Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2018 number 5

A new method of deposition of diamond films with the use of supersonic gas flows activated by a superhigh-frequency discharge is implemented for the first time. The operation principle of the proposed gas-discharge system is similar to that of a microwave electrothermal rocket engine. A mixture of hydrocarbons and hydrogen is used as a plasma-forming gas. It is demonstrated that the proposed method allows the plasma-forming gas to be used at pressures far above the upper limit of the working pressures of modern gas-discharge devices of film deposition in the plasma generated by a superhigh-frequency discharge (approximately 40000 Pa).

The influence of the molecular structure of gas flows on the characteristics of turbulent flows and the effect of the properties molecules on turbulent processes have been studied. This paper presents a review of the results of study of turbulent processes. Data on flows at the boundary of a supersonic jet and in a tube with an expanding input section, and Hagen-Poiseuille flow are given. Experimental study of Hagen-Poiseuille has shown that the molecular properties of the medium affect the critical Reynolds number. It is shown that in comparing the critical Reynolds numbers for flows of different gases at different pressures, the determining parameter is the second virial coefficient.

This paper presents results of an experimental study, numerical calculation, and analysis within the framework of a gas-dynamic model of silicon film deposition by a gas-jet plasma-chemical method. A numerical model of a flow of gas mixtures, flowing out of an annular nozzle unit and flowing into a reactor, is developed, and it allows one to determine a film thickness distribution over the surface of substrates placed in the reactor and describes the experimental data obtained satisfactorily

Direct Simulation Monte Carlo method was used to study plane-parallel flow of hydrogen through an obstacle formed by a series of parallel infinite wires. Particular attention was paid to the influence of the geometric parameters of the wire obstacle, the degree of rarefaction and the velocity of the flow on the degree of hydrogen dissociation due to heterogeneous reactions on the wire surface.

Expansion of near-wall films of liquids with different physical properties accompanied by high-velocity co-current gas flow from a nozzle into vacuum is studied experimentally. Local parameters of liquid films inside the nozzle are measured. Gas-droplet flow structure behind the nozzle exit cross-section is examined. Limiting temperatures of liquid films formed on the nozzle outer surface are measured.

A possibility of using small-scale vacuum setups for experimental investigations of supersonic jets escaping from supersonic nozzles into vacuum or a rarefied space is considered. Results of studying the structure of the secondary supersonic flow formed in supersonic jets with developed condensation, which is detected for the first time, are reported. The present investigations are carried out with the use of photometry and spectrometry of jets with the use of emission excited by an electron beam; flow visualization is also performed. The results obtained in the study are analyzed; capabilities and specific features of various methods of flow registration are considered. An empirical model, which establishes the dependence between the detected secondary flow and the process of formation of large clusters in the flow, is developed and justified.

A self-consistent model for plasma polarization around an isolated dust particle with a size of 10^-6 m under the action of an external electric field is presented. It is shown that, for various intensities of the external electric fields behind the dust particle, there are self-consistent potential oscillations. The calculation results are compared with data obtained by using the known numerical approaches.

The process of folding of villin subdomain HP-35 has been studied using the method of molecular dynamics. To characterize protein conformations, two variables are introduced which correspond to the distances between fluorophores in experiments on protein folding with the Forster resonance energy. The simulation results show that the flow field of the probabilities of transitions between protein states is filled with eddies. It has been found that in contrast to the previously studied cases of hydrodynamic turbulence and turbulence in protein folding in the three-dimensional conformational space, the structure functions of the flows of various orders depend linearly on the increment in the conformational space. An explanation of this linear dependence based on the -model is proposed, and it is shown that this dependence is not due to the choice of variables for describing the folding process.

This paper describes the study of the effect of spatial inhomogeneity of surface temperature on the size of a crater forming in the case of pulsed laser ablation. It is assumed that the surface temperature is linearly dependent on laser radiation energy. Analytical expressions determining the effective radius of an evaporation region, characteristic temperatures of the surface on which evaporation occurs, and evaporation depths in the case of the Gaussian distribution of laser radiation energy are derived. It is shown that the analytical dependences obtained are in good agreement with known numerical calculation results.

The formation of a fluoropolymer coating by chemical deposition has been studied. It has been found that increasing the flow rate of the precursor gas leads to a decrease in the growth rate of the coating. The conditions deposition was analyzed, and the gas dynamic parameters of the process were estimated. It is shown that the estimates are consistent with experimental data.

A conjugated initial-boundary-value problem occurring in the movement of a binary mixture and viscous heat-conductive liquid with a common interface surface under the action of thermal-concentration forces is under consideration. A solution describing a stationary flow in layers, temperature distribution, and concentration distribution is determined. The Laplace transform method is used to obtain a nonstationary solution for the problem in images, which makes it possible to describe the evolution of the movement using the numerical inversion of images.

A Prandtl slope flow model is generalized for the case with a homogeneous stationary source of a heavy impurity that significantly changes the medium density. A stationary analytical solution for a velocity of arising flows, temperature deviations, and impurity distribution is obtained. The model describes, for example, some special features of the dynamics of a ground snowstorm above a slope surface.

Numerical study has been performed to investigate the characteristics and operating modes of an energy storage device based on a pulsed magnetohydrodynamic generator and a step-up transformer with a stored energy of 25 and 50 MJ and a secondary winding current of 250 kA at the final stage of operation. The operating parameters of such storage devices with rail launchers in the mode of rapid-fire launching of several projectiles.

The results of temperature and concentration measurements of secondary electrons in a free jet of argon, activated in an electron beam plasma, carried out using a Langmuir double electrostatic probe. A cold plasmotron prototype with a primary beam energy of 1 keV is used obtain a jet of dense cold plasma with a transverse size of approximately 80 mm and parameters with which silicon layers may be deposited with necessary characteristics in a forvacuum pressure range.

The main methods used to measure viscoelastic properties of materials in a wide range of frequencies from 10^-4 to 10⁶ Hz are reviewed. It is demonstrated that the accuracy of many experimental methods can be increased by taking into account the shape factors, which depend on the specimen type. An example of the shape factor for a cylindrical specimen is provided, which was determined numerically on the basis of a two-dimensional deformation model taking into account the specimen geometry and Poisson's ratio. The importance of the precise determination of Poisson's ratio for rubber-like and complex-structured materials is demonstrated. Requirements to such measurements and a setup satisfying these requirements are described. Two methods for measuring viscoelastic properties of living tissues (compliance and disturbance propagation velocity) are considered. Based on the developed method of measuring these parameters for materials with a fixed thickness, methods for standartization of measurements of viscoelastic characteristics of living tissues are proposed.

This paper considers the two-dimensional problem of high-velocity translational-nonequilibrium flow of a monatomic gas past a surface which was formulated in the theory of viscous hypersonic flows based on macrokinetic 13-moment Grad equations using the approximation of a two-layer thin viscous shock layer (TVSL) near non-thin bodies. A class of similarity variables is proposed that allows the kinetic problem of a TVSL to be reduced to the well-studied Navier-Stokes problem of a TVSL.

An experimental study has been performed to investigate the integral characteristics of the processes of heat and mass transfer and phase transformations during interaction of a droplet flow with the combustion front of a highly porous condensed material. The macroscopic regularities of the suppression of flaming combustion and thermal decomposition of typical forest fuel material due to the removal of heat as a result of its absorption during vaporization and convective cooling were studied. Three versions of interaction of a droplet aerosol with burning forest fuel material were considered. The time of combustion termination and the time of thermal decomposition of forest fuel materials were determined. The mechanisms of the main physicochemical processes occurring during interaction of droplet flow with the combustion front of typical forest fuel materials were established.

The onset of the Benard-Marangoni convection in a horizontal porous layer permeated by a magnetohydrodynamic fluid with a nonlinear magnetic permeability is examined. The porous layer is assumed to be governed by the Brinkman model; it is bounded by a rigid surface from below and by a non-deformable free surface from above and subjected to a non-vertical magnetic field. The critical effective Marangoni number and the critical Rayleigh number are obtained for different values of the effective Darcy number, Biot number, Chandrasekhar number, nonlinear magnetic parameter, and angle from the vertical axis for the cases of stationary convection and overstability. The related eigenvalue problem is solved by using the first-order Chebyshev polynomial method.

Level oscillations and flow in the basin of the Sea of Azov have been studied by hydrodynamic modeling using the POM Princeton Ocean Model). The hypothesis on the role of the resonance mechanism in the occurrence of extremely large amplitudes of storm surge and seiche oscillations depending on the velocity and time of motion of atmospheric fronts of the Sea of Azov has been tested. It is found that at the same wind, baric disturbances moving over the Sea of Azov induce forced oscillations, and after the disturbances cease, free oscillations with amplitudes that are 14% higher than those obtained at constant atmospheric pressure. It is shown that the movement of the atmospheric front (whose speed and time are selected under the assumption that waves with maximum amplitudes are generated) plays an important, but not decisive role in the development of the flow structure and level oscillations in the Sea of Azov.

A lumped-parameter mechanical system consisting of a chain of physically related solids, each of which has one rotational degree of freedom. It is shown that inertial-free elastic elements that connect absolutely rigid bodies of the chain can be chosen in such a way that the mechanical structure acquires the properties of the so-called absolute mechanical filter. The motion of any inertial element of this system is described by the equation of a classical harmonic oscillator with one degree of freedom. Using the system considered as an example, it is shown that there is a relationship between the models of classical and quantum mechanics. From the positions of modern classical mechanics, this lumped-parameter system confirms the Einstein's hypothesis well-known in theoretical physics and stating that a solid is a system of independent oscillators.

It is shown that the classes of exact solutions of Navier-Stokes equations with a linear and inversely proportional dependence between velocity components and some spatial variables can be expanded by adding finite perturbations, being power or trigonometric series or their sections on one of the coordinates. An example of single integration of three-dimensional equations of motion of a viscous liquid, which are reduced to an equation for the potential of two velocity components, is given.

This paper describes an experimental study of the effect of temperature on the fracture of laser welds of Mg- and Cu-containing aviation aluminum alloys. The fracture of alloys and their welds under a uniaxial loading at temperatures of -60, 20, and 85 ^oC is investigated. It is revealed that the strength and ultimate strain of welds of Cu-containing alloys decrease as temperature rises because of the formation of immobile hot spots of localized plastic shifts. Heating and cooling suppress the Portevin- Le Chatelier effect and significantly reduce the ultimate strain of a Mg-containing alloy, even though such reduction is not observed in a weld. It is shown that, at a negative temperature, the maximum limiting lengthening of the weld of a Mg-containing alloy is achieved, while the formation of secondary cracks is activated during heating.

The possibility of using nitrogen-containing plasma that forms in a high-frequency charge is shown, and the plasma effect on changes in the physical and chemical properties of the inner surface of the cylinder is tested. The properties are estimated in accordance with the ISO 14577 standard on a “Nanoskan-3D” device. It is revealed that the microhardness of a bottom hole pump cylinder treated in the plasma of a high-frequency charge increases by a factor of 2 to 2.5, while the elasticity modulus becomes 25 to 40% larger.

Ablation of monocrystalline silicon to atmospheric environment induced by a millisecond pulse of an Nd:YAG optical laser with a wavelength of 1064 nm is studied. Shadowgraphy is applied to study the process of monocrystalline silicon plasma expansion for the laser energy density of 955.4-2736.0 J/cm². It is shown that the outer boundary of the plasma plume diffuses outside with time. Plasma expansion occurs in both axial and radial directions, but the velocity of plasma expansion in the radial direction is smaller than in the axial direction. Two centerlines of the laser action are symmetric. The maximum expansion velocity of 162.1 m/s is reached with the laser energy density of 2376.0 J/cm², and a laser-supported combustion wave is generated in this case. In contrast to monocrystalline silicon under the action of a short-pulse laser, the millisecond laser action can make the plasma expansion velocity increase for the second time. A material splash can be observed from the expansion images in the case of a high laser energy density.

Numerical simulations are performed to systematically investigate the effect of the downstream crescent-shaped block height on the flow field and cooling performance for a configuration with a single row of an infinite number of inclined cylindrical holes at various coolant-to-mainstream blowing ratios. The numerical results show that placing a downstream block can significantly alter the downstream flow field due to generation of an additional anti-kidney vortex pair, which improves the cooling performance. Optimal block heights are determined for various blowing ratios.