D. Kapanadze

DIRICHLET-NEUMANN-IMPEDANCE BOUNDARY VALUE PROBLEMS ARISING IN RECTANGULAR WEDGE DIFFRACTION PROBLEMS

Boundary value problems originated by the diffraction of an electromagnetic (or acoustic) wave by a rectangular wedge with faces of possible different kinds are analyzed in a Sobolev space framework. The boundary value problems satisfy the Helmholtz equation in the interior (Lipschitz) wedge domain, and are also subject to different combinations of boundary conditions on the faces of the wedge. Namely, the following types of boundary conditions will be under study: Dirichlet-Dirichlet, Neumann-Neumann, Neumann-Dirichlet, Impedance-Dirichlet, and Impedance-Neumann. Potential theory (combined with an appropriate use of extension operators) leads to the reduction of the boundary value problems to integral equations of Fredholm type. Thus, the consideration of single and double layer potentials together with certain reflection operators originate pseudo-differential operators which allow the proof of existence and uniqueness results for the boundary value problems initially posed. Furthermore, explicit solutions are given for all the problems under consideration, and regularity results are obtained for these solutions.

Improved algorithm for analytical solution of the heat conduction problem in doubly periodic 2D composite materials

We consider a boundary value problem (BVP) in unbounded 2D doubly periodic composite with circular inclusions having arbitrary constant conductivities. By introducing complex potentials, the BVP for the Laplace equation is transformed to a special -linear BVP for doubly periodic analytic functions. This problem is solved with use of the method of functional equations. The -linear BVP is transformed to a system of functional equations. A new improved algorithm for solution of the system is proposed. It allows one not only to compute the average property but to reconstruct the solution components (temperature and flux) at an arbitrary point of the composite. Several computational examples are discussed in details demonstrating high efficiency of the method. Indirect estimate of the algorithm accuracy has been also provided.

Wave diffraction by a 45 degree wedge sector with Dirichlet and Neumann boundary conditions

The problems of wave diffraction by a plane angular screen occupying an infinite 45 degree wedge sector with Dirichlet and/or Neumann boundary conditions are studied in Bessel potential spaces. Existence and uniqueness results are proved in such a framework. The solutions are provided for the spaces in consideration, and higher regularity of solutions are also obtained in a scale of Bessel potential spaces.

Diffraction by a Strip and by a Half-plane with Variable Face Impedances

A study is presented for boundary value problems arising from the wave diffraction theory and involving variable impedance conditions. Two different geometrical situations are considered: the diffraction by a strip and by a half-plane. In the first case, both situations of real and complex wave numbers are analyzed, and in the second case only the complex wave number case is considered. At the end, conditions are founded for the well-posedness of the problems in Bessel potential space settings. These conditions depend on the wave numbers and the impedance properties.

EXTENDED NORMAL VECTOR FIELD AND THE WEINGARTEN MAP ON HYPERSURFACES

Abstract We present a different method for studying the Weingarten map for a hypersurface in the Euclidean space . Applying the Cartesian coordinates of the ambient space and tangential Günters derivatives we obtain a simple matrix representation formula for the Weingarten map for implicit hypersurfaces, which can be applied, for example, to calculate the mean and Gaußs curvatures without passing to intrinsic coordinates.

Screen type mixed boundary value problems for anisotropic pseudo-Maxwell’s equations

Abstract We investigate screen type mixed boundary value problems for anisotropic pseudo-Maxwell’s equations. We show that the problems with tangent traces are well posed in tangent Sobolev spaces. The unique solvability results are proven based on the potential method and coercivity result of Costabel on the bilinear form associated with pseudo-Maxwell’s equations.

Potential Methods for Anisotropic Pseudo-Maxwell Equations in Screen Type Problems

We investigate the Neumann type boundary value problems for anisotropic pseudo-Maxwell equations in screen type problems. It is shown that the problem is well posed in tangent Sobolev spaces and unique solvability and regularity results are obtained via potential methods and the coercivity result of Costabel on the bilinear form associated to pseudo-Maxwell equations.

Electromagnetic scattering by cylindrical orthotropic waveguide irises

Abstract The paper is devoted to the mathematical analysis of scattered time-harmonic electromagnetic waves by an infinitely long cylindrical orthotropic waveguide iris. This is modeled by an orthotropic Maxwell system in a cylindrical waveguide iris for plane waves propagating in the x 3-direction, imbedded in an isotropic infinite medium. The problem is equivalently reduced to a 2-dimensional boundary-contact problem with the operator div M grad+k 2 inside the domain and the (Helmholtz) operator Δ+k 2 = div grad+k 2 outside the domain. Here M is a 2 × 2 positive definite, symmetric matrix with constant, real valued entries. The unique solvability of the appropriate boundary value problems is proved and the regularity of solutions is established in Bessel potential spaces.

Diffraction by a union of strips with impedance conditions in Besov and Bessel potential spaces

Abstract We consider an impedance boundary‐value problem for the Helmholtz equation which models a wave diffraction problem with imperfect conductivity on a union of strips. Pseudo‐differential operators acting between Bessel potential spaces and Besov spaces are used to deal with this wave diffraction problem. In particular, these operators allow a reformulation of the problem into a system of integral equations. The main result presents impedance parameters which ensure the well‐posedness of the problem in scales of Bessel potential spaces and Besov spaces.