卷 59, 编号 4 (2018)

A mathematical model for the interior ballistics of an electrothermal accelerator of macrobodies was developed which can be used to predict the projectile velocity for given values of the mass and size of the projectile, the electrodynamic parameters of the capacitive energy storage, and accelerator parameters. The problem of determining the projectile velocity was solved in a hydrodynamic formulation by numerical integration of the equations of motion, the energy conservation equation, and the caloric equation of state. In the case of neglecting the dynamically changing friction coefficient and the erosion of the electrodes, the calculation results differ considerably from the experimental data, but the model qualitatively describes the physical processes of interior ballistics of the electrothermal accelerator.

Two-dimensional seiche oscillations in a rectangular basin of constant depth with an open entrance are considered within the framework of the linear theory of long waves. An analytical solution is obtained for the case where a nodal level line is located at the entrance to the basin. It is shown that transverse seiches in a basin with an open entrance are two-dimensional in contrast to similar modes in a completely closed basin, which are one-dimensional. Seiche parameters are calculated for model basins with dimensions and depth characteristic of a number of Sevastopol bays. Comparison of the calculation results with observations data shows that they are in satisfactory agreement.

A new type of ducted pulse thermal actuators with a high pulse repetition frequency is proposed to control wing buffeting at transonic flight velocities. Ducted pulse thermal actuators can operate up to frequencies of about 1 kHz, which is sufficient for controlling the majority of aerodynamic processes at high subsonic flow velocities. As the use of a pulse thermal actuator in the regime of tangential injection of a jet is less efficient from the energy viewpoint than in the regime of boundary layer suction, an ejector-type pulse thermal actuator is proposed for implementation of the suction regime.

Singular integral equations of the first and second kind with the Cauchy kernel on a limiting narrow closed contour are theoretically considered. The initial equations are found to become different on the limiting contour. This singularity of integral equations with the Cauchy kernel does not allow boundary-value problems of the flow around thin airfoils to be solved correctly; therefore, a system consisting of integral equations of the first and second kind is proposed for solving such problems. The results of the present study are tested against an exact solution of the problem of the flow past a flat plate.

The process of airfoil icing caused by incidence of ice crystals is considered. A physicomathematical model of motion of spheroidal crystals in the gas flow and their interaction with the body is formulated. The model takes into account the non-spherical particle orientation with respect to the velocity vector of the gas flow. It is assumed that the particle impact onto the body surface leads to partial destruction of the particle under the action of normal and tangential stresses, and some part of the particle mass remains in the vicinity of the impact point. An inviscid flow around the airfoil with a time-dependent shape is calculated by the method of approximate conformal mapping.

The method of many scales was used to construct an asymptotic expansion up to thirdorder terms for the velocity potential of a fluid of finite depth and the flexural deformations of a floating elastic plate arising from the interaction of harmonics of finite-amplitude progressive surface waves. An expression for the second-harmonic amplitude was obtained, and critical values of the wavenumber were determined. Vibrations of plates with different thicknesses and elastic modulus were analyzed. Vertical displacements of the plate under flexural deformation were studied.

This paper describes a detailed numerical investigation of a stationary high-aspect-ratio rib-roughed rectangular cooling channel with longitudinal intersecting ribs near the gas turbine blade trailing edge region. In order to overcome the heat transfer performance degeneration in the highaspect- ratio channel, longitudinal intersecting ribs are arranged on the channel bottom surface. The effect of the number of longitudinal intersecting ribs on the flow and heat transfer is systematically studied in the Reynolds number range Re = 10 000–30 000. The results show that a heat transfer augmentation region exists just downstream the junction between the longitudinal rib and the angled rib due to additional secondary flows. With more longitudinal intersecting ribs, the heat transfer distributions on the channel surfaces are more uniform. Though the pressure loss is also enlarged with an increase in the number of longitudinal intersecting ribs, the overall thermal efficiency increases in the entire range of Reynolds numbers investigated. The configuration with two sets of longitudinal intersecting ribs shows the best overall thermal efficiency.

Large deformations of elastoplastic cylindrical rods and shells of different thicknesses under tension are studied. The effect of sample geometry and the dependence of stresses on deformations under uniaxial tension on edge effects and necking are estimated. The applicability of the Considere criterion for determining the instance of stability loss of plastic tensile strain is analyzed. The computational experiments confirm that the role of similarity in the processes of nonuniform tensile strain of samples can be played by the ratio of the tangent of the slope of the true strain diagram to the stress intensity.

Results of experiments on indentation of steel balls of various diameters into glass specimens shaped as rectangular parallelepipeds are reported. The limiting load of formation of an annular crack near the contact area and the radius of this crack are experimentally determined. The field of the contact stress in the fracture region is found by using the Huber solution of the Hertz problem of ball indentation into an elastic half-space. Modeling fracture caused by contact interaction is based on using the local criterion of the maximum stress and several nonlocal criteria: average stress criterion, Nuismer criterion, and gradient criterion. For calculating the parameter that has the length dimension and is included into the nonlocal fracture criteria, the ultimate tensile stress and the critical stress intensity factor of glass are experimentally determined for beams without and with a notch. It is demonstrated that the experimental data on the annular crack radius are most adequately predicted by the gradient criterion among all criteria considered in the study. However, this criterion overpredicts the ultimate tensile stress in the course of beam bending, which is caused by the scale factor.

The dynamics of a pulsed signal propagating in an underground pipeline with a damaged section is investigated. Pressure waves propagating in a linear pipeline filled with a fluid are considered. Due to viscous friction and thermal conductivity, dissipation is taken into account in a thin liquid or gas layer near the wall. It is assumed that the damaged pipeline section is a reflecting surface. Conditions on this surfaces are obtained under the assumption that the rate of liquid leakage during wave propagation through the damaged section is determined by the permeability of the soil. It is shown that in weakly permeable soils, signals do not provide full information on damage, and in well-permeable soils, only short (high-frequency) pulsed signals can be used to detect damage.

The problem of parametric vibrations of a longitudinally stiffened orthotropic cylindrical shell in contact with an elastic medium and under internal pressure is solved in a geometrically nonlinear formulation using the variational principle. The influence of the external medium is taken into account using the Pasternak model. Amplitude–frequency curves for parametric vibrations of the stiffened orthotropic cylindrical shell filled the medium are constructed.

This paper describes an experimental study of the strain rate of DP780, DP980, and VN240 high-strength sheet steels on an increase in their plasticity under uniaxial and biaxial tension. The strain rates of the steels vary in the range from 10⁻⁴ to 17 · 10³ s⁻¹.