6 - Active Control of Vibration in Structures书

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1、6ActiveControlofVibrationinStructures6.1IntroductionInthischapterwereviewanumberofdifferentapproachestotheactivecontrolofmechanicalvibrationinstructures.TheseapproachesaredistinguishedfromthosediscussedinChapters3and4inthatthestructureisnowassumedtobegovernedbyapartialdi

2、fferentialequationratherthananordinarydifferentialequation.Inotherwords,thestructureisassumedtobedistributedratherthanhaving'lumped'springs,massesanddampers.Thereareanumberofwaysofdescribingthemotionofsuchastructure,eachofwhichisconsistentwiththegoverningpartialdifferent

3、ialequation.Onewayofexpressingthevelocitydistributionoveranentirestructure,forexample,isintermsofthesumofthecontributionsfromanumberofstructuralmodes.Anotherapproachistodescribethemotionintermsoftheamplitudesofanumberofdifferenttypesofmechanicalwavesinthestructure.Bothof

4、theserepresentationsandtheirrelationtoeachotherwerediscussedinChapter2.Themost'efficient'description,whichrequiresthefewestparameterstodescribethemotionofthestructure,willdependverymuchonthegeometryofthestructure,itsboundaryconditionsandthefrequencyofexcitation.Thesetwod

5、escriptionsofthemotionofadistributedstructureleadtotworatherdifferentapproachestoactivecontrol.Thefirstconcentratesoncontrollingthemodesofastructure.Byactivelyreducingtheamplitudesofthesestructuralmodesthespace-averagemeansquarevelocityoverthewholestructureisreduced,andt

6、hecontrolcanbesaidtobe'global'.Itshouldbeemphasisedthatreducingthetotalvibrationalenergyofadistributedstructuralsystem,forexample,doesnotguaranteethatthesoundradiatedbythestructurewillbecorrespondinglyreduced(duetothenatureofthestructure-acousticcoupling).Theactivereduct

7、ionofsoundradiationfromastructurewillbediscussedinmoredetailinChapters8and9,andfornowwerestrictourselvestoconsideringonlythereductionofvibrationperse.Thisisstillanimportantareaofpracticalapplication,however;forexampleinordertoimprovethepositioningorpointingaccuracyofanan

8、tennaorrobotarm,ortoreducefatigueinhighly-stressedstructures.Whereasthecontrolofstructuralmodestendstoi