Upload
nguyenhanh
View
226
Download
1
Embed Size (px)
Citation preview
Advanced Modal Analysis
Techniques
Advanced Modal Seminar
Brasil, Februari 2017
Realize innovation.Unrestricted © Siemens AG 2016
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 2 Siemens PLM Software
Agenda
Operational Modal Analysis
Rigid Body Properties
Modification Prediction
Operational Modal
Analysis
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 4 Siemens PLM Software
How would you excite these structures ?
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 5 Siemens PLM Software
Operational Modal Analysis
In-operation testing
• Some applications permit the acquisition ofInput - output (FRF) data during normal operation• Require special setups for forced excitation
• Rotating wing-tip vanes• Electromagnetic bearings • Low-frequency exciters • Drop-weights• Unbalance shakers• Pyrotechnics• Control Surface Input• Servo-drive inputs (robots) • …
• Testing complexity• Data quality (undesired ambient sources)
• Some applications permit simulating in-operation conditions in I/O (FRF) tests (car suspension…)
• The normal EMA processes can be followed
© NASA
© EMPA © KUL
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 6 Siemens PLM Software
In-operation EMA example:
Business jet, wing-vane in-flight excitation
• In-flight excitation, 2 wing-tip vanes
• 9 responses
• 2 min sine sweep
• Higher order harmonics
• Very noisy data
Hz
0.10
0.10e-3
Log
g/N
180.00
-180.00
Phase
°
Hz
0.10
1.00e-6
Log
g/N
180.00
-180.00
Phase
°
FRF w ing:vvd:+Z/F200:FED:+Z
FRF back:vde:+Y/F200:FED:+Z
Hz
1.00
0.05
Am
plit
ude
/
Coherence w ing:vvd:+Z/Multiple
Coherence back:vde:+Y/Multiple
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 7 Siemens PLM Software
Operational Modal Analysis
• What ?• Identification of modal
parameters from response data
only
Eigenfrequencies
Damping
Mode shapes
No scaling!
• Using measurements
(accelerations) in operational
conditions
• Why ?• Real operating conditions
laboratory conditions
Non-linearities
Environmental effects
Aero-elastic interaction
Temperature
Boundary conditions
• Inability to measure the inputs
Too difficult, time-
consuming, expensive
• Permanent monitoring
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 8 Siemens PLM Software
Laboratory measurements Modal analysis (FRFs)
CMIF
LSCE,
PolyMax, ...
impact
random
stepped sine
Normal mode testing
Operational measurements
- time histories, spectra
- selection of reference stations
- multiple runsOperational modal analysis(freq, damping, mode shapes)
FRFs
F
E
M
/
B
E
M
Peak picking
- power spectra
- principal comp.
(oper. deflection shapes)
Operational Modal Analysis
Positioning
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 9 Siemens PLM Software
Operational Modal Analysis
• Operational modal analysis = identifying H• Based on Y
• Without knowing U
• Additional ‘input’ poles identified
• No problem if:• poles input system
poles• Low damping,
related to rpm
HU Y
Input System Output
White noise
White noise + harmonic
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 10 Siemens PLM Software
Typically, output-only data
• Fed by correlations between outputs and outputs serving as references
• direct in time domain
• inverse DFT of auto-and crosspower spectra
• Unknown input is assumed to be stationary white-noise (theoretical
assumption)
• in practice: colored noise, impulse excitation,
swept sine,.. = OK The frequency band of
excitation has to include the modes
• Mode shapes cannot be mass-normalized
Colored noise:
• Additional ‘input’ poles identified:
harmonics = low damping, related to rpm
• poles input system poles
Operational Modal Analysis
Background
Sum of
Cross powers
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 11 Siemens PLM Software
0.00 80.00 Hz
10.0e-6
0.10
Log
(g/N
)
0.00 80.00 LinearHz
0.00 80.00 Hz
-180.00
180.00
Phase
°
0.00 6.00 s
-1.07
0.91
Real
(g/N
)
“Traditional” (IO) modal parameter estimation
Modal model
Inverse
Fourier
transform
Frequency domain Time domain
FRF IRF
n
i i
i
i
i
j
A
j
AH
1*
*
)(
n
i
ii
ii
tA
tAth
1
** ee)(
T T
i i i i i iA Q v l iiiiii j 2* 1,
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 12 Siemens PLM Software
PolyMAX
Pre-processing for Operational Modal Analysis
Spectrum estimation: leakage-free
and Hanning window-free
1. High-speed estimation of time-
domain correlations
• Data reduction
2. Exponential window
• Reduces the effect of leakage
• Reduces the influence of noise
• Compatible with the modal model (
Hanning window is not
compatible and leads to biased
damping)
3. Fourier transform of windowed
correlations
921.590.00 s
0.9928
0.9916
Real
g
Time ref:2b06:+Z
10.230.00 s
2.50e-9
-2.50e-9
Real
g2
AutoCorrelation ref:2b06:+Z
AutoCorrelation ref:2b06:+Z
50.000.00 Hz
-100.00
-130.00
dBg2
180.00
-180.00
Phase
°
AutoPow er ref:2b06:+Z
AutoPow er ref:2b06:+Z
Time-domain correlations
Fourier transform
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 13 Siemens PLM Software
Pre-processing for Operational Modal Analysis:
classical and non-classical spectrum estimate
Classical spectrum (“Periodogram”) “Half” spectrum (“Correlogram”)
Operational
data ky
]DFT[window )()( s
k
s yY
Hsss
yy YYS )()()(
P
s
s
yyyy SP
S1
)( )(1
)(
1
0
1 N
k
Tkiki yy
NR
}],...,,...,{DFT[window)( 0 LLyy RRRS
}],...,2/{DFT[window)( 0 Lyy RRS
2.00 8.00 Linear
Hz
1.00e-12
10.0e-9
Log
(m2/s
4
)
autopow er_spectr roof:1:+Z / roof:1:+Z
crosspow er_spect roof:1:+X / roof:1:+Z
2.00 8.00 Linear
Hz
2.00 8.00 Hz
-180.00
180.00
Phase
°
Periodogram
with
Hanning
window
2.00 8.00 Linear
Hz
1.00e-12
1.00e-9
Log
( m/s
2)2
AutoPow er roof:1:+Z
CrossPow er roof:1:+X/roof:1:+Z
2.00 8.00 Linear
Hz
2.00 8.00 Hz
-180.00
180.00
Phase
°
Correlogram
with
exponential
window
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 14 Siemens PLM Software
Why “half spectra”?
• Lower order models
• Exponential window
• Reduces the effect of leakage
• Reduces the influence of the higher time
lags having a larger variance
• Compatible with the modal model
( Hanning window with biased
damping)
Hyyyyyy SSS )()()(
n
i i
ii
i
iiyy
j
gv
j
gvjS
1*
**
)(
0.00 52.00 s
-10e-9
10e-9
Real
( m/s
2)2
Time roof:1:+X Unw indow ed
Time roof:1:+X
0.00 10.00 Linear
Hz
-140
-90
dB
( m/s
2)2
AutoPow er roof:1:+X Unw indow ed
AutoPow er roof:1:+X
0.00 10.00 LinearHz
0.00 10.00 Hz
-180
180
Phase
°
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 15 Siemens PLM Software
Operational Modal Analysis
The Vasco da Gama Bridge
0.00 960.60s
-0.52
0.59
Rea
l
g
0.00 300.00s
-0.02
0.02
Rea
l
g2
0.00 2.50Hz
0.00
0.00
Log
g2
Vertical acc.
Transversal acc.
Time data
Correlations
Spectra
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 16 Siemens PLM Software
Operational Modal Analysis
The Vasco da Gama Bridge
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 17 Siemens PLM Software
Operational Modal Analysis
The Vasco da Gama Bridge
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 18 Siemens PLM Software
Operational Modal Analysis
Measured Cross Spectra vs. Modal Model
0.20 1.05Hz
0.00
0.00
Log
g2
0.20 1.05LinearHz
0.20 1.05Hz
-180.00
180.00
Phase
°
10X-15Z
0.20 1.05Hz
0.00
0.01
Log
g2
0.20 1.05LinearHz
0.20 1.05Hz
-180.00
180.00
Phase
°
10Z-112Z
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 19 Siemens PLM Software
Operational Modal Analysis
Øresund Bridge
m
H
Lnf S
n2
1
Measurements of cable vibrations allow to
monitor cable forces (vibrating string theory)
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 20 Siemens PLM Software
Other Operational Modal Analysis
Applications
In-flight testing
Flutter
High-speed train
Road test of a car
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 21 Siemens PLM Software
Operational Modal Analysis in Ship-Building
Background:
Performing EMA(Experimental Modal Analysis)
on large ships is very difficult
Most customers only perform ODS
(Operational Deflection Shapes) using vibration data
Using the same vibration data, customer can determine
the modal properties of the ship with OMA
(Operational Modal Analysis)
Tokai University - Boseimaru
前後、左右、上下方向
1
1
1
2
Data Measurement
次数成分の周波数比較
0
1
2
3
4
5
6
7
8
9
10
0 0.5 1 1.5 2 2.5 3 3.5
次数(次)
周波数(Hz)
アンカリングテスト
ランアップテスト
Operational Modal Analysis
1st Bending Mode
Correlation with Anchoring Test
Test.Lab & SCADAS-Mobile
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 22 Siemens PLM Software
OMA on Tokai University ship
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 23 Siemens PLM Software
First and second bending
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 24 Siemens PLM Software
Torsion and third bending mode
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 25 Siemens PLM Software
Scania: Enhanced exploitation of oilpan vibration
data by Operational Modal Analysis
• Design of a silent oilpan
• Single measurement for
• Sound level evaluation
• Operational Deflection Shapes creating
the sound
• Operational Modal Analysis
• Benefits
• Reduced testing time
• Consistent data130 650Hz
Big_Block:27:+Z (CH2)
859
2168
rpm
Fly
Wheel (
T1)
-50
0
dB
130 650Hz
Big_Block:44:+Y (CH1)
859
2168
rpm
Fly
Wheel (
T1)
-48
2
dB
130 650Hz
Small_Block:12:+Z (CH3)
859
2168
rpm
Fly
Wheel (
T1)
-38
12
dB
130 650Hz
Big_Block:27:+Z (CH2)
860
2171
rpm
Fly
Wheel (
T1)
-50
0
dB
130 650Hz
Big_Block:44:+Y (CH1)
860
2171
rpm
Fly
Wheel (
T1)
-48
2
dB
130 650Hz
Small_Block:12:+Z (CH3)
860
2171
rpm
Fly
Wheel (
T1)
-38
12
dB
130 650Hz
Big_Block:27:+Z (CH2)
859
2169
rpm
Fly
Wheel (
T1)
-50
0
dB
130 650Hz
Big_Block:44:+Y (CH1)
859
2169
rpm
Fly
Wheel (
T1)
-48
2
dB
130 650Hz
Small_Block:12:+Z (CH3)
859
2169
rpm
Fly
Wheel (
T1)
-38
12
dB
0.00 0.64s
-0.10
0.10
Real
g2
OMA vs. impact modes
(mass and temp diff)
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 26 Siemens PLM Software
Operational Modal Analysis (OMA)
More than Operational Deflection Shapes (ODS)
• Animate: Auto & Cross Spectra,
FRFs, Orders
• Peak picking
• Deformation at a chosen
frequency line
• No damping information
• Combination of modes and forced
responses
• Combination of closely spaced modes
• Phenomena
• Curve-fit: Auto & Cross Spectra
• Modal model
• Frequency
• Damping
• Mode shape
• (No modal scaling)
• Use of system identification
methods
• Structural characteristics
• Separation of closely spaced modes
• Root causes
OMAODS
Vibration problem “root cause” discriminator
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 27 Siemens PLM Software
Conclusions
Operational Modal Analysis is a mature technology
• High-quality data acquisition
• Advanced parameter estimation algorithms
• Commercial software implementations
• Industrial applications
• Only care on the assumption made
• Evolutions since more than 20 years
• Technology
• Usability
• Applicability: no isolated results but part of
engineering workflow
• Civil engineering
• Aerospace engineering
• Automotive engineering
Rigid Body Properties
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 29 Siemens PLM Software
Why are inertia properties needed ?
Verification of CoG & MoI values
Input for simulation models Kinematic and dynamic prediction (multibody
dynamics calculation) Coupling of an FE model with smaller “rigid”
components Accurate Modal based modification or
Substructuring requires flexible modes + rigid body modes
Complete modal model A complete modal model contains 3 components:
• Rigid body modes• Flexible modes• Residual terms
?
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 30 Siemens PLM Software
How to determine inertia properties ?
Pendulum test Based on measured Frequency response
functions
Typical modal test with hammer or
shaker excitation
At least 6 excitation locations (SDOF)
8 – 12 response locations (3 DOF)
Time consuming
Requires multiple suspensions -
difficult for complex structures
No extra equipment is needed
Limited measurement effort
Highly accurate alternative to
conventional pendulum test
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 31 Siemens PLM Software
Rigid body modes
To synthesize rigid body modes based on FRF measurements
Input:
• Geometry (nodes and coordinates)
• FRF data
Output:
• Inertial properties:
• Center of gravity
• Mass
• Moments of inertia
• Directions of the principle axes of inertia
• 3 translational rigid body modes
• 3 rotational rigid body modes
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 32 Siemens PLM Software
Rigid Body Properties Calculation
How does it work - Theory
Approximate structure as Single DOF system
Resonance frequency of this SDOF system is the first actual RBM of the structure
Line above resonance is called the mass line
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 33 Siemens PLM Software
Rigid Body Properties Calculation
How does it work – Test setup
Weigh the test item to obtain mass [kg]
Suspend Test item (once) in free-free conditions
Create geometry wire-frame model in global or local coordinates
Measure FRF matrix preferably with hammer
Test Setup:
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 34 Siemens PLM Software
Rigid Body Properties Calculation
How does it work - Mass line methods
Unchanged FRFs
Rigid body modes and first deformation modes are sufficiently spaced
Measured FRFs are used
Corrected FRFs
Rigid body modes and first deformation modes are not sufficiently spaced
Estimate first set of flexible modes from measured FRFs
Correct measured FRFs by subtraction of contribution of flexible modes
Lower Residual
No accurate FRFs are measured in the frequency range directly above rigid body modes
Lower residuals represent the influence of the modes below the deformation modes, and are
therefore representative of the rigid body modes.
Extract mass line:
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 35 Siemens PLM Software
Rigid Body Properties Calculation
How does it work - Calculation and results
Coordinates of center of gravity
Moments and products of inertia about CoG and any user defined reference point
Principal moments of inertia and their direction
Synthesis of 6 scaled rigid body modes with user defined frequency
and damping for use in simulation models
Least square solution over all measured DOF
Least squares over selected frequency band of mass-line
Validation through animation of rigid body motion
Calculate Rigid Body Properties:
Results:
Modification Prediction
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 37 Siemens PLM Software
Modification Prediction
Why?
The major advantages of Structural
Modification Prediction within prototype
optimization procedures are:
•Prediction of the effect of a
structural modification without
physically changing the structure.
•Evaluation of alternative design
variation without repeated testing
•Evaluation of the impact of a
selected modification on the
structure in a global sense
The LMS Test.Lab Modification
Prediction workbook helps you to:
•Efficiently dissipate vibration
energy using a tuned absorber
•Add masses or change local
stiffness to move resonant
frequencies
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 38 Siemens PLM Software
Modal models for structures with flexible coupling and viscous damping
1. Laplace domain
2. Extended system equation
3. Eigenvalue problem
4. Premultiply extended system equation with
5. Orthogonality condition
6. Transformation to modal space
Modification Prediction
Modification Prediction – Theoretical background (1)
pFpXKCpMp 2
F
FX
XpY
K
MB
CM
MA
FYBAp
0',,
0
0,
0
'
0 ii BA
i
ii
i
t
\\
\
\
\
\
\
\
\
\ abbBandaA tt
qY
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 39 Siemens PLM Software
Modification Prediction
Modification Prediction – Theoretical background (2)
Modification of structure
• Structure modification
• Modified system equation
• Applying modal transformation New Eigenvalue problem in modal space to be
solved
• Modified system poles and modified eigenvectors in modal coordinates
• Back substitution to physical coordinates gives new modal vectors
'FYBBAAp
mrq
mrm qψψ
BAKCM ,,,
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 40 Siemens PLM Software
Modification Prediction
Automotive example
Tuned absorbers in cars:
• 10 – 15 (sometimes up to 30) tuned
absorbers/vehicle
• 100-150 gr / absorber (exceptionally up to 1.5 kg)
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 41 Siemens PLM Software
Modification Prediction
Automotive example
Mass modification on attachment
bracket
Bi-directional tuned
absorber on an engine
anti-roll mount
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 42 Siemens PLM Software
Modification Prediction
Aero examples
Aircraft cabin noise
reduction
Engine vibration reduction
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 43 Siemens PLM Software
Modification Prediction
Aero example
Helicopter design
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 44 Siemens PLM Software
Modification Prediction
Civil construction
Modifications
58 Tuned Absorbers
4 Vertical dampers
17 Chevron dampers
16 Pier dampers
Cost
Construction: £18m
Modifications: £5m !!
Bridge closed for 2 years
“Wobbling Bridge Will Stay Shut” – BBC News
20XX-XX-XX
Unrestricted © Siemens AG 2013 All rights reserved.
Page 45 Siemens PLM Software
Modification Prediction
Other industries
Everyone else interested in the vibration
related product performance
Thank you!Advanced Modal Seminar
Brasil, Februari 2017
Realize innovation.Restricted © Siemens AG 2016