Vol 39, No 8 (2018)

Equations of spatial hydrodynamic interaction of gas bubbles in an ideal incompressible liquid are derived with allowing for small deformations of their surfaces. The derivation is carried out by the method of spherical functions using the Bernulli integral, the kinematic and dynamic boundary conditions on the bubble surfaces. At that, an original expression of transformation of irregular solid spherical harmonics at parallel translation of the coordinate system is applied. The result of the derivation is a system of ordinary differential equations of the second order in the radii of the bubbles, the position-vectors of their centers and the vectors characterizing small deviations of the bubble surfaces from the spherical one. Due to their compactness, these equations are much more convenient for analysis and numerical solution than their known analogs.

The processes of reflection of three-dimensional electromagnetic waves by locally irregular media interfaces are investigated. The boundary value problem for the system of Maxwell equations in an infinite half-space is reduced to the solution of two systems of singular integral equations. To construct a numerical algorithm for solving these systems of singular integral equations, the approximation and collocation method is used. Special attention is focused on calculation of the kernels of these equations. Solutions of systems of singular integral equations are used to calculated the far-field pattern for the scattered field in the far zone.

The solvability conditions of the over-determined boundary value problems for the set of PDE with constant coefficients in semi-spaces are obtained. The equations for complex amplitudes of the wave fields are considered as examples. The method of over-determined boundary value problem is used to obtain the boundary integral equation for the mixed boundary value problems.

Paper focuses on the problem of transverse-electric wave propagation in a lossless cubic-quintic nonlinear waveguide. Using an original tool, we study the problem in detail avoiding the use of special functions. It is shown that a waveguide filled with cubic-quintic nonlinear medium supports infinitely many guided waves in the focusing case. The found solutions are split into a finite number of waves having linear counterparts and an infinite number of waves that stay away from any solution to the corresponding linear problem.

The problem on normal waves in an inhomogeneous metal-dielectric waveguide structure is reduced to a boundary value problem for the longitudinal components of the electromagnetic field in Sobolev spaces. Nonhomogeneous filling and entering of spectral parameter in transmission conditions leads to necessity of special definition of solution of the problem. We formulate the definition of solution using variational relation. The variational problem is reduced to the study of an operator function. We investigate properties of the operators of the operator function needed for the analysis of its spectral properties. We prove theorem of discrete spectrum and theorem of localization of eigenvalues of the operator-function on complex plane.

We propose a new convenient for mathematical investigation formulation of the lasing eigenvalue problem as a spectral problem for an operator-valued function, which involves boundary integral operators. We prove that these integral operators are weakly singular and the operator of the problem is Fredholm with index zero.