Exploration of turbulence by nonlinear acoustic scattering. James E. Parker, III and Murray S. Korman (Department of Physics,. U.S. Naval Academy, Annapolis, ...
interestbe small. Frequencydomain techniqueshave also been developedto performwave vectorfilteringin both dispersiveand nondispersivemedia. Thesetechniquescannotbe usedin real time becauseof the signalprocessingrequirements.In this work, a new time domain techniqueis presentedthat utilizestwo sensorlocationsin conjunctionwith a digital filter, for eachwave type, to providea real time estimateof the complexamplitudeof eachof the travelingwave componentsfor both dispersiveand nondispersive media. The techniqueestimatesthe wave componentsover a band-limitedspectrawhoselimits are dictatedby the spacingbetweenthe sensors(up to a spacingof half a wavelength).A simulationis usedto determinethe performanceof the new techniquein both dispersiveand nondispersive mediaover a rangeof frequencies.
11:45
4EAI3. Application of a new signal processing technique in a multibeam sounder. Bishwajit Chakraborty and Y. Satayanarayana Raju (Natl. Inst. of Oceanogr.,Dona Paula, Goa 403004, India)
WEDNESDAY
MORNING,
13 MAY 1992 WEST END, GRAND
The currentlyusedbeamformingmethodfor multibeamsounding applicationis a delay-summethod, which is also known as a Fourier spectralestimationmethod applicableto directionalestimation.But
array size is one major difficultythat existswith this technique.A solutionto sucha problemis the applicationof a "high-resolution technique" for the beamformingmethod.In this paperbeamformingtechniqueslike the maximumlikelihoodmethod (MLM) and the maximum
entrophymethod(MEM) arepresented for multibeamsounding application. The size of the array is chosento be one-fourth and one-half of
the conventionalarray at an input signal-to-noiseratio of 0 or 10 dB. Both high-resolution techniquesare foundto be suitablefor multibeam soundinguseat a 10-dBsignal-to-noise ratio (input), evenfor a small array size of 16 elements.But relatively wide beamwidthsfor the 45ø direction,whenthe input signal-to-noise ratio is 0 dB, doesnot support its utility for both techniques.The lowestvalue of the standarddeviation angularerror for MEM showsits preferenceover the MLM technique.
BALLROOM
CONCOURSE,
9:00 TO 11:30 A.M.
Session 4ED
Education in Acoustics:UndergraduateProjects in Acoustics(Poster Session) Anthony A. Atchley, Chair Departmentof Physics,CodePH/Ay, Naval Postgraduate School,Monterey,California93943
ContributedPapers All posterswill be on displayand all authorswill be at their postersfrom 9:00 to 11:30a.m.
4EDI. Acoustic related senior projects in Electrical Engineering at Utah State University. Paul A. Wheeler (Dept. of Elec. Eng., UMC-4120, Utah State Univ., Logan, UT 84322)
With the increasein acousticresearchin the ElectricalEngineering Department at Utah State University comesan increasein the number
of acousticrelatedseniorprojects.This posterpresentation will display severalof the seniorprojectsperformed.Theseincludesuchprojectsas: (1) soundsystemdesignsoftwarefor matchingsoundsystemequipment to differentperformanceenvironments;(2) analogaudio synthesizer designs;(3) designof active crossovernetworks;and (4) audio amplifier/equalizerdesigns.Includingacoustic-related seniorprojectsin the electricalengineering curriculumallowsstudentsto applythe theory learned in classesto real-world experiences.It increasesa student's interestin the fieldof acoustics and preparesnewengineers for employment in the audio industry.
4ED2. Experimental investigation on the amplification of hydrodynamic noise generation by the insertion of bubbles in a turbulentflow. CharleneE. HughesandMurray S. Korman (Dept. of Phys., U.S. Naval Academy,Annapolis,MD 21402) An apparatusis constructedto producea turbulent shearflow that is generatedby a submergedcircularjet. The jet is arrangedto flow in
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J. Acoust.Soc. Am., Vol. 91, No. 4, Pt. 2, April 1992
an upright position.Comparisonsare made of the near-fieldhydrodynamicflow noise,whenthejet flowbecomes a composition of two-phase flow that consists of air bubbles in water. The near-field flow noise is
measuredby a hydrophonelocatedat the point, four nozzle diameters from the exit and four nozzle diametersperpendicularto the jet axis. Preliminaryresultsindicatethat the acousticspectraare greatlyamplified in the case where the bubbles are introduced into the flow. Mea-
surementsof the acousticintensityare made as a functionof void fraction B (the ratio of air volumeto total volume) in an effortto verify the theoreticalamplificationpredictionsmade by Crighton and FfowcsWilliams [J. Fluid Mech. 36, 585-603 (1969)] and more recently by Prosperetti[J. Acoust.Soc.Am. 84, 1042-1054 ( 1988)]. Testsare performed in the U.S. Naval Academy HydrodynamicsTow Tank. [This research is a continuation
of the work on ocean noise mechanisms that
is supportedby the National Center for PhysicalAcousticsand the ONR.] 4ED3. Exploration of turbulence by nonlinear acoustic scattering.
JamesE. Parker, III and Murray S. Korman (Departmentof Physics, U.S. Naval Academy,Annapolis,MD 21402) A systemhas been developedto explorethe nuancesof nonlinear scatteringin the presenceof turbulence.The computer-controlled scattering apparatusmakes translational and rotational "crossedbeam"
123rd Meeting:AcousticalSocietyof America
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