**7. References**


**8** 

*Pakistan* 

**Infinite Plates** 

**Magnetohydrodynamic Rotating Flow of a** 

**Fourth Grade Fluid Between Two Parallel** 

*1Department of Basic Sciences, Riphah International University, Sector I-14, Islamabad,* 

Mechanics of non-linear fluids present a special challenge to physicists, mathematician and engineers. The non-linearity can manifest itself in a variety of ways. Materials such as clay coatings and other suspensions, polymer melts, drilling muds, certain oils and greases, elastomers and many emulsions have been treated as non-Newtonian fluids. There is no single model which clearly exhibits all properties of non-Newtonian fluids and there has been much confusion over the classification of non-Newtonian fluids. However, non-Newtonian fluid may be classified as (1) fluids for which the shear stress depends only on the rate of shear; (2) fluids for which the relation between shear stress and shear rate depends on time; (3) the visco-elastoic fluids, which possess both elastic and viscous

It is not possible to recommend a single constitutive equation which exhibits all properties of non-Newtonian fluids due to the great diversity in the physical structure of non-Newtonian fluids. For this reason, several non-Newtonian models or constitutive equations have been proposed and most of them are empirical or semi empirical. One of the simplest ways in which the visco-elastic fluids have been classified is the methodology given in [1,2]. They present constitutive relations for the stress tensor as a function of the symmetric part of the velocity gradient and its higher derivatives. Another class of models is the rate-type fluid models such as the Oldroyd model [3]. Although many constitutive equations have been suggested, many questions are still unsolved. Some of the continuum models do not give satisfactory results in accordance with the available experimental data. For this reason, in many practical applications, empirical or semi empirical equations have been used. A complete and thorough discussion of various models can be found in [4-7]. Various authors [8-12] investigated

**1. Introduction** 

properties.

non-Newtonian fluids.

Corresponding author

 \*

M.A. Rana1\*, Akhlaq Ahmed2 and Rashid Qamar3

*2Department of Mathematics, Quaid-i-Azam University, Islamabad, 3Directorate of Management Information System, PAEC HQ, Islamabad,* 

K. Zhou, J.C. Doyle and K. Glover, (1996). *Robust and Optimal Control*, Prentice Hall.


M.A. Rana1\*, Akhlaq Ahmed2 and Rashid Qamar3

*1Department of Basic Sciences, Riphah International University, Sector I-14, Islamabad, 2Department of Mathematics, Quaid-i-Azam University, Islamabad, 3Directorate of Management Information System, PAEC HQ, Islamabad, Pakistan* 
