浮式平臺(tái)一-結(jié)構(gòu)強(qiáng)度分析基本原理

第二章結(jié)構(gòu)強(qiáng)度設(shè)計(jì)

StructuralStrengthDesignandAnalysis

第一節(jié)結(jié)構(gòu)強(qiáng)度分析根本原理

閆發(fā)鎖

引言

1.船舶結(jié)構(gòu)設(shè)計(jì)的過(guò)程？

2.浮式平臺(tái)結(jié)構(gòu)的設(shè)計(jì)與船舶結(jié)構(gòu)的設(shè)計(jì)具有哪些相似和不同？

浮式平臺(tái)與船舶的結(jié)構(gòu)設(shè)計(jì)過(guò)程一致，細(xì)節(jié)不同。

結(jié)構(gòu)根本設(shè)計(jì)結(jié)構(gòu)分析結(jié)構(gòu)荷載結(jié)構(gòu)總布置確定的前提下，根據(jù)設(shè)計(jì)標(biāo)準(zhǔn)與設(shè)計(jì)經(jīng)驗(yàn)分析反響Outline6hourscourseworkBasicsofstructuralplatingandshellApplicationofplatingandshellinoffshorestructuresLoadingandstressesStructuralfiniteelementanalysisFEAresultsdesignapplicationTableofContentsStrengthDesignFundamentals板殼結(jié)構(gòu)的受力特點(diǎn)板殼結(jié)構(gòu)中的應(yīng)力分布和計(jì)算方法浮式結(jié)構(gòu)常用的應(yīng)力及特點(diǎn)設(shè)計(jì)標(biāo)準(zhǔn)和應(yīng)用靜水壓的局部和整體作用整體力對(duì)板殼結(jié)構(gòu)強(qiáng)度的影響TableofContents(cont)結(jié)構(gòu)的有限元分析StructuralDesignLoadingConditions分析結(jié)果的應(yīng)用和結(jié)構(gòu)設(shè)計(jì)1StressFundamentals2StructureBending,shearandtorsioncolumn,beam,section3plateandshellbending4能量原理5柱，梁板殼的局部和整體屈曲6

FEA原理StrengthDesignFundamentals

StressVectorDefinition

應(yīng)力的矢量定義Stress-StrainRelationship應(yīng)力-應(yīng)變關(guān)系EquivalentStressandPrincipalStresses等效應(yīng)力和主應(yīng)力StressVectorsMaterialRelationshipforLinearMaterialThestressisrelatedtostrain: {s}=[D]{eel}

where:stressvector{s}hasthefollowingcomponents

{s}=[sxsyszsxysyzsxz]T

[D]istheelasticityorelasticstiffnessmatrixorstress-strainmatrix

{eel}istheelasticstrainvector

{eel}={e}–{eth}MaterialRelationshipforLinearMaterialThetotalstrainvector{e}canbeexpressedas:

{e}=[ex

eyezexexyeyzexz] {eth}isthethermalstrainvector

{eel}arethestrainsthatcausestresses

TheFlexibilityorComplianceMatrixWheretypicaltermsare:Ex=Young’smodulusinthexdirectionnxy=majorPoisson’srationyx=minorPoisson’sratioGxy=shearmodulusinthexyplaneTheFlexibilityorComplianceMatrixThe[D]-1matrixispresumedtobesymmetric:nyx/Ey=nxy/Exnzx/Ez=nxz/Exnzy/Ez=nyz/Eynxy,nyz,nxz,nyx,nzy,andnzxarenotindependentquantities,Poisson’sRatioTheuseofPoisson’sratiosfororthotropicmaterialssometimescauseconfusion,sothatcareshouldbetakenintheiruse.AssumingthatExislargerthanEy,nxyislargerthannyx.Hence,nxyiscommonlyreferredtoasthe“majorPoisson’sratio〞,becauseitislargerthannyx,whichiscommonlyreferredtoasthe“minorPoisson’sratio〞.Fororthotropicmaterials,weneedtoinquireofthesourceofthematerialpropertydataastowhichtypeofinputisappropriate.Forisotropicmaterials,itmakesnodifferencewhichtypeofinputisused: Ex=Ey=Ez, nxy=nyx=nxzStress-StrainRelationsex=axDT+sx/Ex–nxysy/Ex-nxzsz/Ex

ey=ayDT-nxysx/Ex+sy/Ey-nyzsz/Eyez=azDT-nxzsx/Ex–nyzsy/Ey+sz/Ezexy=sxy/Gxyeyz=syz/Gyzexz=sxz/GxzWherethetypicaltermsare:ex=directstraininthexdirectionsx=directstressinthexdirectionexy=shearstrainonthex-yplanesxy=shearstressonthex-yplaneIsotropicMaterialForisotropicmaterialandnotemperaturechanges,therelationcanbegreatlysimplified:

DT=0 E=Ex=Ey=Eznxy=nxz=nxy Gxy=Gxz=Gyzex=(sx–nsy–nsz)/Eey=(sy-nsx-nsz)/Eez=(sz-nsx–nsy)/Eexy=sxy/Geyz=syz/Gexz=sxz/GEquivalentStressTheEquivalentStressisalsocalledvonMisesstressse=(sx2+sy2-sxsy+3sxy2)1/2Wheresx,sy,

andsxyrepresentthecomponentstressesintheXandYdirections,andcomponentshearstress,respectively.PrincipalStressesPrincipalstresscalculationsareperformedtohelpidentifyareasofthestructuresubjectedtohighcyclicloads.Theseareasarethengivenspecialattentionforreasonsoffatigue. S1=(sx+sy)/2+{[(sx-sy)/2]2+sxy2}1/2 S2=(sx+sy)/2-{[(sx-sy)/2]2+sxy2}1/2UseofVariousStressesEquivalentstressisusedmostlyinanalysisGlobalstructurecontrolloadcasesselectionGlobalstresscheckStructuralstresslevelcheckComplicatejointstresscheckComponentstressesCheckstressmagnitudeinparticulardirectionUsedforstabilitycheckUsedmostlyinnormalsectionNotapplicableincomplicatecornerortransitionsUseofVariousStresses(cont.)PrincipalstressesFatigueanalysisComplicatejointstresscheckCornerortransitionstabilitycheckStressVectorsStressflowcheckLoadpassHelptounderstandthecomplicatejointsDeformationHelptounderstandstructuralbehaviorSatisfythecode/designbasisrequirementsMaterialCoordinateSystemsThefundamentalassumptionsofplatetheory1.Thematerialiselastic,homogeneous,andisotropic.2.Theplateisinitiallyflat.3.Thedeflectionofmidplaneissmallcomparedwiththethicknessoftheplate..4.Thestraightlines,initiallynormaltothemiddleplanebeforebending,remainstraightandnormaltothemiddlesurfaceduringthedeformation5.Thestressnormaltothemiddleplane,σz,issmallandmaybeneglected6.Sincethedisplacementsofaplatearesmall,itisassumedthatthemiddlesurfaceremainsunstrainedafterbending.Thefundamentalequationsofelasticitytheory

CompatibilityequationsEquilibriumequationsConstitutiveequationsGeometryequationsGoverningdifferentialequationsofplateelementGoverningdifferentialequationsbythedeflectionsBytheforcesBoundaryconditions1Clamped,orbuilt-in,orfixededgey=02Simplysupportededgex=a3Freeedgey=bVariationalprinciplesofsolidmechanicsBoundaryBoundaryconditionsTotalpotentialenergyofadeformedelasticbodyandtheloadsactingonit=U+

ThestrainenergyTheworkdoneexternalforcesInternalVariationalprinciples(a)ThePrincipleofConservationofEnergy(b)ThePrincipleofVirtualWork(c)ThePrincipleofMinimumPotentialEnergySolutionofRectangularPlatesCylindricalbendingofaplate(桶形彎曲，likeabeam〕Purebendingofplates〔純彎曲，Onlymoments〕NAVIER’SMethod(Doubleseriessolution,四邊簡(jiǎn)支)SolutionofRectangularPlates(cont.)TrytofindthesolutionsofrectangularplateswithdifferentboundaryconditionsandloadsSubjectedtoapatchloadofintensityp0=constSubjectedtoaconcentr