Joint unidirectional motion of two viscous heat-conducting fluids in a tube

This paper studies an invariant solution of the problem of joint motion of two heat-conducting viscous immiscible fluids which have a common interface in a cylindrical tube under an unsteady pressure gradient. The problem reduces to a coupled initial-boundary-value problem for parabolic equations. A priori estimates of velocity and temperature perturbations are obtained. The steady state of the system is determined, and it is proved that if, in one of the fluids, the pressure gradient rapidly approaches zero, the perturbations of all quantities tend to zero. It is shown that if the pressure gradient has a nonzero limit, the solution reaches a steady state. In this case, the velocity field in the limit is the same as in conjugate Poiseuille flow, and the temperature is represented as a polynomial of the fourth order on the radial coordinate.     

Nonstationary indentation of a rigid blunt indenter into an elastic layer: A plane problem

The nonstationary indentation of a rigid blunt indenter into an elastic layer is studied. An approach to solving a mixed initial-boundary-value problem with an unknown moving boundary is developed. The problem is reduced to an infinite system of integral equations and the equation of motion of the indenter. The system is solved numerically. The analytical solution of the nonmixed problem is found for the initial stage of the indentation process __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 3, pp. 55–65, March 2008.     

Thermal-Concentration Convection in a System Of Viscous Liquid and Binary Mixture in a Plane Channel with Small Marangoni Numbers

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.     

Acceleration of a conducting gas in a strong nonstationary electromagnetic field

The problem of nonstationary acceleration of a conducting gas in a channel is solved, together with the problem of a discharge in an electric-circuit. As distinct from other papers, in which the typical solution assumed a thin cluster subject to acceleration, we examine the case in which the gas flow fills the entire channel. The motion of the gas in the channel is examined in one-dimensional formulation, under the assumption that the particle transit time in the channel is small compared to the discharge time and that the electromagnetic force is large compared to the pressure gradient.For impulsive acceleration of the conducting gas, use is made of a discharge with a certain capacitance. Since the (time-variable) resistance of the channel and, consequently, the behavior of the discharge depend upon the channel flow of the conducting gas, the correct solution of the problem of gas acceleration in the induced electromagnetic field can be obtained only by analyzing simultaneously the magnetogasdynamic channel flow and the discharge process in the entire electric circuit. On the other hand, the acceleration of the gas itself is a function of the instantaneous potential difference at the electrodes. Hitherto, such simultaneous solutions were obtained by many investigators under the assumption, proposed in [1], that a channel gas flow may be treated as the motion of a unique narrow cluster, whose length is negligible as compared to the channel length. Experiments and theoretical estimates show, however, that in many cases the conducting gas fills the entire channel length during the acceleration process, so that the assumption of a narrow cluster is not even approximately fulfilled [4, 5].     

Characteristic properties of the system of equations for an incompressible viscoelastic Maxwell medium

Characteristics of a system of equations that describe three-dimensional motion of an incompressible viscoelastic Maxwell medium with the upper and lower convective derivatives and the rotational Jaumann derivative being used in the rheological relation are calculated. An initial-boundary-value problem is formulated for the system linearized in the vicinity of the state at rest, and its unique solvability is established.     

Development of magnetohydrodynamic boundary layers associated with the sudden initiation or deceleration of a supersonic flow at the boundary of a half-space

The problem of nonstationary magnetohydrodynamic flow of a viscous fluid in a half-space resulting from the motion of an infinite plate has received much attention. In [1], for example, solutions are presented for the case of isotropic conductivity, while in [2] a solution of the Rayleigh problem is offered for the case of anisotropic conductivity. In these instances the fluid was assumed incompressible and uniform, and the system of equations was found to be linear. In problems involving nonstationary flow of a gas in a transverse magnetic field resulting from the deceleration of a high-velocity gas flow at the boundary of a half-space or the motion of an infinite plate at supersonic speed relative to a stationary gas it becomes necessary to take into account the compressibility of the gas and the temperature dependence of the conductivity. It is then possible to have flows in which the gas becomes electrically conducting and begins to interact with the magnetic field solely as a result of the increase in temperature due to viscous dissipation of energy. The magnetic field, interacting with the conducting gas, exerts an effect on the drag and heat transfer to the surface of the plate. At sufficiently low gas pressures and strong magnetic fields a Hall effect may be observed. The system of equations describing the motion of a compressible gas with variable conductivity is essentially nonlinear. The present article is devoted to a study of such motions.     

Mathematical model of heat transfer in a fluid with account for its relaxation properties

Using the terms that take account for the temporal and spatial nonlocality (time variation of the heat flux and the temperature gradient) in the formula of Fourier’s law for the heat flux a differential equation for a fluid in motion is derived that contains the second time derivative and themixed derivative with respect to the spatial and temporal variables. Numerical solution of the problem of heat transfer in the laminar fluid flow in a plane channel demonstrates that, in view of the lag in the time variation of the heat flux from zero to a certain maximum value, the boundary condition of the first kind (thermal shock) cannot be instantaneously realized. The process of its stabilization on the wall is characterized by a certain time interval, whose duration is determined by the relaxation properties of the fluid. At large values of the dimensionless coefficients of the heat flux relaxation and the temperature gradient the boundary condition of the first kind can be realized only as the steady state is attainted, as Fo→∞. In this case, the flow does not contain temperature jumps and negative temperature values.     

Impact of a long thin body on a cylindrical cavity in liquid: A plane problem

An approach is developed to the investigation of the shock interaction between a long thin cylindrical body and a cylindrical cavity in an infinite compressible perfect liquid. This process accompanies the supercavitation of the body. Three typical cases of cross-sectional dimensions of the body and the cavity are examined. For each case, a mixed nonstationary boundary-value problem with an unknown moving boundary is formulated. The unknown quantities are expanded into Fourier series. An auxiliary problem is solved using the Laplace transform to establish the relationship between the pressure and the velocity on the cavity surface. As a result, the problem is reduced to an infinite system of Volterra equations of the second kind solved simultaneously with the equation of transverse motion and the equation of the contact boundary. An asymptotic solution valid at the initial stage of interaction is obtained for all the three cases, and a numerical solution is found for the most typical case __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 6, pp. 32–53, June 2006.     

Diffraction of a sound wave by a slit

The diffraction of a sound wave by a slit in an unbounded plane is analyzed as an initial-boundary-value problem with a moving boundary for the two-dimensional wave equation. The initial-boundary-value problem is solved by the formation and inversion of Volterra integral equations. A solution is obtained in closed form in quadratures for an arbitrary angle of inclination of the incident wave front relative to the plane. The solution is presented in the form of recursion formulas, which take into account the influence of diffraction waves occurring in succession at the boundaries of the slit.     

均布荷载作用下功能梯度悬臂梁弯曲问题的解析解

采用弹性力学半逆解法,假设所有材料常数沿梁厚度方向按同一函数规律变化,求得了功能梯度悬臂梁在均布载荷作用下的解析解.该解退化到各向同性均匀弹性情况时与已有的理论解相一致.对弹性模量按指数函数梯度变化的算例进行了分析.所得到的解对任意梯度函数均成立,可作为数值解以及简化理论的检验依据.     

A uniqueness theorem in the theory of elastic materials with voids

In the context of the linear theory of homogeneous and isotropic elastic materials with voids, an initial-boundary-value problem in terms of stress and volume fraction fields is formulated and the uniqueness of its solution established.     

Effect of wall conductances on convective magnetohydrodynamic channel flow

Summary The problem of convective magnetohydrodynamic channel flow in a vertical channel subjected simultaneously to an axial temperature gradient and a pressure gradient is examined when the thermal and the electrical conductance of the channel walls are arbitrary. The effects of wall conductances on the flow rate and heat transfer are found and discussed. When the vertical temperature gradient is negative, which is the case of heating from below, there exists a critical Rayleigh number at which the fluid becomes unstable. The critical Rayleigh number is also found as a function of the wall conductances.On leave from the State University of New York at Buffalo.     

Electrohydrodynamic peristaltic flow of a dielectric Oldroydian viscoelastic fluid in a flexible channel with heat transfer

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.     

Control of the Nonstationary Motion of a Hopping Machine (Path Tracking)

The problem on control of the nonstationary motion of a hopping machine is solved. It is shown that similarly to a walking machine, this problem can be reduced to finding a periodic solution of the discrete Riccati equation. The simulation results are indicative of the efficiency of the algorithm proposed     

Solution of a problem of flow in a porous medium with limiting gradient

For the law of flow in a porous medium with limiting gradient studied previously in [1], an exact solution is found for the problem formulated in [2] of the plane steady motion of an incompressible fluid in a channel with a rectangular step. Particular cases of the solution obtained are given; these represent the solutions of the problem of flow past a broken wall and of motion from a point source in a strip.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 76–78, January–February, 1985.     

Motion of gas bubbles in a liquid under the influence of a temperature gradient

This study deals with the motion of a gas bubble developing under the influence of surface-tension forces in an imponderable viscous liquid with a temperature gradient. A theory of steady-state motion of a bubble in a field with constant temperature gradient is given for the case of small Reynolds numbers. Experimental results that show qualitative agreement with the theory are presented.The authors wish to thank M. A. Lavrent'ev for formulating the problem and giving constant attention to their work.     

Motion of particles in a nonstationary layered flow of an incompressible fluid

The motion of spherical particles in a nonstationary layered flow are considered. It is assumed that the fluid is incompressible and that the particles do not interact with one another or influence the parameters of the fluid. Allowance is made for the influence of the pressure gradient, the apparent mass, the Magnus force, and the viscosity of the fluid on the motion of the particles. The formulation of the problem corresponds to the conditions of motion of the two-phase mixture in the channels of the rotatory-pulsatory apparatus [1] used in technology to realize various processes such as solution, emulsification, dispersing, etc. The processes in such an apparatus are strongly nonsteady and have hitherto been hardly investigated at all.Translated from 'Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 53–58, July–August, 1981.We thank A. R. Gurvich for making the calculations.     

Wave processes in a perfect liquid layer impacted on by a blunted solid

The problem of impact of a smooth blunt solid upon a compressible-liquid layer of finite depth is addressed. A mixed initial-boundary-value problem with an unknown moving boundary is formulated. In the general case, the problem is reduced to an infinite system of integral Volterra equations of the second kind. It is solved numerically, using quadrature formulas and truncation method. An exact analytic solution to the problem is obtained in the special case where the body moves with a constant velocity at the initial stage of submergence. This solution makes it possible to examine the effect of successive wave reflections on the pressure at the frontal point and inside the layer __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 3, pp. 37–47, March 2007.     

Dusty-gas flow in a channel with horizontalwalls

An unsteady motion of a dilute gas-particle mixture in a plane channel under the action of a constant longitudinal pressure gradient and the transverse gravity force is studied theoretically. Within the Euler approach, a combined problem of finding the velocity components of the gas and the dust phase is formulated. The flow similarity parameters are found. The solution of the problem formulated is calculated using a finite-difference method. Asymptotic formulas are obtained, which describe the two-phase flow parameters for limiting values of the similarity parameters. The cases of both monodisperse and polydisperse particles are considered.     

Effects of non-uniform heating on a variable viscosity Rayleigh�CB��nard problem

This study presents a natural convection problem with a temperature-dependent viscosity fluid, driven by buoyancy and influenced by horizontal temperature gradients. A numerical linear stability analysis of the stationary solutions is studied. The horizontal temperature gradients tend to localize motion near the warmer zones and favour pattern formation in the direction perpendicular to the gradient. In fact, the problem is almost 2D in the uniform heating case, but becomes totally 3D in the non-uniform heating case.