SHIP Buoyancy Stability Presentation
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Transcript of SHIP Buoyancy Stability Presentation
8/19/2019 SHIP Buoyancy Stability Presentation
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Stability &Stability &BuoyancyBuoyancy
8/19/2019 SHIP Buoyancy Stability Presentation
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ObjectivesObjectives
• Principles of StabilityPrinciples of Stability• Archimedes PrincipleArchimedes Principle
• Terminology of ship’sTerminology of ship’s
hydrostaticshydrostatics• Stability & moments -> stayingStability & moments -> staying
uprightupright
• etacenter! "enter of #ravity!etacenter! "enter of #ravity!"enter of $uoyancy! etc%"enter of $uoyancy! etc%
• Stability curvesStability curves
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Principles of StabilityPrinciples of Stability• loating object is acted on by forces of gravity and forces of buoyancyloating object is acted on by forces of gravity and forces of buoyancy
• Static e'uilibriumStatic e'uilibrium ΣΣFFii = 0= 0
• Three conditions of static e'uilibrium(Three conditions of static e'uilibrium(• Stable(Stable( return to same position if tippedreturn to same position if tipped
• )eutral()eutral( *hen rotated! *ill come to rest in any position*hen rotated! *ill come to rest in any position
• +nstable(+nstable( *ill come to rest in ne* position if force acts on it*ill come to rest in ne* position if force acts on it
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Archimedes PrincipleArchimedes Principle•
,a*( a body oating or,a*( a body oating orsubmerged in a uid is buoyedsubmerged in a uid is buoyed
up by a force e'ual to theup by a force e'ual to the
*eight of the *ater it*eight of the *ater it
displacesdisplaces
• .epth to *hich ship sin/s.epth to *hich ship sin/s
depends on density of *ater 0depends on density of *ater 0
1 2 ton345ft1 2 ton345ft44 sea*ater6sea*ater6
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Archimedes PrincipleArchimedes Principle•
Ship sin/s until *eight ofShip sin/s until *eight of*ater displaced by the*ater displaced by the
under*ater volume is e'ual tounder*ater volume is e'ual to
the *eight of the shipthe *eight of the ship• orces of gravity(orces of gravity( # 1 m# 1 mshipshipgg
1717shipship
• orces of buoyancy(orces of buoyancy( $ 1$ 1
*ater*ater88displaceddisplaced
WWshipship == ρρwaterwaterVVdisplaceddisplaced
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Archimedes PrincipleArchimedes Principle
• orces act every*here on shiporces act every*here on ship-> too tough to analy9e-> too tough to analy9e
• "enter of #ravity 0#6("enter of #ravity 0#6( allall
gravity forces as one forcegravity forces as one forceacting do*n*ard throughacting do*n*ard through
ship’s geometric centership’s geometric center
•
"enter of $uoyancy 0$6("enter of $uoyancy 0$6( allallbuoyancy forces as one forcebuoyancy forces as one force
acting up*ard throughacting up*ard through
under*ater geometric centerunder*ater geometric center
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Archimedes PrincipleArchimedes Principle•
"enter of #ravity 0#6("enter of #ravity 0#6(• "hanges position only by"hanges position only bychange3shift in mass of shipchange3shift in mass of ship
• .oes not change position.oes not change position *ith*ithmovement of shipmovement of ship
• "enter of $uoyancy 0$6("enter of $uoyancy 0$6(• "hanges position"hanges position *ith movement of*ith movement of
ship -> under*ater geometric centership -> under*ater geometric center
movesmoves
• Also a:ected by displacementAlso a:ected by displacement
#
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;ydrostatics;ydrostatics
TerminologyTerminology• .isplacement(.isplacement( total *eight of ship 1total *eight of ship 1
total submerged volume of shiptotal submerged volume of ship
0measured in tons60measured in tons6
• .raft(.raft( vertical distance from *aterline tovertical distance from *aterline to
/eel at deepest point 0measured in feet6/eel at deepest point 0measured in feet6• <eserve $uoyancy(<eserve $uoyancy( volume of *atertightvolume of *atertight
portion of ship above *aterlineportion of ship above *aterline
0important factor in ship’s ability to0important factor in ship’s ability to
survive ooding6survive ooding6• reeboard(reeboard( vertical distance fromvertical distance from
*aterline to main dec/ 0rough indication*aterline to main dec/ 0rough indication
of reserve buoyancy6of reserve buoyancy6
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;ydrostatics;ydrostatics
TerminologyTerminology
• As draft & displacement increase!As draft & displacement increase!
freeboard and reserve buoyancy decreasefreeboard and reserve buoyancy decrease
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omentsoments
• .ef’n( tendency of a force to.ef’n( tendency of a force toproduce rotation or to move anproduce rotation or to move an
object about an a=isobject about an a=is• .istance bet*een the force and.istance bet*een the force and
a=is of rotation is the moment arma=is of rotation is the moment arm
• "ouple( t*o forces of e'ual"ouple( t*o forces of e'ual
magnitude in opposite andmagnitude in opposite and
parallel directions! separatedparallel directions! separatedby a perpendicular distanceby a perpendicular distance• # and $ are a couple# and $ are a couple
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omentsoments• .epending on location.epending on location
of # and $! t*o typesof # and $! t*o typesof moments(of moments(• <ighting moment(<ighting moment(
tends to return ship totends to return ship to
upright positionupright position• +psetting moment(+psetting moment(
tends to overturn shiptends to overturn ship
• agnitude of rightingagnitude of righting
moment(moment(• < 1 7 #?< 1 7 #? 0ft-tons60ft-tons6
• #?( moment arm#?( moment arm 0ft60ft6
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etacenteretacenter
• .ef’n( the.ef’n( the
intersection of t*ointersection of t*o
successive lines ofsuccessive lines of
action of the forceaction of the forceof buoyancy asof buoyancy as
ship heels throughship heels through
small angles 06small angles 06• @f angle too large! @f angle too large!
moves o: centerlinemoves o: centerline
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etacenteretacenter•
etacentricetacentric;eight 0#6;eight 0#6• .etermines si9e of.etermines si9e of
righting3upsettingrighting3upsetting
arm 0for angles arm 0for angles BBoo66
#? 1 #sin#? 1 #sin
• ,arge # -> large,arge # -> large
righting arm 0sti:6righting arm 0sti:6• Small # -> smallSmall # -> small
righting armrighting arm
0tender60tender6
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etacenteretacenter
• <elationship bet*een # and <elationship bet*een # and • # under ( ship is stable# under ( ship is stable
• # 1 ( ship neutral# 1 ( ship neutral
•
# over ( ship unstable# over ( ship unstable
STABLESTABLE UNSTABLEUNSTABLE
bili S bili
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etacenter v% Stabilityetacenter v% Stability
"urves"urves• At this point! *e could useAt this point! *e could use
lots of trigonometry tolots of trigonometry to
determine e=act values ofdetermine e=act values of
forces! etc for all angles ->forces! etc for all angles ->
too much *or/too much *or/
• # used as a measure of# used as a measure of
stability up to BC! after thatstability up to BC! after that
values of #? are plotted atvalues of #? are plotted at
successive angles to createsuccessive angles to create
the stability curvethe stability curve
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Stability "urveStability "urve
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Stability "urveStability "urve• Plot #? 0righting arm6 vs% angle of heelPlot #? 0righting arm6 vs% angle of heel
• Ship’s # does not change as angle changesShip’s # does not change as angle changes• Ship’s $ al*ays at center of under*aterShip’s $ al*ays at center of under*ater
portion of hullportion of hull
• Ship’s under*ater portion of hull changesShip’s under*ater portion of hull changes
as heel angle changesas heel angle changes• #? changes as angle changes#? changes as angle changes
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DuestionsDuestions
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