Journal of Applied Mechanics and Technical Physics最新文献

Effect of the main parameters of a nonlocal continuum model on stress concentration is studied when solving a problem of tension of a plate with an elliptical cut at its center, also known as the Kirsch problem. The effect of thermal expansion of the medium on the stress-strain state of the plate is described. The results obtained in this study are compared with the classical results. It is shown that there is an decrease in maximum stress and heat flux density, as well as a decrease in the strain in the stress concentration regions.

The dispersion, spatial propagation, and settling of aerosol particles generated by a pulsed method using the energy of high-energy materials have been studied. Such aerosols are produced to decontaminate harmful gas or aerosol formations. A mathematical description of the evolution of a decontaminating aerosol cloud is proposed, and the results of experiments on the dispersion of an aerosol of titanium oxide particles are presented.

This paper presents the results of calculations of liner implosion without the formation of shock waves under the influence of a current up to 70 MA and a magnetic field induction up to 20 MGs (magnetic pressure up to 16 Mbar) in devices with a disk explosive magnetic generator. It is shown that during deep implosion of two-layer Cu–W and Cu–Ta liners, the shockless pressure in tungsten and tantalum can reach 40 Mbar (hydrodynamic cumulation). The inner part of the liner, whose mass is more than 32% of its total mass, can remain in a dynamically strengthened solid state at a temperature of its copper skin layer up to 38 eV.

The dispersion of a single-component fluid (water) by a model simplex atomizer is studied in detail using the local time-shift method with a SpraySpy device and high-speed visualization. The mean size and velocity distributions of droplets are measured depending on the pressure drop for the atomizer. The spraying of two immiscible fluids (kerosene and water) supplied to the same atomizer is visualized by shadow photography. It was found that the two-component emulsion disintegrated almost instantaneously in close proximity to the atomizer outlet orifice, resulting in significant deformation of the spray cone.

The paper describes a methodology for the experimental study of a powerful heat release in a microsized probe immersed in a two-component solution with a lower critical solution temperature. Experimental data on superheating relative to the liquid–liquid spinodal and thermal impact on the stability of the system for a water–PPG-425 solution are presented. The following conclusion is made for a solution whose near-critical mass fraction of PPG-425 is 30%: despite the high density of the heat flux through the heater surface (9.2–13.7 MW/m²), its temperature stabilizes at a value exceeding the equilibrium temperature of the liquid–liquid system by approximately 150 K. It is shown that the heat exchange process is stable against changes in the heating parameters: the nature of heat transfer by the solution remains the same. It is revealed that the heat transfer coefficient is several times greater than the corresponding value obtained for water.

This paper describes a numerical study of heat exchange in a droplet-laden turbulent flow behind a single square obstacle with variation in initial mass concentration and in dispersed phase particle diameter. In the case of a flow past an obstacle, adding droplets to the flow significantly intensifies the heat exchange (almost twofold) as compared to a single-phase air flow. It is shown that, when a two-phase flow flows past a transverse obstacle, there is an approximately 12% difference between the coordinates of the maximum heat exchange intensity and those at the flow attachment point. An increase in obstacle height leads to a decrease in heat exchange intensity.

New modifications of spiral generators with meander striplines have been proposed in which the inductive and capacitive parts of the generator to be separated in space. The proposed modification allows separate regulation of the wave impedance of the double-bus spiral stripline and the generator winding inductance and capacitance. The characteristics of the generators have been studied experimentally, and theoretical models adequately describing the operation of these devices have been proposed. The developed generators can be used to produce pulsed X-ray apparatuses with explosive electron emission.

The influence of spanwise-uniform roughness elements (streaks) on the laminar–turbulent transition in the boundary layer on a swept wing with predominance of crossflow instability in the presence of unsteady and steady free-stream vortices is studied. The measurements are performed for rectangular (in the plane parallel to the flow and normal to the wall) roughness elements shaped as streaks of different heights, which have two different widths in the chordwise direction. The experiments are performed in a low-turbulence wind tunnel at low subsonic velocities of the incident flow with the use of hot-wire anemometry. The studies are conducted in the range of unit Reynolds numbers (based on the streamwise component of velocity at the boundary layer edge at the beginning of the rough surface region) from (0.687cdot 10^6) to (1.568cdot 10^{6}) 1/m. The results are obtained in 76 regimes of measurements for two types of free-stream vortex disturbances induced by two turbulence-generating grids: with predominance of unsteady disturbances and combination of steady and unsteady disturbances.

In this study, the thermal and fluid flow characteristics of a piezoelectric fan are experimentally evaluated by altering its height and distance from single-fin and plate-fin heat sinks. Based on the thermal resistance of heat sinks, the piezoelectric fan performance is assessed. Particle image velocimetry is used to study the flow velocity field generated by the piezoelectric fan.

This study is aimed at optimizing the design parameters (winding angle, fiber volume fraction, elasticity modulus of fibers, and radius-thickness ratio) of the fiber-wound pressure vessel for achieving a stable strength ratio based on a hybrid method of Particle Swarm Optimization and Grey Wolf Optimization (HPSOGWO). A three-dimensional linear elasticity theory is used to solve the problem numerically.