同濟(jì)大學(xué)結(jié)構(gòu)動(dòng)力學(xué)簡答題

1、Whatarethestep-by-stepmethodsforcalculatingstructuraldynamicresponse?(有哪些方法)AInterpolationofexcitationmethodACentraldifferencemethodANewmarksmethodAWilson-methodAStatespacemethodDegreeoffreedom:Thenumberofindependentdisplacementrequiredtodefinethedisplacedpositionsofallthemassesrelativetotheirorigin

2、alpositionsiscalledthenumberdegreesoffreedom(DOFs)(chopra)Thenumberofdisplacementquantitiesthatmustbeconsideredtorepresenttheeffectsofallsignificantinertiaforceiscalledthenumberoffreedomsofasystem.RoyR.CraigEffectofdampinginvibration:NaturalfrequencyofdampedsystemNaturalPeriodofdampedsystemExistence

3、ofdampingwillreducethenaturalfrequencyFornormalstructureThedisplacementamplitudedecaysexponentiallywithtimeTheeffectofdampingisontherateatwhichfreevibrationdecaysModeShape:itassociateswithfrequency.And,itisdeformedmodeofobjectatthatfrequency.Example:resonanceoccurredwhen,itmakesthemaximumdeformation

4、,differentshape(deformation),differentfrequency.ModeshapeistheproportionalrelationshipamongthedisplacementofDOFs.AModeshapeismostlikelytooccurintheformofthedeformation,andthefirstmodeistheeasiestone.Therefore,shapefunctionsareselectedascloseaspossibletothemodeshapetosimplifytheanalysis.Namesofmethod

5、sfordeterminingthefirstseveralvibrationsmodesofaMDOFsystem?ASuperpositionmethodARayleigh-RitzmethodAReyleighmethodAMatrixiterationmethodAJacobiiterationmethodASubspaceiterationmethodStodolaiterationmethodForSDOFsystemunderharmonicloading,whenthefrequencyration一isverysmalltheamplitudefactoriscloseto1

6、,whenbecomesverylargebecomesverysmall,explainwhy?Displacementresponseamplificationfactor2二J03S76S4321D2二J03S76S4321D憫4ooe/VI,Rd1單自由度系統(tǒng)承受諧波荷載，當(dāng)頻率比很小時(shí)，振幅放大系數(shù)接近于1，當(dāng)頻率比很大時(shí)，振幅放大系數(shù)較小。請簡要解釋原因。Thesingle-degree-of-freedomsystembearsharmonicload.Whenthefrequencyratioissmall,theamplitudeamplificationcoefficien

7、tiscloseto1.Whenthefrequencyratioislarge,theamplitudeamplificationcoefficientissmall.Pleasebrieflyexplainwhy.“具有粘滯阻尼的系統(tǒng)，理論上其自由振動(dòng)永遠(yuǎn)不會(huì)停止”，這種說法是否正確？為什么？Isittruethatasystemwithviscousdamping,intheory,willneverceasetovibratefreely?Why?什么情況下多自由度體系的動(dòng)力反應(yīng)不能采用疊加法計(jì)算，需要采用逐步法計(jì)算？Underwhatcircumstancescanthedynami

8、cresponseofamulti-degree-of-freedomsystemnotbecalculatedbythesuperpositionmethod,butbythestepwisemethod.請舉出土木工程領(lǐng)域避免和利用結(jié)構(gòu)振動(dòng)的各兩個(gè)例子。Pleasegivetwoexamplesofavoidingandutilizingstructuralvibrationinthefieldofcivilengineering.CivilEngineeringVibrationmonitoringincivilengineeringisatopicthatcoversawiderang

9、eofapplications,includingallthepossiblevibrationsourcesthatcanaffectastructureoraconstructionsite.Itspurposeisdouble:fromonesideitisimportanttoassurethatvibrationsdonotaffectstructuresorpeopleandontheothersideitisimportanttoobtaininformationonthestructuredynamicsandonthephenomenaanalyzed.Thetypicali

10、nstrumentationrequiredisusuallytemporaryandincompliancewithregionalornationalstandarddirectives.THEMAINAPPLICATIONSINTHISFIELDARE:CONSTRUCTIONSITESThestructuresinproximityofaconstructionsiteneedatemporaryinstrumentationdedicatedtothevibrationmonitoringinordertoevaluatethestructuraldamageandthehumanc

11、omfort(onlyincaseofbuildings).Automaticalertsmustbeimmediatelysentincaseofhighvibration,exceedingthresholdlevels.Specificsitealarmsareusefultoforceareductionoftheworkintensity.RAILWAYMONITORINGTherailwaymonitoringsurveyistypicallya24hoursvibrationmeasurementwiththreemono-axialvelocitysensorsatadistanceofabout10metersbetweentwoconsecutivesensors,wherethemaximumvelocitiesarecollectedandanalyzed.Therelevantfrequencycontentisusuallyintherangeof15Hzto80Hz.復(fù)雜結(jié)構(gòu)(超過十