Stti Surfe ores Stti Surfe ores 8m wter hinge? 4 m ores on plne res ores on urved surfes Buont fore Stbilit of floting nd submerged bodies ores on Plne res Two tpes of problems Horizontl surfes (pressure is ) onstnt nlined surfes dp Two unknowns Totl fore Line of tion dz Two tehniques to find the line of tion of the resultnt fore Moments Pressure prism ores on Plne res: Horizontl surfes Wht is the fore on the bottom of this tnk of wter? h pd p d p =weight g of overling fluid! p = h is norml to the surfe nd towrds the surfe if p is positive. entroid psses through the of the re. h Side view h = Vertil distne to free surfe Top view
ores on Plne res: nlined Surfes Diretion of fore Norml to the plne Mgnitude of fore integrte the pressure over the re pressure is no longer onstnt! Line of tion Moment of the resultnt fore must equl the moment of the distributed pressure fore HW#.89,.,.6,.7,.9,.0,.8,.4,.44,.47 ores on Plne res: nlined Surfes ree surfe h entroid h O B O Mgnitude of ore on nlined Plne re pd sin d sin p h sin d enter of pressure The origin of the is is on the free surfe h h p h is the vertil distne between free surfe nd entroid p is the pressure t the entroid of the re
irst Moments Seond Moments d Moment of n re bout the is lso lled moment of inerti of the re d d Lotion of entroidl is h d is the nd moment with respet to n is pssing through its entroid nd prllel to the is. Prllel lis theorem or plte of uniform thikness the intersetion of the entroidl es is lso the enter of grvit Produt of nerti mesure of the smmetr of the re d Produt of inerti = 0 = 0 f = or = is n is of smmetr then the produt of inerti is zero. b b b d Properties of res b 0 b b d b b bd 6 7 4 4 0
Properties of res ores on Plne res: Center of Pressure: 4 4 0 b b b 0 4 4 4 6 8 4 The enter of pressure is not t the entroid (beuse pressure is inresing with depth) oordinte of enter of pressure: pd Moment of resultnt fore = sum of moment of distributed fores pd sin p sin sind sin d Center of Pressure: Center of Pressure: d d Produt of inerti Prllel is theorem pd pd sin d Sum of the moments sin sind d p sin Prllel is theorem
nlined Surfe indings The horizontl enter of pressure nd the horizontl entroid oinide id when the surfe hs either horizontl or vertil is of smmetr The enter of pressure is lws below the entroid The vertil distne between the entroid nd the enter of pressure dereses s the surfe is lowered deeper into the liquid ( inreses) Wht do ou do if there isn t free surfe? 0 >0 Emple using Moments n elliptil gte overs the end of pipe 4 m in dimeter. f the gte is hinged t the top, wht norml fore pplied t the bottom of the gte is required to open the gte when wter is 8 m deep bove the top of the pipe nd the pipe is open to the tmosphere on the other side? Neglet the weight of the gte. Solution Sheme Mgnitude of the fore pplied b the wter Lotion of the resultnt fore 8 m ind using moments bout hinge wter hinge 4 m Mgnitude of the ore Lotion of esultnt ore p b 8 m h = 0 m Depth to the entroid p = h hb N 9800 0 m π.5 m m = 54MN.54 m wter =.5 m b = m hinge 4 m h 8 m Slnt distne.5 m to surfe b b bb 4b 4 5m.5 4 4.5 m 0.5 m r wter =.5 m b = m hinge 4 m p
ore equired to Open Gte ores on Plne Surfes eview How do we find the required fore? Moments bout the hinge M hinge 0 =l tot - l p l l p tot.54 0 6 N.65 m 5 m 8 m l p =.65 m r wter.5 m hinge 4 m p l tot The verge mgnitude of the pressure fore is the pressure t the entroid The horizontl lotion of the pressure fore ws t (WHY?) The gte ws smmetril bout t lest one of the entroidl es. The vertil lotion of the pressure fore is below the entroid. (WHY?) Pressure inreses with depth. = 809 kn b = m ores on Plne res: Pressure Prism simpler pproh tht works well for res of onstnt width ( ) retngles f the lotion of the resultnt fore is required nd the re doesn t interset the free surfe, then the moment of inerti method is bout s es ores on Plne res: Pressure Prism ree surfe h h h O h ore = Volume of pressure prism p h pd d Center of pressure is t entroid of d pressure prism
Emple : Pressure Prism Emple : Pressure Prism O h/os 8 m wter h=0 m 4º Dm hinge h = Volume = (h/os)(h)(w)/ = (0 m/0.95)(9800 N/m *0 m)(50 m)/ = 6 MN m 5m 8 m 4 m 5 m (retngulr onduit) 4 m Solution : Pressure Prism ores on Curved Surfes Mgnitude of fore (9800 N/m =.96 MN Lotion of resultnt fore h h )(0 m)(5 m)(4 m) h mesured from hinge 5m h Horizontl omponent Vertil omponent w h w h h 5 m 8 m m 0 m 6 w h h w0 m 6 =.667 m
ores on Curved Surfes: Horizontl Component Wht is the horizontl omponent of pressure fore on urved surfe equl to? The enter of pressure is loted using the moment of inerti or pressure prism tehnique. The horizontl omponent of pressure fore on losed bod is. zero ores on Curved Surfes: Vertil Component Wht is the mgnitude of the vertil omponent of fore on the up? = p p = h =hr =W! r h ores on Curved Surfes: Vertil Component The vertil omponent of pressure fore on urved surfe is equl to the weight of liquid vertill bove the urved surfe nd etending up to the (virtul or rel) free surfe. Streeter, et. l Wht if the up hd sloping sides?
Emple: ores on Curved Surfes ind the resultnt fore (mgnitude nd lotion) on m wide setion of the irulr r. V = W + W m W = ( m)( m)( m) +/4( m) ( m) wter = 58.9 kn + 0.8 kn = 89.7 kn H = p p h = (4 m)( m)( m) = 78.5 kn m m W Emple: ores on Curved Surfes The vertil omponent line of tion goes through the entroid of the volume of wter bove the surfe. Tke moments bout vertil is through. 4 m W 4( m) wter V ( m) W W 4( m) m W ( m)(58.9 kn) (0.8 kn) (89.7 kn) m = 0.948 m (mesured from ) with mgnitude of 89.7 kn Emple: ores on Curved Surfes Emple: ores on Curved Surfes The lotion of the line of tion of the horizontl omponent is given b b b ( m)( m) / = 0.667 m 4 wter m W m m W 4.08 m 0.948 m 78.5 kn 89.7 kn horizontl vertil 4 m 4 0667m 0.667 4 m 4.08 m 4 m m m 9. kn resultnt
Clindril Surfe ore Chek Curved Surfe Trik 0.948 m C 89.7kN ll pressure fores pss C through h point C. The pressure fore.08 m pplies no moment bout point C. The resultnt t must pss through point C. 78.5kN (78.5kN)(.08m) - (89.7kN)(0.948m) = 0 ind fore required to open the gte. ll the horizontl fore is rried b the hinge m W The pressure fores nd fore wter O pss through O. Thus the hinge W fore must pss through O! Hinge rries onl horizontl fores! ( = ) W + W m Curved Surfe Trik Solution Sheme Trditionl w: M hinge 0 : (89.7)( 0.948) (78.5)(.08) () 89.7 (kn) Sme s v = W +W.08 m 78.5kN C 0.948 m 89.7kN Determine pressure dtum nd lotion in fluid where pressure is zero ( origin) i Determine totl elertion vetor () inluding elertion of grvit Define h tngent to elertion vetor (ll this vertil!) Determine if surfe is norml to, inlined, or urved
Stti Surfe ores Summr Buont ore ores used b grvit (or ) totl elertion on submerged surfes horizontl surfes (norml to totl elertion) h Lotion where p = p ref inlined surfes ( oordinte hs origin t free surfe) h urved surfes h Horizontl omponent Vertil omponent ( ) weight of fluid bove surfe Virtul surfes The resultnt fore eerted on bod b stti fluid in whih it is full or prtill submerged The projetion of the bod on vertil plne is lws. zero The vertil omponents of pressure on the top nd bottom surfes re different Buont ore: Thought Eperiment Ple thin wll blloon filled with wter in tnk of wter. Wht is the net fore on the B blloon? zero Does the shpe of the blloon mtter? no Wht is the buont fore on the blloon? Wi Weight of wter displed Where is the line of tion of B =V the buont fore? Thru entroid of blloon Buont ore: Line of tion The buont fore ts through the entroid of fth the displed d volume of ffl fluid id( (enter of buon) = volume d = distributed fore = entroid of volume V dv V V V dv
Buont ore: pplitions Buont ore: pplitions > Using buon it is > possible to determine: Weight of n objet Volume of n objet Speifi grvit of n objet W W ore blne V W V W (With,,, nd given) V W V W (fore blne) Equte weights Equte volumes V V W W V V W W V W V W Suppose the speifi weight of the first fluid is zero Buont ore (Just for fun) ottionl Stbilit of Submerged Bodies silbot is siling on Lke Brn. The ptin is in hurr to get to shore nd deides to ut the nhor off nd toss it overbord to lighten the bot. Does the wter level of Lke Brn ----------- inrese or derese? Wh? The nhor disples less wter when it is ling on the bottom of the lke thn it did when in the bot. ompletel submerged bod is stble when its enter of grvit is below the enter of buon B G B G
End of Chpter Question End of Chpter Write n eqution for the pressure ting on the bottom of onil tnk of wter. Write n eqution for the totl fore ting on the bottom of the tnk. L d Wht didn t ou understnd so fr bout sttis? sk the person net to ou Cirle n questions tht still need nswers d Grnd Coulee Dm Gtes http://users.owt.om/hubbrd/gdm/html/gller.html
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