The transient squeezing flow of a magneto-micropolar biofluid in a noncompressible porous medium intercalated between two parallel plates in the presence of a uniform strength transverse magnetic field is investigated. The partial differential equations describing the two-dimensional flow regime are transformed into nondimensional, nonlinear coupled ordinary differential equations for linear and angular momentum (micro-inertia). These equations are solved using the robust Homotopy Analysis Method (HAM) and also numerical shooting quadrature. Excellent correlation is achieved. The influence of magnetic field parameter (Ha), micropolar spin gradient viscosity parameter (Γ) and unsteadiness parameter (S) on linear and angular velocity (micro-rotation) are presented graphically, for specified values of the micropolar vortex viscosity parameter (R), Darcy number (Da i.e. permeability parameter) and medium porosity parameter (e). Increasing magnetic field (Ha) serves to decelerate both the linear and angular velocity i.e. enhances lubrication. The excellent potential of HAM in bio-lubrication flows is highlighted.

Homotopy analysis of transient magneto-bio-fluid dynamics of micropolar squeeze film in a porous medium: a model for magneto-bio-rheological lubrication

Combined effects of MHD and surface roughness on couple-stress squeeze film lubrication between porous circular stepped plates

This article presents predictive analysis of load-carrying capacity, tractive efficiency and response time of parallel annular discs intervened with a film of lubricant under combined shear and squeeze film motions. This configuration represents operational characteristics of viscous coupling systems. In particular, the case of viscous dampers for tractive torque generation and distribution in all-wheel-drive off road vehicles is studied. Various forms of lubricant behaviour, from idealised Newtonian to that of non-Newtonian silicone-based fluids and incompressible isothermal electrically conducting couple stress fluids, subjected to a magneto-hydrodynamic field are studied. The solution for the magneto-hydrodynamics includes combined solution of modified Reynolds equation and Stoke's micro-continuum for couple stress fluids in squeeze and shear with rotational fluid inertia, an approach not hitherto reported in the literature. It is shown that in general magneto-hydrodynamic couple stress fluids enhance the load-carrying capacity of the contact and inhibit the incidence of thin films, which can result in direct contact of surfaces. Rotational inertia decreases the load-carrying capacity, although in general the magneto-hydrodynamic fluids show better load-carrying capacity and tractive efficiency than the other alternatives. However, they exhibit a lower response time under the assumed isothermal condition. Nevertheless, the magneto-hydrodynamic fluids are best suited to applications in viscous coupling systems because of their controllability.

/pdf/magneto-hydrodynamics-of-couple-stress-lubricants-in-3fd45figoc.pdf

Magneto-hydrodynamics of couple stress lubricants in combined squeeze and shear in parallel annular disc viscous coupling systems:

We make an effort to analyze the behavior of squeeze film characteristics of different finite plates with couple stress fluid in the presence of a transverse magnetic field. On the basis of the Stokes couple stress fluid model and hydromagnetic flow model, a modified Reynold's equation is derived, which is solved by using appropriate boundary conditions to obtain squeeze film pressure, load-carrying capacity, and squeeze film time. The graphical representation of the results suggests that the different bearing systems register an enhanced performance with couple stresses compared to that of a bearing system working with a conventional lubricant in the presence of a transverse magnetic field. It is observed that the effect of applied magnetic field on the squeeze film lubrication between different finite plates with conducting couple stress fluids is to increase the load-carrying capacity significantly and to delay the time of approach compared to the corresponding nonconducting Newtonian case. It is seen ...

Modified Reynolds Equation for Different Types of Finite Plates with the Combined Effect of MHD and Couple Stresses

The accuracy and utility of rotordynamic models for machinery systems are greatly affected by the accuracy of the constituent dynamic bearing models. Primarily, the dynamic behavior of bearings is modeled as linear combination of mass, damping, and stiffness coefficients that are predicted from a perturbed Reynolds equation. In the present paper, an alternative method using Computational Fluid Dynamics (CFD) with a moving boundary is used to predict the dynamic coefficients of slider bearings and the results are compared with the more commonly employed perturbed Reynolds equation model. A linear slider bearing geometry is investigated and the results serve as precursors to similar investigations involving the more complex journal bearing geometries. Time and frequency domain methods for the estimation of dynamic coefficients are shown to give comparable results. For CFD with a moving boundary, temporal inertia is found to have a significant effect for a reduced, squeeze Reynolds number less than one. The temporal inertia effect is captured through an added mass coefficient within the dynamic model of the bearing.

Comparison of Perturbed Reynolds Equation and CFD Models for the Prediction of Dynamic Coefficients of Sliding Bearings

Considering the transient squeezing motion, the magneto-hydrodynamic (MHD) steady and dynamic characteristics of one-dimensional slider bearings lubricated with an electrically conducting fluid in the consideration of a transverse magnetic field are numerically investigated. Using the MHD motion equations and, the continuity equation, we have derived a MHD dynamic Reynolds-type equation, which is applicable to slider bearings taking into account the squeezing effect ∂ h/ ∂ t, in which the general film-shape function is described by h=h(x, t). A closed-form solution for the pressure of an inclined-plane slider is obtained and applied to predict the MHD dynamic stiffness and damping characteristics of bearings. According to the results obtained, the application of externally applied magnetic fields signifies an apparent increase in the MHD steady film pressure. Comparing with the classical non-conducting-lubricant case, the applied magnetic-field effects characterized by the Hartmann number provide ...

Dynamic stiffness and damping characteristics of one-dimensional magneto-hydrodynamic inclined-plane slider bearings:

The study of squeeze film characteristics between rotating circular discs with an electrically conducting lubricant in the presence of a transverse magnetic field has been presented in the present paper. The magneto-hydrodynamic (MHD) Reynolds-type equation for rotating squeezing circular discs is derived using the MHD motion equation together with the continuity equation. A closed-form solution for the MHD film pressure is obtained, and applied to evaluate the MHD squeeze film characteristics. From the results obtained, the influence of rotational inertia results in a lower MHD load-carrying capacity; however, the presence of externally applied magnetic fields provides an increase in the MHD load-carrying capacity and the MHD response time. On the whole, the squeeze film characteristics of rotating circular discs are improved by the use of an electrically conducting fluid in the presence of a transverse magnetic field.

Magneto-hydrodynamic squeeze film characteristics between circular discs including rotational inertial effects

On the basis of the momentum integral method and the microcontinuum theory, the combined effects of total fluid inertia forces and non-Newtonian couple stresses on the non-linear squeeze film characteristics between parallel circular discs are presented The squeeze-film lubrication equation is derived from the Stokes couple-stress motion equation retaining total fluid inertia terms to take into account the effects of non-Newtonian couple stresses resulting from the base oil blended with various types of additives, and the effects of local fluid inertia and convective fluid inertia The non-linear motion equation for the squeezing disc is then numerically solved by using fourth-order Runge-Kutta method Comparing with the Newtonian-lubricant inertialess case, the combined effects of fluid inertia forces and non-Newtonian couple stresses provide a significant increment in the response time of the squeeze film The operating life of squeeze film discs are therefore lengthened, especially for larger 

http://pij.sagepub.com/content/221/4/535.full.pdf

Combined effects of non-Newtonian rheology and fluid inertia forces on the non-linear transient behaviour in circular squeeze films

Combined effects of convective fluid inertial forces and non-Newtonian couple stresses on the of a characteristics squeeze film for a long partial journal bearing are presented. Using Stokes’ microcontinuum theory and the averaged momentum integral principle, a lubrication equation has been derived to investigate the behaviour of the squeeze film between a convex and a concave surface. A closed-form solution for the behaviour of the squeeze film has been derived for long partial journal-bearing system. According to the results, the combined effects of convective inertial forces and non-Newtonian couple stresses provide an increase in the load-carrying capacity and the approaching time, compared with the non-inertial Newtonian-lubricant case. On the whole, the quantitative effects of convective inertial forces and non-Newtonian couple stresses on the improved characteristics are further emphasized for higher squeeze-film Reynolds numbers, non-Newtonian couple-stress parameters, and eccentricity ratios.

C-R Hung

Papers

Dynamic stiffness and damping characteristics of one-dimensional magneto-hydrodynamic inclined-plane slider bearings:

Magneto-hydrodynamic squeeze film characteristics between circular discs including rotational inertial effects

Combined effects of non-Newtonian rheology and fluid inertia forces on the non-linear transient behaviour in circular squeeze films

Combined effects of fluid inertia and non-Newtonian couple stresses on the squeeze film characteristics of a long partial journal bearing