Coherent Laser Radar vibrometry for modal analysis in earthquake engineering
Vronique JOLIVET, Philippe GUEGUEN,Clotaire MICHEL and Anne-Sophie SCHVEITZER
(presented by Matthieu VALLA)
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
2
Outline
Overview Description of the experiment
Target building Velocimeter measurement Vibrometer measurement
Experimental results Modal analysis using velocimeter measurement Frequency spectra measured by laser vibrometer Cross-validation of the two systems
Conclusion
Perspective
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
3
Spe
ctru
m
Spe
ctru
m
Frequencies, mode shapes and damping ratio under AV could be helpful to:
fix the elastic properties of buildings used for modelling, investigate the experimental dynamic behaviour of the buildings evaluate the modifications of the building response (retrofitting or post-
earthquake integrity)
AV survey: install accelerometers or velocimeters in the target building record ambient vibrations using digital and handheld acquisition system.
Need for a remote sensing system to get the resonance frequency of buildings
to improve safety in post-earthquake assesment To take advantadge from the fast operability (large set of buildings)
Test of Laser vibrometer based on coherent Lidar
Overview
Dunand, 2005, PhD Thesis, UniversityJ. Fourier,
Grenoble
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
4
Outline
Overview Description of the experiment
Target building Velocimeter measurement Vibrometer measurement
Experimental results Modal analysis using velocimeter measurement Frequency spectra measured by laser vibrometer Cross-validation of the two systems
Conclusion
Perspective
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
5
Description of the experiment
Goal: Common measurements of a building modal frequencies with a laser vibrometer and some velocimeters to validate the use of remote sensing Lidar
Target Building: RC shear wall structure in two blocks B1 has 11 storeys B2 has 13 storeys
Frequency range: 0 to 30 Hz
Vibration velocity: >some m/s
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
6
Description of the experiment
AV recording system: CityShark acquisition system with four Lennartz 3D 5s velocimeters One kept as reference on building B1 roof 40 recording points 15 min recording, sampled at 200 Hz
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
7
Lidar measurement:
Description of the experiment
Range: 150 m 2 recording points in B1 and B210s recording
All-fiber 1.5 m architectureCompactEasy to alignReliable components
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
8
Coherent Lidar Vibrometer
Laser: Signal: Keopsys amplifier, Ps=1 W, LO : Koheras, Pol= 500 W
Fiber collimators: f=11mm
V.J
OLI
VE
T S
oute
nanc
e de
ths
e 26
sep
tem
bre
2008
9
Frequency (U.A)
Spe
ctru
m
I htrodyne
0( ) .cos( ( )) .cos(2 . . .sin(2 . . ))het mi t E w t E f t f t = = +
01 . ( ( )) . .co s(2 . . )
2 2inst m mf w t f f f t
t
= = +
Signal Processing: Use of Spectrogram to frequency demodulate the heterodyne current
Coherent laser vibrometer
temps
Frequency
velocityShort term Fourier transform
Vibration velocity along time
t
V
Maximum
Fourier transform
f
PSD
Vibration spectrum
PS
D (d
B)
time (s)
Trade-off sensitivity / frequency range
V.J
OLI
VE
T S
oute
nanc
e de
ths
e 26
sep
tem
bre
2008
10
Outline
Overview Description of the experiment
Target building Velocimeter measurement Vibrometer measurement
Experimental results Modal analysis using velocimeter measurement Frequency spectra measured by laser vibrometer Cross-validation of the two systems
Conclusion
Perspective
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
11
Experimental results
Modal analysis using velocimeter measurement: Use of Frequency Domain Decomposition (FDD) method
Fourier spectra of the cross-correlation matrix Calculation of the eigenvalues of the system Mode shapes and modal frequencies selection
F=1,30 Hz
F=1,46 Hz
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
12 Page 12
Zone 1 Zone 2 Zone 3
One measure spectrum mean of 60 measures
Experimental results: laser vibrometry
Precision improvement by mean of 60 measures
Frquence (Hz)Frquence (Hz)
DS
P (U
.A.)
DS
P (U
.A.)
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
13
Velocimeter on the platform and on the floor (Synchronous measurements)
Experimental results
Frequency spectra measured by laser vibrometer Mean of 60 measures
Lidar on the platform
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
14
Experimental results
Cross-validation of the two systems (synchronous measures) x,y,z velocimeter measurements are projected along the laser line of
sight
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
15
Outline
Overview Description of the experiment
Target building Velocimeter measurement Vibrometer measurement
Experimental results Modal analysis using velocimeter measurement Frequency spectra measured by laser vibrometer Cross-validation of the two systems
Conclusion
Perspective
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
16
Conclusion and perspectives
Coherent lidar laser vibrometer can measure main modal vibration frequencies of a structure.
Sensitivity is good enough to detect ambiant vibrations Low velocity and low frequency measurements are possible
A scan should be implemented to perform mode shape assessment
Long range system could be limited by atmospheric piston noise because of the low velocities and low frequencies
Future work includes remote sensing of urban area for pre-and post-seismic application
V.J
OLI
VE
T -
14 W
CE
E
oct.
2008
-12
-03-
0107
17
Thank you.
Coherent Laser Radar vibrometry for modal analysis in earthquake engineeringOutlineOverviewOutlineDescription of the experimentDescription of the experimentDescription of the experimentCoherent Lidar VibrometerCoherent laser vibrometerOutlineExperimental resultsDiapositive numro 12Experimental resultsExperimental resultsOutlineConclusion and perspectivesDiapositive numro 17
