Numerical solution of the three-dimensional stationary diffraction problem for elastic waves

Three-dimensional problems concerning the propagation of stationary elastic oscillations in media with three-dimensional inclusions are solved numerically. By applying potential theory methods, the original problem is stated as a system of two singular vector integral equations for the unknown internal and external densities of auxiliary sources of waves. An approximate solution of the original problem is obtained by approximating the integral equations by a system of linear algebraic equations, which is then solved numerically. The underlying algorithm has the property of self-regularization, due to which a numerical solution is found without using cumbersome regularizing algorithms. Results of test computations and numerical experiments are presented that characterize the capabilities of this approach as applied to the diffraction of elastic waves in three-dimensional settings.     

A hollow ellipsoidal needle in an orthotropic elastic medium

The problem of the stress distribution on the surface of a hollow ellipsoidal needle in an orthotropic elastic medium and a homogeneous external field is solved. Explicit expressions are obtained for the stresses on the needle surface in terms of the elastic constants of the medium and parameters of the ellipsoid in a local system of coordinates connected to the normal to the surface at each point of the needle. The general solution of the problem of the stress concentration on an ellipsoidal inhomogeneity /1/ and the passage to the limit cases of an ellipsoidal cavity based on the presence of small parameters /2/ is used.     

Exact solution of thermal stress problem of an inhomogeneous hygrothermal piezoelectric hollow cylinder

The closed-form exact solution for the hygrothermal response of inhomogeneous piezoelectric hollow cylinders is obtained. The interaction of electric potentials, electric displacement and elastic deformations is presented. The present cylinder is subjected to both a mechanical load and an electric potential. The material properties coefficients of the present cylinder are assumed to be changed in the radial direction by different distribution forms. The field quantities like displacement, stresses and electric potentials in the inhomogeneous piezoelectric cylinders are determined. The significant of influences of material inhomogeneity, initial temperature, final moisture, and the load and electric ratios in the field quantities are investigated. The concluding remarks and suitable discussions are made.     

Dispersion of elastic waves in the contact-impact problem of a long cylinder

Numerical dispersion of two-dimensional finite elements was studied. The outcome of the dispersion study was verified by the numerical and analytical solutions to the longitudinal impact of two long cylindrical bars. In accordance with the results of the dispersion analysis it was demonstrated that the quadratic elements showed better accuracy than the linear ones.     

On the longitudinal wave propagation in a viscoelastic cylinder

Résumé L'auteur étudie le calcul des déplacements d'un matériau visco-élastique linéaire dans un cylindre d'étendue finie qui sont produits par des oscillations longitudinales. Il montre qu'avec une approximation pour le cas des basses fréquences, on arrive au même résultat que celui obtenu de façon rigoureuse par un autre auteur. De plus, il montre que cette méthode peut être utilisée dans la region de hautes fréquences.     

Numerical simulations of flows in an elastic cylinder with two chambers

We present a mathematical model of valveless pumping in a tube with two elastic chambers, which are motivated by the Liebau's two-tank model. The tube consists of partially soft and partially (almost) rigid. We employ a two-dimensional model using the immersed boundary method. In this new model, we have showed the important features of valveless pumping as the previous experiments and mathematical models have been discovered. For instance, we have observed that the direction and the amount of a net flow are sensitively dependent on the pumping frequency. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Homogeneous solutions in the equilibrium problem of an elastic cylinder of finite length

The problem of the equilibrium of a finite elastic cylinder, under the action of axisymmetric normal and tangential loads on its surface, is considered. Within the framework of the method of homogeneous solutions, one establishes the connection between the representations of the displacement vector in the cylinder in the form of series in layer and cylindrical homogeneous solutions. The expansion coefficients in both representations are expressed in terms of the solution of an infinite regular system of linear algebraic equations.Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 20, pp. 3–9, 1989.     

Numerical solution of an equilibrium problem for an elastic body with a thin delaminated rigid inclusion

Under consideration is a 2D-problem of elasticity theory for a body with a thin rigid inclusion. It is assumed that there is a delamination crack between the rigid inclusion and the elastic matrix. At the crack faces, the boundary conditions are set in the form of inequalities providing mutual nonpenetration of the crack faces. Some numerical method is proposed for solving the problem, based on domain decomposition and the Uzawa algorithm for solving variational inequalities.We give an example of numerical calculation by the finite element method.     

A numerical-analytic method of studying the dispersion of elastic waves in a fixed orthotropic cylinder with a simply connected curvilinear section

We give a method of constructing the dispersion equations for waveguides made of recitilinearly orthotropic materials and having a section that is either elliptic or approximately that of a regular 2n-gon (n>-2) with rounded corners. The equations of motion for the waveguide can be integrated in series of basic particular solutions of exponential type. The dispersion functions are obtained in the form of reduced infinite determinants from homogeneous functional boundary conditions on the lateral surface of the waveguide after these conditions have been algebraized using orthogonal series expansions. Translated fromTeoreticheskaya i Prikladnaya Mekhanika, No. 25, 1995, pp. 97–102.     

On the propagation of elastic waves in two-phase media

At the present time a number of papers has been already devoted to the dynamics of two-phase media. One may mention the papers by Frenkel' [1], Rakhmatulin [2], Biot [3,4], Zwikker and Kosten [5], and others. However, the basic problem of the setting up of the equations of motion in two-phase media still cannot be considered solved and requires additional study and experimental verification.

This paper is concerned with the study of the simplest case of motion, which is the propagation of elastic waves in a homogeneous isotropic medium consisting of a solid and a fluid phase. The problems of the reflection of plane waves and surface waves at the free boundary of the half-space are solved. It is shown that the stress-strain relations established by Frenkel' are equivalent to the analogous relations proposed by Biot and that the equations of motion of the latter are more general.     

Numerical solution of the problem of the stress-strain state in hollow cylinders using spline approximations

The three-dimensional theory of elasticity is used for a study of the stress-strain state in a hollow cylinder with varying stiffness. The corresponding problem is solved by a method that is partly analytical and partly numerical in nature: Spline approximations and collocation are used to reduce the partial differential equations of elasticity to a boundary-value problem for a system of ordinary differential equations of higher order for the radial coordinate, which is then solved using the method of stable discrete orthogonalization. Results for an inhomogeneous cylinder for various types of stiffness are presented.     

Calculation of thermal stresses in an orthotropic cylinder

The present article describes the determination of thermal stresses in an orthotropic cylinder with an axially symmetric temperature field taking into account the change in the elasticity constants over the cylinder radius. A closed solution is given for constant elasticity coefficients.P. I. Baranov Central Institute of Aircraft-Engine Building, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 310–314, March–April, 1972.     

The solution of the problem of the caustic in an elastic medium

The problem of the caustic in an elastic medium is solved by the method of local expansions.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 42, pp. 255–268, 1974.     

The Reissner-Sagoci type problem for a non-homogeneous elastic cylinder embedded in an elastic non-homogeneous half-space

The problem considered is that of the torsion of a non-homogeneouselastic cylinder, which is embedded in a non-homogeneous elastichalf-space (matrix) of different rigidity modulus. A rigid discis bonded to the flat surface of the cylinder and torque isapplied to the cylinder through a rigid disc. It is assumedthat there is perfect bonding at the common cylindrical surface.Using integral transformation techniques the solution of theproblem is reduced to dual integral equations. Later on thesolution of the dual integral equations is transformed intothe solution of a Fredholm integral equation of the second kind.Solving the Fredholm integral equation numerically the numericalresults for torque and shear stress inside the cylinder areobtained and displayed graphically to demonstrate the effectof non-homogeneity of the elastic material on the torque andshear stress.     

The propagation of elastic waves in a piezoelectric

Formulas of the ray method are developed in the case of the propagation of high-frequency waves in a piezoelectric. It follows from the equations of the paper that in first approximation the energy of the wave field propagates along rays.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 42, pp. 155–161, 1974.     

Numerical solution of the elastic body-plate problem by nonoverlapping domain decomposition type techniques

The purpose of this paper is to provide two numerical methods for solving the elastic body-plate problem by nonoverlapping domain decomposition type techniques, based on the discretization method by Wang. The first one is similar to an older method, but here the corresponding Schur complement matrix is preconditioned by a specific preconditioner associated with the plate problem. The second one is a ``displacement-force' type Schwarz alternating method. At each iteration step of the two methods, either a pure body or a pure plate problem needs to be solved. It is shown that both methods have a convergence rate independent of the size of the finite element mesh.