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1、翻译：英文原文DefinitionsandTerminologyofVibrationvibrationAllmatter-solid,liquidandgaseous-iscapableofvibration,e.g.vibrationofgasesoccursintailductsofjetenginescausingtroublesomenoiseandsometimesfatiguecracksinthemetal.Vibrationinliquidsisalmostalwayslongitudinalandcancausela
2、rgeforcesbecauseofthelowcompressibilityofliquids,e.g.popesconveyingwatercanbesubjectedtohighinertiaforces(or“waterhammer”)whenavalveortapissuddenlyclosed.Excitationforcescaused,saybychangesinflowoffluidsorout-of-balancerotatingorreciprocatingparts,canoftenbereducedbyatte
3、ntiontodesignandmanufacturingdetails.Atypicalmachinehasmanymovingparts,eachofwhichisapotentialsourceofvibrationorshock-excitation.Designersfacetheproblemofcompromisingbetweenanacceptableamountofvibrationandnoise,andcostsinvolvedinreducingexcitation.Themechanicalvibration
4、sdealtwithareeitherexcitedbysteadyharmonicforces(i.e.obeyingsineandcosinelawsincasesofforcedvibrations)or,afteraninitialdisturbance,bynoexternalforceapartfromgravitationalforcecalledweight(i.e.incasesofnaturalorfreevibrations).Harmonicvibrationsaresaidtobe“simple”ifthere
5、isonlyonefrequencyasrepresenteddiagrammaticallybyasineorcosinewaveofdisplacementagainsttime.Vibrationofabodyormaterialisperiodicchangeinpositionordisplacementfromastaticequilibriumposition.Associatedwithvibrationaretheinterrelatedphysicalquantitiesofacceleration,velocity
6、anddisplacement-e.g.anunbalancedforcecausesacceleration(a=F/m)inasystemwhich,byresisting,inducesvibrationasaresponse.Weshallseethatvibratoryoroscillatorymotionmaybeclassifiedbroadlyas(a)transient;(b)continuingorsteady-state;and(c)random.TransientVibrationsdieawayandareus
7、uallyassociatedwithirregulardisturbances,e.g.shockorimpactforces,rollingloadsoverbridges,carsdrivenoverpotholes-i.e.forceswhichdonotrepeatatregularintervals.Althoughtransientsaretemporarycomponentsofvibrationalmotion,theycancauselargeamplitudesinitiallyandconsequenthighs
8、tressbut,inmanycases,theyareofshortdurationandcanbeignoredleavingonlysteady-statevibrationstobeconsider
