Generation of waves by a moving plate in stratified shallow water

The generation of waves inside an ideal two-layer stratified shallow water by the uniform motion of a vertical plate partially immersed in the fluid mass is studied in two dimensions. The fluid is assumed to occupy an infinite channel of constant depth. Two distinctive cases are studied according to whether the submerged part of the moving plate is smaller or greater than the upper layer's depth. In the first case, the lower fluid layer is not influenced by the motion of the plate up to the second order of approximation and local perturbations, only, are created in the upper layer. For the second case, progressive waves of the first order are shown in both layers besides local perturbations of the second order in the lower layer only. Passing to the limit of homogeneous fluids, local perturbations only remain. This passage to the limit shows that the stratification of the fluid mass is significant for the generation progressive waves. The systems of stream lines are drawn for stratified and homogeneous fluids.     

Solution of the stationary problem of heat conduction of laminated anisotropic inhomogeneous plates by the method of initial functions

The problem of stationary heat conduction of laminated plates of constant and variable thickness is formulated in the three-dimensional statement. We reduce the three-dimensional problem to a twodimensional one by the method of initial functions. For plates with layers of variable thickness, a system of resolving equations with variable coefficients is obtained. The obtained two-dimensional boundary-value problems are analyzed. For plates with homogeneous layers of constant thickness, we construct a solution in an analytic form. It is shown that this solution coincides with a solution obtained by the method of separation of variables.     

The property of orthogonality and energy transfer by three-dimensional eigenwaves in transversely isotropic laminated plates with and without contact with a liquid

The properties of eigenwaves in laminated plates with anisotropy in a transforse directon properties are studied. The most general form of the solutions, dispersion relations, power flows and generalized orthogonality relations are analysed. The similarity and difference in the properties of the waves as compared with isotropic media and ideal fluids, as well as the extension to the case of layered spaces and half-spaces, is investigated. A method of determining the coefficients for the eigenwaves radiated in the plate is proposed in the case of a problem with dynamical sources of finite size. A method of summing the series over eigenwaves is suggested.     

Effects of functionally graded interlayers on dispersion relations of shear horizontal waves in layered piezoelectric/piezomagnetic cylinders

The effects of functionally graded interlayers on dispersion relations of shear horizontal waves in layered piezoelectric/piezomagnetic cylinders are studied. First, the basic physical quantities of elastic waves in piezoelectric cylinder are derived by assuming that the SH waves propagate along the circumferential direction steadily. Then the transfer matrices of the functional graded interlayer and outer piezomagnetic cylinder are obtained by solving the state transfer equations with spatial-varying coefficients. Furthermore, making use of the electro-magnetic surface conditions of the outer cylinder, the dispersion relations for the shear horizontal waves in layered piezoelectric/piezomagnetic cylinders are obtained and the numerical results are shown graphically. Seven kinds of functionally graded interlayers and four kinds of electro-magnetic surface conditions are considered. It is found that the functionally graded interlayers have evident influences on the dispersion relations of shear horizontal waves in layered piezoelectric/piezomagnetic cylinders. The high order modes are more sensitive to the gradient interlayers while the low order modes are more sensitive to the electro-magnetic surface conditions.     

Buckling forms of homogeneous and sandwich plates in pure shear in tangential directions

The mathematical problem of the plane shear buckling form (BF) of sandwich plates and plates homogeneous across the thickness in pure shear is considered. The solution to this problem is compared with the solution to the problem of a flexural BF which is realized in these plates with the formation of oblique waves. It is established that, in the case of plates homogeneous across the thickness, the critical loads corresponding to the plane shear BF are maximum for isotropic ones. In real one-layer structural elements manufactured both of isotropic homogeneous and orthotropic composite materials, these critical loads cannot be reached since they exceed considerably the critical loads for the flexural BFs with oblique waves. The critical loads corresponding to the two BFs are comparable only for relatively thick plates. However, the plane shear BF can be realized in sandwich plates earlier than the flexural one even if the plates are thin. Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 2, pp. 215–228, 2000.     

Homogeneous and strictly homogeneous criteria for partial structures

The Galois closure on the set of relations invariant to all finite partial automorphisms (automorphisms) of a countable partial structure is established via quantifier-free infinite predicate languages (infinite languages with finite string of quantifiers respectively). Based on it the homogeneous and strictly homogeneous criteria for a countable partial structure as well as an ultrahomogeneous criterion for a countable relational structure are found. Next it is shown that infinite languages with a finite string of quantifiers cannot determine the corresponding Galois closure for relations invariant to all automorphisms of an uncountable partial structure.     

Surface acoustic waves in the testing of layered media. The waves’ sensitivity to variations in the properties of the individual layers

Research on the use of surface acoustic waves for the nondestructive testing of layered media is reviewed. A model to describe horizontally polarized surface acoustic waves in layered anisotropic (monoclinic) media is constructed. A modified transfer-matrix method is developed to obtain a solution. Non-canonical type waves with horizontal transverse polarization are investigated. Dispersion curves are constructed for a multilayer composite in contact with an anisotropic half-space. It is shown that the variation of the physical characteristics and the geometry of any of the internal layers leads to a variation in the dispersion curves. This opens up the possibility of using dispersion analysis for the nondestructive testing of the properties of the individual layers.     

Dispersion Equations for Rayleigh Waves in a Piezoelectric Periodically Layered Structure

Dispersion equations are proposed for acoustoelectric Rayleigh waves in a periodically layered piezoelectric half space with various types of boundary conditions. The properties of the medium are specified by the determining relations for the 6mm crystallographic class. These equations are obtained using the mathematical formalism of periodic hamiltonian systems. This approach makes it possible to include the anisotropy and the piezoelectric interaction of the mechanical and electric fields and is valid for stratified media with arbitrary variations in the properties along the periodicity axis. Numerical results are presented for alternating layers of CdS and ZnO. The influence of the piezoelectric effect and type of boundary conditions on the dispersion spectra of surface waves is examined.     

Model of a layered plate considering nonideal contact between layers

We propose a mathematical model for doing calculations for layered plates, allowing for both rigid and sliding contact in the presence of frictional forces between the sliding layers. The model takes into account the distribution of tangential and normal displacements across the thickness of the sliding layered stack, and also the distribution of transverse normal stresses. The strain tensor is obtained using the Cauchy relations; the stress tensor is obtained based on Hooke's law. Tne Lagrange variational principle allows us to obtain the resolvent system of differential equations and the corresponding boundary conditions. The spatial model for deformation of a layered plate has a number of special features compared with familiar models. The system of differential equations has operators no higher than second order. It is described relative to displacements on the faces of the stack. This is convenient in solving problems involving sliding of layers with and without friction.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 5, pp. 671–676, September–October 1995.     

Effective high-order approximations of layered coatings and linings of anisotropic elastic,viscoelastic and nematic materials

Beginning at low frequencies, asymptotically exact models of anisotropic coatings and linings with a small ratio of the half-thickness to the longitudinal deformation scale are constructed. The requirement on the conditions of contact with the substrate, where at least one of the boundary conditions must contain a displacement component of the strain in explicit form is “non-classical” here. The action of the coating/lining on a thicker body is approximated by impedance boundary conditions at the interface. The error of the model is reduced to the third order for layered packets and to the sixth order for a single layer. The physical limit of the applicability is the frequency of the first quasi-resonance in the corresponding deformed system. A comparison with the propagator matrix and numerical testing for partial waves shows satisfactory accuracy, comparable with the accuracy of the theory of classical plates of similar order. The results can be used in contact problems and for rapid algorithms for calculating the spectrum of the eigenwaves in half-spaces and thick layered plates with any number of coatings and linings. An extension to the case of viscoelastic materials and nematic elastomers is given.     

Asymptotic Behavior of the Eigenvalues of the Schrodinger Operator with Transversal Potential in a Weakly Curved Infinite Cylinder

In this paper, we derive sufficient conditions for the existence of an eigenvalue for the Laplace and the Schrodinger operators with transversal potential for homogeneous Dirichlet boundary conditions in a tube, i.e., in a curved and twisted infinite cylinder. For tubes with small curvature and small internal torsion, we derive an asymptotic formula for the eigenvalue of the problem. We show that, under certain relations between the curvature and the internal torsion of the tube, the above operators possess no discrete spectrum.__________Translated from Matematicheskie Zametki, vol. 77, no. 5, 2005, pp. 656–664.Original Russian Text Copyright ©2005 by V. V. Grushin.     

Extensional wave motion in homogenous isotropic thermoelastic plate by using asymptotic method

The present investigation is concerned with the study of extensional wave motion in an infinite homogenous isotropic, thermoelastic plate by using asymptotic method. The governing equation for the extensional wave motions have been derived from the system of three-dimensional dynamical equations of linear coupled theory of thermoelasticity. All coefficients of the differential operator are expressed as explicit functions of the material parameters. The velocity dispersion equation for the extensional wave motion is deduced from the three-dimensional analog of Rayleigh–Lamb frequency equation for thermoelastic plate waves. The approximations for long and short waves and expression for group velocity are also derived. The thermoelastic Rayleigh–Lamb frequency equations for the considered plate are expanded in power series in order to obtain polynomial frequency and velocity dispersion relations whose equivalence is established to that of asymptotic method. The dispersion curves for phase velocity and attenuation coefficient are shown graphically for extensional wave motion of the plates.     

INVERSE SCATTERING BY AN INHOMOGENEOUS PENETRABLE OBSTACLE IN A PIECEWISE HOMOGENEOUS MEDIUM

This paper is concerned with the inverse problem of scattering of time-harmonic acoustic waves by an inhomogeneous penetrable obstacle in a piecewise homogeneous medium. The well-posedness of the direct problem is first established by using the integral equation method. We then proceed to establish two tools that play important roles for the inverse problem: one is a mixed reciprocity relation and the other is a priori estimates of the solution on some part of the interfaces between the layered media. For the inverse problem, we prove in this paper that both the penetrable interfaces and the possible inside inhomogeneity can be uniquely determined from a knowledge of the far field pattern for incident plane waves.     

Inverse scattering by an inhomogeneous penetrable obstacle in a piecewise homogeneous medium

This paper is concerned with the inverse problem of scattering of time-harmonic acoustic waves by an inhomogeneous penetrable obstacle in a piecewise homogeneous medium. The well-posedness of the direct problem is first established by using the integral equation method. We then proceed to establish two tools that play important roles for the inverse problem: one is a mixed reciprocity relation and the other is a priori estimates of the solution on some part of the interfaces between the layered media. For the inverse problem, we prove in this paper that both the penetrable interfaces and the possible inside inhomogeneity can be uniquely determined from a knowledge of the far field pattern for incident plane waves.     

On Effective Models of Porous Stratified Media with a Sliding Contact Between Layers

In order to study wave propagation in porous layered media with a sliding contact between the elastic phases on the interfaces, effective models of these media are investigated. For these models, the front sets of four waves excited by point sources are established and formulas for the wave velocities along the axes are derived. The methods of constructing the front sets applied in this paper allow one to point out special features of these front sets such as loops and juts. The particular case where all of the layers are identical and a sliding contact occurs between layers is also considered. Bibliography: 8 titles.     

Stress State of Multilayer Thin-Walled Elements with Interfacial Defects of Structure

Based on the discrete-structural theory of thin plates and shells, a calculation model for thin-walled elements consisting of a number of rigid anisotropic layers is put forward. It is assumed that the transverse shear and compression stresses are equal on the interfaces. Elastic slippage is allowed over the interfaces between adjacent layers. The solution to the problem is obtained in a geometrically nonlinear statement with account of the influence of transverse shear and compression strains. The stress-strain state of circular two-layer transversely isotropic plates, both without defects and with a local area of adhesion failure at their center, is investigated numerically and experimentally. It is found that the kinematic and static contact conditions on the interfaces of layered thin-walled structural members greatly affect the magnitude of stresses and strains. With the use of three variants of calculation models, in the cases of perfect and weakened contact conditions between layers, the calculation results for circular plates are compared. It is revealed that the variant suggested in this paper adequately reflects the behavior of layered thin-walled structural elements under large deformations. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 6, pp. 761–772, November–December, 2005.     

Buckling stability of multilayer plates and shells with interfacial structural defects under axial compression

Based on the discrete-structural theory of thin plates and shells, a variant of the equations of buckling stability, containing a parameter of critical loading, is put forward for the thin-walled elements of a layered structure with a weakened interfacial contact. It is assumed that the transverse shear and compression stresses are equal on the interfaces. Elastic slippage is allowed over the interfaces between adjacent layers. The stability equations include the components of geometrically nonlinear moment subcritical buckling conditions for the compressed thin-walled elements. The buckling of two-layer transversely isotropic plates and cylinders under axial compression is investigated numerically and experimentally. It is found that variations in the kinematic and static contact conditions on the interfaces of layered thin-walled structural members greatly affect the magnitude of critical stresses. In solving test problems, a comparative analysis of the results of stability calculations for anisotropic plates and shells is performed with account of both perfect and weakened contacts between adjacent layers. It is found that the model variant suggested adequately reflects the behavior of layered thin-walled structural elements in calculating their buckling stability. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 4, pp. 513–530, July–August, 2007.     

Interaction of Plane Stress Waves in a Three-Layer Structure. 1. Degenerate Solutions in Terms of Characteristics for a Homogeneous Structure

Exact expressions in terms of characteristics for calculating the normal-stress waves propagating across the layers of different materials are deduced. A one-dimensional boundary-value problem is considered for a three-layer structure of sandwich type. The faces of the layered structure are free from loads or one of them is rigidly fixed (variant 1), or one face is rigidly fixed and the other is subjected to an impact of a mass M with a speedV₀ (variant 2). For the boundary conditions of variant 1, relationships are obtained which allow one to reduce the analytical continuation of a solution in time to a periodic procedure if solely the initial disturbances of the strain field in the layers are given. It is shown that, in this case, the Cauchy problem with the initial strain field is reduced to graphoanalytically constructing the superposition patterns of the forward and backward waves. The fundamental features of the construction are demonstrated for a uniform bar with a piecewise constant distribution of strains along its length. To solve the problem of impact loading in variant 2, analytical results for a uniform plate are used, which allows us to account for the direction of mass forces in collision. In the latter case, the possibility of mass recoil is revealed in the first and second time cycles. The analytical constructions presented are focused on an exact calculation of stresses upon response of a layered plate to initial disturbances within its layers, as well as to an external dynamic action. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 5, pp. 585–606, September–October, 2005.     

Propagation of axisymmetric longitudinal waves in a finitely prestrained circular cylinder imbedded in a finitely prestrained infinite elastic body

Within the framework of a piecewise homogeneous body model and with the use of the three-dimensional linearized theory of elastic waves in initially stressed bodies (TLTEWISB), the propagation of axisymmetric longitudinal waves in a finitely prestrained circular cylinder (fiber) imbedded in a finitely prestrained infinite elastic body (matrix) is investigated. It is assumed that the fiber and matrix materials have the same density and are in compressible. The stress-strain relations for them are given through the Treloar potential. Numerical results regarding the influence of initial strains in the fiber and matrix on wave dispersion are presented and discussed. These results are obtained for the following cases: the fiber and matrix are both without initial strains; only the fiber is prestretched; only the matrix is prestretched; the fiber and matrix are both prestretched simultaneously; the fiber and matrix are both precompressed simultaneously. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 5, pp. 665–684, September–October, 2008.     

Concentration of the point spectrum on the continuous one in problems of linear water-wave theory

For the linear theory of water waves, we find out families of submerged or surface-piercing bodies in an infinite three-dimensional canal, which depend on a small parameter ε > 0 and have the following property: for any positive d and natural J, there exists ε(d, J) > 0 such that, for ε ∈ (0, ε(d, J)], the segment [0, d] of the continuous spectrum of the problem contains at least J eigenvalues. These eigenvalues are associated with trapped modes, i.e., solutions of the homogeneous problem, which decay exponentially at infinity and possess finite energy. Bibliography: 27 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 348, 2007, pp. 98–126.