On the inverse problem of finding the coefficient of heat transfer

We establish conditions for the existence and uniqueness of a solution to the problem of finding the coefficient of heat transfer in a boundary condition of third kind. We give an explicit formula for computing this coefficient. Translated fromMatermaticheskie Metody i Fiziko-Mekhanicheskie Polya, No. 37, 1994, pp. 45–50.     

Dissipative Boundary Conditions for Finite-Difference Problems in Elasticity Theory

Dissipative differential-difference boundary conditions for elasticity equations are derived and investigated. These conditions completely eliminate the longitudinal and transverse waves reflected from the boundary in case of normal incidence and substantially reduce the reflected waves in a wide range of other incidence angles. The dissipative boundary conditions reduce computer resource requirements for simulation of seismic wave propagation in unbounded regions. Grid analogues of the dissipative boundary conditions are constructed for a two-layer finite-difference scheme. Comparative results are reported for the solution of two-dimensional seismic problems using these boundary conditions for various incidence angles. __________ Translated from Prikladnaya Matematika i Informatika, No. 18, pp. 83–92, 2004.     

Stability of a family of weighted finite-difference schemes

Existence and uniqueness theorems are proved for a weighted finite-difference scheme approximating the heat equation with a nonlocal boundary condition containing a parameter. Bounds are derived that guarantee stability of the solution in the initial values in the mean-square grid norm. Translated from Prikladnaya Matematika i Informatika, No. 29, 2008, pp. 64–87.     

Nonlocal boundary-value problem for linear partial differential equations unsolved with respect to the higher time derivative

We study the well-posedness of the problem with general nonlocal boundary conditions in the time variable and conditions of periodicity in the space coordinates for partial differential equations unsolved with respect to the higher time derivative. We establish the conditions of existence and uniqueness of the solution of the considered problem. In the proof of existence of the solution, we use the method of divided differences. We also prove metric statements on the lower bounds of small denominators appearing in constructing the solution of the problem. __________ Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, No. 3, pp. 370–381, March, 2007.     

On the Well-Posedness of a Two-Point Boundary-Value Problem for a System with Pseudodifferential Operators

We investigate the problem of the well-posedness of a boundary-value problem for a system of pseudodifferential equations of arbitrary order with nonlocal conditions. The equation and boundary conditions contain pseudodifferential operators whose symbols are defined and continuous in a certain domain H ⊂ ℝ _σ ^m . A criterion for the existence and uniqueness of solutions and for the continuous dependence of the solution on the boundary function is established. __________ Published in Ukrains'kyi Matematychnyi Zhurnal, Vol. 57, No. 8, pp. 1131 – 1136, August, 2005.     

Artificial boundary conditions for two-dimensional equations of fluid dynamics. 1. Convective wave equation

The article models external flow problems on artificially bounded regions. In the linear approximation we examine the reflection of acoustic waves in a moving medium, incident at various angles on a fixed boundary. We consider the construction of various boundary conditions and estimate their reflecting properties for plane waves and waves from point sources. The plane wave approximation is justified theoretically. A method is proposed for estimating the integral reflection coefficient for waves with a whole range of incidence angles. __________ Translated from Prikladnaya Matematika i Informatika, No. 24, pp. 76–110, 2006.     

Nonlinear nonlocal problems for a parabolic equation in a two-dimensional domain

We establish the convergence of the Rothe method for a parabolic equation with nonlocal boundary conditions and obtain an a priori estimate for the constructed difference scheme in the grid norm on a ball. We prove that the suggested iterative process for the solution of the posed problem converges in the small. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 49, No. 2, pp. 244–254, February, 1997.     

Stationary nonlinear nonlocal problem of radiative–conductive heat transfer in a system of opaque bodies with properties depending on the radiation frequency

We consider a stationary nonlinear nonlocal boundary value problem governing radiative–conductive heat transfer in a system of opaque bodies with surfaces whose properties depend on the radiation frequency. We establish the existence and uniqueness of a solution and prove a comparison theorem. Results on the exponential summability and boundedness of the solution are also obtained. Bibliography: 32 titles.     

Stability in the right-hand side of nonlocal difference schemes

Prior bounds expressing stability in the right-hand side are constructed for difference schemes approximating the heat equation with nonlocal boundary conditions. The constraints on the grid increment guaranteeing stability in the right-hand side are identical with the previously established criteria for stability in initial values. __________ Translated from Prikladnaya Matematika i Informatika, No. 23, pp. 134–139, 2006.     

Construction of Solutions and L^1-error Estimates of Viscous Methods for Scalar Conservation Laws with Boundary

This paper is concerned with an initial boundary value problem for strictly convex conservation laws whose weak entropy solution is in the piecewise smooth solution class consisting of finitely many discontinuities. By the structure of the weak entropy solution of the corresponding initial value problem and the boundary entropy condition developed by Bardos-Leroux Nedelec, we give a construction method to the weak entropy solution of the initial boundary value problem. Compared with the initial value problem, the weak entropy solution of the initial boundary value problem includes the following new interaction type： an expansion wave collides with the boundary and the boundary reflects a new shock wave which is tangent to the boundary. According to the structure and some global estimates of the weak entropy solution, we derive the global L^1-error estimate for viscous methods to this initial boundary value problem by using the matching travelling wave solutions method. If the inviscid solution includes the interaction that an expansion wave collides with the boundary and the boundary reflects a new shock wave which is tangent to the boundary, or the inviscid solution includes some shock wave which is tangent to the boundary, then the error of the viscosity solution to the inviscid solution is bounded by O（ε^1/2） in L^1-norm; otherwise, as in the initial value problem, the L^1-error bound is O（ε｜ In ε｜）.     

A Mixed Problem for the Heat Equation with Advanced Time in Boundary Conditions

We study a one-dimensional mixed problem for the heat equation, with time advance in nonlocal and non-self-adjoint boundary conditions, describing a real physical process. Under minimal conditions on the initial data, we prove its unique solvability and obtain an explicit representation for the solution.     

Approximate Description of the Dynamics of Thin Isotropic Elastic Coatings and Interlayers by Using Asymptotics of High Order of Accuracy

Asymptotically accurate low-frequency models for isotropic elastic coatings and interlayers are developed. The main constraint is the requirement on contact conditions for the layer and the base that at least one of the boundary conditions must include the displacement component in an explicit form. The displacement and stress fields in the three-dimensional elastic system are sought in the form of asymptotic expansion into power series of a small parameter — the ratio between the half-thickness of the layer and the minimum length of the wave in the longitudinal direction. The action of the layer is approximated by impedance boundary conditions, which are transferred to the contact surface with the basic, more thick body. These conditions are obtained with an asymptotic error up to and including the sixth order of magnitude. A numerical testing, which is carried out with the example of partial waves, shows a satisfactory accuracy, comparable with that of high-order theories of plates. The results obtained can be utilized in fast algorithms for calculating spectra of natural waves in half-spaces, thick laminated plates, and shallow shells with coatings and interlayers. The physical limit of applicability of the theory developed is the frequency of the first quasi-resonance in the corresponding deformable system. The number of alternating interlayers is unlimited. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 6, pp. 783–794, November–December, 2005.     

Excitation of elastic waves at the boundary of a prismatic orthotropic body with thin inextensible face coatings

In three-dimensional formulation we construct a numerical-analytic solution of the problem of describing the wave field in a semi-infinite orthotropic prismatic body at whose end dynamic forces are applied. We apply the method of series in basic homogeneous normal waves. We study numerically the dynamic boundary effects near the excitation surface. Five figures. Bibliography: 4 titles. Translated fromTeoreticheskaya i Prikladnaya Mekhanika, No. 28, 1998, pp. 131–137.     

Dispersion of normal waves in a linearly orthotropic circular cylinder with a clamped lateral surface

We propose a method of obtaining the dispersion equation for normal waves in an orthotropic cylinder from the boundary conditions on the rigidly clamped boundary using a system of exponential particular solutions of the three-dimensional equations of its stationary wave motions. We compute the real and imaginary branches of the dispersion spectrum for a waveguide made of monocrystalline strontium sulfate. On figure. Bibliography: 7 titles. Translated fromTeoreticheskaya i Prikladnaya Mekhanika, No. 26, 1996, pp. 96–99.     

The Sturm-Liouville problem with a nonlocal boundary condition

In this paper, we consider the Sturm-Liouville problem with one classical and another nonlocal boundary condition. We investigate general properties of the characteristic function and spectrum for such a problem in the complex case. In the second part, we investigate the case of real eigenvalues, analyze the dependence of the spectrum on parameters of the boundary condition, and describe the qualitative behavior of all eigenvalues subject to of the nonlocal boundary condition. Dedicated to N. S. Bakhvalov (1934–2005) Published in Lietuvos Matematikos Rinkinys, Vol. 47, No. 3, pp. 410–428, July–September, 2007.     

Nonlocal and Multipoint Boundary Value Problems for Linear Evolution Equations

We derive the solution representation for a large class of nonlocal boundary value problems for linear evolution partial differential equations (PDE) with constant coefficients in one space variable. The prototypical example of such PDE is the heat equation, for which problems of this form model physical phenomena in chemistry and for which we formulate and prove a full result. We also consider the third‐order case, which is much less studied and has been shown by the authors to have very different structural properties in general. The nonlocal conditions we consider can be reformulated as multipoint conditions , and then an explicit representation for the solution of the problem is obtained by an application of the Fokas transform method. The analysis is carried out under the assumption that the problem being solved is well posed, i.e., it admits a unique solution. For the second‐order case, we also give criteria that guarantee well posedness.     

Green’s functions for stationary problems with nonlocal boundary conditions

In this paper, we investigate Green’s functions for various stationary problems with nonlocal boundary conditions. We express the Green’s function per Green’s function for a problem with classical boundary conditions. This property is illustrated by various examples. Properties of Green’s functions with nonlocal boundary conditions are compared with those for classical problems. The research was partially supported by the Lithuanian State Science and Studies Foundation, grant No. T-73/09.     

Exact boundary controllability for 1‐D quasilinear wave equations with dynamical boundary conditions

By equivalently replacing the dynamical boundary condition by a kind of nonlocal boundary conditions, and noting a hidden regularity of solution on the boundary with a dynamical boundary condition, a constructive method with modular structure is used to get the local exact boundary controllability for 1‐D quasilinear wave equations with dynamical boundary conditions. Copyright © 2016 John Wiley & Sons, Ltd.     

A multiwave approximate Riemann solver for ideal MHD based on relaxation II: numerical implementation with 3 and 5 waves

In the first part of this work Bouchut et al. (J Comput Phys 108:7–41, 2007) we introduced an approximate Riemann solver for one-dimensional ideal MHD derived from a relaxation system. We gave sufficient conditions for the solver to satisfy discrete entropy inequalities, and to preserve positivity of density and internal energy. In this paper we consider the practical implementation, and derive explicit wave speed estimates satisfying the stability conditions of Bouchut et al. (J Comput Phys 108:7–41, 2007). We present a 3-wave solver that well resolves fast waves and material contacts, and a 5-wave solver that accurately resolves the cases when two eigenvalues coincide. A full 7-wave solver, which is highly accurate on all types of waves, will be described in a follow-up paper. We test the solvers on one-dimensional shock tube data and smooth shear waves.     

Representation of green’s function for the heat equation on a compact lie group

We obtain an explicit formula which presents the solution of the heat equation on a compact Lie group as the limit of finite-to-one convolutions of Green’s function for the heat equation in Euclidean space. Translated fromMatematicheskie Zametki, Vol. 67, No. 3, pp. 397–413, March, 2000.