In a rectangular domain the first boundary value problem is considered for a singularly perturbed elliptic equation

ε 2∆u − ε ^αA(x, y) ∂u/∂y = F(u, x, y, ε)

with a nonlinear on u function F. The complete asymptotic solution expansion uniform in a closed rectangle is constructed for α > 1. If 0 < α < 1, the uniform asymptotic approximation is constructed in zero and first approximations. The features of the asymptotic behavior are noted in the case α = 1 .

Considered are so-called finite-dimensional flutter systems, i.e. systems of ordinary differential equations, arising from Galerkin approximations of certain boundary value problems of aeroelasticity theory as well as from a number of radiophysics applications. We study small oscillations of these equations in case of 1 : 3 resonance. By combining analytical and numerical methods, it is concluded that the mentioned resonance can cause a hard excitation of oscillations. Namely, for flutter systems shown is the possibility of coexistence, along with the stable zero state, of stable invariant tori of arbitrary finite dimension as well as chaotic attractors.

A nonlinear differential equation is considered for describing nonlinear waves in a liquid with gas bubbles. Classical and nonclassical symmetries of this equation are investigated. It is shown that the considered equation admits transformations in space and time. At a certain condition on parameters, this equation also admits a group of Galilean transformations. The method by Bluman and Cole is used for finding nonclassical symmetries admitted by the studied equation. Both regular and singular cases of nonclassical symmetries are considered. Five families of nonclassical symmetries admitted by this equation are constructed. Symmetry reductions corresponding to these families of generators are obtained. Exact solutions of these symmetry reductions are constructed. These solutions are expressed via rational, exponential, trigonometric and special functions.

In this paper we solve problems of stabilization of unstable cycle by the delay feedback. We study a model equation with qubic nonlinearity. In this case only one multiplicator is located outside a unit circle. Delay time is proportional to the cycle period. The D-partition of the parameter plane is obtained. The main result is analytically found conditions for parameters of delay control such that the initial cycle is stable. Also, we have found necessary and sufficient conditions of solvability of the stabilization problem. As a consequence, the problem of stablity of the Stuart–Landau equation periodic solution is completely solved.

In the paper we propose a mathematical model of a mechanical system consisting of a rigid body and two rigidly connected elastic straight rods located in the same plane. The system rotates around the axis passing through the mass center of a rigid body and perpendicular to the plane of the rods. The rods are modeled by the Euler–Bernoulli beam. The mathematical model is an initial-boundary value problem for a hybrid system of differential equations. The cases of fast and slow rotations of the system are considered.

We considered a logistic equation with delay and studied its local dynamics. The critical cases have been found in the problem of the equilibrium state stability. We applied standard Andronov-Hopf biffurcation methods for delay differential equations and an asymptotic method, developed by one of the authors, based on the construction of special evolution equations that define the local dynamics equations with delay. It is shown that all solutions of the equation tend to an equilibrium state or result in a single stable cycle. The results of numerical modelling are presented in this paper. The study has proved that analytical and numerical modeling results have a good correlation.

The problem about the local dynamics of the logistic equation with rapidly oscillating time-periodic piecewise constant coefficient of delay was considered. It was shown that the averaged equation is a logistic equation with two delays. The criterion of equilibrium point stability was obtained. Dynamical properties of the original equation was considered provided that the critical case of equilibrium point stability problem was implemented. It was found that an increase of delay coefficient oscillation frequency may lead to an unlimited process of “birth” and “death” steady mode.

We study the dynamics of finite-difference approximation on spatial variables of a logistic equation with delay and diffusion. It is assumed that the diffusion coefficient is small and the Malthusian coefficient is large. The question of the existence and asymptotic behavior of attractors was studied with special asymptotic methods. It is shown that there is a rich array of different types of attractors in the phase space: leading centers, spiral waves, etc. The main asymptotic characteristics of all solutions from the corresponding attractors are adduced in this work. Typical graphics of wave fronts motion of different structures are represented in the article.

A pair of diffusion connected FitzHugh–Nagumo oscillators with an asymmetric interaction are considered. The problem is investigated in the close to critical case, where the matrix of the linear part of the system has a pair of purely imaginary eigenvalues. The normal form is constructed and its coefficients are determined depending on the initial parameters. The source system may be in two different situations: stable singlefrequency oscillations with two different frequencies coexist or a single-frequency mode branches from the equilibrium. The obtained asymptotic results are supplemented by the numerical analysis.