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Fluid Engineering MechanicsFluid Engineering Mechanics
Course Code: CIVL213Course Code: CIVL213
Dr.Dr. MajedMajed SubhiSubhi AbuAbu SharkhSharkh
College of Engineering and ArchitecturalCollege of Engineering and Architectural
Civil and Environmental Engineering DepartmentCivil and Environmental Engineering Department
University ofUniversity of NizwaNizwa
Semester, Fall 2010Semester, Fall 2010--20112011
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Chapter OneChapter One
Basic ConceptsBasic Concepts
1.1 Introduction.1.1 Introduction.
1.2 Classification of Fluids.1.2 Classification of Fluids.
1.3 Fluid Science Applications.1.3 Fluid Science Applications.
1.4 Dimensions, Units, and Systems of Measurement1.4 Dimensions, Units, and Systems of Measurement..
1.51.5 Fluid Properties: mass density; specific volume; specificFluid Properties: mass density; specific volume; specific
weight; specific gravity; relative density.weight; specific gravity; relative density.
1.6 Viscosity.1.6 Viscosity.
1.7 Bulk Modulus of Elasticity.1.7 Bulk Modulus of Elasticity.
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Introduction-Concepts:
Mechanics: is the oldest physical science that deals with
both stationary and moving bodies (substances either
solids or non-solids) under the influence of forces.
Statics: the branch of mechanics that deals with bodies atrest.
Dynamics: the branch that deals with bodies in motion is
called dynamics.
Fluid Mechanics: is defined as the science that deals withthe behavior of fluids at rest (fluid statics) or in motion (fluid
dynamics), and the interaction of fluids with solids or other
fluids at the boundaries.
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Introduction:
The matteris exists in two states: Solid and Fluid
Solid: is a substance when subjected to shear stress is not
deform or yield until internal resistance to deformation
equals the externally applied stress. Ex. wood, steel, etc.
Fluid: is a substance which deforms or yield continuously
when shear stress is applied to it, no matter how small it
is. Ex. water, gas, air, oil, etc.
The fluid is also divided in two states:Liquids: water, oil, blood, honey, glycerin, paint, etc
Gases: air, gas hydrogen, etc.
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Difference Between Solids and Fluids:
Distinction between a solid and a fluid is made on the basis
of the:
1) Distances between different molecules: intermolecular
bonds are strongest in solids and weakest in fluids. The
molecules in solids are closely packed together, whereas
in fluid they are separated by relatively large distances.
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Difference Between Solids and Fluids:
2) Substances ability to resist an applied stress: shear (or
tangential) stress that tends to change its shape.
A solid can resist an applied shear stress by deforming,
whereas a fluid deforms continuously under the influenceof shear stress, no matter how small.
In solids, stress is proportional to strain, but in fluids
stress is proportional tostrain rate
. When a constantshear force is applied, a solid eventually stops deforming,
at some fixed strain angle, whereas a fluid never stops
deforming and approaches a certain rate of strain.
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Difference Between Solids and Fluids:
Distinction between solid and fluid?
Solid: can resist an applied shear by deforming. Stress is
proportional to strain.
Fluid: deforms continuously under applied shear. Stress
is proportional to strain rate.
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Classification of Fluids:
Fluid can be subdivided into liquids and gases.
Liquids:
Occupy a certain volume and have free surface.
The volume does not change appreciably when subjectedto normal stress or temperature.
Gases:
Have a tendency to expand and fill container in which
they are kept; they don not have free surface.
The volume change considerably when subjected to
normal stress or temperature.
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Fluid Behavior:
Stress is defined as the force per unit area.
Normal component: normal stress In a fluid at rest,
the normal stress is called pressure.
Tangential component:
shear stress.
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Classification of Fluids:
A liquid takes the shape of the container it is in and forms
a free surface in the presence of gravity.
A gas expands until it encounters the walls of the
container and fills the entire available space. Gases
cannot form a free surface.
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Fluid Science Applications:
RiverHydraulics Blood Pumping Air Pollution
Means of Transportation
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Fluid Science Applications:
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Dimensions and Units:
In fluid mechanics we must describe various fluid
characteristics in terms of certain basic quantities such as
length, time and mass.
A dimension is the measure by which a physical variableis expressed qualitatively, i.e. length is a dimension
associated with distance, width, height, displacement.
Basic of Primary quantities: Length L, Time T, Mass M.
We can derive any secondary quantity from the primary
quantities i.e. Force = (mass) x (acceleration) : F= M LT-2
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Dimensions and Units:
A unit is a particular way of attaching a number to the
qualitative dimension: Systems of units can vary from
country to country, but dimensions do not.
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Primary
Dimension
System
International (SI)
British
Gravitational (BG)
English
Engineering (EE)
Mass [M] Kilogram (kg) Slug Pound-mass (lbm)
Length [L] Meter (m) Foot (ft) Foot (ft)
Time [T] Second (s) Second (s) Second (s)
Temperature [] Kelvin (K) Rankine (R) Rankine (R)
Force [F] Newton (N Pound (lb) Pound-force (lbf)
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Fluid Properties:
Density of a fluid (Rho): is the amount of mass per unit
volume of a substance:
= m / V (kg/m3) and (M/L3)
For liquids: weak function of
temperature and pressure
For gases: strong function of T and P
Specific weight (Gama): is the amount of weight per unit
volume of a substance.= weight/volume= W / V = mg/V = g
Dimensionally: M/L2T2 and the unit is N/m3
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Fluid Properties:
Specific Volume : is the volume per unit weight and hence
= Volume/weight
Dimensionally: L2T2 /M and the unit is m3/N
Specific Gravity or Relative Density SG: is the ratio of mass
density to mass density of pure water at standard
pressure of 101.325 N/m2 and temperature of 4oC.
SG = / H2O, 4oC
Pressure P: is the force acting on unit area normal to it.
P = lim F/ A (unit: N/m2= Pascal)
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Fluid Properties:
Temperature:
Temperature Scale
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Fluid Properties:
A flow is classified as:
Incompressible Fluid: if the density of the fluid remains
nearly constant, the flow is incompressible. Liquid flows
are typically incompressible, (= constant).
Compressible Fluid: if the density of the fluid change, the
flow is compressible. Gas flows are often compressible,
especially for high speeds , (= change).
Mach number, Ma = V/c is a good indicator of whetheror not compressibility effects are important.
Ma < 0.3: Incompressible; Ma < 1: Subsonic;
Ma=1:Sonic;Ma > 1 : Supersonic; Ma >> 1 : Hypersonic
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Viscosity:
Viscosity: is that property of fluid by which it offers
resistance to shear acting on it. According to Newtons
law of viscosity the shear force F acting between two
layers of fluid is proportional to difference in their
velocities u and area A, and inversely proportional tothe distance y between them as shown in the Figure-1.
Figure-1: Shear and Velocity Distribution
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Viscosity:
F = A u / y
The fluid ability to resist the shear force; i.e. the resulted
shear stress is directly proportional to the rate of strain.
The constant is a measure to the fluid VISCOSITY.
is called the dynamic or absolute viscosity or viscosity
of a fluid, where, = N. s . m-2 or kg/m.s
One gm/cm.s dynamic viscosity is known as poise (P)
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Viscosity:
The ratio of the viscosity and the density often occurs in
fluid flow situation. This ratio,
= /
Is called the kinematic viscosity and has units m2/s. Thisgives a measure of the amount of viscosity per unit mass.
It is a matter of taste whether the kinematic or dynamic
viscosity is the primary quantity.
The other unit of kinematic viscosity is stocks,
1 stocks = 1 cm2/s
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Bulk Modulus of Elasticity:
Modulus of Elasticity:A property that is commonly used to
describe compressibility of fluids.
Where v is the specific volume and dv is the change in v
due to increase dP. E is expressed in N/m2 or kN/m2.
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