?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=http%3A%2F%2Fd-scholarship-dev.library.pitt.edu%2F20111%2F&rft.title=Nondestructive+Evaluation%2FStructural+Health+Monitoring+of+Immersed+Plates+by+Means+of+Guided+Ultrasonic+Waves&rft.creator=Pistone%2C+Elisabetta&rft.description=Studies+conducted+in+the+last+two+decades+have+demonstrated+the+effectiveness+of+guided+ultrasonic+waves+(GUWs)+for+the+nondestructive+evaluation+(NDE)%2C+as+well+as+for+structural+health+monitoring+(SHM)+of+waveguides%2C+such+as+pipes%2C+plates%2C+and+rails.+Owing+to+the+ability+of+travelling+relatively+large+distances+in+dry+structures+with+little+attenuation%2C+GUWs+allows+for+the+inspection+of+long+waveguides%2C+locating+cracks+and+notches+from+few+monitoring+points%2C+while+providing+full+coverage+of+the+cross+section.+Laser+pulses+are+one+of+the+most+effective+methods+to+generate+ultrasonic+bulk+and+guided+waves+in+dry+structures.+In+this+dissertation+we+propose+a+non-contact+NDE+method+based+on+the+generation+of+broadband+ultrasonic+signals+by+means+of+laser+pulses+to+inspect+underwater+structures.+The+waves+are+then+detected+by+means+of+an+array+of+immersion+transducers+and+analyzed+by+means+of+statistical+analysis+to+search+for+damages+on+the+wet+structure+of+interest.+%0D%0AIn+this+study+we+first+investigated+the+effect+of+water%E2%80%99s+depth%2C+temperature%2C+and+pressure%2C+and+the+laser+energy+and+wavelength+on+the+amplitude+of+the+laser-induced+ultrasonic+waves.+The+results+showed+that+the+0.532+%CE%BCm+wavelength+is+the+most+suitable+for+our+applications.+A+good+range+of+nominal+laser+energy+is+comprised+between+160+mJ+and+190+mJ.+Furthermore%2C+the+variations+of+temperature+and+pressure+have+minimal+effects+on+the+ultrasonic+signals.+The+following+phase+showed+the+ability+of+the+technique+to+detect+various+types+of+defects+in+an+immersed+plate%2C+which+we+achieved+by+building+in+house+A+B-scan+system%2C+controlled+by+National+Instrument+PXI+running+under+LabVIEW.+We+designed+two+series+of+tests+in+which+the+number+of+transducers%2C+their+spatial+arrangement%2C+as+well+as+the+types+of+features+extracted+from+the+time%2C+the+frequency+and+time-frequency+domain+varied.+By+developing+two+unsupervised+algorithms+based+on+outlier+analysis%2C+we+revealed+that+the+method+is+capable+of+successfully+detecting+a+crack+and+a+hole-through.+Next%2C+the+variation+of+the+energy+peak+in+the+time-frequency+space+was+shown+to+decrease+with+a+dependence+on+the+plate+thickness.+A+range+of+peak+energy+was+experimentally+tabulated+and+the+experimental+group+velocities+of+the+first+fundamental+symmetric+mode+were+calculated+for+six+plates+of+different+thickness%2C+varying+between+1+mm+and+10+mm.+Finally%2C+the+ability+of+a+focused+transducer+to+interrogate+the+damage+state+of+the+original+aluminum+plate+was+shown.+As+predicted%2C+our+multivariate+algorithm+successfully+detected+all+the+five+defects+devised+on+the+plate.+This+work+concluded+with+a+comparison+between+the+two+methods.+The+results+showed+that+both+the+hybrid+laser-immersion+transducer+technique+and+the+focusing+technique+can+be+successfully+used+for+the+noncontact+monitoring+of+immersed+plates.%0D%0A&rft.date=2014-01-29&rft.type=University+of+Pittsburgh+ETD&rft.type=PeerReviewed&rft.format=application%2Fpdf&rft.language=en&rft.identifier=http%3A%2F%2Fd-scholarship-dev.library.pitt.edu%2F20111%2F1%2FEPistone_Pitt2013.pdf&rft.identifier=++Pistone%2C+Elisabetta++(2014)+Nondestructive+Evaluation%2FStructural+Health+Monitoring+of+Immersed+Plates+by+Means+of+Guided+Ultrasonic+Waves.++Doctoral+Dissertation%2C+University+of+Pittsburgh.++++(Unpublished)++