简介:Acomplianttowerismodeledasapartiallydry,partiallytapered,dampedTimoshenkobeamwiththesuperstructuremodeledasaneccentrictipmass,andanon-classicaldampedboundaryatthebase.Thefoundationismodeledasacombinationofalinearspringandatorsionalspring,alongwithparallellinearandtorsionaldampers(Kelvin-Voigtmodel).Thesuperstructureaddstothekineticenergyofthesystemwithoutaffectingthepotentialenergy,therebyreducingthenaturalfrequencies.Theweightofthesuperstructureactsasanaxialcompressiveloadonthebeam,reducingitsnaturalfrequenciesfurther.Theemptyspacefactorduetothetruss-typestructureofthetowerisincluded.Theeffectofsheardeformationandrotaryinertiaareincludedinthevibrationanalysis;withthenon-uniformbeammode-shapesbeingaweightedsumoftheuniformbeammode-shapessatisfyingtheendcondition.TheweightsareevaluatedbytheRayleigh-Ritz(RR)method,andverifiedusingfiniteelementmethod(FEM).Theweightofthesuperstructureactsasanaxialcompressiveloadonthebeam.Kelvin-Voigtmodelofstructuraldampingisincluded.Apartofthestructurebeingunderwater,thevirtualaddedinertiaisincludedtocalculatethewetnaturalfrequencies.Aparametricstudyisdoneforvariousmagnitudesoftipmassandvariouslevelsofsubmergence.ThecomputationalefficiencyandaccuracyoftheRayleigh-Ritzmethod,ascomparedtotheFEA,hasbeendemonstrated.Theadvantageofusingclosed-formtrialfunctionsisclearlyseenintheefficacyofcalculatingthevariousenergycomponentsintheRRmethod.
简介:国际海事组织(IMO)启动了GMDSS现代化的相关工作。2012年,COMSAR第16次会议确定了GMDSS复审和现代化的任务范围,同年海上安全委员会(MSC)第90次会议正式批准并启动了“GMDSS复审与现代化”项目,项目包括高级复审、详细复审和现代化计划三部分内容;2013年,COMSAR第17次会议开始起草GMDSS高级复审结果的初步草案,在同年召开的IMO/ITU联合专家组第9次会议上,该草案正式形成:2014年,航行、通信和搜救分委会(NCSR)第1次会议审议通过了高级复审结果草案,并讨论通过了详细复审大纲;2016年,NCSR第3次会议审议通过了详细复审结果草案,并针对GMDSS现代化计划草案提出意见。2017年,NCSR第4次会议审议通过了GMDSS现代化计划草案,并计划将草案提交至MSC第98会议核准通过。