Journal of Applied Mechanics and Technical Physics最新文献

An approach is proposed to model hemodynamics in an arteriovenous malformation and its vascular environment during neurosurgical embolization. This approach is based on a combination of the filtration flow model for blood and embolic agent in the malformation and the hydraulic approximation for the vessels surrounding the malformation. The model is described mathematically by a system of integrodifferential hyperbolic equations. The parameters and functions included in the model are determined using clinical data from real patients. Based on this model, the problem of optimal control of multistage embolization was formulated and studied numerically in a special class of controls. Optimal embolization regimes were found for which there is good agreement between the calculated and clinical data. The proposed approach can be used to develop preoperative recommendations about the optimal surgical intervention tactics.

This paper presents experimental measurements of flame temperature in the presence of an impact surface and a liquid phase added to the flow. The temperature is measured using laser-induced fluorescence. In the case of a flame of a pre-mixed methane-air mixture with a stoichiometric coefficient (Phi = 0.92) and a Reynolds number (mathrm{Re}= 1000), a reverse flow zone is detected near the impact surface when this surface is located at a distance of three calibers from the nozzle exit. The temperature field of a gas-droplet flame is measured using laser-induced fluorescence.

This paper presents a solution of the two-dimensional unsteady problem of the development of wave motion in a two-layer fluid of finite depth under ice cover modeled by a thin elastic plate taking into account longitudinal compression forces. The cases are considered where, in the unperturbed state, one of the layers is at rest and in the other (top or bottom) layer, the horizontal flow velocity varies linearly over the thickness. Dispersion relations are derived for three wave modes arising in the presence of shear flow. Vertical deflections of the ice cover caused by the presence of a pulsating source of perturbations in the initially motionless fluid layer are calculated. A special case is also considered where the fluid is bounded at the top by a solid lid. The problem is considered in a linear formulation, and the fluid is assumed to be ideal and incompressible.

This paper touches upon the effect of an amplitude of a deflector introduced into a laminar jet flow on the linear change coefficient of the radial component of a stationary perturbation. Methods for introducing and measuring the perturbations are described. It is shown that a decrease in the deflector amplitude has no effect on the flow pattern, cannot prevent an algebraic growth mechanism, and causes a proportional decrease in the radial component of the stationary velocity perturbation. Turbulence is established after reaching some radial expansion value that is independent of the initial perturbation amplitude.

Previously obtained analytical formulas for natural frequencies and vibration modes of inhomogeneous hourglass-shaped rods are applied to obtain geometric and elastic characteristics of samples and to estimate the amplitudes of axial stresses obtained during experimental studies of fatigue strength of metal alloys under high-frequency cyclic loading. A numerical method based on a multi-regime fatigue failure model is proposed for calculating damage kinetics under high-frequency cyclic tension-compression loading of hourglass-shaped specimens at different stress ratios. The calculations based on the proposed model are compared with the results of experiments on hourglass-shaped titanium alloy samples. The proposed model and calculation method make it possible to construct fatigue curves with sufficient accuracy for various cyclic loading conditions and stress ratios. This problem requires knowing the base points of the bimodal fatigue curve for a fully reverse cycle.

This paper presents a solution to the problem of forced bending vibrations of a flat rod with two cantilevers and a finite-length fixed region on one of the outer surfaces. The cantilever deformation processes are described using the Timoshenko model with no account for transverse compression and the fixed region: the same deformation model with allowance for transverse compression, modified by considering the presence of an unmoving fixed region. Conditions for the kinematic coupling of the cantilevers and the fixed region are formulated. The Hamilton–Ostrogradsky variational principle serves as a basis for equations of motion, boundary conditions, and force conditions for the coupling of the rod regions. Exact analytical solutions to the equations of motion under the influence of a harmonic transverse force at the end of one of the cantilevers are obtained. The passage of resonant vibrations through a finite-length fixed region in duralumin and fiber composite rods with and without account for the transverse compression of the fixed region is studied in numerical experiments. There is a significant increase in the vibration amplitude of the end of the unloaded cantilever of a duralumin rod due to transverse compression of the fixed region. The vibration amplitude for the composite rod increases slightly.

The movement of dissolved salt in melting snow is considered based on the equations of non-isothermal two-phase filtration. The thermal conductivity of snow and the dependence of the water freezing point on salinity were verified using available experimental data. The influence of the presence of dissolved salt on the phase transition was evaluated by numerical experiments.

The local flow structure in a turbulent gas-droplet flow behind a single obstacle has been studied numerically with varying initial mass fraction and diameter of dispersed particles. The effect of evaporating droplets flowing over a single square obstacle on the local mean and fluctuating flow structure and dispersed-phase propagation has been analyzed. The mean longitudinal velocity profiles for the gas and dispersed phases are similar to those for single-phase flow. The gas velocity in the gas-droplet flow is insignificantly (less than 3%) higher than that in single-phase flow. The turbulence kinetic energy increases in approaching the obstacle. Maximum gas-phase turbulence was obtained on the obstacle at (x/h= -1{-}0), and it is more than 50% higher than the turbulence kinetic energy before and after the obstacle.

Results of tensile and low-cycle fatigue testing of samples made of an aluminum–lithium alloy of the Al–Mg–Li system obtained by plasma-assisted laser cutting performed by a pulsed CO₂ laser in an argon jet with the laser beam and optical discharge plasma simultaneously affecting the material are reported. Low-cycle fatigue tests show that the number of loading cycles survived by the sample obtained by plasma-assisted laser cutting is more than twice greater than the number of cycles survived by the samples obtained by conventional laser cutting with a continuous beam.

The influence of the jet pressure ratio ((n=1.18{-}3.35)) in a nonisobaric supersonic jet of a vibrationally excited gas SF₆ exhausting from a convergent axisymmetric nozzle 0.25 mm in diameter is studied numerically and experimentally. The experiments aimed at studying the gas-dynamic structure of the jets are performed in a specially designed jet setup of the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences. The numerical simulations are performed by solving two-dimensional Navier–Stokes equations within the framework of the ANSYS Fluent software and the thermally perfect gas model. The influence of excitation of vibrational degrees of freedom of the SF₆ gas is studied in both an equilibrium gas and a vibrationally nonequilibrium gas. The nonequilibrium state of vibrational degrees of freedom is simulated with the use of a two-temperature model of relaxation flows. It is shown that the jet pressure ratio of the SF₆ gas affects the cell length of the wave structure, which is responsible for the change in the vibrational relaxation rate. The coefficient of density amplitude reduction in gas-dynamic cells is derived as a function of the jet pressure ratio.