الفهرس 
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Abstract
A porous medium is literally a solid which contains a number of small holes distributed throughout the solid. Porous media are
very much prevalent in nature and, therefore the study of flow through porous medium is important role in agricultural and extracting pure petrol from crude oil. The study of the flow
through porous medium is also important in many other branches of engineering and science, for example, ground water hydrology,reservoir engineering, soil science, soil mechanics and chemical engineering. Movement of underground water and oils are some important examples of flow through porous medium. As good
biological examples on the porous medium, the human lungs, the gall bladder and bile duct with stones. The basic purpose of this thesis is to study the effect of the presence of the porous medium
on the fluid flow through different cases.
The thesis has six chapters, summary of the main results in both Arabic and English, and a list of references.
In chapter I,
We give some different information about the following items:
* Development of fluid mechanics.
* Some properties of fluid.
* Plasma physics.
* Concept of hydrodynamic stability.
* Perturbation method.
* What is the magnetohydrodynamics (MHD)?
In chapter II,
We discuss the instability of two superposed homogeneous streaming fluids under gravitational force and uniform magnetic field in porous medium. The two streams are moving in opposite
directions with equal velocities parallel to the horizontal plane.
The solution has been obtained through the normal mode technique, and the most general dispersion relation has been obtained as 20th-order equation for the growth rate with quite
complicated coefficients.
Solving numerically the dispersion relation for appropriate boundary conditions with high Alfvén and sound velocities, it is found that fluid velocities and porosity of porous medium have
stabilizing effects, and Alfvén and sound velocities have destabilizing effects, while medium permeability has a slightly.