Fluids: Eulerian View, Compressibility, Continuity, Stress Tensor, Slides of Classical Mechanics

An introduction to the study of fluids, focusing on the eulerian view, compressibility, fluid change, continuity equation, and stress. The eulerian view describes the points in space and their bulk properties, while compressibility measures the relationship between volume change and pressure. Fluid change is related to the divergence, and the continuity equation ensures mass conservation. Stress is a surface force per unit area, with normal and shear components, and the stress tensor represents the stress function as a symmetric tensor with six components.

Typology: Slides

2012/2013

Uploaded on 07/24/2013

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Download Fluids: Eulerian View, Compressibility, Continuity, Stress Tensor and more Slides Classical Mechanics in PDF only on Docsity!

Fluids

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Eulerian

View

In

a

Lagrangian

view

each

body

is

described

at

each

point

in

space.

Difficult

for

a

fluid

with

many

particles.

In

an

Eulerian

view

the

points

in

space

are

described.

Bulk

properties

of

density

and

velocity

0

t

r

r

tr

t

r

v

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Fluid

Change

A

change

in

a

property

like

pressure

depends

on

the

view.

In

a

Lagrangian

view

the

total

time

derivative

depends

on

position

and

time.

An

Eulerian

view

is

just

the

partial

derivative

with

time.

Points

are

fixed

^

^

2

2

2

2

2

x

l

x l x l k F

 

p

v

p t

dp dt

 

 

dz^ dt

p z

dy dt

p y

dx dt

p x

p t

dp dt

^ 

 

 

 

 

 

v

t

d dt

p^ t

dp dt

const

r

 

 

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Volume

Change

Consider

a

fixed

amount

of

fluid

in

a

volume

V

Cubic,

Cartesian

geometry

Dimensions

x

,^

y

, 

z

.

The

change

in

V

is

related

to

the

divergence.

Incompressible

fluids

must

have

no

velocity

divergence

z

v z

z

d dt

y

v y

y

d dt

x

v x

x

d dt

x y z

z

y

x

v z

v y

v x

V

d dt

z

y

x

V

v

V

d dt

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Stress

A

stress

measures

the

surface

force

per

unit

area.

A

normal

stress

acts

normal

to

a

surface.

A

shear

stress

acts

parallel

to

a

surface.

A

fluid

at

rest

cannot

support

a

shear

stress.

 F

 F

A

A

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Force

in

Fluids

Consider

a

small

prism

of

fluid

in

a

continuous

fluid.

Describe

the

stress

P

at

any

point.

Normal

area

vectors

S

form

a

triangle.

The

stress

function

is

linear.

1 S d

2 S d

2

1

S

d

S

d

2 S d

P

1 S d

P

2

1

S

d

S

d

P

S

d

P c

S

cd

P

S d P S d P

2

1

2

1

S d S d P S d P S d P

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Force

Density

The

force

on

a

closed

volume

can

be

found

through

Gauss’

law.

Use

outward

unit

vectors

A

force

density

due

to

stress

can

be

defined

from

the

tensor.

Due

to

differences

in

stress

as

a

function

of

position

next

S

dS n

F

P

V

dV

F

P

P

Sf

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