22446488 fluid bio mechanics slide show

8/14/2019 22446488 Fluid Bio Mechanics Slide Show

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Fluid BiomechanicsFluid Biomechanics

The study of forces that develop

when an object moves through a

fluid medium.

Two fluids of interest

Water

Air


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Fluid forcesFluid forces

Four major fluid forces of interest:

Weight

Buoyant Force

rag

!ift

"ther Forces


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FloatationFloatation

Equilibrium:

weight of object = buoyant force

Floatation:

specific gravity < 1

weight of object < max. buoyant force


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Specific gravity:

# $ Wbody

Wwater

Center of buoyancy:

The point that is %& of volume of water

e'ual to the volume and shape of the

submerged body

CB is closer to the chest region

CG is closer to the pelvic region


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(aturalfloater


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Truefloater


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True sin)er


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Buoyant ForceBuoyant Force Archimedes Principle:

"bject in a fluid is acted on a buoyant force.

buoyant force $ weight of the fluid displaced by

the object

A body that is partially or totally immersed in

a fluid will experience an upward buoyantforce that is equal to the weight of the

volume of fluid displaced by that body


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Center of buoyancy &Center of buoyancy &

swimming performanceswimming performance


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Vwater !"#

Vboat $Vwater # $ "# $


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Vwater !"#

Vboat $Vwater "# $ "# #


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Vwater #

Vboat $Vwater "# $ # "#


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DragDragForceForce

Along the direction of motion

Opposite of relative flow

lows down the speed

!esistance

Affected by cross"section area

Affected by surface smoothness

#$ = % &$A '(


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Skin Friction / Surface DragSkin Friction / Surface Drag

Boundary layer: layer of affectedair

epends on

relative velocity

surface area

smoothness of surface

fluid *viscosity+

fabric *swim suit+, shaving body inswimming


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Profile Drag/Form DragProfile Drag/Form Drag

ue to separation of the fluid

from the boundary of the object

-ddy currents

ressure gradient

#treamlining


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Profile Drag/Form DragProfile Drag/Form Drag

depends on

cross/section

shape of the body

smoothness of the surface

bicyclist in upright v. crouched position


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Wae DragWae Drag

0esistance at the interface, due to wave


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!ift!ift

erpendicular to the direction of motion

%reated by different pressures on opposite

sides of an object due to fluid flow past theobject

Bernoulli1s principle: velocity is inversely

proportional to pressure


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Bernoullis LawBernoullis Law

Where the flow velocity is fast, the

pressure is low; where the flowvelocity is slow, the pressure is high

F! $ 2 %!A 34


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Effect of Lift in SportEffect of Lift in Sport

Variables influencing aerodynamic

lift force

Angle of rojection5 angle betweenhori)ontal and &* of projectile

!ine of Flight

Attitude Angle5 angle between hori)ontal

and long axis of projectile


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%enter of ressure

Angle of Attac) at 0elease5 angle

between projectile1s long a6is and

projection angle

Effect of Lift in SportEffect of Lift in Sport


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"he #agnus $ffect"he #agnus $ffect

The 7agnus effect

describes the curved

path that is observed

by spinning

projectiles


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"he #agnus $ffect"he #agnus $ffect

-6plained by

Bernoulli1s principleand the pressure

differences caused

by relative

differences in flow

velocities


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"op Spinning"op Spinning

3elocity of superior boundary

layer decrease

3elocity of inferior boundary

layer increase

(-T Force5 ownward


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Back SpinningBack Spinning

'elocity of superiorboundary layer

increase

'elocity of inferiorboundary layer

decrease

+,- #orce upward

!ebound


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flow

NET FORCE (up)


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Side SpinningSide Spinning

%t& spinRt side ! low pressure "one

#t side ! high pressure "one

(-T Force5 to 0t. side

't& Spin

#t side ! low pressure "oneRtside ! high pressure "one

(-T Force5 to !t. side


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22446488 fluid bio mechanics slide show

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