Download - Operational Modal Analysis Case Studies
Operational Modal Analysis
Application cases
2 LMS Web Seminar 2009 – Operational modal analysis Part 2
Overview
Part 1
What is Operational Modal Analysis
Why Operational Modal Analysis ?
What is the difference between ODS, EMA and
OMA ?
LMS PolyMAX Parameter Estimation
Automatic operational modal analysis
Part 2
Applications cases
Conclusion
3 LMS Web Seminar 2009 – Operational modal analysis Part 2
What is Operational Modal Analysis ?
In-operation Testing
Identification of modal parameters from data
measured on a structure during operational
conditions.
Eigenfrequencies
Damping ratios
Mode shapes
Operational modal analysis = identifying H
Based on Y
Without knowing U (BUT white noise
assumption)
HU Y
Input System Output
White noise
White noise + harmonic
4 LMS Web Seminar 2009 – Operational modal analysis Part 2
Operational Modal Analysis
Case Studies
5 LMS Web Seminar 2009 – Operational modal analysis Part 2
Application example
Civil engineering
Drivers
Artificial excitation problems
Testing complexity
Expensive
Data quality (still ambient
sources active)
High-quality sensors and data
acquisition systems
Operational Modal Analysis
Advanced algorithms
Commercial software
Real-life references
Forced vibration tests Ambient vibration testsEvolution
6 LMS Web Seminar 2009 – Operational modal analysis Part 2
Z24-Bridge
Ambient Vibration Test
Operational Modal Analysis
Quantify variance on modal
parameters due to environmental
influences
Damage detection by changes in
modal parameters
Test Setup
Ambient excitation
170 DOFS
9 setups 0.00 50.00 Hz
500e-18
10.0e-12
Log
g2
0.00
1.00
Am
plit
ude
7 LMS Web Seminar 2009 – Operational modal analysis Part 2
Z24-Bridge
Operational pole estimation for different runs
0
2
4
6
8
10
12
0 1 2 3 4
mode no.
natu
ral fr
eq
.(H
z)
scatter plot
0
1
2
3
4
5
0 1 2 3 4
mode no.
da
mp
ing
ra
tio
(%
)
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Z24-Bridge
Typical synthesis results
3.00 30.00 Linear
Hz
10.0e-15
10.0e-12
Log
g2
deck:120:+Z
Synthesized Crosspow er deck:120:+Z/ref:1:+Z
3.00 30.00 LinearHz
3.00 30.00 Hz
-180.00
180.00
Phase
°
3.00 30.00 Linear
Hz
1.00e-15
10.0e-12
Log
g2
deck:120:+Z
Synthesized Crosspow er deck:120:+Z/ref:2:-Y
3.00 30.00 LinearHz
3.00 30.00 Hz
-180.00
180.00
Phase
°
3.00 30.00 Linear
Hz
100e-15
100e-12
Log
g2
deck:120:+Z
Synthesized Crosspow er deck:120:+Z/ref:2:+Z
3.00 30.00 LinearHz
3.00 30.00 Hz
-180.00
180.00
Phase
°
9 LMS Web Seminar 2009 – Operational modal analysis Part 2
Z24-Bridge
Merge Modes
10 LMS Web Seminar 2009 – Operational modal analysis Part 2
Z24-Bridge
Merge Modes
11 LMS Web Seminar 2009 – Operational modal analysis Part 2
Z24-Bridge
Eigenfrequencies and damping ratios
OMA - Ambient EMA - Shaker
A B
Freq A [Hz]
Freq B [Hz]
Damp. A [%]
Damp. B [%] MAC [%]
Mode 1 Mode 1 3,86 3,87 0,71 1,43 99,44
Mode 2 Mode 2 4,89 4,82 1,30 1,57 94,66
Mode 3 Mode 3 9,75 9,78 1,56 1,56 60,57
Mode 4 Mode 4 10,31 10,46 1,19 1,52 88,97
Mode 5 Mode 5 12,49 12,41 2,66 2,99 96,06
Mode 6 Mode 6 13,43 13,23 3,51 4,58 86,10
Mode 7 Mode 7 17,36 17,52 3,20 3,98 53,03
Mode 8 Mode 8 19,10 19,26 1,73 2,61 6,39
Mode 9 Mode 9 19,84 19,75 2,10 5,08 75,30
Mode 10 Mode 10 26,53 26,65 1,79 3,03 49,88
All 10 modes were found!
12 LMS Web Seminar 2009 – Operational modal analysis Part 2
Operational Modal Analysis Ambient noise
Experimental Modal Analysis Shaker test
Z24-Bridge
Mode shapes
13 LMS Web Seminar 2009 – Operational modal analysis Part 2
Bradford & Bingley Stadium
Crowd-structure interaction
Remote Monitoring System
Time histories measured during soccer match
Empty stadium
People filling stadium
People sitting during match
Half-time
Goal
People leaving stadium
Changes in natural frequencies for Mode 1
2,9
2,95
3
3,05
3,1
3,15
3,2
3,25
3,3
3,35
3,4
Mode 1
Fre
qu
en
cy [
Hz] Empty PolyMax
Filling PolyMax
Leaving PolyMax
Half-time PolyMax
Sitting PolyMax
Goal PolyMax
Changes in damping ratios for Mode 1
0,00%
0,50%
1,00%
1,50%
2,00%
2,50%
3,00%
Mode 1
Dam
pin
g r
ati
o
Empty PolyMax
Filling PolyMax
Leaving PolyMax
Half-time PolyMax
Sitting PolyMax
Goal PolyMax
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Application example
Aircraft in-flight testing
Test setup
5 flights
30 responses / flight
2 reference points
Different conditions:
Taxi
Climbing
Level flight (3 altitudes, 4 air speeds)
Steady turn
Descend
Objectives
Compare with GVT results
Tracking of frequency and damping
15 LMS Web Seminar 2009 – Operational modal analysis Part 2
Aircraft in-flight testing
Analysis procedure
Flight data
Correlation functions
Modal parameter
estimation
Modal model
Model Validation
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Aircraft in-flight testing
Stabilization diagram
LMS PolyMAX
17 LMS Web Seminar 2009 – Operational modal analysis Part 2
Aircraft In-flight Testing
Crosspower synthesis
DOF on wing DOF on tail
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Aircraft In-flight Testing
Evolution of frequency & damping
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Flight test
Ground Vibration test
Aircraft In-flight Testing
Mode Shapes
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Identify modal parameters
Launcher
Main constituents
Using in-flight data
Practical, economical and safety reasons (no GVT)
Validation and updating of FE models
Influence of gradual mass decrease
Damping
Application case
ARIANE-5 Launcher
21 LMS Web Seminar 2009 – Operational modal analysis Part 2
Flight 501
+- 100 accelerations
booster segments, booster skirts, booster attachments
LH2 and LOX tanks in the main cryogenic stage
MMH and N204 tanks in the EPS stage
VULCAIN and AESTUS engines
ARIANE-5 Launcher
22 LMS Web Seminar 2009 – Operational modal analysis Part 2
-1.00 620.00 s
-131.45
49.56
Rea
l
(m/s
2 )
0.00
1.00
Am
plitu
de
-1.00 620.00 s
-145.37
90.27
Rea
l
(m/s
2 )
0.00
1.00
Am
plitu
de
-1.00 154.24 s
-147.88
48.41
Rea
l
(m/s
2 )
0.00
1.00
Am
plitu
de
Channels synchronized to common time t0
Non-equidistant
Rounding errors, losses, …
Different sample frequencies
Static components
Drop-outs, spikes
ADC bit resolution
Intensive data preparation
ARIANE-5 Launcher
Characteristics ARIANE-5 Flight Data
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8 signals measured at 4 fuel tanks in the
EPS stage
Signals resampled at 93.4Hz
Analyses performed for 4 time data
segments
S1 : 4 - 14s
S2 : 14 - 26s
S3 : 26 - 36s
S4 : 4 - 36s
ARIANE-5 Launcher
Analyses
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Integral
Application case
Integral Sine Qualification Test
Multi-shaker single axis qualification test
350 DOF’s
Range 5 - 100 Hz
Repeated modes – symmetric setup
Mode shapes from base-driven test
Y-axis qualification sweep data
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Integral Sine Qualification Test
Broadband / High-order Analysis
LMS Test.Lab PolyMAX
26 LMS Web Seminar 2009 – Operational modal analysis Part 2
Integral Sine Qualification Test
Crosspower Synthesis
15.06 67.04 Linear
Hz
1.01
45.96
Log
(m2/s
4 )CrossPow er UNIV:796:+X/UNIV:706:+Y
15.06 67.04 LinearHz
15.06 67.04 Hz
-180.00 180.00
Phase
°15.06 67.04 Linear
Hz
1.00
17.01
Log
(m2/s
4 )
CrossPow er UNIV:401:+X/UNIV:706:+Y15.06 67.04 Linear
Hz
15.06 67.04 Hz
-180.00 180.00
Phase
°
15.06 67.04 Linear
Hz
1.03
21.72
Log
(m2/s
4 )
CrossPow er UNIV:313:+Y/UNIV:706:+Y15.06 67.04 Linear
Hz
15.06 67.04 Hz
-180.00 180.00
Phase
°15.06 67.04 Linear
Hz
1.01
181.16
Log
(m2/s
4 )
CrossPow er UNIV:707:+Y/UNIV:706:+Y15.06 67.04 Linear
Hz
15.06 67.04 Hz
-180.00 180.00
Phase
°
Payload module
Service module Antenna
Solar Panel
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Integral Sine Qualification Test
Mode Shapes
28 LMS Web Seminar 2009 – Operational modal analysis Part 2
Application
Rotating machinery
Sweeping harmonics (run-up)
Harmonics excite broad
frequency band
Useful excitation – no
filtering!
“End-of-order” effects
Fixed (or slowly varying)
harmonics
Harmonics hamper the
identification process
Have to be removed from
data
He
lic
op
ter
in-f
lig
ht
da
taC
ar
en
gin
e r
un
-up
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Industrial examples
Key to the method is the knowledge of the fundamental
frequency of the disturbing harmonics:
Tacho probe during operational test
“Tacho-less rpm extraction”
Hilbert transform
Example: band-pass filtered helicopter roof accelerations
0.50 29.50s
Am
plit
ude
g
0.50 29.50sA
mplit
ude
0.50 29.50s
Am
plit
ude
Hilbert transform magnitude Hilbert transform phase
Instantaneous frequency estimation
derivative
30 LMS Web Seminar 2009 – Operational modal analysis Part 2
In-flight mode shapes
Industrial example – helicopter in-flight OMA
In-flight acceleration spectrum before
and after applying the harmonic filter
31 LMS Web Seminar 2009 – Operational modal analysis Part 2
Industrial example – large Diesel engine OMA
Helicopter data: even without filtering, some
modes could be identified
Quasi-stationary running large engine:
Harmonics:
• High-amplitude
• Closely-spaced
OMA: no single structural mode found
Need for harmonic filtering
32 LMS Web Seminar 2009 – Operational modal analysis Part 2
Industrial example – large Diesel engine OMA
Quasi-stationary running large engine
Filtering the harmonics from the time
series
OMA successfully applied
• in good agreement with the modal
parameters identified using classical
impact testing
33 LMS Web Seminar 2009 – Operational modal analysis Part 2
Road noise analysis
Booming Noise at 80 Hz
Transfer Path Analysis points to rear
suspension
Experimental Acoustical Cavity Mode: 80 Hz
Acoustic wave is maximum for rear passenger
80 Hz
rear seats
front seats
34 LMS Web Seminar 2009 – Operational modal analysis Part 2
Road noise analysis
Operational modal analysis of the rear suspension
Rollerbench test with bumps on rollers
Impulsive excitation
High data consistency
2 runs / 45 dofs each
6 ref dofs0.00 21.00 s
-11.00
10.00
Real
(m/s
2 )
0.00
1.00
Ampli
tude
0.00 512.00 Hz
-60.00
-30.00
dBg2
0.00
1.00
Am
plit
ude
F AutoPow er FARG:21:+Z Susp_Run1
F AutoPow er FARG:21:+Z Susp_Run2
35 LMS Web Seminar 2009 – Operational modal analysis Part 2
Road noise analysis
Stabilization diagram
LMS PolyMAX
36 LMS Web Seminar 2009 – Operational modal analysis Part 2
Road noise analysis
Crosspower synthesis
0.00 180.00 Linear
Hz
1.00e-6
10.0e-3
Log
g2
Synthesized Crosspow er FARG:21:-X0.00 180.00 Linear
Hz
0.00 180.00 Hz
-180.00
180.00
Phase
°
Synthesized Crosspow er FARG:21:-X
0.00 180.00 Linear
Hz
100e-6
10.0e-3
Log
g2
Synthesized Crosspow er AMAR:813:+Y/FARG:21:+Y0.00 180.00 Linear
Hz
0.00 180.00 Hz
-180.00
180.00
Phase
°
Synthesized Crosspow er AMAR:813:+Y/FARG:21:+Y
0.00 180.00 Linear
Hz
1.00e-6
1.00e-3
Log
g2
Synthesized Crosspow er LONG:302:+Z/FARG:21:+Y0.00 180.00 Linear
Hz
0.00 180.00 Hz
-180.00
180.00
Phase
°
Synthesized Crosspow er LONG:302:+Z/FARG:21:+Y
0.00 180.00 Linear
Hz
10.0e-6
10.0e-3
Log
g2
Synthesized Crosspow er TRAR:608:+Z/FARG:21:+Y0.00 180.00 Linear
Hz
0.00 180.00 Hz
-180.00
180.00
Phase
°
Synthesized Crosspow er TRAR:608:+Z/FARG:21:+Y
37 LMS Web Seminar 2009 – Operational modal analysis Part 2
Car Road Noise
Results
Source problem: Bending of twist beam
Solution: Tuned Vibration absorber or stiffen twist beam
38 LMS Web Seminar 2009 – Operational modal analysis Part 2
5 : Belgian blocks
1 : runups
2 : ramps
3 : asphalt
4 : ramps
Car on the road
Road Tests
39 LMS Web Seminar 2009 – Operational modal analysis Part 2
Car on the road
Run Up Test
Measurements
20 km/h -> 60 km/h on ordinary road in 2nd gear
24 dofs (± 45 sec.)
Different acquisition runs,
Down sampling to 100 Hz
Analysis
Balanced Realization technique
0Hz - 35 Hz: Excitation especially in this frequency band
Mainly rigid body and first flexible modes
40 LMS Web Seminar 2009 – Operational modal analysis Part 2
Car on the road
6 Important Modes
Torsion mode:
• 30.47 Hz
• Damping: 3.84 %
Rigid body modes
First flexible modes
41 LMS Web Seminar 2009 – Operational modal analysis Part 2
Car on the road
Belgian Blocks
Constant velocity : 20 km/h
Extra rigid body mode
High level excitation of the first two rigid
body modes
42 LMS Web Seminar 2009 – Operational modal analysis Part 2
Use of OMA for Updating
Moan Noise
Roller bench testing
320Hz
Brake suspension
43 LMS Web Seminar 2009 – Operational modal analysis Part 2
Use of OMA for Updating
Moan Noise
Test (320Hz) FE (312Hz)
44 LMS Web Seminar 2009 – Operational modal analysis Part 2
Damage detection: Sports Car
Fatigue problem attachment power train to body
During test-track endurance test
Detailed test-track data analysis
Laboratory EMA and test-track OMA
Dynamic fatigue calculations
Controlled laboratory endurance tests
45 LMS Web Seminar 2009 – Operational modal analysis Part 2
Part 1
Mature technology Robust algorithms
Many relevant industrial applications
Complements Experimental Modal Analysis
Better exploitation of operational data
Use PolyMAX to make OMA easy Crystal-clear stabilization diagrams
User-independent results
Part 2
Applications include Troubleshooting
Design verification / FE correlation
Trend analysis
Damage detection / Health monitoring
Operational Modal Analysis
Conclusion
46 LMS Web Seminar 2009 – Operational modal analysis Part 2
Invitation
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