Underwater Acoustics Research Group CAV Workshop 3 May 2010 POC: Chris Barber Applied Research Laboratory Penn State University PO Box 30 State College, PA 16804-0030 (814) 865-3837 [email protected]
Underwater Acoustics Research Group
CAV Workshop3 May 2010
POC:Chris BarberApplied Research LaboratoryPenn State UniversityPO Box 30State College, PA 16804-0030(814) [email protected]
Underwater Acoustics at Penn State
• Ocean Acoustics– Propagation– Acoustical Oceanography– Marine Bioacoustics– Underwater Noise Sources
• Transducers and Instrumentation– Piezoelectric Transducers– Vector (Intensity) Sensors– Sonar Arrays
• Signal Processing– Sonar signal processing– Beamforming and array processing– Noise source localization
ARL Acoustics Division
• Division in the Research and Academic Programs Office– 16 Staff Members– 18 Students (was 20 – 2 PhDs graduated this fall)
• Majority of staff:– Teach at both undergraduate and graduate level in various
departments of PSU– Advise/guide graduate students– Conduct research as PI’s for sponsor direct funded programs
• Major Sponsor: ONR
• Inter-laboratory and Inter-university collaboration
• Outside collaboration
ARL Acoustics Division
International Collaboration
• Australia – Visiting Scientist – AUV G&C Studies
• Canada – Visiting Scientists – Geophysical Inversion– LF Seafloor Backscatter
• Germany – Visiting Scientist – Signal Processing
• Denmark – Visiting Scientist – Harbor Defense Studies
• NURC – Exchange Scientists – Shallow Water Propagation– AUV Studies– At-sea Experiments – Seafloor Scattering
• Korea – At-sea Experiments – Shallow Water Propagation
• France – Naval Academy Grads – Seafloor Studies
Broadband Seafloor Clutter Initiative 500 m
note 5m rise of bathymetry on NE trending track
Regular spikes on temp data are artifacts from modem
AUV altitude
CWH
CTD data from AUV indicates warmer, fresher water venting from NE flank of MV (fault).
PI: Charles W. HollandSea trials with NATO Undersea Research Centre, Defence Research & Development Canada, Naval Research Lab
Harbor Defense
PI: Kyle M. Becker
Sponsor: Office of Naval Research
Students:1 Ph.D. (Graduated)1 MS (Aug 2010)
Collaboration: NUWC/Newport
ARL/UTBAE SystemsPSU Mech Engr Dept
Assessment (Measurements)
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J-15-3 40-600 Hz 175 dBHLF-1D 196 dB @ 260 Hz(~190 dB @ 100 Hz)
Transverse Acoustic Variability Experiment (TAVEX)
Experiment location is within the Northern East China Sea
Towed CTD area is approximately 33X10km
300 and 500Hz acoustic sources and 96 hydrophone HLA (NRL)
300kHz ADCP southwest of tow area (KORDI)
IEODO station (KORDI) 11
PI: David L. Bradley
Sponsor: Office of Naval Research
Students: USNA Trident Scholar (MS)Acoustics Graduate Student (MS)
Collaboration: Republic of Korea, Naval Research Laboratory, Applied Physics Laboratory / University of Washington
Susan ParksPresidential Early Career Award for Scientists and Engineers (PECASE) recipient – 13 January 2010
16 / 20
Range (m) Range (m)
Leve
l (dB
) –5
dB In
crem
ents
Leve
l (dB
) –5
dB In
crem
ents
Low Frequency (32Hz)
Mid-Frequencies (6300 Hz)
Estimation of Ship Radiated Noise in the Near Field
• Problem: Simple source models coupled with simplified propagation assumptions inadequate to capture sound field variability for real sources in shallow water
PI: Chris Barber
Sponsor: Office of Naval Research
Students: Engineering Honors Undergradute
Collaboration: Naval Research Laboratory Naval Surface Warfare CenterALION
Background –Radiated Noise Characterization
• Propagation models treat a ship as a spatially-compact simple harmonic source
λ >> a ka << 1
• Far field acoustic pressure assumed to have range varying component given by
• Leads to familiar expression for spherically spreading sound pressure level (SPL)
• For source with directivity
kcω
=
( ) 0 jkrjk cSp r er
ωρ −=
( ) ( ) ( )2
2
( )10log 20logsref
p rSPL r L rp r
⎛ ⎞⎜ ⎟= = −⎜ ⎟⎝ ⎠
( ) ( ) ( ), , ,j t j tp r e p r H eω ωθ φ θ φ=
Near-Field Radiated Noise
• Far-field approximation– source-to-receiver distance much greater than the spatial extent of
the source, r >>a– Receiver distance large in terms of wavelength, r >> λ
• Near-field scenario– Simple source model breaks
down as source-receiver separation is reduced
– Ship appears as distributedsource to close receivers
– Ranges small in terms of wavelength
– Environment typically cannot be ignored
Typical Acoustic Environment and Source-Receiver Geometry
Far Field Radiated Noiseby Numerical Methods
• Approaches to obtain estimates of radiation from realistic hull structures have been presented in the literature, including – Recent developments in efficient finite element methods– High frequency SEA methods– Superposition / SVD computational approach (Koopmann)
• Limitations – limited low frequency regime over which computation is practical– application limited to global hull modes of radiation– Fully detailed computational model of a realistic ship structure remains
impractical– Simplified models do not capture structural details critical to near-
field radiation
Far Field Radiated Noise Estimates by Transfer Function
• From Helmhotz integral theorem
• In matrix form assuming forcing function F
– Theoretically possible to compute transfer function given sufficient number of velocity points (sensor density)
– In practice, transfer function estimated by spatial averaging of available sensor data
• Far field radiated noise estimated from
( ) 0i s nS
Gp p j u G dSn
ωρ∂⎛ ⎞= − −⎜ ⎟∂⎝ ⎠∫r
[ ]{ } [ ][ ] 1{ } { }far np u F−= Φ = Φ Ψ
( )( )( )
2
2
,10 log
ii
P fTF
A fθ
θ=
∑
( ) ( ) ( )SPL f A f TF fθ θ= +
Sound Field Variability - Source
Near Field
– multi-source interference– multi-modal interference– directivity
Far Field– Simple source representation
(monopole x directivity)
• Source Characteristics– Spatial distribution of localized
(simple) sources
– Source directivity
– Radiation from complex (non-simple) distributed sources
• Sound Field Characterization
Near-Field Primitive Model Inverse Source Computation (U)
Near Field Estimate from Near field Measurements
Radiated Noise Estimation from NAH Measurements
• Measure pressure over a nearby conformal surface to recover normal velocity of the source surface– NRL Approach (Valdivia and Williams)
• Measure pressure on conformal surface, solve for density function on source surface
• Apply Euler’s equation to recover velocity on source surface• Numerical computation implemented via Indirect Boundary Element
Method (IBEM) or Equivalent Source Method (ESM) approximation
• Given knowledge of normal velocity of the source surface and source density function, compute received acoustic field due to ship radiation at tactically significant ranges – Apply inverse of computational algorithms used to recover normal
velocity
Radiated Noise Estimation from NAH Measurements - Analysis
• Source and path analysis for machinery sources based on NAH and interior hull vibration data– Local (plate theory) radiation– Excitation of global hull modes
• Contribution of local radiation vs global hull modes to received acoustic field for machinery sources– Use of hull-mounted sensors to identify global hull mode radiation
in-situ– Transfer function uncertainty
• Limits of simple-source (monopole x directivity factor) assumption– Agreement with near-field direct measurements– Convergence to measured far-field measurements