processing oscillatory data with the pdv (u)
TRANSCRIPT
Processing Oscillatory Data with the PDV (U)
Ted Strand, Randy Bonner,Daron Hester, Jerome Solberg,
Dan White, Tony Whitworth
Lawrence Livermore National Laboratory
This work was performed under the auspices of the U.S. Department of Energy by the University ofCalifornia, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
2nd Annual PDV WorkshopAugust 16-17, 2007
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We recently fielded the PDV on a series ofpulsed power tests
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current
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currentLarge magnetic pressure
tends to collapse inner tube
The test fixture provides validation datafor new ALE3D codes
We had 4 probes mounted at the mid-planeat 90 degree angles
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This portable rack holds a 4-channelPhotonic Doppler Velocimeter System
2 W CW laser
Customfiber/detector
chassisFast
DigitizingScope
Shock-mountedcarrying casewith wheels
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We were told to expect low velocities(less than 100 m/s)
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PDVDetectorChassis
Digitizer
Laser
ScreenRoom
Hi-Bay
Trigger
TimingFid
1
2 3
4
Note: the probe numbering schemeis as seen from the high-current cables.
40 µs/div100 ps/pt100 mV/div
The beat amplitude goes to zero at zero velocitywhen the moving surface changes direction
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-0.2
-0.1
0.0
0.1
0.2
Beat
Am
plit
ude (
volt
s)
100usec806040200
Time (µs)
The spectrogram looks empty becausethe velocities are so low
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3000
2000
1000
0
0 100 200 300 µs
m/sProcessed with 1.64 µs FT windows
Expand the image near f = 0
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3000
2000
1000
0
0 100 200 300 µs
m/sProcessed with 1.64 µs FT windows
The spectrogram shows the oscillatory behavior
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8
6
4
2
0
0 50 100 150 200 (µs)
Velo
city
(m/s
)
Analyzing this is very cumbersome
radiallyinward
radiallyoutward
etc….
This laser has a sideband at 1.5 GHzExpand the image around the sideband
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3000
2000
1000
0
0 100 200 300 µs
m/sProcessed with 1.64 µs FT windows
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1165 m/s
We see the sum and difference velocitieson either side of the 1.5 GHz sideband
Use the analysis code to extractthe desired velocities
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Use the analysis code to extractthe desired velocities
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Extract the velocity time historyfrom the spectrogram
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1175
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Appare
nt
Velo
cit
y (
m/s)
160140120100806040200
Time (µs)
Sideband velocity= 1164.62 m/s
Subtract the sideband velocity and integrateto obtain displacement vs time
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-5
0
5
10
Velo
cit
y (
m/s)
160140120100806040200
Digitizer Time (µs)
-150
-100
-50
0
50
100
Dis
pla
cem
ent
(µm
)
160140120100806040200
Time (µs)
This analysis is much easierthan working with
the baseband solution
Velocity vs Time
Displacement vs Time
integrate
Conclusions
We used the PDV to obtain data from oscillatory motions
Analyzing the baseband velocity is cumbersome
Fortunately, our laser has a 1.5 GHz sideband
Analyzing the data around the sideband is much easier
Moral: a sideband in your laser is not always bad, but we will sendthe laser to the shop after this series of experiments is over
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