浮式平臺一-結構強度分析基本原理

第二章結構強度設計

StructuralStrengthDesignandAnalysis

第一節(jié)結構強度分析根本原理

閆發(fā)鎖

引言

1.船舶結構設計的過程？

2.浮式平臺結構的設計與船舶結構的設計具有哪些相似和不同？

浮式平臺與船舶的結構設計過程一致，細節(jié)不同。

結構根本設計結構分析結構荷載結構總布置確定的前提下，根據(jù)設計標準與設計經(jīng)驗分析反響Outline6hourscourseworkBasicsofstructuralplatingandshellApplicationofplatingandshellinoffshorestructuresLoadingandstressesStructuralfiniteelementanalysisFEAresultsdesignapplicationTableofContentsStrengthDesignFundamentals板殼結構的受力特點板殼結構中的應力分布和計算方法浮式結構常用的應力及特點設計標準和應用靜水壓的局部和整體作用整體力對板殼結構強度的影響TableofContents(cont)結構的有限元分析StructuralDesignLoadingConditions分析結果的應用和結構設計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

應力的矢量定義Stress-StrainRelationship應力-應變關系EquivalentStressandPrincipalStresses等效應力和主應力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,四邊簡支)SolutionofRectangularPlates(cont.)TrytofindthesolutionsofrectangularplateswithdifferentboundaryconditionsandloadsSubjectedtoapatchloadofintensityp0=constSubjectedtoaconcentr