Journal of Applied Mechanics and Technical Physics最新文献

The efficiency of fluid atomization by an atomizer is studied as a function of the spray energy. The dependence of the maximum values of energy on the fluid flow rate is analyzed. A linear dependence is obtained for flow rates smaller than 80 g/s, which testifies to a high efficiency of fluid atomization. For flow rates greater than 80 g/s, the droplet energy is seen to decrease drastically, leading to an increase in the spray droplet size, which shows that the atomization quality is deteriorated. This behavior is observed in all regimes considered in the study.

Direct numerical simulation is used to study the effect of wall heating on the characteristics of a near-wall reverse flow during a turbulent stream of various coolants in a duct. A temperature field is considered both in a passive scalar approximation and in a low Mach number approximation. Qualitative and quantitative results are obtained that characterize the probability of occurrence of a near-wall reverse flow in all the cases considered at a Reynolds number (mathrm{Re}= 3150) based on mean flow velocity and duct half-height. It is revealed that, in the cases considered, the wall heating causes a two- or a threefold increase in the probability of near-wall reverse flow formation .

A heat conduction equation within the framework of the coupled dynamic theory of thermoelasticity is considered. Coupling in the heat conduction equation is estimated for a space with a constant initial temperature. This space contains a flat semi-infinite crack propagating at a constant velocity, and a constant temperature lower than an initial one (thermal shock) is instantly established on the edges of this space. The movement of the crack and the thermal shock on its shores determine dynamic effects that should be taken into account to estimate coupling in the heat conduction equation. It is demonstrated that, under real conditions of a thermal shock on massive bodies with cracks, one may ignore dynamic effects and coupling for materials that satisfy certain conditions imposed on their thermomechanical constants. This significantly simplifies the process of solving thermoelasticity problems for such bodies.

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.