高等结构动力学

第一章绪论 一 现代结构动力学的研究内容1 外载荷分析确定性 周期性 瞬态 动力机械 旋转机械产生的激励碰撞 爆炸 冲击等瞬态荷载随机性 风荷载 波浪荷载 地震荷载 车辆等路面行驶引起的荷载2 结构系统的动力响应时域 载荷可以是非线性的 系统也可以是非线性的 解析解法 数值解法频域 目前仅能处理线性化系统 谱分析方法 优点 计算效率高时频混合分析方法 将时域解法与频域解法的优点结合 提高计算效率和求解精度解析法 数学上直接求解 许多实际结构难以采用该方法数值解法 工程上可以应用的近似解法 有限元法 边界元法 随机样条法 有限条法 1 3 结构系统的辨识和参数估计动力学的拟问题 1 已知input和output 识别结构参数 2 已知input满足一定假设 output可测 识别结构参数 3 Healthmornitoring a 有无结构失效b 损伤位置c 损伤程度 2 4 容许标准和可靠性分析评估结构系统在某种载荷激励下的可靠性 系统寿命评估 系统疲劳分析等 5 结构振动控制大型结构如高层 潜艇 海洋平台等 环境荷载比较恶劣 在使用过程中会出现幅度比较大的振动 这些振动会诱发 1 疲劳破坏 2 降低系统的可靠度 3 给居住会作业人员带来身体不适措施 在结构上安装控制设备 装置 使结构具有自动调节的能力 从而使其振动减小 避免破坏 在建筑结构中主要是抵抗风 地震载荷 桥梁的振动上海电视塔 杨浦大桥等都安装了减振装置 日本的200多个高层建筑海洋结构主要抵抗波浪 风荷载控制方法主要有 被动式控制 调谐质量阻尼器 调谐液体阻尼器 粘弹性阻尼器等主动控制 主动质量驱动器等半主动控制 主动变刚度 主动变阻尼 磁流变阻尼器 电流变阻尼器混合式控制6 结构动力优化设计按照设计要求确定可控变量或设计变量使结构系统达到预期的状态 或者达到最优设计目标 最优综合或最优设计 3 SpecialtopicI Dynamicresponse动态响应 4 5 6 7 不同方法计算whipping响应的比较 8 Springinganalysis 激励频率 固有频率 9 Inwhippingandspringingthereare 10 11 12 通过分析结构能量传递途径 采用改变结构参数实现抑制振动向目标区域传递 13 14 结构破坏指数 15 冰载测量 16 17 18 19 20 21 22 结构动力学的前沿和热点问题主动控制技术海洋工程动力学海上陆色能源开发的动力学问题 23 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 24 SepecialtopicII IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 脉冲压力载荷与响应评估 24 25 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 DamagedstructureduetoBowSlamming艏部砰击下的结构损伤 Damagedplate外板损伤 Damagedstiffener骨材损伤 INTRODUCTION 25 26 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 DamagedstructureduetoSternSlamming艉部砰击下的结构损伤 Damagedplate外板损伤 Damagedstiffener骨材损伤 26 27 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 DamagedstructureduetoSloshing晃荡引起的结构损伤 Damagedcorrugation ImpactedArea 27 28 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 DamagedstructureduetoGreenWater上浪引起的结构损伤 28 29 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 Structuraldesignagainstimpulsivepressureloadingsfromslamming sloshingandgreenwaterhasalwaysbeenadifficulttask Manyshipshavestillreportedexperiencingstructuraldamageduetoimpulsivepressureloadings Thisindicatesthattherelevantrulesofclassificationsocietiesneedstobeimprovedregardingimpulsivepressureloadings 受脉冲压力载荷 砰击 晃荡 上浪等 作用的船体结构的设计总是一件棘手的事情 到目前为止 脉冲载荷引起的结构损坏还是时有发生 表明船级社现行的相关规范需要进一步改进 Whenthedurationofanimpulsivepressureloadingismuchshorterthanthenaturalperiodoftheimpactedstructure theimpulsemayrepresenttheloading However ifthedurationislongenoughascomparedtothenaturalperiod theamplitudeofpressuremayplayanimportantrole 当脉冲压力载荷的持续时间远远小于结构的固有周期时 可以用脉冲特性来描述载荷 当脉冲压力载荷的持续时间远远大于结构的固有周期时 可以用压力峰值来描述载荷 Inextremecases thestructuraldesignagainstimpulsivepressureloadingsmaybetreatedasanultimatelimitstateoranaccidentlimitstateproblem However formoreprobablesituations thiscanbesolvedasaserviceabilitylimitstateproblemespeciallyfromtheimpactsofslammingwherebythetolerableextentofdamageneedstobeprovided 在极端情况下 脉冲压力载荷作用下的结构设计可以用极限强度或事故强度问题处理 但在更多的情况下 可以将该问题当作服务强度来处理 29 Modelandfull scaletest模型和实船试验技术Modeltest 模型试验 droptestoncontainershipsternsection Yang etal 2007 集装箱船尾部剖面落体试验 droptestonrigidanddeformablecone shapedsamples Peseux etal 2005 刚性和弹性锥形体落体试验 droptestonflatplate HigoandYamada 2006 平板落体试验 planningcraftmodelinobliquewaves RosenandGarme 2004 滑行艇模型斜浪中试验Fullscaletest 实船试验 deep Vpleasurecraft CarreraandRizzo 2005 深V型游艇 containershipintheNorthPacificOcean Lee etal 2007 北太平洋集装箱船试验 30 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING LOCALSLAMMING 30 Numericalsimulation数值模拟 VOF VolumeofFluid andSPH SmoothedParticleHydrodynamics explicitFEManalysisfor2Drigidwedge Stenius etal 2005 二维刚体显式有限元法 directcouplingofFEMandWagnerrepresentationforelasticbodyofsmalldead riseangle Korobkin etal 2006a 小斜升角问题的有限元与Wagner砰击压力直接耦合法 numericalsimulationoftrappedaireffects Dobashi 2006 2007 气垫效应数值模拟Analyticalprediction解析计算 publicationaboutanalyticalmethodshasbeenrareinrecentyears 很少 analyticalsolutionfor2Dwedge Yettou etal 2007 Yettou提出了一种新的解析算法 31 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING LOCALSLAMMING 31 Practicalproceduresindeterminingdesignslammingpressure确定设计砰击压力的实用过程 computationalprocedurefortheanalysisofaship smotionsinwavesandspatialmeanslammingpressures Ould etal 2005 波浪中船舶运动以及平均砰击压力空间分布的计算流程 numericalproceduretopredictslammingloadsonoffshoresupplyvessel Schellin 2006 carcarrier HermundstadandMoan 2005 cruiseship HermundstadandMoan 2007 海洋工程供应船 滚装船 游船的砰击载荷预报流程 feed forwardneuralnetworktopredicthorizontalforce Fullerton etal 2007 peakvalueofslammingpressure ChenandXiao 2005 利用神经网络技术预报横向力和砰击压力峰值 32 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING LOCALSLAMMING 32 33 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING LOCALSLAMMING局部砰击 Pressurecoefficientsobtainedusingacommercialpackage Yang etal 2007 经典理论 经典模型试验 新模型试验 CFD计算的比较 33 Background背景 Ingeneral theglobalslammingresponseneedstobecombinedwiththesimultaneouslyobtainedglobalandlocalsteadystateloadeffects intermsofextremevaluesforultimatelimitstatechecksandcyclicloadhistoriesforfatiguedesignchecks 总体砰击载荷响应一般与稳态波浪载荷相叠加 用于极限强度和疲劳强度校核 Generally 3Deffectscanreducethe2Dslammingpressureforcebyapproximately30 Fully3Dslammingpredictionmethodsarenotreadyforuseinaglobalresponseanalysis Correctionfactorson2Destimatesmaybeappliedtoyieldreasonablevaluesfordesign 计入三维效应可以减小30 的砰击力 但三维砰击理论尚不成熟 34 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING GLOBALSLAMMING Measuredandcalculatedplammingpressure 34 GlobalStructuralModeling总体结构模型 ThehullmaybemodelledbythebeamtheoryorFEshellmodels Whileverticalbendingisrelativelywellrepresentedbybeamelements modellingoftorsionalbehaviourofopenshipssuchascontainervesselsaswellascatamaransismorechallenging 船体结构可用梁理论或有限元模型进行分析 垂向弯曲问题可用梁理论较好的表示 但大开口船的扭转问题和双体船则比较麻烦 Quiteaccurateresultsareobtainedifthebeammodelisbasedonanadvancedthin walledgirdertheory AmoredetailedFEmodelwillbenecessaryifthe1Dbeamistobeappliedinthedynamicanalysis toobtainresponsevaluesespeciallyforfatiguedesign 利用先进的薄壁梁理论可以较准确的结果 对于疲劳等问题 有限元方法比一维梁理论更好 Nopublicationsseemtohavebeenpublishedonslamminginducedtorsionalresponseofships 砰击引起的扭转振动问题目前未见有文章发表 35 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING GLOBALSLAMMING总体砰击 35 WhippingAnalysis Extremevaluesforultimatestrengthdesign颤振分析 极限强度设计 experimentontheshort termprobabilitydistributionofthemidshipsverticalhoggingbendingmoment DrummenandMoan 2007 通过模型试验确定载荷的短期概率分布 numericalandexperimentalstudytomeasureshipresponsestoextremewaveimpact 数值和试验研究极限砰击下的船体响应 Minamietal 2006 hybridmethodforcalculatingwave inducedlinearandnonlineargloballoadeffectsinshipswithhullflexibility WuandMoan 2005 线性与非线性混合法 experimentalandnumericalinvestigationoftheeffectofbowflareandsternslamminginducedwhippinginlargepassengervessels Cusanoetal 2007 大型游船艏艉砰击下颤振响应的模型与数值研究 experimentontheVBMresponsetosternslammingloadsonalargemodernpassengership Dessietal 2007 大型豪华游船艉砰击 long termanalysisofextremesloshingandwhipping inducedpressuresandstructuralresponseoftheMarkIIIcontainmentsystemforLNG Graczyketal 2007 MarkIII型大型LNG船围护系统极端晃荡和颤振压力长期预报和结构响应 36 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING GLOBALSLAMMING总体砰击 36 WhippingAnalysis Cyclicstresshistoryforfatigueanalysis颤振响应 疲劳分析中的循环载荷 Fullscalemeasurements 实船试验Capesizeironorecarriers Moeetal 2005 andStorhaugetal 2006 矿砂船4000TEUcontainership Drummenetal 2006 2007 集装箱船10000dwt generalcargoship AalbertsandNieuwenhuijs 2006 一般货船6800TEUcontainership Toyodaetal 2006 Forcontainerships thepredictedtotalfatiguedamageforthemidshipssectionwasapproximately50 higherthanthedamagedeterminedexperimentally 对集装箱船 理论预报的疲劳损伤比试验值大50 左右 Highfrequencydamagecanbesignificantlyreducedbyincludingthesteadywavefortherelevantship 当包含稳态载荷引起的破坏时 高频疲劳损伤的程度相对明显减轻 37 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING GLOBALSLAMMING总体砰击 37 38 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING SLOSHING晃荡 Sloshingtestequipments试验装置 Modelandfull scaletests模型和实船试验 forquasifullscalemodel准实船 for intermediate scalemodel中模型 forsmallscalemodel小模型 38 Modelandfull scaletests模型和实船试验 Smallscalemodeltestsgiveareasonableoverviewoftheoverallsloshingmotionsinsidethetankbutthelocalpressuresmeasurementsarestilldifficulttoobtainduetothehighlylocalized intimeandspace pressureswhichoccurduringimpact Theproblemoftransferringthesepressurestoafullscalerepresentsabigchallenge 小模型可获得晃荡运动整体特征 但由于砰击压力在时间和空间上的特征 测量困难 转换成实船更难 Importantdatabasesofthequasifullscalemeasurementswererealizedusingthesetestsinvariousresearchprojects butmanyproblemswerereportedwithrespecttotherepeatabilityofthemeasurementthatmakestheproperinterpretationanduseoftheresultsverydifficult 在不同的项目中 准实船试验积累了很多数据 但结果离散性问题使利用和解释这些结果变得困难 Intermediate modeltestswillallowforthedetailedvalidationofthesimplifiedsemianalyticalandmoresophisticatednumericalmodels Indeed alltheimportantimpactparameterscanbemeasuredwithverygoodprecisionandthisallowsforpropervalidationofalltheintermediatemodellingsteps 中模型试验可以为简化的半解析预报方法和复杂的数值计算模型提供详细的验证 39 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING SLOSHING晃荡 39 Numericalmodellingofhydro structureinteractionsduringimpacts砰击中流固耦合的数值模拟 Evenifsomeattemptsweremadetosolvethe3Dimpactproblems the2Dmodellingoffluidflowisusedmostoften Onthestructuralsidethe3DeffectsoftheresponsecanbetreatedbythestandardFEMcodes二维流动模型比三维模型更常用 结构的三维效应用有限元模拟CFDNumericalsimulationsCFD数值模拟 themostpopularmethodsbelongtothefamilyoftheVOF VolumeofFluid techniqueandtothesocalledSPH SmoothedParticleHydrodynamics method However allCFDmethodssufferfromvariousnumericalproblemswhenitcomestotheevaluationofhighlylocalizedpressures VOF和SPH法最常用 但当涉及到砰击压力时 所有的数值方法都存在问题 40 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING SLOSHING晃荡V 7 Typicalsloshingmotionssimulated 40 41 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING SLOSHING晃荡 Comparisonofthequasi staticandhydroelasticstructuralresponses准静态和水弹性结构响应 41 Combinedsemianalytical fluidflow andfiniteelement structure models半解析 流体 和有限元方法的组合 Semianalyticalimpactmodelsrepresentanothertypeofmethodforsloshingimpactproblems Theideaistoidentifythemosttypicalimpactsituationsandthensimplifytheminordertobeabletodescribethemwithsimplegeometryincludingthefewmostimportantphysicalparameters 半解析砰击模型是晃荡砰击的另一类解法 找出最典型的砰击 通过简化 以几个简单但重要的物理参数去描述砰击 42 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING SLOSHING晃荡 Aeratedimpactandcorrespondingsimplification left realsituation middle geometricalsimplification right mathematicalmodel 42 Experimentalinvestigations试验研究 Anonintrusivequantitativevelocitymeasurementtechnique PIV ParticleImageVelocimetry andBIV BubbleImpactVelocimerty highlightedturbulenceintensitythroughoutthedifferentphasesoftheimpingement runup overtoppingsequence ThisscenariosuggestedtheapplicationofRitter sdam breakingflowsolutiontogreenwaterproblem PIV测量上浪瞬态速度场 BIV测量平均速度场 溃坝理论的实用性 43 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING GREENWATER上浪 InstantaneousvelocityfieldusingPIVandmeasuredmeanvelocityfieldusingBIV Ryuetal 2007a 43 Experimentalinvestigations试验研究 ThemodeltesttosimulatethegreenwaterscenariosforafixedFPSOindicatedthattheplungingwaveplusthedam breakingtypeeventasthemostcommonwater ondeckscenario whereastheso calledhammer fisttypewasfoundtobethemostdangerousone 44 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING GREENWATER上浪 Hammer fisttypeevent evolutionoftheshippedwater Grecoetal 2007 44 Numericalsimulations数值模拟 Impactingflowfeatures Domaindecompositiontechnique Navier Stokessolverwithalevelset LS0techniqueandBEMsolver Grecoetal 2007 Dambreakingproblem Volume of fluid VOF scheme Kleefsmanetal 2005 VOFtechniquewithafinitevolumemethod Zhangetal 2005 andEdge basedstabilizedfiniteelementsolverusingVOFextensions EliasandCoutinho 2007 Two layerflowovertoppingafixedbodywithaverticalwall Modifiedmarkerabdcell MAC method Yamasakietal 2005 Freesurfaceoverfixeddeckwitharoundprofile movingparticlemethod ShibataandKoshizuka 2007 Watershippingproblem smoothedparticlehydrodynamics SPH method VioleauandIssa 2007 45 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING GREENWATER上浪 Two layerflowovertoppingafixedbodywithaverticalwall Modifiedmarkerandcell MAC method Yamasakietal 2005 45 Loadalleviation PhamandVaryani 2006 comparedtheperformancesofV shapeandvanetypebreakwatersfordifferentvaluesofthegeometricalparameters TheyconcludedthattheconfrontinganglehaslessinfluenceinbothcasesforloadalleviationandthattheV shapebreakwaterismoreeffectiveinsustainingpartofthewaterflowotherwisefullydirectedtowardcontainersandstructuresplacedbehind 挡浪板的效果 46 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING GREENWATER上浪 46 Experimentalandnumericalsimulation试验和数值模拟 Theenergyoftheexplosiveisconsumedbytheshockwavesandagasbubbleandapproximately 60 intoshockwaveand40 tothegasbubbles 爆炸能量的60 转换成冲击波 40 为气泡 Sturtevant 2007 describedthefullshipshocktrials FSST donebyUSNavy ThecurrentFSSTpracticeconsistsofthreeUNDEXshotsof10 000poundHBXexplosivechargeweightdetonatedinseriesatlargestand offdistancesabeamoftheship Thecostsassociatedwiththetestcanexceed 50millionpertrial 美国海军实船试验 每个试验花费5000万美元 Bubblecollapseunderasubmergedflatplate RANSE Reynolds averagedNavier Stokesequations basedfinitedifferenceEquationIndependentTransientAnalysisComputerCode Kanetal 2005 浸没平板下的气泡溃灭数值计算 Shocktransparency basiclinearmethod Iakovlev 2006 2007 冲击波透射 基本线性法 47 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING UNDERWATEREXPLOSION水下爆炸 Fullshipshocktrial FSST Sturtevant 2007 47 Experimentalandnumericalsimulation数值与模型试验 Effectofbulkcavitationandattenuationoffloatingstructuresresponse ExplicitfiniteelementapproachwithBEM Gong 2006 Nearcontactcalculations Thechinooksolverwiththelargedeformationfluid structureinteraction Gregson 2006 Hullwhippingresponse Thesource sinkmethod Noma 2006 Ultimatestrengthofhullgirder ExplicitFEMforbendingmoment BEMforlocalpressurefrombubblejetandFEMforlocalstructuraldamage Yasuda 2006 2005 Explosionbubble BEMcoupledwithstructuralFEcode Klaseboer 2005 Classificationsocietyrules船级社规范 Lloyd sRegisterRulesandRegulations 2008 describehowaship sstructureisdesignedbytakingUNDEXintoaccount Italsogivesgeneralinformationaboutshockwaves bubblepulses bubblejetsandtheireffectstostructuralresponse Lloyd sdefinesthreelevelsofshocknotationsfortheeffectsofaninitialshockwave Inadditiontotheshocknotations itdefinesdesignlevelsforwhippinginducedbyexplosionbubbleeffectsandanothernotationsforresidualstrengthassessment 英国劳氏规范 2008 有水下爆炸问题的较多规定和方法 48 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 IMPULSIVEPRESSURELOADING UNDERWATEREXPLOSION水下爆炸 48 49 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 Cumulativeeffectofmultipleimpacts多次冲击变形累积 DAMAGETOSTRUCTURESANDTHEIRRESIDUALSTRENGTH结构破坏和剩余强度 Deformedshapeofstiffenedplate加筋板变形 EffectsofmultipleimpactsandTrippingofstiffener a P 0 631MPa b P 1 656MPa c P 2 070MPa 49 COMPARISONOFCLASSIFICATIONSOCIETIESRULES规范比较 ShipType OILTANKERwithD W 39 000TonLBP 172 mBreadth mld 31 40mDraft Scantling mld 10 95mBlockCoefficient 0 785DesignSpeed 14 5knot油船底部砰击压力下板厚沿船长分布要求 四个规范 50 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 Requiredthicknessofthebottomplatebythebottomslammingpressure 50 ShipType OILTANKERwithD W 39 000TonLBP 172 mBreadth mld 31 40mDraft Scantling mld 10 95mBlockCoefficient 0 785DesignSpeed 14 5knot油船艏外飘砰击压力下板厚沿高度分布要求 四个规范 51 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 Requiredthicknessofsideshellplatebybowflareslammingpressure 51 52 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 H TankHeight 15 1mLc Longitudinaldistanceofthetank 17 40mbc Transversedistanceofthetank 24 94mh FillingHeight 10 57m 0 7H Calculatedpoint 10 57m 0 7H 油船晃荡砰击压力下的板厚比较 横舱壁 纵舱壁 Requiredplatethicknessbysloshingpressure mm 52 53 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 Requiredthicknessofthedeckplatebygreenwaterloads上浪砰击下的甲板厚度要求 53 ImpulsivepressureloadsgeneralEventhoughsignificantprogresshasbeenmadeoverthelastdecade theproperdeterminationofrelativeimpactgeometry relativevelocityandamountofentrappedairstillremainsextremelychallenging sincetheoverallsea keepingproblemofshipsailingwitharbitraryforwardspeedinwavesisstillanopenproblem 由于船舶航行条件的复杂性 砰击过程中的相对砰击面 速度 气垫等的确定仍然存在困难LocalslammingNumericalpredictionsofslammingpressuresaccountingforviscousflowseparation entrappedair compressionoffluidsandelasticityofstructuresneedtoenhancetheiraccuracy stabilityandefficiency Morevalidationswithtestsresultsareneededfortheapplicationofthesemethodsindesignpractice 对局部砰击 数值计算方法的精度 稳定性和计算效率需要进一步提高 为提高这些计算方法的实用性 试验验证工作需要加强 54 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 54 GlobalslammingGenerally 3Deffectscanreducethe2Dslammingpressureforcesignificantly Fully3Dslammingpredictionmethodsarenotreadyforuse Correctionfactorson2Destimatesmaybeappliedtoyieldreasonablevaluesfordesign Thecontributionfromvibratoryresponsemaydoublethefatiguedamageinducedbywave frequencyloads Thedampingmayplayanimportantroleinnumericalanalysisandmeasurements Therefore itisimportanttocontrolthedampinginmodelteststocorrespondtothatforrealships 对总体砰击 计入三维效应可明显降低二维砰击载荷 但三维计算方法还不成熟 二维方法加三维修正可以得到更合理的设计值高频振动响应引起的疲劳损伤可与波频载荷相当 其中阻尼的作用很大 因此在模型试验中考虑阻尼与实船的相似性很重要 55 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 RECOMMENDATIONSFORSTRUCTURALDESIGNGUIDANCE结构设计指导性意见V 7 55 SloshingTheFroudescalinglaw whichisusuallyappliedforsmallscalemodeltests yieldsconservativevaluesformaximumpressure However thetimeisalsodifferentlyscaledbyvariousscalinglaws Therefore theeffectofscalingthepressuretimehistoriesmayonlybeassessedbyanalyzingthedynamicresponseofthecontainmentsystem Inspiteoftheeffortstoproperlysolvethesloshingimpactissues manykindofuncertaintiesstillpersist ThefullscalemonitoringoftherealLNGshipsundernormaloperationwouldcertainlybeveryhelpfulbutitseemstobeverydifficulttoperform 对于晃荡 按Froude相似率进行模型试验将使最大压力幅值偏大 LNG船的实船试验十分重要但也十分困难 56 IMPULSIVEPRESSURELOADINGANDRESPONSEASSESSMENT V 7 56 GreenwaterForwatershippingproblems abenchmarkingsystemwouldbeappreciabletocomparebothaccuracyand