On the force acting on a heated spherical drop moving in a gaseous medium

The flow around a heated spherical drop in a viscous non-isothermal gaseous medium with uniformly distributed constant-power heat sources (sinks) acting inside is theoretically described in the Stokes approximation. It is assumed that the mean temperature of the drop surface can differ substantially from the temperature of the ambient gaseous medium. An analytical expression for the drag force and drift velocity in the gravity field is derived by solving hydrodynamic equations with allowance for the temperature dependence of viscosity, thermal conductivity, and density of the gaseous medium.     

Response of a spherical cavity in an elastic viscoplastic medium under a variable internal pressure

A closed-form solution is given for the problem of a spherical cavity in an infinite elastoviscoplastic medium with kinematic hardening, when the cavity is subjected to an internal pressure that varies in any prescribed way.Under certain assumptions this problem takes account of the unit weight of the medium, and is particularly applicable to the deep underground storage of natural gas in rock salt.Some typical loading cases are shown.     

Structure of the temperature field in a flow over heated waves

Liquid crystal thermometry (LCT) was used to quantify temperature fields in a flow over resistively heated waves and assess the effect of the large-scale longitudinal structures that were previously obtained in the velocity field for an isothermal flow (A. Günther and P. Rudolf von Rohr, submitted article, 2002). The wavelength 6 was 10 times larger than the amplitude, and the considered Reynolds numbers were 725 and 3300, defined with the bulk velocity and the half-channel height. A constant heat flux was imposed at the wavy bottom wall. For the first time, LCT was used to determine the fluid temperature in a wall-bounded flow with heat transfer. The dominant spanwise scale obtained from a proper orthogonal decomposition (POD) of the fluid temperature field above an uphill location of the wavy wall was 1.56. It agrees well with the one previously obtained for a decomposition of the streamwise velocity.     

Non-fourier temperature field in a solid homogeneous finite hollow cylinder

Analytical solution of the non-Fourier Axisymmetric temperature field within a finite hollow cylinder is investigated considering the Cattaneo-Vernotte constitutive heat flux relation. The solution is found for the most general linear time-independent boundary conditions. The material is assumed to be homogeneous and isotropic with temperature-independent thermal properties. The standard method of separation of variables is used. The present solution can be reduced to special problems of interest by choosing appropriate boundary condition parameters. The solution is applied for two special cases including constant heat flux and the Gaussian distribution heating of a cylinder, and their respective non-Fourier thermal behavior is studied.     

Bifurcation of poloidal field in the flow induced by a radial electric current

A study is made of the steady-state flow of a viscous conducting incompressible fluid in a half-space, induced by an electric current spreading from a point source on a solid surface. There is a critical finite value of the current at which the velocity on the axis becomes infinite. It is shown that for a high-conductivity medium bifurcation of a new MHD regime with nonzero poloidal field and rotation takes place for arbitrarily large values of the current. The axisymmetric MUD dynamo effect detected does not contradict the Cowling-Braginskii antidynamo theorem, since the conditions of the theorem are not fulfilled. In the case of low conductivity the paradox can be resolved using the model of an infinitely narrow turbulent jet. Here, too, self-excitation of the field and rotation are detected and their strengthening leads to suppression of the turbulence and relaminarization of the jet.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 4–11, March–April, 1993.     

Development of the temperature fields in an electric arc struck on a point electrode in a homogeneous gas stream

A study is made of the problem of a point electric source in a homogeneous gas stream and operating in the arc discharge regime. The development of an electric arc struck on a point cathode in a medium which moves without deformation is studied. The stationary problem of a two-dimensional electric arc that develops in a medium with piecewise constant electrical conductivity is solved. Expressions are obtained for the temperature fields, the thickness of the arc, the current-voltage characteristics, and the power in the arc. The stability of this stationary state with respect to short-wavelength perturbations is investigated. The critical electrical current at which instability commences is determined.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 91–99, March–April, 1981.I thank O. N. Sinkevich and I. M. Rutkevich for discussing the work, and also V. I. Grabovskii and V. A. Mareev for making some calculations.     

The problem of the electric field of an electrode with a pre-electrode potential drop in a medium with tensor conductivity

We investigate the nonlinear current distribution in an electrode of finite dimensions with a pre-electrode layer in which the potential locally depends on the current density. The electrode is in contact with a medium of anisotropic conductivity caused by the Hall effect. The problem is reduced to the solution of a nonlinear integrodifferential equation. It is shown that the structure of the field is determined by the Hall parameter and the form of the volt-ampere characteristic in the pre-electrode layer.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 19–23, January–February, 1971.     

Estimate of the temperature field in a compressible medium

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 1, pp. 23–26, January–February, 1992.     

Analytical solution for temperature field in thin film initially heated by a short-pulse laser source

Analytical solution for electron and lattice temperature distribution in the solid initially heated by a laser short-pulse is presented. Strained parameters method is introduced when formulating electron and lattice temperature distributions. Laser short pulse heating of gold film is simulated numerically and temperature data at the end of the heating pulse are adopted as initial condition to the governing equations of energy transport for analytical solutions. This enables to solve the governing equations of energy analytically in the cooling period. It is found that electron temperature decays sharply while lattice site temperature increases gradually in the surface regions during the cooling cycle. As the depth from the surface increases change in both temperatures become gradual.     

Breakup mode transformation of leaky dielectric droplet under direct current electric field

The breakup behavior of leaky dielectric droplet in the presence of direct current electric field is investigated by simultaneously solving the electric field equations and the full incompressible Navier-Stokes equations. The coupled Level Set and Volume of Fluid method is proposed to capture the motion of droplet interface. The present numerical method is validated and is well consistent with acceptable results in the literature. This paper mainly focuses on the effects of electric capillary number Ca and viscosity ratio λ on the mode transformation of droplet breakup. With increasing Ca, the droplet experiences the transformation from jet-like breakup to dumbbell-like breakup, while the increase of λ results in the shift from dumbbell-like breakup to jet-like breakup. The numerical experiments demonstrate that the mode transformation of droplet breakup depends on the evolutions of velocity field and pressure field.     

Parametric instability of a nonuniformly heated horizontal layer of liquid dielectric in a variable electric field

The parametric instability of a nonuniformly heated horizontal layer of liquid dielectric with free isothermal boundaries in a transverse electric field is studied analytically. An instability map is obtained. It is shown that instability can develop at some critical electric field strength which depends on the frequency and is several times greater than the critical strength of the constant electric field.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, pp. 184–186, September–October, 1993.     

交变电场作用下骨表面温升的实验研究

骨具有力电性质,这一性质可促进骨组织生长。骨既是生理器官又是介电材料,在交变电场作用下,其表现行为可能有生理作用。为此,本文测量了骨悬臂梁试样在交变电场下的表面温升与顶端挠度。发现在电压70V,频率为10~70kHz的交流电场下,最大表面温升达到2~4℃,最大挠度变化为9.0~78.7μm;在频率10kHz,电压为70~175V的交流电场下,最大表面温升达到4~6℃,最大挠度变化为13.0~114.3μm。同时测量了两种经典介电材料有机玻璃和聚乙烯在交变电场下的温升与顶端挠度,最大温升低于0.5℃,但是挠度与骨试样相当,所以相对高温升是骨特有的性质。将交流电压有效值替换成相同幅值的直流电压时,最大温升也低于0.5℃,基本没有挠度变化,所以相对的高温升反映了骨的交流性质。分析后认为,骨在交变电场作用下的温升由胶原的介电损耗引起。实验数据显示,骨在交变电场下,表面温度变化与加载电压的平方成正比,且在实验加载的10~70kHz频段内,骨的介电常数随频率的变化明显。     

Magnetic field and magneto elastic stress in an infinite plate containing an elliptical hole with an edge crack under uniform electric current

Two-dimensional solutions of the electric current, magnetic field and magneto elastic stress are presented for a magnetic material of a thin infinite plate containing an elliptical hole with an edge crack under uniform electric current. Using a rational mapping function, the each solution is obtained as a closed form. The linear constitutive equation is used for the magnetic field and the stress analyses. According to the electro-magneto theory, only Maxwell stress is caused as a body force in a plate which raises a plane stress state for a thin plate and the deformation of the plate thickness. Therefore the magneto elastic stress is analyzed using Maxwell stress. No further assumption of the plane stress state that the plate is thin is made for the stress analysis, though Maxwell stress components are expressed by nonlinear terms. The rigorous boundary condition expressed by Maxwell stress components is completely satisfied without any linear assumptions on the boundary. First, electric current, magnetic field and stress analyses for soft ferromagnetic material are carried out and then those analyses for paramagnetic and diamagnetic materials are carried out. It is stated that the stress components are expressed by the same expressions for those materials and the difference is only the magnitude of the permeability, though the magnetic fields H_x, H_y are different each other in the plates. If the analysis of magnetic field of paramagnetic material is easier than that of soft ferromagnetic material, the stress analysis may be carried out using the magnetic field for paramagnetic material to analyze the stress field, and the results may be applied for a soft ferromagnetic material. It is stated that the stress state for the magnetic field H_x, H_y is the same as the pure shear stress state. Solving the present magneto elastic stress problem, dislocation and rotation terms appear, which makes the present problem complicate. Solutions of the magneto elastic stress are nonlinear for the direction of electric current. Stresses in the direction of the plate thickness are caused and the solution is also obtained. Figures of the magnetic field and stress distribution are shown. Stress intensity factors are also derived and investigated for the crack length and the electric current direction.     

Polarization of a plasma in an electric field

A study has been made of the electrostatic polarization of a plasma in an applied electric field, i. e., the process of charge separation in the case when a steady current flow through the plasma is excluded.The authors are deeply grateful to G. A. Lyubimov and S. A. Regirer for useful discussion.