Chapter D IceSnow Impact

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1、DIce/SnowImpactD.1IntroductionAgreatdealofworkhasbeencarriedoutoniceimpactingoniceoronstructures.Majorworkhasalreadybeenreportedinthistextregardingthepredictionofimpactloadsbefore,duringandafterindentationandcollapseconditions.D.2Finite-ElementAnalysisFinite-elementanalysishasbeencarriedo

2、utonaconcreteplatformsubjecttoiceimpact.Non-linearvisco-elasticitybasedonthedisplacementmethodwasconsidered.Ateachtimestep,asuccessivesubstitution-typeiterationwasappliedtotheglobalequationsofmotion,whileaNewton–Raphsonmethodcombinedwiththeα-methodofnumericaltimeintegrationwasusedinthecon

3、stitutiveequationsattheGaussintegrationpointsinthefinite-elementmesh.Variableinterfaceconditionsbetweentheiceandthestructureweresimulatedtolimittheeffectsofinterfaceadfreezeorfriction.Toallowthedeliberatedevelopmentofcertainnormalcompressivestressesattheinter-face,anadaptiveprocedurewasused

4、tofreethosepointsattheinterface.Themechanicalbehaviouroftheseaicewasmodelledasanisothropicmate-rialwithcreeplaws.Thethree-dimensionalyieldsurfacewasrepresentedbyJones’stri-axialtestsandisgiveninFig.D.1a,b.TherangeofstrainratescoveredcanbeseeninFig.D.1b.Asanexample,aCondeep-typeplatform(Fi

5、g.D.2)wasassumedtolieintheiceenvironmentandtobesubjectedtoiceimpact.Themajorparametersfortheicebergimpactingtheplatformare:Icebergsize:50,000tonEquivalentdiameter:38.2mFreeboard:3.8m988DIce/SnowImpacts3s2s(a)1.0.23GeneralŒ=70Œs=-12ºC.-1Œ=strainrateins.+-2)Œ=1.410230.1Œ=5.4+10-3.2Œ=1.4+10-

6、3.3Œ=5.4+10-4(MN/m3.4Œ=1.4+10-4..5-sŒŒ=5.5+10-31201.6Œ=1.4+10-3.7Œ2Œ.=1.4+10-48.Œ3.10Œ4.DeviatoricstresssŒ5.Œ6.Œ7.Œ8-20020406080100120140Confiningpressures(MN/m2)(b)3Fig.D.1.Jones’stri-axialtests.(a)Yieldsurfaceforisotropicice,newformulation;(b)Jones’stri-axialstressDraft:34.4mInitialvelo

7、city:1.0ms−1√K=YF(t)/D1.5=0.08MPamY=1.72(D/D)−1.27,IC1nD.2Finite-ElementAnalysis989icebergupto50000tonnessteelat2knotsdecktrussthreeconcretetowersFig.D.2.ConcretegravityplatformsubjecttoiceimpactwhereD,Dn=originalandnotchrootdiameters,respectively.DataforicebergsAdd