Acoustic intensity properties in an ocean waveguide
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Acoustic intensity properties in an ocean waveguide Measurement and simulation of waveguide intensity structures David Dall’Osto and Peter H. Dahl Applied Physics Laboratory University of Washington Pacific Rim Underwater Acoustics Conference 2011 5-7 October 2011 Jeju Island, Korea
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Acoustic intensity properties in an ocean waveguide Measurement and simulation of waveguide intensity structures David Dall ’ Osto and Peter H. Dahl Applied Physics Laboratory University of Washington. Pacific Rim Underwater Acoustics Conference 2011 5-7 October 2011 Jeju Island, Korea. - PowerPoint PPT Presentation
Transcript of Acoustic intensity properties in an ocean waveguide
Acoustic intensity properties in an ocean waveguide
Measurement and simulation of waveguide intensity structures
David Dall’Osto and Peter H. Dahl
Applied Physics LaboratoryUniversity of Washington
Pacific Rim Underwater Acoustics Conference 20115-7 October 2011Jeju Island, Korea
TAVEX Experiment
ρb = 1650 kg/m3 cb = 1600 m/s
Weight (1 ton)
Bulb sourceDepth: ~35 m
Range : 190 ~ 920 m
Weight
Acoustic release
Battery & Data Acquisition frames
16 channelsseperation : 3mfs : 20.47 kHz
R/V Sunjin NRL VLA
12 bulb implosions (~40 m depth) measured on a VLA
A1 pressure signal (190 m)
Acoustic Intensity
pt
v
0(conservation of momentum)
221 pp
p
dtd
ppv
t
x
0
12
0
1
)}(Re{)}(Re{)( tvtptS
MM
MM
tvitvtv
tpitptp
)(ˆ)()(
)(ˆ)()(
)()()(
2
)()()(
*
tQitItI
tvtptI
c
c
Hilbert Transform measured signal 90° out of phase
c
tptptI p
0
* )()()(
Finite Difference Approximation
pressure at midpoint
complex signal from real signal
particle velocity along array
Scalar Intensity
Instantaneous Intensity
Complex Intensity
Active Intensity Envelope
)(Re)( tItI c
)(Im)( tItQ c
Reactive Intensity Envelope
Requires collocated measurement of both pressure and particle velocity
Complex Intensity: 190 m
27.5 m
)()()( tQitItIc
2
)()(Re)(
* tvtptI
2
)()(Im)(
* tvtptQ
Active Intensity Envelope Reactive Intensity Envelope
27.5 m
DA
TA
SIM
ULA
TIO
N
Intensity structures: frequency domainB = 300 Hz fc = 210 Hz
)(
)(*
tI
tII
p
zz
)(
)(*
tI
tQQ
p
zz
1* I
1* Q
1* I
1* Q
• Crests (pressure/intensity maxima)
• Dislocations (pressure/intensity nulls)
Normalized Quantity: pressure-intensity index
crestnull
scalar intensity: f = 210 Hz (pekeris)
*zI
Frequency/Range StructureDATA (190 m) PE SIMULATION
dr
dr
waveguide invariant
1~
*zQ
Waveguide invariant observed in broadband measurements*zQ
*zI
Broadband every 50 m
NB 210 Hz
PE
si
mul
atio
nD
AT
A
*zQExperimental Visualization
Summary
• Complex Vertical Intensity:– Active: direction of energy propagation– Reactive: energy focusing/interference
• Intensity structures: pressure-intensity index– crests: |pI|<1 and |pQ|<1– nulls/dislocations: |pI|>1 and |pQ|>1
• The waveguide invariant:– map frequency to range– contours depict the modal structure of waveguide
