Biomedical Engineering Reference
In-Depth Information
CHAPTER
2
Fundam
entals of Fluid M
echanics
LEARNING OUTCOMES
1.
Describe fluid mechanics principles
2.
Identify the principle relationships and laws
that govern fluid flow
3.
Specify different analysis techniques that
can be used to solve fluid mechanics
problems
4.
Describe the continuum principle
5.
Evaluate the pressures and stresses that act
on differential fluid elements
6.
Define kinematic relationships for fluid
flows
7.
Explain the relationships among shear rate,
shear stress and viscosity
8.
Define different classifications for fluids
9.
Describe fundamental changes at the
microscale level
2.1 FLUID MECHANICS INTRODUCTION
In the broadest sense, fluid mechanics is the study of fluids at rest and in motion. A fluid
is defined as any material that deforms continually under the application of a shear stress,
which is a stress directed tangentially to the surface of the material. In other words, no
matter how small the applied shear stress acting on a fluid surface, that fluid will flow
under the applied stress (for some fluids a yield stress must be met before the fluid flows;
however, once this yield stress is met, the previous definition applies. See
Section 2.7
for
more information about these types of fluids.) Some define a fluid as any material that
takes the shape of the container in which it is held. It is easily seen that any substance in
the liquid or the gas phase would fall under all of these definitions and are, therefore,
fluids. The distinction between a fluid and a solid is also clear from these definitions
because solids do not take the shape of their containers; for instance, a shoe in a shoebox
is not a rectangular cuboid that only takes the shape of a foot when worn. Also, if you
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