Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2014 number 4

Results of experimental measurements of Young's modulus, burning rate, and specific heat of condensed high-energy polymer compositions (solid propellants) subjected to microwave radiation are reported. Experimental equipment and arrangement of experiments are described; the results obtained are analyzed.

An analytical model describing the motion of vortex rings in an incompressible fluid is constructed. The model is valid both for homogeneous and inhomogeneous vortices buoyant in the gravity field, as well as for combined vortices. The expansion angle of the buoyant vortex is found through characteristic parameters that define the flow rather than specified on the basis of experiments. Significant differences in the expansion angles of homogeneous and buoyant vortex rings are explained. The calculation results for the proposed model are compared with the results of laboratory experiments and data on rising of the cloud formed by an atomic explosion.

This paper discusses the effects of a vertical a.c. electric field and heat transfer on a peristaltic flow of an incompressible dielectric viscoelastic fluid in a symmetric flexible channel. The mathematical modeling includes interactions among the electric field, flow field, and temperature. The perturbation solution of the modeled problem is derived by considering a small wave number. The influence of pertinent parameters is demonstrated and discussed. The numerical results show that the possibility of flow reversal increases near the lower bound of the channel and decreases near the upper bound of the channel as the electrical Rayleigh number, the Reynolds number, and the Weissenberg number increase, whereas the opposite effect is observed as the temperature parameter and the Weissenberg number increase. It is observed that the size of the trapped bolus decreases at the upper bound of the channel and increases at the lower bound of the channel with increasing electrical Rayleigh number, whereas the opposite effect is observed as the temperature parameter increases. The results also show that the trapped bolus in the case of an Oldroydian fluid is smaller than that for a Newtonian fluid.

A method of determining the time of relaxation of shear stresses and characteristics of dislocation structures in the process of shock compression of polycrystalline metals with the use of strain diagrams obtained by the Kolsky method with the help of the split Hopkinson bar is developed on the basis of the rheological Maxwell model and dislocation-kinetic relations. Characteristics of seven types of aluminum-based alloys are analyzed by this method.

A criterial analysis of the effect of forced vibrations of airfoil surface elements on the shock wave structure of a transonic flow around the airfoil is performed. The parameter responsible for regimes of interaction of vibrationally moving zones of the airfoil with the closing shock wave is determined. The influence of this parameter on the wave drag of the airfoil is studied.

Results of numerical simulations and experimental investigations of self-oscillations arising in the case of impingement of an overexpanded or underexpanded jet onto an obstacle with a spike are reported. The mechanisms of the emergence and maintaining of self-oscillations for overexpanded and underexpanded jets are elucidated. It is demonstrated that self-oscillations are caused by disturbances in a supersonic jet, which induce mass transfer between the supersonic flow and the region between the shock wave and the obstacle. The feedback is ensured by acoustic waves generated by the radial jet on the obstacle. These waves propagate in the gas surrounding the jet, impinge onto the nozzle exit, and initiate disturbances of the supersonic jet parameters. In the overexpanded jet, these disturbances penetrate into the jet core, where they are amplified in oblique shock waves.

This paper mainly investigates the optimum parameters for the fabrication of uniform diamond-like carbon (DLC) films on the electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) reaction chamber by analyzing the effect of the reacting gas velocity on the film properties. This work makes use of computational fluid dynamics (CFD) approach to model surface chemical reactions, flow and temperature fields, as well as heat and mass transfer phenomena. The simulation has shown that natural convection and mass transfer affect the recirculating flow within the reactor and, therefore, the distribution of material deposition. In other words, as a result of attaching an endplate (baffle) at the top of the substrate, the deposition rate of the substrate is appreciably enhanced. However, the surface uniformity of the substrate is obviously deteriorated.

In this paper we demonstrate the advantages of the LES-WALE model coupled with the PDF approach to resolve a set of aerothermochemistry equations for turbulent lean premixed prevaporized combustion. The main issue is the modeling of the closure in the turbulent combustion equations. So, combustion problems involve a strong coupling between dynamic and scalar parameters. The validation is based on comparisons of three parameters: mean longitudinal velocity, fluctuation of longitudinal velocity, and length of recirculation zones. In line with what was observed by an experimental reference study, the simulation succeeds to detect the flame zone and to model the flow morphology for different equivalence ratios and inlet mass flow rates.

A steady problem of a slow axisymmetric flow of a viscous incompressible fluid around an oblate spheroid covered by a viscous film is solved analytically with the use of the Stokes approximation. Surface tension on the interface between the fluids is taken into account. Expressions for velocity components and stream functions are presented. A formula for determining the force action of the incoming flow onto the oblate spheroid is derived.

The present work reports a numerical simulation of mixed convection in an inclined square cavity. The vertical sidewalls are assumed to have a nonuniform temperature distribution. The finite volume method is used to solve dimensionless governing equations. Simulations are performed for different Richardson numbers, amplitude ratios, phase deviations, and cavity inclination angles. The results are presented graphically. The mean heat transfer significantly increases in the buoyancy-dominated mode on increasing cavity inclination angle if both walls have identical heating and cooling zones.

Numerical simulation of the sublimation of the surface of an ice crystal has shown that the presence of a non-condensable gas substantially reduces the sublimation rate. It has been found that the slowing of the sublimation due to the adsorption of gas molecules on the crystal surface that fill the vacancies during sublimation prevents the formation of vacancy islands on the surface of the crystal required for evaporation of the surface molecular layer. The available results of studies that explain the slowing of the sublimation by the presence of a diffusion layer formed in the vapor medium near the sublimating surface are supplemented with new data showing that molecular processes on the crystal surface play an equally important role as the diffusion layer. Cases have been found where crystal sublimation is accelerated by the sorption of gas molecules. The obtained results refining the theory of sublimation can be used to develop methods for controlling sublimation.

A technique of the state space approach and the inversion of the Laplace transform method are applied to dimensionless equations of an unsteady one-dimensional boundary-layer flow due to heat and mass transfer through a porous medium saturated with a viscoelastic fluid bounded by an infinite vertical plate in the presence of a uniform magnetic field is described. Complete analytical solutions for the temperature, concentration, velocity, and induced magnetic and electric fields are presented. The inversion of the Laplace transforms is carried out by using a numerical approach. The proposed method is used to solve two problems: boundary-layer flow in a viscoelastic fluid near a vertical wall subjected to the initial conditions of a stepwise temperature and concentration and viscoelastic fluid flow between two vertical walls. The solutions are found to be dependent on the governing parameters including the Prandtl number, the Schmidt number, the Grashof number, reaction rate coefficient, viscoelastic parameter, and permeability of the porous medium. Effects of these major parameters on the transport behavior are investigated methodically, and typical results are illustrated to reveal the tendency of the solutions. Representative results are presented for the velocity, temperature, concentration, and induced magnetic and electric field distributions, as well as the local skin-friction coefficient and the local Nusselt and Sherwood numbers.

Full a-dislocations on the (0001) basal plane, (1010) prismatic plane, and (1011) and (1012) pyramidal planes in pure magnesium are investigated by using the Peierls-Nabarro model combined with generalized stacking fault (GSF) energies from first-principles calculations. The results show that the (1011)1120 and (1012)1120 slip modes have nearly the same GSF energy barriers, which are obviously larger than the GSF energy barriers of the (0001) 1120 and (1010)1120 slip modes. For both edge and screw full dislocations, the maximum dislocation densities, Peierls energies, and stresses of dislocations on the (1010), (0001), (1011), and (1012) planes eventually increase. Moreover, the Peierls energies and the stresses of screw full dislocations are always lower than those of edge full dislocations for all slip systems. Dislocations on the (1011) and (1012) pyramidal planes possess smaller core energies, while the (1010) prismatic plane has the largest ones, implying that the formation of full dislocations on the (1010) plane is more difficult.

An approximate solution to the problem of compression of an infinite layer of material between rough parallel plates is constructed with the creep equations being fulfilled. Constitutive relations in accordance with which the equivalent stress tends to a finite value as the equivalent strain rate tends to infinity are used. The behavior of the solution in the neighborhood of the maximum friction surface is studied. It is shown that the existence of the solution depends on one of the parameters included in the constitutive equations. If the solution exists, the equivalent strain rate tends to infinity in the neighborhood of the maximum friction surface, and the asymptotic behavior of the solution depends on the same parameter. It is established that there is a range of this parameter in which the nature of the change in the equivalent strain rate near the maximum friction surface is the same as in the solutions for rigid plastic materials.

A solution describing the displacement and stress fields around expanding spherical and cylindrical cavities with allowance for pore collapse is constructed using the theory of small elastic deformations of a homogeneous isotropic porous medium in closed form. Transition of the medium into a plastic state is modeled using the Tresca-Saint Venant yield condition. Porosity change is described on the basis of a mathematical model developed taking into account the increase in the stiffness of the porous material at the moment of pore collapse. It is shown that in the elastic deformation stage, the porosity does not change; an increase in the pressure leads to the formation of a region of plastic compression, in part of which, the pores collapse. Stress and displacement fields in the porous medium during unloading are constructed. It is shown that under certain conditions, the elastic unloading stage is followed by the plastic reflow stage to form a region of pore expansion. As the pressure decreases, the boundary of this region simultaneously reaches the region of plastic reflow and the region of pore collapse.

Deformation of annular plates with different structures of helical reinforcement is studied. It is demonstrated that the use of the classical theory for calculating steady-state creep for thick reinforced plates subjected to bending leads to underprediction of the compliance of thin-walled metal-composite structures. It is also shown that there are significant shear strain rates in the binder of such plates, which has to be taken into account and which is mainly responsible for creep strain accumulation. Results calculated by two different models, which take into account the composite structure, are compared.

A method for calculating the loose packing structure of polydisperse spherical particles with a predetermined size distribution function is proposed. The coordinates of the particle centers in the loose layer are determined as the result of random fall of single spheres on a substrate under the action of gravity, assuming the inelastic collision of the spheres and considering the force of their adhesive interaction, and also assuming that the motion of one sphere on the surface of the other is pure slip. Numerical simulation is used to obtain the pattern of arrangement of polydisperse spherical particles in the loose powder layer, whose porosity depends on the particle size distribution function. The results are compared with experimental data.

The method of precision electrochemical machining is studied by using a model in which the current output has the form of a step function of current density. The problems of maximum stationary and quasistationary machining are formulated and solved, which made it possible to study the nonstationary process with sufficient accuracy.