respectively. It has frequently been stated that the strong shock is unstable and that, therefore, only the weak shock could occur. However, a convincing proof of this instability has apparently never been given. The aim of this paper is to understand this open problem. More concretely, we will establish the global existence and stability of a transonic shock solution for 2-D full Euler system when the downstream pressure at infinity is suitably given. Meanwhile, the asymptotic state of the downstream subsonic solution is determined.     

二阶周期边值问题的多重正解

考虑如下周期边值问题:其中x~([1])(t)=p(t)x'(t).总假设p(t)>0,q(t)>0,且f(t,x)是[0,1]×(0,+∞)→[0,+∞)的连续函数,f在z=0可以有奇性.利用锥不动点定理以及格林函数的正性,给出周期边值问题单个和多个正解存在性证明的一种新方法.在实际中,定理的条件很容易验证.     

Justification of the Courant-Friedrich's hypothesis in the case of a weak shock. Part I. Presentation of solution to linear problem

As is well known, two solutions of the problem of a supersonic stationary inviscid nonheatconducting gas flow onto a planar infinite wedge are theoretically possible: the solution with a strong shock (the flow speed behind the shock is subsonic) and the solution with a weak shock (the flow speed behind the shock is supersonic). Unlike the well-studied case of a strong shock that is generically unstable [A.M. Blokhin, D.L. Tkachev, L.O. Baldan, Study of the stability in the problem on flowing around a wedge. The case of strong wave, J. Math. Anal. Appl. 319 (2006) 248-277; A.M. Blokhin, D.L. Tkachev, Yu.Yu. Pashinin, Stability condition for strong shock waves in the problem of flow around an infinite plane wedge, Nonlinear Anal. Hybrid Syst. 2 (2008) 1-17], R. Courant and K.O. Friedrichs [R. Courant, K.O. Friedrichs, Supersonic Flow and Shock Waves, Interscience Publishers, New York, 1948] assumed that the solution with a weak shock is asymptotically stable by Lyapunov. Presentation of classical solution to the corresponding problem which is found in the present paper is the first step on the way to justification of Courant-Friedrichs hypothesis on linear level.     

The effect of transverse shear upon the buckling stability of inelastic orthotropic plates

The problem of buckling of inelastic orthotropic plates is analyzed. The phenomena associated with the transverse strains of the plate are considered in the framework of the Ambartsumyan theory of plates, which excludes the hypothesis of undeformed normals. The problem is solved with the aid of the localized strains theory, and it is shown that in the case of orthotropic materials, i.e., those characterized by a large E/G ratio, the effect of the transverse shear must be taken into account in determining the critical stress for a plate under compressive loads parallel to its surface.Mekhanika Polimerov, Vol. 1, No. 2, pp. 133–136, 1965