Journal of Applied Mechanics and Technical Physics最新文献

An approach is proposed for simulating and evaluating the parameters of thin-walled elastic open shells and plates under postbuckling in large. A finite element model of the longitudinal bending of such a plate with fluted section is considered. A quasi-zero stiffness effect of the plate is numerically modeled. And then an effectiveness of this plate as an elastic element for a vibration isolating mechanism is performed. The validation of the finite element model and an assessment of control possibility the quasi-zero stiffness of the plates were performed by comparison of the results of analytical modeling and physical experiment. The results demonstrate a possibility for a widespread use of such elastic elements in vibration isoltuion systems for the ground and airborne equipment..

The properties of honey are studied experimentally. It is shown that honey becomes less viscous as with an increase in its moisture content or temperature. Close results are obtained when measuring the surface tension coefficient of white honey using several methods: the drop weight method, the capillary rise method, and the air bubble detachment method. A formula is derived that allows one to estimate the dynamic viscosity of the fluid using the known surface tension coefficient and the known air bubble shape recovery rate in a fluid after the stretching the bubble twice its size at the same measurement temperature.

This paper touches upon the formation of thermomagnetic convection in a stratified magnetic colloid that fills up a Hele–Shaw cell placed in an external nonuniform magnetic field and heats up from the side of a narrow edge in such a way that the constant field strength gradient is codirected with the temperature gradient. The Galerkin method is applied to obtain critical magnetic Rayleigh numbers for the cases of monotonous convection and oscillatory convection arising due to the nonuniformity of the concentration of magnetic nanoparticles caused by thermal diffusion and magnetophoresis. In the case of oscillatory instability, the dependence of the neutral oscillation frequency on the mixture separation parameter and the concentration Rayleigh number is determined. For supercritical monotonous and oscillatory convection regimes, the stream function, temperature, and concentration distributions are presented, and the behavior of the amplitudes of various spatial harmonics is investigated.

The propagation of disturbances generated by a heat source in a supersonic boundary layer interacting with an oblique shock wave is studied by direct numerical simulation. Calculations are performed using the HyCFS-R hybrid code. The generation and evolution of unstable boundary-layer disturbances, the effect of the incident shock wave on the development of disturbances and the effect of disturbances on boundary-layer separation and flow development in the regions of separation and laminar-turbulent transition are investigated. The influence of heat pulse duration on the generation and development of unstable waves in the boundary layer and the interaction region is examined. The generation of disturbances by a pair of sources located some distance apart is considered. Decreasing the heat pulse duration is shown to lead to an increase in the amplitudes of the first and second harmonics of the fundamental unstable mode. As result, the spectrum of disturbances in the interaction region changes and the flow transition to turbulence speeds up, leading to a decrease in the size of the separation region.

The interaction of a shock wave with a boundary layer on a half-airfoil model has been studied. Experiments were performed in a wind tunnel at a freestream Mach number ( approx {kern 1pt} 0.75) and a stagnation pressure ({{P}_{0}}{{ = 10}^{5}}) Pa. The half-airfoil model was mounted on the wall of the test section of the wind tunnel. Pressure distributions on the model surface were obtained using pressure sensitive paints and pressure taps. Visualization of the surface streamlines on the model by means of oil flow visualization technique and measurements of surface temperature distribution using infra red CCD camera were performed. Numerical simulation of the flow was performed with experimental parameters using the Reynolds-averaged Navier–Stokes approach. The three-dimensional flow structure was analyzed, and significant differences were found between the measurement results and numerical simulation data for flow in the corner separation regions.

The paper describes an experimental study of the process in which a cluster of monodisperse drops of isoparaffin oil rises to the surface in distilled water in a range of Reynolds numbers Re = 200–800. It is shown that the initial volume concentration of drops in the cluster is one of the main parameters determining its dynamics. The study also touches upon the motion of two types of clusters, characterized by the presence or absence of collisions of the drops contained in it. Experimental dependences of the rising velocity of the drop cluster on the Reynolds number are obtained for different values of the initial volume concentration of drops. The limiting value of the initial volume concentration of drops is determined, corresponding to the onset of cluster motion with a velocity exceeding the velocity of a single drop.

The main objective of the present study is to apply spanwise periodic rows of cylindrical turbulators to investigate the mechanism of forced turbulization of a swept-wing boundary layer with predominant cross-flow instability. The experiments are carried out using hot-wire anemometry in a low-turbulence wind tunnel at the Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, at low subsonic freestream velocities on a 25-degree swept-wing model. The results of detailed precision measurements of the mean and fluctuating flow structure are obtained in a wide spatial region in 12 different measurement regimes for five types of turbulators (and without them) at two flow velocities. The studied range of Reynolds numbers based on the cylinder height lies between 565 and 3613. This is the first part of this study, and it describes the main scenarios of turbulator-induced transition to turbulence. The high efficiency of turbulators is demonstrated. This study continues in part 2 [1].

Incompressible gas flow past a two-dimensional backward-facing step on the surface of a flat plate is studied experimentally under conditions of controlled low-frequency forcing of the separated flow. It is found that flow oscillations whose frequency is an order of magnitude lower than the characteristic frequency of convective instability of the separated boundary layer cause significant changes in the time-averaged and fluctuating characteristics of the flow in the separation region.

A moving edge dislocation in an infinite elastic medium is considered, simulating a stationary shear rupture in the Earth’s crust at a depth of seismic activity, which increases as quickly as transverse waves travel. Based on the expansion of the vector displacement field into the sum of the potential and solenoidal fields, an exact singular solution to the problem in a plane formulation is constructed in the form of convergent series. An approximate solution in the form of series segments is analyzed in the Matlab computer system using numerical differentiation and integration procedures. It is shown that the invariant (J)-integral, whose value is equal to the driving force of the dislocation (the energy spent on the movement of the dislocation by a unit distance), is independent on its velocity.

To develop a technology of drill pipe fracture and extraction from a well at a depth of more than 5000 m, we performed a numerical study of shock-wave loading of the inner surface of the pipe by the detonation of a special cylindrical charge. Two cases of detonation of the cylindrical explosive charge are considered: plane-front detonation and diverging spherical detonation. The computational model is a layered structure which consists of a cylindrical explosive charge in a copper case, a steel pipe, and drilling mud. The shock-wave impact on the drill pipe is calculated in a three-dimensional formulation using the multicomponent Eulerian approach. The calculations confirmed the possibility of drill pipe fracture in the region of the lock joint. It is shown that shock-wave loading by the plane-front detonation causes much more damage to the pipe than the impact by diverging spherical detonation. The minimum charge length sufficient for drill pipe fracture was determined by additional calculations.