!!!！！Nontarget Image-Based Technique for Small Cable

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1、NontargetImage-BasedTechniqueforSmallCableVibrationMeasurement12Y.F.JiandC.C.ChangAbstract:Inthispaper,aproof-of-conceptimage-basedtechniqueisproposedformeasuringsmallcablevibration.Thetechniqueanalyzesanimagesequenceofavibratingcablesegmentcapturedbyacamera.Anopticalßowmethodisusedtocalculate

2、variationofopticalintensityofanarbitraryselectedregionofinterest
ROIonthecableimagesequence.TheobtainedopticalßowvectorprovidesthedirectionofvibrationfortheROIonthecablesegment,whichthencanbeusedtoestimatedisplacementoftheROIontheimageplane.Furthermore,actualdisplacementoftheROIcanbeextracted

3、whensomeconditionsaremet.TheproposedtechniqueisvalidatedbothinthelaboratoryusingarigidpipeandintheÞeldonasmallpedestrianbridgecable.Resultsshowthatthetechniqueisabletomeasurethepipemotionandthecablevibrationaccurately.Theproposedtechniquerequiresonlyonecommercialcamera,andnopriorcameracalibrat

4、ionisneeded.Inaddition,theuseofanopticalßowmethodeliminatestheneedtoattachanytargettothecableandmakesthetechniqueveryeasytoimplement.Despitetheseadvantages,thetechniquestillneedsfurtherdevelopmentbeforeitcanbeappliedtolong-spanbridgecables.DOI:10.1061/
ASCE1084-0702
200813:1
34CEDatabasesub

5、jectheadings:Vibration;Displacement;Measurement;Bridges,cable-stayed.Introductionexistintherecords
Hudson1979.ThelaserDopplervibrometerhasalsobeenusedforcablevibrationmeasurement
Cunhaetal.Cablesareavitalload-carryingcomponentofcable-stayed2001.Thisdeviceisnoncontactandcanprovideaccuratedis-

6、bridgesandneedtobemonitoredandassessedperiodicallytoplacementmeasurementatmultiplelocationswithinitsapplicableensurethesafetyofthebridges.Bridgecablescomewithlowdistance.Whencableforceistheobjectofmeasurement,there-ßexuralrigidity,lowweight,andarelativelysmallcrosssection,centlydevelopedelectr

7、omagnetic
EMsensorsprovideamoreandhencearepronetowind,rain,andtrafÞc-inducedvibration.directandaccurateapproach
Wang2005.ThesensorsneedtobeAccelerometershavecommonlybeenusedtomeasurecablevi-placedaroundtheanchoragelocation,andtheircal