Home – Home – Jornals – Advanced Search

New modifications of helical generators with meander shaped striplines have been proposed, which allow the inductive and capacitive parts of the generator to be separated in space. The proposed change allows separate regulation of the characteristic impedance of a double-bus helical line and the generator inductance and winding capacity. The characteristics of the generators have been studied experimental, and theoretical models adequately describing the operation of these devices have been proposed. The developed generators can be used to produce pulsed X-ray devices with explosive electron emission.

The normal coordinates method is used in conservative mechanical systems to reduce two quadratic forms to a sum of squares. In this case, a system of differential equations is split into a system of independent oscillators. A linear dissipative mechanical system with a finite number of degrees of freedom is determined by three quadratic forms: kinetic and potential energy of the system, as well as the Rayleigh dissipative function, which, generally speaking, cannot be reduced to a sum of squares. Conditions are considered under which all three quadratic forms are reduced to a sum of squares by a single transformation exactly or approximately. It is shown that, for such systems, normal coordinates can be introduced in which the system is split into independent second-order systems. This allows one to construct exact or approximate analytical solutions in general form and with an estimated relative error in the case of an approximate solution. The advantages of this approach are shown for problems of theoretical mechanics and electrical engineering, in which analytical solutions are constructed and optimization analysis is carried out. In this case, traditional methods allow only numerical calculations to be performed for given parameter values.

Asymptotic behavior of solutions of initial-boundary-value problems arising in simulation of motion of incompressible viscoelastic fluids is studied in the case of various combinations of small relaxation parameters (stress relaxation time at constant strain and strain relaxation time at constant stress), one of which can be equal to zero.

Publications dealing with investigations of corkscrew fluid flows with collinear velocity and vortex vectors are reviewed. New solutions are presented for the Navier-Stokes equations for an incompressible fluid and second-order fluid equations, which are two-dimensional analogs of corkscrew flows.

The existence of a classical solution was established for a one-phase radial viscous fingering problem in a Hele-Shaw cell under surface tension (original problem) by means of parabolic regularization for a certain subsequence {ε_n}_n∈N, ε_n > 0. In this paper, we prove the uniqueness of the classical solution to the original problem with the use of parabolic regularization for the full sequence of the parameter {ε}, ε > 0.

A viscous fluid flow between two wavy horizontal surfaces unlimited in longitudinal and transverse directions is considered. The full Navier-Stokes equations are applied to study the linear stability of such a flow with respect to various three-dimensional disturbances. Two types of wall waviness are studied: longitudinal and transverse periodic corrugation. At the first stage, the main solution is obtained and the initial equations are linearized in the vicinity of this solution. At the second stage, the generalized problem of determining eigenvalues is solved and the entire possible spectrum of disturbances is analyzed. The varied parameters are the Reynolds number, amplitude, period, and shape of the corrugation. Disturbances of velocity and pressure fields are generally characterized by two wave numbers, which are additional parameters. The influence of the parameters and shape of the wall waviness on the region where the laminar-turbulent transition begins is investigated.

This paper examines two-dimensional flows near a free critical point of an incompressible viscoelastic Maxwell medium using the Johnson-Segalman convected derivative. The flow is assumed to be axisymmetric, and its velocity profile is linear along the axial coordinate. A general exact analytical solution is found for the problem of the distribution of the stress tensor components near the stagnation point.

Rotational sedimentation of neutrally buoyant particles in suspensions is studied by mathematical simulation in the case of two-dimensional circular flows between two cylinders. Particle separation in the absence of gravity is caused by rotation of the inner cylinder. It is revealed that sedimentation depends on particle rotation. Within the framework of the Cosserat continuum, the suspension is considered as a micropolar fluid. The effect of the eccentricity of noncoaxial cylinders on the sedimentation front is investigated.

The role of the hidden integral of motion for correct description of the far field of velocities and pressures is discussed based on the complete Navier-Stokes equations for the case of non-self-similar submerged jets of an incompressible viscous fluid when the source of motion has a non-zero characteristic size. It is shown that the emergence of the hidden conservation integral is due to the fact that the coordinates of the point of the effective momentum source and the point of the effective mass source may not coincide for real spatially extended sources of jet flow. Using special functions, an exact analytical solution for all terms of the asymptotic expansion of the far field of a non-self-similar submerged jet was obtained that is described by all integrals of motion: conservation of the total momentum flux, conservation of the total angular momentum flux, conservation of the total mass flux, and the additional hidden conservation integral associated with the conservation of the total angular momentum flux. It is shown that the hidden integral was actually first obtained by L. G. Loitsyansky in studying a non-self-similar solution for a submerged jets within the boundary layer approximation, but it was mistakenly interpreted as the integral of conservation of the mass flux flowing from source of the jet. The obtained exact solution was used to perform calculations of velocity and pressure fields at different Reynolds numbers and different values of the hidden integral for the model of the jet outflow from a circular tube of finite size. The influence of the hidden integral of motion on the flow pattern is analyzed.

The influence of the main hydrochemical parameters, ionic and elemental composition of natural waters with different anthropogenic loads on the efficiency of photocatalytic processes is investigated for the oxidation of model organic pollutants: azo dye (methyl orange, MO), phenothiazine dye (methylene blue, MB). Comparative studies of water quality in two small rivers located within the boundaries of Khabarovsk (the Krasnaya River) and beyond (the Polovinka River) from April to October 2023 were carried out using the methods of chemical analysis, mass spectrometry with inductively coupled plasma and spectrophotometry. It was shown that the highest concentrations (>5 mg/dm³) were observed for ions (HCO₃^-, Cl^-, SO₄^2-) and elements (Na, Ca) in rivers draining urban areas (large highways, industrial enterprises, residential areas) and suburban territories (agricultural lands, country house areas). The efficiencies of photocatalytic destruction of anionic (MO) and cationic (MB) model pollutants dissolved in distilled water, water from small rivers, distilled water in the presence of Na⁺, HCO₃^-, Cl^-, SO₄^2- ions were compared. The time of photodestruction was assessed for model pollutant transformation degree equal to 90 % at the final stage of photocatalytic experiment. The degree of reduction in the efficiency of photocatalytic processes when conducting experiments in waters from small rivers was assessed with respect to the experiment in distilled water. The time of photodestruction of samples from real water bodies (at the degree of pollutant transformation 90 %) was demonstrated to increase with respect to the experiment in distilled water by a factor of 4.8-7.3 (MB) and 1.9-4.7 (MO) for the samples from the Krasnaya river, 3.7-6.3 (MB) and 1.1-2.2 (MO) for the Polovinka river. Value scattering was due to the seasonality of sampling.