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Journal of Applied Mechanics and Technical Physics

2019 year, number 1

Influence of an External Air Flow on a System of high-Voltage Asymmetrical Electrodes

M. Malik, J. Primas, M. Kotek, D. Jašikova, V. Kopecky
Technical University of Liberec, Liberec, 461 17, Czech Republic
Keywords: поток воздуха, асимметричная система электродов, электрогидродинамика, высокое напряжение, метод слежения за частицами, велосиметрия, air flow velocity, asymmetrical electrodes, electrohydrodynamics, high voltage, particle image velocimetry (PIV)

Abstract >>
The paper deals with the problem of ascertaining the value of air flow velocity necessary to prevent electric current through the motion of ionized air between two asymmetrical electrodes. By means of this experiment, the authors aim to prove the ion basis for the phenomenon of a mechanical force generated by a system of asymmetrical electrodes connected to high voltage. Particle image velocimetry (PIV) is used to precisely map the vector field of the air flow around the electrodes. The calculated and measured values of air flow velocity are compared, and good agreement between them is found.

Development of the Air Blowing and Suction Technology for Control of a Turbulent Flow on an Airfoil

V. I. Kornilov, I. N. Kavun, A. N. Popkov
Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090, Russia
Keywords: крыловой профиль, турбулентный пограничный слой, мелкоперфорированная поверхность, вдув, отсос, аэродинамическое качество, подъемная сила, сопротивление, airfoil, turbulent boundary layer, finely perforated surface, blowing, suction, lift-to-drag ratio, lift force, drag force

Abstract >>
The possibility of using a combined method of control of an incompressible turbulent boundary layer on the NACA 0012 airfoil is studied experimentally and numerically. The method is based on air blowing and suction through finely perforated walls, which are parts of the airfoil. The study is performed for Reynolds numbers Rec=0.7 · 106 and angles of attack α =-6 - 60. It is demonstrated that the mechanism responsible for changes in the aerodynamic characteristics of the airfoil is the same for all variants of the control action in the form of air blowing and suction: an increase in pressure due to air blowing on one side of the airfoil and a decrease in pressure due to air suction on the opposite side lead to an increase in the lift force and, finally, to a gain in the lift-to-drag ratio of the airfoil, which reaches three units at α ≈ 0o. Unfortunately, the efficiency of this method of boundary layer control decreases with increasing α.

Internal Gravity Waves Excited by a Moving Oscilatting Source in a Stratified medium with Variable Buoyancy

V. V. Bulatov, Yu. V. Vladimirov
Ishlinsky Institute for Problems in Mechanics, Russian Academy of Sciences, Moscow, 119526, Russia
Keywords: стратифицированная среда, внутренние гравитационные волны, переменная частота плавучести, stratified medium, internal gravity waves, variable buoyancy frequency

Abstract >>
A problem of a far field generated by internal gravity waves from an oscillating point source of perturbations that moves in a vertically infinite stratified medium with variable buoyancy. For a simulated quadratic distribution of buoyancy frequencies, analytical solutions of the main boundary-value problem are obtained, expressed through parabolic cylinder functions. Asymptotic solutions constructed in this paper make it possible to describe amplitude-phase characteristics of far fields generated by internal gravity waves in a stratified medium with a variable Brunt- Väiää frequency.

Effect of Different Flows on the Shear Branding of a Liquid with a Non-Monotonic Flow Curve

Yu. L. Kuznetsova, O. I. Skul'skiy
Institute of Continuous Media Mechanics, Ural Branch, Russian Academy of Sciences, Perm, 614013, Russia
Keywords: расслоение сдвигового течения, модифицированная модель Виноградова - Покровского, немонотонность кривой течения, множественность решений, время установления, shear banding of the shear flow, modified Vinogradov-Pokrovsky model, non-monotonic flow curve, multiple solutions, determination time

Abstract >>
A Couette flow of liquid, described by a modified Vinogradov-Pokrovsky model with a non-monotonic flow curve is simulated. It is shown that the analytical solution of the stationary problem has an infinite set of solutions. The time-dependent problem is numerically simulated in the assumption that the components of the structural tensor take values corresponding to a current change in the velocity field. It is determined that the time it takes for the plate velocity to reach a given value significantly affects the velocity profile and the dependence of tangential stresses on an operating shear rate. It is shown that, as this time decreases, the shear banding of the flow is observed not only for shear rates corresponding to the downward branch of the flow curve, but also in the entire domain of its ambiguity.

Oil Filtration in a Porous Medium in the Presence of Graphene Nanoparticles

Yu. V. Pakharukov1,2, F. K. Shabiev1,2, B. V. Grigoriev2, R. F. Safargaliev2, I. R. Potochnyak2
1Tyumen Industrial University, Tyumen, 625000, Russia
2Tyumen State University, Tyumen, 625003, Russia
Keywords: фильтрация нефти, графеновая суспензия, микрогетерофазная структура, oil filtration, grapheme suspension, microheterophase structure

Abstract >>
The filtration of a graphene suspension through a core sample has been studied experimentally. It has been found that at the oil-water interface in the porous medium of the core sample, a transient multilayer microheterophase structure consisting of planar graphene nanoparticles, hydrocarbon oil molecules and surfactants is formed. It has been found that with an increase in the concentration of graphene nanoparticles, the volume fraction of the displaced oil increases and the volume fraction of water in oil decreases.

Gas Filtration in a Low-Permeability Formation with a Hydraulically Fractured Well

A. Ya. Davletbaev1, Z. S. Muchametova2
1Bashkir State University, Ufa, 450074, Russia
2Ufa State Oil Technical University, Ufa, 450000, Russia
Keywords: фильтрация газа, трещина, гидравлический разрыв пласта, низкопроницаемый коллектор, газодинамические исследования скважин, gas filtration, fracture, hydraulic fracturing, low-permeability formation, gas well testing

Abstract >>
This paper presents the results of the numerical calculation of gas filtration in a low-permeability gas formation with a fractured well. It is assumed that finite-conductivity filtering is described by Darcy law. The Peng-Robinson equation was used to take into account the dependence of the PVT properties of the gas on pressure. We studied the effect of fracture conductivity and formation permeability on the distribution of pressure and gas properties in a “fracture-formation” system and on the dynamics of pressure of the well and the gas production rate in the well during well-testing.

Longitudinal waves in a Saturated Porous Medium

A. Begmatov
National University of Uzbekistan, Tashkent, 100174, Uzbekistan
Keywords: волна, пористость, затухание, скорость, частота, дисперсия, асимптотика, wave, porosity, attenuation, velocity, frequency, variance, asymptotics

Abstract >>
Longitudinal waves in a saturated porous medium simulated by a double-phase medium are under study. Exact expressions for a wave propagation velocity and attenuation coefficient are obtained. High-frequency and low-frequency wave asymptotics is investigated, and partial cases of soft and dry soils are considered.

Effect of a Passive Swirler on the Superheated Liquid Flow

K. A. Busov, A. V. Reshetnikov, N. A. Mazheiko, O. A. Kapitunov
Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences, Ekaterinburg, 620016, Russia
Keywords: перегретая жидкость, пассивный завихритель, взрывное вскипание, полный распад струи, эффект Коанда, superheated liquid, passive swirler, explosive boiling, full disintegration of the jet, Coanda effect

Abstract >>
The boiling in a superheated water jet discharged from a short cylindrical nozzle in the presence of a passive swirler has been experimentally investigated. The evolution of the disintegration of the boiling liquid jet with an increase in the degree of superheating has been studied. Characteristic structures and forms of the flow have been identified. The correlation between the jet shape and boiling regimes has been found. Significant fluctuations and flow instability at certain temperatures was noted. The possibility of influencing the flow pattern has been experimentally shown.

Temperature State of a Hollow Cylinder Made of a Polymer Dielectric with Temperature-Dependent Characteristics

V. S. Zarubin, V. N. Zimin, G. N. Kuvyrkin
Bauman Moscow State Technical University, Moscow, 105005Ю, Russia
Keywords: нелинейная математическая модель, полимерный диэлектрик, одномерное распределение температуры, интегральные соотношения, nonlinear mathematical model, polymer dielectric, one-dimensional temperature distribution, integral relations

Abstract >>
A mathematical model is constructed to describe a steady one-dimensional temperature distribution in a hollow circular cylinder made of a polymer dielectric with a constant difference in the electric field potentials on the cylinder surfaces. Based on systematized data on the dependence of the thermal conductivity and electrical conductivity of polymer materials used as dielectrics in engineering on temperature, a qualitative analysis of the model is performed for a prescribed density of the heat flux supplied to the inner surface of the cylinder and intensity of convective heat transfer on the outer surface. The results obtained in the study allow one to determine the area of applicability of polymer dielectrics used in various electrical engineering applications, including electrical insulation of DC high-voltage cables, and to formulate the conditions for the thermal breakdown of the cylindrical layer of the dielectric.

Experimental Determination of the Fire Break Size and Specific Water Consumption for Effective Control and Complete Suppression of the Front Propagation of a Typical Ground Fire

R. S. Volkov, G. V. Kuznetsov, P. A. Strizhak
National Research Tomsk Polytechnic University, Tomsk, 634050, Russia
Keywords: лесной горючий материал, термическое разложение, пламенное горение, фронт пожара, локализация, подавление, заградительная полоса

Abstract >>
This paper presents the results of an experimental study of the occurrence and control of flaming combustion and thermal decomposition of typical forest combustible materials by creating a fire break in the form of a wetted layer with a fixed width, length, and depth and a given volume of the contained liquid. The ranges of parameter values that ensure stable suppression of the flaming combustion and thermal decomposition of forest combustible material were determined. Experiments were performed for all major types of forest combustible materials: leaves, needles, twigs, and mixtures of the listed materials. Prediction of the required (minimum) water volumes and sizes of the fire break for guaranteed control of the combustion of forest combustible materials of the types studied was made.

Lifetime Cycle Testing of Model Nozzles Made of a Carbon--Carbon Composite Material in an Oxygen-Hydrogen Liquid-Propellant Rocket Motor

A. V. Anikin, R. D. Berdov, N. N. Volkov, L. I. Volkova, I. N. Gurina, S. M. Tsatsuev
Keldysh Research Center, Moscow, 125438, Russia
Keywords: огневые испытания, жидкостный реактивный двигатель, насадки, композиционные материалы, firing tests, liquid-propellant rocket motor, nozzles, composite materials

Abstract >>
Results of a series of firing tests of two model nozzles made of a carbon--carbon composite material are reported. This material can be used to fabricate nozzles for a large-scale liquid-propellant rocket motor. The tests are performed in an experimental setup operating on oxygen and hydrogen. It is shown that the thermochemical loads on the nozzle material in model tests are greater than those under real conditions. The temperature of the outer surface of the nozzle is measured in each experiment by thermocouples and an infrared imager. The level of linear erosion of the wall material during the entire test period is determined. It is demonstrated that the results of firing tests can be used for estimating the operation performance of a large-size motor. A simple analytical dependence is proposed for recalculating the results of model tests on material erosion to full-scale conditions.

Steady-State Creep of a Long Membrane in a Rigid Matrix with a Piece-Constant Dependence of the Rate of Change in Transverse Pressure Versus Time

A. M. Lokoshchenko1, E. A. Abrosimova1,2
1Research Institute of Mechanics, Moscow, 119192, Russia
2Moscow Aviation Institute, Moscow, 125993, Russia
Keywords: membrane, steady-state creep, matrix, transverse pressure, perfect slip, no-slip, non-stationary loading

Abstract >>
This paper deals with the problem of steady-state creep of a rectangular membrane in a rigid matrix with a ratio of the height to width of not less than 0.5 in the case of piecewise constant dependence lateral velocity over time. The creep of the membrane with a single change in the rate of transverse pressure over time is investigated. Two variants of the contact conditions of the membrane and matrix: perfect slip and no-slip are considered. Three stages of creep of the membrane are investigated. The analysis is carried out until the time at which the membrane is in almost complete contact with the walls of the matrix. Time dependences of the variable thickness of the membrane and the stress intensity in the membrane are obtained. It is shown that in this problem, the rule of summation of partial times is not performed.

Contact Problem of a Periodic System of Variable Width Slits with Partially Interacting Edges in the Presence of End Zones of Plastic Deformation

V. M. Mirsalimov1,2
1Azerbaijan Technical University, Baku, AZ1073, Azerbaijan
2Institute of Mathematics and Mechanics, National Academy of Sciences of Azerbaijan, Baku, AZ1073, Azerbaijan
Keywords: изотропная среда, периодическая система щелей переменной ширины, концевые зоны пластических деформаций, контактные напряжения, зоны сцепления, зоны проскальзывания, isotropic medium, periodic system of variable width slits, end zones of plastic deformation, contact stress, adhesion zones, slippage zones

Abstract >>
A problem of compression of an isotropic medium with a periodic system of variable width slits compared with elastic displacements is under consideration. The edges of the slits are under the action of internal pressure. It is assumed that the ends of the slits have zones of plastic deformation. The presence of several zones of contact of the edges of each slit is studied in the assumption that one of the section may have slippage. The problem of equilibrium of the periodic system of slits with partially contacting edges under the action of a compressive load reduces to the problem of linear coupling of analytical functions. Contact stresses and the sizes of contact zones, adhesion zones, and end zones of plastic deformations are determined.

Transversely Isotropic Tensor Closest in Euclidean norm to a Given Anisotropic Elastic Modulus Tensor

N. I. Ostrosablin
Lavrent'ev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090, Russia
Keywords: модули упругости, неприводимые инвариантные разложения, трансверсально-изотропный тензор, евклидово расстояние, ближайшие тензоры, elastic moduli, irreducible invariant decompositions, transversely isotropic tensor, Euclidean distance, closest

Abstract >>
The problem of determining the transversely isotropic tensor closest in Euclidean norm to a given anisotropic elastic modulus tensor is considered. An orthonormal basis in the space of transversely isotropic tensors for any given axis of symmetry was obtained by decomposition of a transversely isotropic tensor in the general coordinate system into an isotropic part, two deviator parts, and a nonoric part. The closest transversely isotropic tensor was obtained by projecting the general anisotropy tensor onto this basis. Equations for five coefficients of the transversely isotropic tensor were derived and solved. Three equations that are stationary conditions were obtained for the direction cosines of the axis of rotation (symmetry). Solving these equations yields the absolute minimum distance from the transversely isotropic tensor to the given anisotropic elastic modulus tensor. The transversely isotropic elastic modulus tensor closest to the cubic symmetry tensor was found.

Plane Harmonic Waves in Thermoelastic Materials with a Memory-Dependent Derivative

M. Bachher
Media Girls' High School, Gobardanga, North 24 Parganas, West Bengal, India
Keywords: модель Лорда - Шульмана, производная с памятью, время запаздывания, функция ядра, потенциал смещений, Lord-Shulman model, memory-dependent derivative, time delay, kernel function, displacement potential

Abstract >>
The Lord-Shulman theory of generalized thermoelasticity based on a memory-dependent derivative is employed to study the propagation of plane harmonic waves in a two-dimensional semi-infinite thermoelastic medium. The numerical solution is analyzed for various values of the time delay parameter.

Fracture of a Three-Layer Material with a Normal Detachment Central Crack

A. I. Seyfullayev
Institute of Mathematics and Mechanics of the National Academy of Sciences of Azerbaijan, Baku, AZ1141, Azerbaijan
Keywords: слоистые композиты, трещина, коэффициент интенсивности напряжений, layered composites, crack, stress intensity factor

Abstract >>
This paper describes a problem of the theory of elasticity for a three-layer material in which two layers located symmetrically relative to the central layer have identical properties. The central layer has a normal detachment crack whose tops are located in the neighboring layers. The solution of this problem is reduced to solving a system of Fredholm integral equations of the second kind. A stress intensity factor for normal detachment cracks is determined, and its dependence on the problem parameters is investigated.

Production and Machining Performance Study of Nano Al2O3 Particle Reinforced LM25 Aluminum Alloy Composites

T. P. Thankachan
Rajagiri School of Engineering Technology, Kochi, India
Keywords: макрогетерогенные металлические композиты, механические свойства, литье, metal matrix composites (MMCs), mechanical properties, casting

Abstract >>
The purpose of this study is to prepare specimens of 10 and 20% nano Al2O3 particle reinforced LM25 metal matrix composites (MMCs) by stir casting. Another goal is to develop models using the response surface methodology (RSM) approach for predicting the surface roughness parameters and cutting force components during machining of the MMCs by a CBN7020 tool. With the help of the model developed, comparisons of 10 and 20 wt. % nano Al2O3 particle reinforced LM25 MMCs are performed. Combined effects of three cutting parameters (cutting speed, feed rate, and depth of cut) on the surface roughness parameters and cutting force components are explored by using the analysis of variance (ANOVA). The resultant values of the parameters are found to agree well with available experimental values.

Analyzing the Correctness of Problems of Bending of Equal Strength Composite Profiled Beams

A. N. Polilov1, N. A. Tatus'1, Sh. Tyan2
1Mechanical Engineering Research Institute, Russian Academy of Sciences, Moscow, 101990, Russia
2Xi'an University, Xi'an, 710049, China
Keywords: листовая пружина, профилированная балка, равнопрочная балка, прочность, жесткость, упругая энергия, оптимальная форма, композитная плоская пружина, spring sheet, profiled beam, equal strength beam, strength, rigidity, elastic energy, optimal shape, composite plane spring

Abstract >>
This paper describes the simplest cases of a rectangular cantilever beam loaded by an concentrated force that is distributed by the load or dead weight. There are five geometric parameters whose optimal values can be calculated on the basis of five requirements: rigidity (or concentrated elastic energy), strength, equal strength, ratio of sectional sizes, and resistance to the shear force (strength condition in interlaminar shear). The parameter range is determined, outside of which the linear beam theory cannot be used to correctly calculate the bending of equal strength beams loaded by distributed forces or dead weight.

Constitutive Relations of the Mechanics of a Damaged Medium for Evaluating the Long-Term Strength Structural Alloys

I. A. Volkov1, L. A. Igumnov2, D. A. Kazakov2, D. N. Shishulin3, I. S. Tarasov1, I. V. Smetanin1
1Volga State University of Water Transport, Nizhny Novgorod, 603950, Russia
2Research Institute of Mechanics, Nizhny Novgorod, 603022, Russia
3Alekseev Nizhny Novgorod State Technical University, Nizhny Novgorod, 603950, Russia
Keywords: неустановившаяся ползучесть, длительная прочность, степень повреждения среды, численные и лабораторные эксперименты, unsteady creep, long-term strength, degree of damage, numerical and laboratory experiments

Abstract >>
The main regularities of the degradation of the strength properties of structural materials (metals and alloys) resulting in a decrease in long-term strength were investigated. A mathematical model describing the viscoplastic deformation and damage accumulation in polycrystalline structural alloys in creep was developed using the equations of the mechanics of damaged media. The paper presents the results of experimental studies of the short-term creep of 12Kh18N9 steel and VZh-159 high-temperature alloy at constant temperatures and different stresses set in the samples and the results of experimental studies of creep recovery in some structural steels. The deformation and damage accumulation were studied numerically and the results were compared with the data of field experiments.

Localized Structural Instability and Dynamic Strength of Brittle Materials

Yu. I. Meshcheryakov, A. K. Divakov, N. I. Zhigacheva, G. V. Konovalov
Institute of Problems of Mechanical Engineering, Russian Academy of Sciences, Saint-Petersburg, 199178, Russia
Keywords: ударные испытания, локализованное хрупкое разрушение, откольная прочность, shock tests, localized brittle fracture, spall strength

Abstract >>
Four brittle materials are subjected to shock tests: gabbrodiabase, two modifications of cast iron, melted quartz, and beryllium. An interferometer is used to locally probe a free surface in order to calculate its velocity, thereby determining the criterion of the initial stage of brittle fracture of all materials tested - the formation of horizontal steps at the forefront of a compression pulse, which indicate the presence of local sources of fracture of the material. It is determined that the brittle material resists the shock compression as long as it has the reversible transfer of momentum and energy of the processes occurring at meso- and macrolevels.

Analytical Solution for the External Stress Acting on the Lining in a Deep-Buried Circular TBM Tunnel Considering the Seepage Field

Q. Yan1, C. Zhang1,2, W. Wu1, Y. Zhang1, T. Ma3
1Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, 610031, Chengdu, China
2Smart Material and Structure Laboratory, Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA
3China Railway Eryuan Engineering Group Co. Ltd, 610031, Chengdu, China
Keywords: облицовка туннеля, горнопроходческая машина, подземные воды, контролируемый дренаж, внешняя нагрузка, фильтрационные силы, упругое решение, TBM tunnel lining, groundwater, controlled drainage, external loading, seepage force, elastic solution

Abstract >>
Based on the elastic theory and the seepage flow theory, a new analytical solution with consideration of the seepage force is proposed to determine the external stress on the lining of a circular TBM tunnel. According to this solution, the relationships between the permeability coefficient of rock masses and the maximum allowable drainage flow are studied. The influence of the controlled drainage flow and the elastic modulus of surrounding rocks on the external stress is discussed. Moreover, in order to validate the results obtained from the elastic analytical solution developed in this paper, a comparison between the results obtained from the solution considering the seepage force and that without consideration of the seepage force is performed.