CE 204 FLUID MECHANICS - Okan University · Chapter 1 Introduction Liquids and Gases, The Continuum...
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Chapter 1 Introduction Liquids and Gases, The Continuum Assumption, Dimensions and Units CE 204 FLUID MECHANICS Onur AKAY Assistant Professor Onur Akay, Ph.D. CE 204 Fluid Mechanics 1 Okan University Department of Civil Engineering Akfırat Campus 34959 Tuzla-Istanbul/TURKEY Phone: +90-216-677-1630 ext.1974 Fax: +90-216-677-1486 E-mail: [email protected]
Transcript of CE 204 FLUID MECHANICS - Okan University · Chapter 1 Introduction Liquids and Gases, The Continuum...
Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
CE 204
FLUID MECHANICS
Onur AKAY
Assistant Professor
Onur Akay, Ph.D. CE 204 Fluid Mechanics 1
Assistant Professor
Okan University
Department of Civil Engineering
Akfırat Campus
34959 Tuzla-Istanbul/TURKEY
Phone: +90-216-677-1630 ext.1974
Fax: +90-216-677-1486
E-mail: [email protected]
Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
MECHANICS: Field of science focuses on the motion of material bodies.
-Involves force, energy, motion, deformation, and material properties.
When mechanics applies to material bodies in the solid phase, the discipline is called solid
mechanics.
When the material body is in the gas or liquid phase, the discipline is called fluid
mechanics.
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A fluid is a substance whose molecules move freely past each other. A substance that will
continuously deform –that is, flow under the action of a shear stress.
Both liquids and gases are classified as fluids.
Intermolecular cohesive forces are large in a solid, smaller in a liquid, and extremely small
in a gas.
Liquids and gases differ because of forces between the molecules.
Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
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Fluid mechanics applies concepts related
to force and energy to practical problems
such as the design of gliders.
Fluid mechanics studies flow in open
channels as well as closed conduits.
Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
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Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
The Continuum Assumption:
A fluid often behaves as if it were comprised of continuous matter that is infinitely divisible
into smaller and smaller parts.
When this assumption is valid, engineers can apply limit concepts from differential
calculus.
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Avogadro’s number: 6x1023 molecules/mole
10-13 mm3 of water contains at least a million (106) molecules
Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
Dimension and Units:
A dimension is a category that represents a physical quantity such as mass, length, time,
momentum, force, acceleration, and energy.
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Secondary dimensions such as force, momentum and energy can be related to primary
dimensions.
Newton’s second law of motion, F=ma
The primary dimensions of force are mass times length
divided by time squared.
Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
Dimension and Units:
A unit assigns a number to the physical quantity so that the dimension can be measured.
For example, measurement of volume (a dimension) can be expressed using units of liters.
Most dimensions have multiple units that are used for measurement. The dimension of
“force” can be expressed using units of newtons or kilogram force.
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Unit Systems:
The International system of Units (abbreviated SI from the French “Le Systéme International
d’Unités”):
-Length (meter- m)
-Mass (kilogram- kg)
-Force (Newton- N)
-Time (second- s)
Other systems: U.S. Customary System (foot-pound-second), British Gravitational System
Prefixes used in the SI system
G (giga) = 109 c (centi) = 10-2
M (mega)= 106 m (milli) = 10-3
k (kilo) = 103 μ (micro) = 10-6
Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
Dimensionless Groups
Engineers often arrange variables so that primary dimensions cancel out.
Mach number, M
Fluid speed, V
Speed of sound. c
Reynolds number, Re
Density, ρ
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Density, ρ
Velocity. V
Length, L
Viscosity, µ
Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
Dimensionless Homogeneity
When the primary dimensions on each term of an equation are the same, the equation is
dimensionally homogeneous. For example, consider the equation for vertical position s of
an object moving in a gravitational field:
gravitational acceleration, g
time, t
vertical component of initial velocity, v
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This equation is dimensionally homogeneous because the primary dimension of each
term is length L.
vertical component of initial velocity, v0
vertical component of initial position, s0
Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
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Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
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Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
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Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
The Grid Method
Because fluid mechanics involves complex equations, carrying and canceling units is
helpful.
Estimate the power P required to ride a bicycle at a speed of V=30 km/h. The engineer
estimated that the required force to move against wind drag is F=2 kgf.
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Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
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Chapter 1 Introduction
Liquids and Gases, The Continuum Assumption, Dimensions and Units
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