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)制定的STCW78/95公约的实施,全方位地影响了航海教育和船员培训,对船员培训的质量提出了更高的要求.为了履行STCW78/95公约,符合ISM规则的要求,提高我国船员的GMDSS专业知识水平和实际操作技能,有效地实施国际海上搜救公约(SAR),确保海上人命的安全,我国积极开展了GMDSS专业培训工作,并取得了一定的成效.但是自GMDSS在海上实施以来,误报警事件屡见不鲜.究其原因,除了现有GMDSS设备本身的缺陷外,还与高级船员对其设备不甚了解和缺乏严格的训练有关.为了保证GMDSS的有效实施,充分发挥其作用,必须加强对高级船员的GMDSS专业培训,切实提高培训质量.