A finite-difference solution to the unsteady free and forced convection flow of a dissipative fluid through a homogeneous porous medium past an infinite vertical isothermal plate is derived. Velocity and temperature profiles are shown graphically whereas the numerical values of the skin-friction and the rate of heat transfer are listed in a table. It is observed that the velocity decreases when the permeability parameter 'sigma' or the Grashof number G or the Eckert number E increase. Temperature and the rate of heat transfer are found to increase with increasing 'sigma' but the skin-friction decreases with increasing 'sigma'. The skin-friction decreases with increasing 'sigma'. The skin-friction increases but the rate of heat transfer decreases with increasing G, E (Eckert number) or time t.

     The distribution due to line source in a homogeneous isotropic thermoelastic half space has been investigated by applying a combination of the Laplace and Fourier transform technique in the context of generalised theories of thermoelasticity. The inverse transform integrals have been evaluated by using the Cagniard method to obtain the exact closed algebraic expressions for the displacement and temperature as a function of time and horizontal distances, which are valid for all epicentral distances. The displacement and temperature so obtained in the physical domain have been computed numerically and are presented graphically for an aluminum epoxy composite material. A comparison of results valid in different theories of thermoelasticity has also been made.

     The effect of the Suction-Injection-Combination (SIC) on the onset of Rayleigh-Benard convection in suspensions is studied in a porous medium using the Rayleigh-Ritz technique. The critical eigenvalue is obtained for free-free, free-rigid and rigid-rigid boundary combinations with isothermal or adiabatic temperature condition. The microrotation of the suspended particles is assumed to vanish at the boundaries. The effect of the SIC on the critical eigenvalue is shown to be dependent on whether it is gravity-aligned or anti-gravity. The classical results on the effect of suspended particles on convection is found to be unaltered by the SIC. The problem has industrial applications.

     Efforts have been made to study the effect of longitudinal surface roughness on the performance of a hydrodynamic squeeze-film between a non-rotating spherical surface and a hemispherical bearing under a steady load using the general stochastic analysis without using a specific probability distribution for describing random roughness, It is assumed that the bearing surface as well as the surface of the approaching sphere have random roughness, which is distributed throughout the surfaces. The stochastic film thickness characterizing the roughness is considered to be symmetric with non-zero mean ('alpha') and variance ('sigma'²). In order to get the expression for pressure the modified Reynolds equation is solved. Then by making use of this expression we obtain the expressions for load carrying capacity, which in turn is used to find the expression for response time. These expressions are numerically computed and the results are presented graphically as well as in tabular form. It is observed that the composite roughness of the surfaces affects the performance of the bearing significantly.

     The paper presents a description of pine wood failure under compression. From among various failure criteria, the anisotropic failure Ascenazi criterion was used for description, assuming that wood is an orthotropic material. The experiments and description were carried out in one of the main orthotropy planes. An attempt to describe the dependence of compression strength on the density mass was made. The tests confirmed that for some assumptions the failure description of pine wood using the Askenazi criterion was possible.

     This paper describes a theoretical analysis of transient motion of a viscous incompressible fluid in a vertical channel. The motion of the fluid is caused by the buoyancy force arising from the temperature gradient as a result of constant heat flux at one wall and an adiabatic condition on the other wall. Expressions for the velocity and temperature fields are derived with the help of the Laplace transform technique. The influence of the various parameters is extensively discussed with the help of graphs. It has been observed that the temperature is not influenced by the presence of an adiabatic condition on the other plate for large values of the Prandtl number.

     The distribution due to line source in a homogeneous isotropic thermoelastic half space has been investigated by applying a combination of the Laplace and Fourier transform technique in the context of generalised theories of thermoelasticity. The inverse transform integrals have been evaluated by using the Cagniard method to obtain the exact closed algebraic expressions for the displacement and temperature as a function of time and horizontal distances, which are valid for all epicentral distances. The displacement and temperature so obtained in the physical domain have been computed numerically and are presented graphically for an aluminum epoxy composite material. A comparison of results valid in different theories of thermoelasticity has also been made.

     The present paper is a theoretical study of the motion of an inclined cavity of a paraboloid form filled with an ideal and incompressible fluid. The cavity is placed in the gravity field and its roto-translation motion is unknown. We look for determining the translation and rotation velocities of the cavity, the velocity potential of the fluid particles as well as the form of the fluid free surface. To this end, we shall use both the analytical and numerical methods. Numerical examples are presented in tables and graphs to elucidate the accuracy and efficiency of the proposed method.

     In this paper, we present a polar fluid model for electrorheological fluids using the methods of extended irreversible thermodynamics. In the first part of this paper, the fluid is described as a non-polar fluid. We show that certain well-known models emerge as special cases of our rate-type constitutive equations for the extra stress and the electric displacement. In the second part, we account for the induced structure in the fluid by using a polar theory. We derive rate-type constitutive equations for the (non-symmetric) extra stress, the couple stress and the corresponding electric displacement. After discussing the transition from rate type to differential type, we compare the predicted shear stresses of both models for a viscometric flow configuration and show that only the polar model can account for different material responses, if the constant electric field is oriented either perpendicular or parallel to the flow direction.

     In this note, we construct a 3-D solution to the heat equation by means of the Fourier sine transform. If there exists no source of heat and the initial inner temperature of the body is zero our solution depends on x, y, z and t only by the similarity variables _ , _ and _ . Moreover, the corresponding 2-D and 1-D solutions appear as limiting cases for _ or _ and _ .

     On the basis of the Stokes microcontinuum theory and the Christensen stochastic model, a theoretical study of squeeze film performance for isotropic rough rectangular plates with couple stress fluids as lubricants is presented. A stochastic non-Newtonian Reynolds-type equation is derived and solved analytically for the mean film presure distribution. Squeeze film characteristics are then evaluated. According to the results, bearing surfaces with isotropic roughness pattern result in poor bearing characteristics as compared to the smooth-surface case. However. the isotropic rough plates with a non-Newtonian couple stress fluid provide a significant increase in the mean load-carrying capacity, and compensate the response time by more than the reduction caused by surface roughness.

     A mathematical description of a mixture of a Newtonian fluid infused with particulate solids is presented within the context of Mixture Theory. In the absence of any thermal effects, the balance of mass and balance of linear momentum equations for each component are averaged over the cross section of the flow to obtain ordinary differential equations describing developing flow between parallel plates. The resulting coupled equations describe the variation of the average velocities and volume fraction in the direction of flow, and represent a simplified approximate set of equations which are used in engineering applications.

     Different failure mechanisms are possible in cyclic contact phenomena, from wear to surface or subsurface fatigue. The limit of the material elastic shakedown is a critical parameter, because an early failure has to be expected when it is exceeded. It depends on all the tribological quantities involved in the process, which determine the effective stress field in the bulk of contacting bodies. This paper presents a program developed just to solve sequentially both the EHDL problem and the stress problem. A complete interface between these two parts of the program has been developed, thus permitting the user to make a fast evaluation of the failure risk. The effects of the rheological parameters on the limit of elastic shakedown are finally shown. The hypothesis of surface hardened components, i. e. in the presence of a material with strength varying along the depth, is also taken into consideration.

     Electro-rheological and magneto-rheological fluids react to electric and magnetic fields respectively undergoing changes in their mechanical characteristics, viscosity and stiffness in particular. Their macroscopic behaviour is represented by the Bingham plastic model. In the last decade there has been an increasing attention toward the employment of ER and MR fluids in active bearings and active squeeze film dampers in rotordynamics. In the literature some applications of ER fluids in rotor squeeze film dampers can be found. However, nothing is reported on similar test rigs set up for MR dampers. After a review of the theoretical and experimental work reported in the literature, a feasibility study of an ER squeeze film damper and an MR one is presented and the two solutions compared.

     This paper addresses the inversion threshold between equilibrium and self-sustained oscillations through an energy-balance approach quite suitable for moderately non-conservative mechanical systems with non-linear friction/speed characteristics. The analysis leads to the definition of an inversion surface in the coordinate space of the variables, emphasizing the influence of the friction curve shape. A global insight into the system stability is presented. Several experimental results for the dry contact between a rubber belt and a pulley are also shown.

     The influence of the labyrinth seals on the dynamic behaviour of a flexible rotor in journal bearings is investigated. In particular a code which makes possible the determination of the stiffness and damping coefficients and the calculus of the stability threshold in the absence of unbalance is discussed. The pressure field in journal bearings and in the labyrinth seal is determined using Warner's hypothesis and the bulk-flow model with two-control-volume, respectively.

     A test rig for the experimental validation of the rotordynamic coefficients of annular and labyrinth seals using Active Magnetic Bearings (AMBs) exciters is presented. The rotordynamic coefficients for annular and labyrinth seals are obtained, with two computer programs using the Reynolds' gas lubrication equation and the bulk flow model with two volume control, respectively. The AMBs exciters allow the rotor to levitate without contact, and to excite it with user-defined sinusoidal forces at the same time. The dynamic experiments can be conducted at various rotor speeds, whirling speeds, and with different pressure drops across the seal.

     In the present work, a wear evaluation of the UHMWPE tibial insert of a total knee joint is attempted based on a simple wear model. A user subroutine has been written and integrated into a commercial finite element program to allow for a structural-kinematic model of the joint. The kinematic model simulates the relative angular velocity and linear movements between tibia and femur during walking. The input data consist of internal-external rotation and flexion-extension angle as taken from the literature. In the simulation, the femoral and tibial components are compressed vertically under gait loads, while at different orientations as determined by the kinematic model. A stress history of each element during the gait cycle is determined. The calculation of the product between the contact pressure and the node relative velocity, as given by the kinematic model, is then used for a qualitative determination of wear maps.