Vol 52, No 5 (2016)

On a finite interval, we consider a parametric differential pencil of the singular irregular type with an n-fold multiple characteristic and with boundary conditions all of which except for the last are posed at the left end of the interval. We solve the problem on the n-fold expansion of n arbitrary functions in series in Keldysh derived chains of eigenfunctions and associated functions (root functions) of the pencil.

On the basis of the method of Lyapunov vector functions, we obtain a sufficient test for the uniform partial boundedness of solutions with partially controlled initial conditions. We introduce the notions of partial equiboundedness, partial equiboundedness in the limit, and partial uniform boundedness in the limit of solutions with partially controlled initial conditions. By the method of Lyapunov vector functions, we obtain sufficient tests for the partial equiboundedness of solutions and for the partial uniform boundedness in the limit and partial equiboundedness in the limit of solutions with partially controlled initial conditions.

We study a boundary contact problem for a micropolar homogeneous elastic hemitropic medium with regard of friction; in the considered case, friction forces do not arise in the tangential displacement but correspond to a normal displacement of the medium. We consider two cases: the coercive case (in which the elastic body has a fixed part of the boundary) and the noncoercive case (without fixed parts). By using the Steklov–Poincaré operator, we reduce this problem to an equivalent boundary variational inequality. Existence and uniqueness theorems are proved for the weak solution on the basis of properties of general variational inequalities. In the coercive case, the problem is unconditionally solvable, and the solution depends continuously on the data of the original problem. In the noncoercive case, we present closed-form necessary conditions for the existence of a solution of the contact problem. Under additional assumptions, these conditions are also sufficient for the existence of a solution.

For a degenerate system of equations such as the equations of motion of immiscible fluids in porous media, we study the solvability of an initial–boundary value problem. Using the process of capillary imbibition of a wetting fluid as an example, we study a class of self-similar solutions with degeneration on the movable boundary and on the entry into the porous layer. The considered problem can be reduced to the analysis of properties of a nonlinear operator equation. For the classical solution of the original problem, we prove existence and uniqueness theorems.

We study the solvability of a boundary value problem for a system of nonlinear second-order partial differential equations under given boundary conditions, which describes the equilibrium of elastic shallow shells with hinged edges in the framework of the Timoshenko shear model. The study method implies the reduction of the original system of equations to a single nonlinear differential equation whose solvability is proved with the use of the contraction mapping principle.

We indicate the maximum order of the general and partial (with an initial polar angle) strong higher-order isochronism of Cauchy-Riemann systems with homogeneous polynomial perturbations of a linear center.

We consider a class of nonlinear total differential equations with a single singular line. For the case in which the consistency condition is satisfied identically, we find the solution manifold of such systems and analyze the behavior of solutions on the degeneration line.