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Kovalev V.A.,Moscow City Government University of Management | Radaev Y.N.,Samara State University
Mechanics of Solids | Year: 2010

In the present paper, we consider basic relations of the mathematical theory of plasticity for the spatial state corresponding to the edge of the Coulomb-Tresca prism, which follow from the generalized associated flow law restricting the plastic flow freedom for the above states to the minimal possible extent. We found that the spatial relations of the theory of plasticity, formulated by A. Yu. Ishlinsky in 1946, can be derived from the above version of the theory of flow. We show that the A. Yu. Ishlinsky constitutive relations for states on the Coulomb-Tresca prism edge express the commutativity of the stress tensor and the tensor of plastic strain increments. We obtained one explicit form of the constitutive relation relating the stress tensor to the plastic strain increments for the stressed states corresponding to the Coulomb-Tresca prism edge. © 2010 Allerton Press, Inc.

Kovalev V.A.,Moscow City Government University of Management | Radaev Y.N.,Russian Academy of Sciences
Mechanics of Solids | Year: 2012

The divergence representation of a null Lagrangian that is regular in a star-shaped domain is used to obtain its general expression containing field gradients of order ≤ 1 in the case of spacetime of arbitrary dimension. It is shown that for a static three-component field in the three-dimensional space, a null Lagrangian can contain up to 15 independent elements in total. The general form of a null Lagrangian in the four-dimensional Minkowski spacetime is obtained (the number of physical field variables is assumed arbitrary). A complete theory of the null Lagrangian for the n-dimensional spacetime manifold (including the four-dimensional Minkowski spacetime as a special case) is given. Null Lagrangians are then used as a basis for solving an important variational problem of an integrating factor. This problem involves searching for factors that depend on the spacetime variables, field variables, and their gradients and, for a given system of partial differential equations, ensure the equality between the scalar product of a vector multiplier by the system vector and some divergence expression for arbitrary field variables and, hence, allow one to formulate a divergence conservation law on solutions to the system. © 2012 Allerton Press, Inc.

Kovalev V.A.,Moscow City Government University of Management | Radaev Y.N.,Russian Academy of Sciences
Mechanics of Solids | Year: 2011

In the framework of the classical field theory and using the theory of action variational symmetries, we consider the construction of canonical energy-momentum tensors for a coupled micropolar thermoelastic field taking account of the nonlocality of the Lagrangian density, which is typical of continuum micromechanics. We use the algorithms of group analysis to calculate the Noether currents and the energy-momentum tensors in three cases where the Lagrangian depends on the gradients of field variables of orders not exceeding 1, 2, and 3. In each of these cases, we present explicit formulas for the components of the canonical energy-momentum tensor. We construct the energy-momentum tensor for micropolar thermoelastic bodies in which the heat conduction process is characterized by a generalized heat equation of hyperbolic analytical type. In the equations of micropolar thermoelastic field, all possible restrictions on the microrotations are taken into account. © 2011 Allerton Press, Inc.

Kovalev V.A.,Moscow City Government University of Management | Radaev Y.N.,Russian Academy of Sciences
Mechanics of Solids | Year: 2014

The paper deals with issues related to the construction of solutions, 2 π-periodic in the angular variable, of the Mathieu differential equation for the circular elliptic cylinder harmonics, the associated characteristic values, and the azimuthal numbers needed to form the elementary elliptic cylinder wave functions. A superposition of the latter is one possible form for representing the analytic solution of the thermoelastic wave propagation problem in long waveguides with elliptic cross-section contour. The classical Sturm-Liouville problem for the Mathieu equation is reduced to a spectral problem for a linear self-adjoint operator in the Hilbert space of infinite square summable two-sided sequences. An approach is proposed that permits one to derive rather simple algorithms for computing the characteristic values of the angular Mathieu equation with real parameters and the corresponding eigenfunctions. Priority is given to the application of the most symmetric forms and equations that have not yet been used in the theory of the Mathieu equation. These algorithms amount to constructing a matrix diagonalizing an infinite symmetric pentadiagonal matrix. The problem of generalizing the notion of azimuthal number of a wave propagating in a cylindrical waveguide to the case of elliptic geometry is considered. Two-sided mutually refining estimates are constructed for the spectral values of the Mathieu differential operator with periodic and half-periodic (antiperiodic) boundary conditions. © 2014 Allerton Press, Inc.

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