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Journal of Applied Mechanics and Technical Physics

2013 year, number 5

Structure of the Disturbed Region of the Atmosphere after the Nuclear Explosion in Hiroshima

M. D. Shcherbin, K. V. Pavlyukov, A. A. Salo, S. F. Pertsev and A. V. Rikunov
Keywords: atmosphere, convection, explosion, rain, tornado, electric field

Abstract >>
An attempt is undertaken to describe the development of the disturbed region of the atmosphere caused by the nuclear explosion over Hiroshima on August 6, 1945. Numerical simulation of the phenomenon is performed using the dynamic equations for a nonconducting inviscid gas taking into account the combustion of urban buildings, phase changes of water, electrification of ice particles, and removal of soot particles. The results of the numerical calculation of the development of the disturbed region indicate heavy rainfall, the formation of a storm cloud with lightning discharges, removal of soot particles, and the formation of vertical vortices. The temporal sequence of these meteorological phenomena is consistent with the data of observations. Because of the assumptions and approximations used in solving the problem, the results are of qualitative nature. Refinement of the results can be obtained by a more detailed study of the approximate initial and boundary conditions of the problem.

Numerical Study of Solidification of a Nano-Enhanced Phase Change Material (NEPCM) in a Thermal Storage System

S. Kashani, A. A. Ranjbar, M. M. Madani, M. Mastiani and H. Jalaly
Keywords: nanoparticle, phase change material, thermal storage, natural convection

Abstract >>
The effects of nanoparticle dispersion on solidification of a Cu–n-hexadecane nanofluid inside a vertical enclosure are investigated numerically for different temperatures of the left vertical wall. An enthalpy porosity technique is used to trace the solid-liquid interface. The resulting nanoparticle-enhanced phase change materials (NEPCMs) exhibit enhanced thermal conductivity in comparison to the base material. The effect of the wall temperature and nanoparticle volume fraction are studied in terms of the solid fraction and the shape of the solid-liquid phase front. It has been found that a lower wall temperature and a higher nanoparticle volume fraction result in a larger solid fraction. The increase in the heat release rate of the NEPCM shows its great potential for diverse thermal energy storage applications.

Closed-Form Model for the Analysis of W-Type Shaped Charges

A. Mahdian, M. Ghayour and G. H. Liaghat
Keywords: secondary jet formation theory, W-type shaped charge

Abstract >>
This paper presents a closed-form model for the analysis of symmetric planar W-type shaped charges (WSCs) with two V-sections, which produce two primary cores and two primary jets. If these two V-sections have proper asymmetry, these primary cores will force two primary jets into a secondary core formed on the axis of symmetry of a planar symmetric WSC. For the analysis of such a planar WSC, a complete generalized model for an asymmetric planar V-shaped charge (VSC) with any desired order of asymmetry is mandatory. In this paper, the model is applied to describe the secondary jet formation in the WSC. By presenting a closed-form analysis of the WSC, the secondary jet specifications can be easily evaluated and, thus, can be compared with respect to the jet quantities in symmetric or asymmetric VSCs. Finally, for the primary and secondary jets, the coherency conditions are investigated, and the critical parameters responsible for these conditions are determined.

Numerical Study of a Single Drop Impact onto a Liquid Film up to the Consequent Formation of a Crown

T. Jiang, J. Ouyang, X. Li, J. Ren and X. Wang
Keywords: SPH, droplet impact, liquid film, surface tension, splashing

Abstract >>
In this paper, the whole dynamic process of a single drop impact onto a thin liquid surface up to the consequent formation of a thin crown is numerically studied using the smoothed particle hydrodynamics (SPH) method. Especially, the gravity, artificial viscosity, and surface tension are introduced into the model. The obtained SPH numerical results are compared with experimental results. The numerical model of the SPH method is valid for simulating the dynamic process of a single drop impact onto a liquid surface. Meanwhile, it is found that the whole dynamic process mainly depends on the depth of the liquid pool and the initial velocity of the droplet.

Bifurcations of the Flow Characteristics of an Adjustable Supersonic Nozzle

S. A. Rashkovskii, Yu. M. Milekhin, A. N. Kluchnikov and A. V. Fedorychev
Keywords: adjustable nozzle, flow characteristics, bifurcation, flow separation

Abstract >>
A ground-based experimental study of the flow characteristic of an adjustable high-altitude nozzle was performed. It is shown that the flow characteristic of the adjustable nozzle can significantly depend on the design of its supersonic part and operation conditions. It is found that the operation such nozzles can involve different flow regimes of the working fluid depending on the position of the regulator; under certain conditions, there may be an abrupt change in the flow regime, which leads to an abrupt change (bifurcation) of the flow characteristic of the nozzle.

Unsteady Flow of an Incompressible Viscous Fluid around a Deformable Spherical Body

A. Zh. Karsyan
Keywords: viscous fluid, unsteady flow, hydrodynamic impact, small radial displacements of the body surface, Stokes approximation

Abstract >>
An unsteady flow of a viscous incompressible fluid around a deformable spherical body is considered in the approximation of low Reynolds numbers with a predetermined flow velocity. The hydrodynamic impact of the flow incoming onto the body is determined with allowance for small radial displacements of the body surface. The effect of spherical body surface deformation on the magnitude of the incoming flow impact force is taken into account, in particular, the dependence of small radial displacements of the body surface on the time is found, which makes it possible to minimize the physical impact of the incident flow.

Stability of an Overheated Liquid Containing Vapor-Gas Bubbles

V. Sh. Shagapov, V. V. Koledin and N. K. Vakhitova
Keywords: stability, metastable liquid, vapor-gas bubble, increment, critical mass of the bubble

Abstract >>
The problem of the stability of an overheated liquid containing bubbles of an insoluble gas is considered. The critical conditions for the masses of gas bubbles, their radii, and volume concentrations are determined for the case of the stable state of the system consisting of a liquid and vapor-gas bubbles. Theory of spontaneous solutions is constructed which describes the exit of the overheated vapor-gas bubble system from the unstable state. On the basis of such solutions, the dynamics of transition of the overheated liquid to a stable state is studied.

Simulation of Operation Modes of a Centrifugal Conductive Magnetohydrodynamic Pump

S. S. Katsnel'son and G. A. Pozdnyakov
Keywords: mathematical simulation, magnetic hydrodynamics, molten metal, MHD pump, disk channel, governing parameters

Abstract >>
A mathematical model of a centrifugal conductive magnetohydrodynamic (MHD) pump that calculates the distributions of velocity, current density, and pressure along the channel is developed. The viscous forces in the original system of MHD equations are taken into account on the basis of the known square law of the drag for a turbulent flow in a pipe, generalized for the case of plane flows in a channel. Dependences of the drag coefficient on the main governing parameters (metal flow rate, current intensity, and intensity of magnetic induction), which provide the agreement of the calculated and experimental data on the pressure at the pump outlet for different operation modes, are obtained. It is shown that these dependences have a universal character and the proposed model can be used to design pumps of this type and to manage their operation in production industry.

Wavy Flow of a Liquid Film in the Presence of a Cocurrent Turbulent Gas Flow

Yu. Ya. Trifonov
Keywords: viscous film flows, nonlinear waves, cocurrent and countercurrent flow, ripple waves

Abstract >>
Wavy downflow of viscous liquid films in the presence of a cocurrent turbulent gas flow is analyzed theoretically. The parameters of two-dimensional steady-state traveling waves are calculated for wide ranges of liquid Reynolds number and gas flow velocity. The hydrodynamic characteristics of the liquid flow are computed using the full NavierStokes equations. The wavy interface is regarded as a small perturbation, and the equations for the gas are linearized in the vicinity of the main turbulent flow. Various optimal film flow regimes are obtained for the calculated nonlinear waves branching from the planeparallel flow. It is shown that for high velocities of the cocurrent gas flow, the calculated wave characteristics correspond to those of ripple waves observed in experiments.

On One Slip Condition for the Equations of a Viscous Fluid

V. V. Shelukhin and U. A. Khristenko
Keywords: micropolar fluid, mud cake, joint flow

Abstract >>
By studying the joint flow of a viscous and a micropolar fluid, we obtained a new boundary condition for the equations of the viscous fluid for the case where a thin layer of a granular fluid is present on the interface with the solid. Examples of using this condition in problems of drilling mud flow in the presence of a mud cake on the borehole wall are given.

Hydrodynamics of the Fluid Layer on the Drum of an Adhesion Skimmer

A. I. Filippov and T. A. Ishmuratov
Keywords: drum oil skimmer, adhesion, critical mode, NavierStokes equations, flow in a layer

Abstract >>
An approximate model is proposed to describe the hydrodynamic processes of viscous fluid flow on a moving rotating cylinder in a stationary formulation. Expressions for the critical and optimum thickness of the fluid layers are obtained, and conditions for the existence of a roll in front of the moving cylinder are determined. The obtained solutions are used to derive relations between the physical and geometrical parameters of a rotating adhesion skimmer.

Method for Determining Relative Permeabilities from Data on Unsteady Filtration by Combined Physical and Computer Modeling

D. M. Orlov, A. E. Ryzhov and T. A. Perunova
Keywords: hydrodynamics of a porous medium, multiphase flow, computer modeling

Abstract >>
A method for determining relative permeabilities from data on unsteady filtration is proposed based on analytical solution of the inverse problem of filtration in the Buckley–Leverett approximation (JohnsonBosslerNaumann method), verification of the results by numerical solution of the direct problem, and developing recommendations for changing the filtration conditions in subsequent experiments. It is shown that to improve the agreement between natural phase permeabilities and those obtained under laboratory conditions, it is advisable to combine physical and numerical experiments.

Thermomechanical and Thermophysical Properties of Repulsive Clathrates

V. A. Eroshenko and Ya. G. Grosu
Keywords: porous solids, liquids, interfacial surface, lyophobic property, hysteresis, capillary pressure, compression-expansion isotherm, specific heat, adiabatic exponent

Abstract >>
The range of the characteristic properties of repulsive clathrates (RKs), which are new working media used for efficient energy conversion in thermomechanical systems, has been extended. The dissipation, storage, and conversion of energy by means of RCs is based on the use of the intermolecular forces acting on the interface of the system of a liquid and a nonwetting solid capillary-porous matrix and leading to ejection of the liquid from the pores of the matrix. It has been shown that it is possible to control characteristics of RCs such as compressibility, amount of the dissipated (accumulated) mechanical energy, specific heat, and thermal parameters of the compression-expansion process. The properties of RCs providing unique operation modes of power systems that are not realizable with conventional working media (gas, steam).

Effect of the Medium Inhomogeneity on the Evolution Equation of Plane Shock Waves

V. E. Ragozina and Yu. E. Ivanova
Keywords: nonlinear elastic medium, inhomogeneity, shock waves, bulk and shear deformation, evolution equation

Abstract >>
Using the method of matched asymptotic expansions, solutions of boundary-value problems of shock deformation of nonlinear elastic weakly inhomogeneous semispaces are obtained. It is shown that nonlinearity of the model and various properties of the inhomogeneity lead to new evolution equations in the frontal areas of longitudinal and transverse shock waves, the transition to which is due to transformations of all independent coordinates of the problem.

Diffusion in a Generalized Thermoelastic Solid in an Infinite Body with a Cylindrical Cavity

J. N. Sharma, N. Kumari and K. K. Sharma
Keywords: cylindrical cavity, infinite space, diffusion, thermoelasticity, small time approximation

Abstract >>
A dynamic problem of an infinite isotropic cylinder of radius r subjected to boundary conditions of the radial stress, temperature, or concentration of the diffusing substance is studied by using the equations of state of a elastothermodiffusive solid with one relaxation time and the Laplace transform technique. The distributions of the displacement, temperature, and concentration are displayed graphically and analytically.

Method of Calculating the Characteristics of Ablation of Materials on the Basis of Invariant Solutions of Equations in Partial Derivatives

G. V. Druzhinin and F. K. Smorodin
Keywords: gas flow, thermal effect, melting, ablation, thermal protection, radiation emission, subgroup, differential equation

Abstract >>
On the basis of an invariant H2-solution, an analytical solution of a reduced problem of melting of a crystalline material is obtained. A formula that determines material ablation in a molten state in the vicinity of the stagnation point is derived.

Optimization of Geometry of Elastic Bodies in the Vicinity of Singular Points on the Example of an Adhesive Lap Joint

V. P. Matveenko, N. V. Sevodina and A. Yu. Fedorov
Keywords: adhesive joints, simple lap joint, stress singularity, finite element analysis, compound shape, geometry optimization

Abstract >>
The stress state in adhesive lap joints with various geometric shapes of spew fillet is studied. It is noted that the applied design models of the considered problem include singular points at which infinite stress values are possible if one uses the linear elasticity theory to calculate the stress state. Based on the conclusions of the solution of the geometry optimization problem in the vicinity of the singular points of elastic bodies, variants of the geometry of spew fillet, which provide the most significant decrease in the concentration of stresses in adhesive lap joints, are proposed.

An Efficient and Simple Refined Theory for Nonlinear Bending Analysis of Functionally Graded Sandwich Plates

A. Kaci, K. Draiche, M. Zidi, M. S. A. Houari and A. Tounsi
Keywords: refined plate theory, nonlinear analysis, energy method, sandwich plate, functionally graded material

Abstract >>
In this paper, an efficient and simple refined theory is presented for nonlinear bending analysis of functionally graded sandwich plates. The theory presented is variationally consistent, does not require the shear correction factor, and gives rise to transverse shear stress variations such that the transverse shear stresses vary parabolically across the plate thickness, satisfying shear-stress-free surface conditions. The energy concept along with the present theory and the first- and third-order shear deformation theories is used to predict the large deflection and the stress distribution across the thickness of functionally graded sandwich plates.

Rock Tests in Nonuniform Fields of Tensile Stresses

V. P. Efimov
Keywords: strength, tension, bending, Brazilian method, structural parameter

Abstract >>
This paper presents experimental data on the strength of samples tested for bending and diametrically compressed core-shaped samples with a central hole. The obtained strengths of the samples are compared with the strength of samples under uniaxial tension using nonlocal strength criteria. It is shown that the calculated and measured strengths of the rock samples are in good agreement with each other when using a common approach to strength evaluation based on the NeuberNovozhilov integral fracture criterion.