船舶专业英语07

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1、Stabilityatlarge7anglesThestabilityofabodyforsmallmovementswasdiscussedinanearlierchapter.Thestabilityforlargerdisturbancesmustnowbeconsidered.Atwood'sformulaSofaronlyaship'sinitialstabilityhasbeenconsidered.Thatisforsmallinclinationsfromthevertical.V~entheangleofinclinationisgreaterthan,s

2、ay,4or5degrees,thepoint,M,atwhichtheverticalthroughtheinclinedcentreofbuoyancymeetsthecentrelineoftheship,cannolongerberegardedasafixedpoint.Metacentricheightisnolongerasuitablemeasureofstabilityandthevalueoftherightingarm,GZ,isusedinstead.Assumetheshipisinequilibriumundertheactionofitswei

3、ghtandbuoyancywithW0L0andW1L1thewaterlineswhenuprightandwheninclinedthroughq~respectively.Thesetwowaterlineswillcutoffthesamevolumeofbuoyancybutwillnot,ingeneral,intersectonthecentrelinebutatsomepointS.AvolumerepresentedbyWoSW]hasemergedandanequalvolume,representedbyLoSL1hasbeenimmersed.Le

4、tthisvolumebev.UsingthenotationinFigure7.1,thehorizontalshiftofthecentreofFigure7.1Atwood'sformula104STABILITYATLARGEANGLES105buoyancy,isgivenby:BoR=vXh,,hi/VandGZ=BoR-BoGsinThisexpressionforGZisoftencalledAtwood'sformula.STABILITYCURVESCurvesofstaticalstabilityByevaluatingvandhet~forarang

5、eofanglesofinclinationitispos-sibletoplotacurveofGZagainst~.AtypicalexampleisFigure7.2..E

6、sleverisgreaterthanthevalueofGZatA.ItbecomesunstableoncethepointBhasbeenpassed.OBisknownastherangeofstability.ThecurveofGZagainstq~istermedtheGZcurveorcurveofstaticalstability.Becauseshipsarenotwall-sided,itisnoteasytodeterminethepos-itionofSandsofindthevolumeandcentroidpositionsoftheemerg

7、edandimmersedwedges.OnemethodisillustratedinFigure7.3.TheshipisfirstinclinedaboutaforeandaftaxisthroughOonthecentre-line.Thisleadstounequalvolumesofemergedandimmersedwedgeswhichmustbecompensatedforbyabodilyriseorsinkage.Inthecaseillustratedtheshiprises.Usingsu