ADirect Method for the Problem of the Solid Cylinder in Elasticity

§１．　ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅＳａｉｎｔＶｅｎａｎｔｐｒｏｐｏｓｅｄｔｈｅｆａｍｏｕｓｓｅｍｉ－ｉｎｖｅｒｓｅｓｏｌｕｔｉｏｎｍｅｔｈｏｄ［１］，ｔｈａｔｓｏｍｅａｐｐｒｏ－ｐｒｉａｔｅａｓｓｕｍｐｔｉｏｎｓｔｏｔｈｅｄｅｆｏｒｍａｔｉｏｎｓｈｏｕｌｄｂｅｍａｄｅｂｅｆｏｒｅｈａｎｄｔｏｆｉｎｄｔｈｅｓｏｌｕｔｉｏｎ，ａｆｔｅｒ－ｗａｒｄｓｃｈｅｃｋｉｎｇｔｈｅａｓｓｕｍｐｔｉｏｎｓｂｅｉｎｇｖａｌｉｄ．Ｔｈｅｒｅａｆｔｅｒ，ｔｈｅｓｅｍｉ－ｉｎｖｅｒｓｅｓｏｌｕｔｉｏｎｂｅｃｏｍｅｓｔ…     

Torsion of a circular cone with static and dynamic loading

Integral transformation methods—the Mellin transform for statics and the Lebedev-Kontorovich transform for dynamics—are used to construct analytic solutions of the problem of the torsion of an elastic circular cone. Assuming that external forces are concentrated in the neighbourhood of the vertex of the cone, the asymptotic behaviour of the far field is investigated. It is shown that the leading term of the asymptotic expansion is governed by the magnitude of the moment of the external forces, so that the St Venant principle is satisfied in the cases under consideration.     

On the modeling and simulation of boundary flow through partially open pipe ends

The determination of boundary conditions for the Euler equations of gas dynamics in a pipe with partially open pipe ends is considered. The boundary problem is formulated in terms of the exact solution of the Riemann problem and of the St. Venant equation for quasi-steady flow so that a pressure-driven calculation of boundary conditions is defined. The resulting set of equations is solved by a Newton scheme. The proposed algorithm is able to solve for all inflow and outflow situations including choked and supersonic flow.Received: August 7, 2002; revised: November 11, 2002     

一组适合于带纵向裂纹柱体圣维南扭转的等参数元素

本文给出一组新的适合于带纵向裂纹柱体圣维南扭转的等参数元素,它们分别是八结点等参数元素、在裂纹尖端具有r-1/2奇异性的“1/4”八结点等参数元素及八结点过渡元素.利用这些元素,对含有径向纵裂纹的圆柱体进行了圣维南扭转计算.计算结果表明,本文给出的等参数元素有较高的精度、较好的收敛性及快的收敛速度,同时还具有程序简单、省机时等优点,所以特别适合于实际的工程计算.     

Stability of Surface Rayleigh Waves in an Elastic Half‐Space

This paper is concerned with nonlinear analysis for the propagation of Rayleigh surface waves on a homogeneous, elastic half‐space of general anisotropy. We show how to derive an asymptotic equation for the displacement by applying the second‐order elasticity theory. The evolution equation obtained is a nonlocal generalization of Burgers' equation, for which an explicit stability condition is exhibited. Finally, we investigate examples of interest, namely, isotropic materials, Ogden's materials, compressible Mooney–Rivlin materials, compressible neo‐Hookean materials, Simpson–Spector materials, St Venant–Kirchhoff materials, and Hadamard–Green materials.     

On Asymptotic Expansions and Error Bounds in the Derivation of Two-Dimensional Shell Theory

Known results on asymptotic two-dimensional equations for circular cylindrical shells, including the effects of transverse shear and normal stress deformation, are supplemented by upper- and lower-bound determinations of influence coefficients, using minimum-potential and complementary energy principles in conjunction with asymptotic-expansion results. The new bound analysis shows that the consequences of the asymptotic two-dimensional theory are in exact agreement, except for terms which are small of higher order, with the corresponding consequences of three-dimensional theory, for some classes of edge conditions. The analysis also shows the nature of the differences between results of two- and three-dimensional theory, as a function of geometrical and elastic parameters, where this difference is of importance because of the effect of a St. Venant boundary layer.     

Another aspect of Saint-Venant's principle in elasticity

An energy decay estimate of the Saint-Venant type is obtained for an elastic cylinder whose curved surface is displacement free, and a plane end of which is subjected to tractions which are not necessarily self-equilibrated.

---

Résumé On obtient une appréciation du type St. Venant pour l'attenuation de l'énergie dans un cylindre élastique dont la surface courbée ne subit pas de déplacement et dont une extremité plane subit des tractions qui ne sont pas forcément en equilibre.

     

辛求解体系下功能梯度材料平面梁的完整解析解

采用辛弹性力学解法,求取弹性模量沿轴向指数变化,而Poisson比保持不变的功能梯度材料平面梁的完整解析解．通过求解被Saint-Venant原理覆盖的一般本征解,建立起完整的解析分析过程,进而给出平面梁位移和应力的精确分布规律．传统的弹性力学分析方法常常忽略被Saint-Venant原理覆盖的解,但这些衰减的本征解对材料的局部效应起着较大的影响作用,可能导致材料或结构的突然失效．采用辛求解方法,充分利用本征向量之间的辛共轭正交关系,得到了功能梯度材料梁的完整解析解．两个数值算例分别将功能梯度材料平面梁的位移和应力分布与相应均匀材料情形的结果进行比较,研究了材料非均匀性对位移和应力解的影响．     

Linearization method to stability analysis for nonlinear hyperbolic systems

It is shown that the linearization principle is true for a class of nonlinear hyperbolic systems with two independent variables, time and space. To keep clear exposition, our proof is based on the Saint Venant equation. More results can be proven by using the Lyapunov function candidate that we give here.     

Global controllability between steady supercritical flows in channel networks

We consider a tree‐like network of open channels with outflow at the root. Controls are exerted at the boundary nodes of the network except for the root. In each channel, the flow is modelled by the de St. Venant equations. The node conditions require the conservation of mass and the conservation of energy. We show that the states of the system can be controlled within the entire network in finite time from a stationary supercritical initial state to a given supercritical terminal state with the same orientation. During this transition, the states stay in the class of C1‐functions, so no shocks occur. Copyright 2004 John Wiley & Sons, Ltd.     

Modelling and numerical aspects in 2d river flow simulation

Flow simulation in rivers is used for the prediction of waterlevel and runoff quantities. The presently used simulation by the German Federal Institute of Hydrology is based on a network approach with coupled 1d models in which the river flow is described by the St. Venant‐equations. Work is underway to extend this by 2d submodel elements using the shallow water equations to allow simulations in greater detail. The wetting and drying of parts of the river bed at varying waterlevels force us to formulate the flow simulation as free boundary problem. The constraints of embedding the 2d model into the existing network approach suggest to use a fixed grid approach. This leads to the problem of solving the shallow water equations on the whole grid. However, the shallow water equations degenerate for dry beds and therefore do not allow a straight forward discretisation.     

Another approach to linearized elasticity and Korn's inequality

We describe and analyze an approach to the pure traction problem of three-dimensional linearized elasticity, whose novelty consists in considering the linearized strain tensor as the ‘primary’ unknown, instead of the displacement itself as is customary. This approach leads to a well-posed minimization problem, constrained by a weak form of the St Venant compatibility conditions. It also provides a new proof of Korn's inequality. To cite this article: P.G. Ciarlet, P. Ciarlet Jr., C. R. Acad. Sci. Paris, Ser. I 339 (2004).     

Stability of Viscous St. Venant Roll Waves: From Onset to Infinite Froude Number Limit

We study the spectral stability of roll wave solutions of the viscous St. Venant equations modeling inclined shallow water flow, both at onset in the small Froude number or “weakly unstable” limit \(F\rightarrow 2^+\) and for general values of the Froude number F, including the limit \(F\rightarrow +\infty \). In the former, \(F\rightarrow 2^+\), limit, the shallow water equations are formally approximated by a Korteweg-de Vries/Kuramoto–Sivashinsky (KdV–KS) equation that is a singular perturbation of the standard Korteweg-de Vries (KdV) equation modeling horizontal shallow water flow. Our main analytical result is to rigorously validate this formal limit, showing that stability as \(F\rightarrow 2^+\) is equivalent to stability of the corresponding KdV–KS waves in the KdV limit. Together with recent results obtained for KdV–KS by Johnson–Noble–Rodrigues–Zumbrun and Barker, this gives not only the first rigorous verification of stability for any single viscous St. Venant roll wave, but a complete classification of stability in the weakly unstable limit. In the remainder of the paper, we investigate numerically and analytically the evolution of the stability diagram as Froude number increases to infinity. Notably, we find transition at around \(F=2.3\) from weakly unstable to different, large-F behavior, with stability determined by simple power-law relations. The latter stability criteria are potentially useful in hydraulic engineering applications, for which typically \(2.5\le F\le 6.0\).     

Application of Richardson extrapolation to the numerical solution of partial differential equations

Richardson extrapolation is a methodology for improving the order of accuracy of numerical solutions that involve the use of a discretization size h. By combining the results from numerical solutions using a sequence of related discretization sizes, the leading order error terms can be methodically removed, resulting in higher order accurate results. Richardson extrapolation is commonly used within the numerical approximation of partial differential equations to improve certain predictive quantities such as the drag or lift of an airfoil, once these quantities are calculated on a sequence of meshes, but it is not widely used to determine the numerical solution of partial differential equations. Within this article, Richardson extrapolation is applied directly to the solution algorithm used within existing numerical solvers of partial differential equations to increase the order of accuracy of the numerical result without referring to the details of the methodology or its implementation within the numerical code. Only the order of accuracy of the existing solver and certain interpolations required to pass information between the mesh levels are needed to improve the order of accuracy and the overall solution accuracy. Using the proposed methodology, Richardson extrapolation is used to increase the order of accuracy of numerical solutions of the linear heat and wave equations and of the nonlinear St. Venant equations in one‐dimension. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009     

Justification de la théorie non linéaire de Kirchhoff–Love,comme application d'une nouvelle méthode d'inversion singulièreJustification of the nonlinear Kirchhoff–Love theory,as the application of a new singular inverse method

In the framework of nonlinear elasticity, we consider a three-dimensional plate made of a St Venant–Kirchhoff isotropic and homogeneous material of thickness 2ε and periodic in the two other directions. By a change of scales, the problem can be mapped on a fixed open set, and seen as a nonlinear singular perturbation problem. We introduce a new singular inverse method. Applying this method, we prove that for fixed and small enough exterior forces, the three-dimensional displacement converges to the solution of the nonlinear Kirchhoff–Love theory of plate as the thickness 2ε tends to zero. The limit plate model contains in particular that of von Kármán. We also give a quantitative estimate of the convergence. To cite this article: R. Monneau, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 615–620.     

Analytical and numerical Riemann solutions of the Saint Venant equations for forward- and backward-facing step flows

Analytical solutions of the Saint Venant equations for five typical Riemann problems over a forward- or backward-facing step are constructed. These analytical solutions are used as reference ones to estimate the accuracy of simulated discontinuous solutions based on the regularized shallow water equations.     

Radial deformation of a nonhomogeneous spherically isotropic elastic sphere with a concentric spherical inclusion

The elasticity of a spherically isotropic medium bounded by two concentric spherical surfaces subjected to normal pressures is discussed. The material of the structure is spherically isotropic and, in addition, is continuously inhomogeneous with mechanical properties varying exponentially as the square of the radius. An exact solution of the problem in terms of Whittaker functions is presented. The St. Venant’s solution in the case of homogeneous material and Lamé’s solution in the case of homogeneous isotropic material are derived from the general solution. The problem of a solid sphere of the same medium under the external pressure is also solved as a particular case of the above problem. Finally, the displacements and stresses of a composite sphere consisting of a solid spherical body made of homogeneous material and a nonhomogeneous concentric spherical shell covering the inclusion, both of them being spherically isotropic, are obtained when the sphere is under uniform compression.     

A Saint-Venant type principle for Dirichlet forms on discontinuous media

We consider certain families of Dirichlet forms of diffusion type that describe the variational behaviour of possibly highly nonhomogeneous and nonisotropic bodies and we prove a structural Harnack inequality and Saint Venant type energy decays for their local solution. Estimates for the Green functions are also considered.

---

Sunto Si considerano certe famiglie di forme di Dirichlet di tipo diffusione che descrivono il comportamento di corpi fortemente non omogenei e non isotropi e si provano per le relative soluzione locali una diseguaglianza di Harnack strutturale e stime tipo Saint Venant della decrescita dell'energia. Si studiano inoltre stime per la funzione di Green.

     

Neumann Problem in Domains with Outlets of Bounded Diameter

We study the Neumann problem for the Laplace equation in domains having quasicylindrical outlets. The aim is to collect and sort known results spread over the literature and to fill in the gaps of the theory which still exist. Namley, solutions with finite Dirichlet integral are found applying on the one hand the Helmholtz decomposition and on the other hand the Riesz representation theorem. We investigate generalizations for the non-Hilbert space setting and collect several types of Saint Venant estimates.