lms webex - supporting high frequency noise analysis
TRANSCRIPT
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
1/29
High frequency FRF testingTom knechten LMS Engineering Services
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
2/29
2
Webex overview
Challenges with acoustic excitation
Noise level
Directivity Sensor freq response
Housing radiation
Challenges with structural excitation
Accessibility
Mass loading
Sensor freq response
Housing radiation
Reproducability
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
3/29
3
LMS Qsources hardware completes LMS NVH test solution
LMS ES provides unique structural and acoustic excitation hardware &services used in NVH by engineering.
Focus on performance attributes: system dynamics, comfort/sound quality.
Offering:
Standard set of structural and acoustic exciters covering most of the typicalapplications. EMA, ASQ, TPA, body isolation testing,
Innovative customized solutions
Benefits:
Increased efficiency of Transfer Function (FRF) measurements by enablingreciprocal measurements.
Extended measurement capability - Excitation at difficult to reach locations.
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
4/29
4
14.000.00 s
Time
6000.00
0.00
Hz
GEAR:-X(CH4)
0.00
-90.00
dB g
AutoPow er GEAR:-X WF 163 [152.07-949 .89 rpm]
Identify all the orders on the same waterfall diagram
Time Domain
Engine related
MG1 related
MG2 related
PSD related
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
5/29
5
FRF information
FRF measurements on vehicle bodies enables various analyses:
Body sensitivity to dynamic structural or acoustic loads
Body isolation Mode frequencies
Input data for Transfer-Path-Analysis model(TPA), Airborne Source Quantification(ASQ)
In order to increase measurement efficiency reciprocal measurements are common.
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
6/29
6
Reciprocal acoustic excitation
The reciprocity principle:
Vibro-acoustic system transfer Acoustic system transfer
Volume acceleration enables measuring vibro-acoustic FRFs without post-processing asmost common motion sensors are accelerometers which output an acceleration signal.
1
2
2
1
Q
a
F
p
&
=
1Q&
2x&&
1p
2F
2
1
1
2-F
p
Q
x=
&&&
Reciprocal FRF Direct FRF
2
1
1
2
p
p
p
p=
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
7/29
7
LMS Qsources Mid Frequency Volume SourceWorking principle
1. An electrodynamic speaker to excite the structure
2. A reference signal to measure sound source strength
of the speaker.
Compared to a normal speaker:
High SPL output
Designed to behave like a point/monopole source
Internal sound source strength reference sensor
Electronic protection against overload
Comments on design:
A small nozzle to reduce diffraction effect of speaker. A flexible tube enabling fast & easy positioning
Reference sensor integrated in nozzle of sound source to define the excitation
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
8/29
8
Challenges with high frequency acoustic excitationDirectivity of noise emission
Directivity becomes more relevantas frequency increases as ratio
between wavelength andhardware size decreases.
Directivity plot shows 3frequency ranges [dB]
1000Hz
4000Hz
10000Hz
Pressure measurement at 0.5meter distance, every 30
Mic frequency response chartFreefield-pressure @ 00 incidence
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
9/29
9
Challenges with high frequency acoustic excitationDirectivity of sensors
The frequency response of the measurementequipment should be acceptable for high
frequencies.
20000100 Hz
10000
100
1000
200
300
400
500
600
700
800
900
2000
3000
4000
5000
6000
7000
8000
Log
Mic frequency response chartFreefield-pressure @ 00 incidence
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
10/29
10
2238789 Octave 1/3
Hz
100
20
30
40
50
60
70
80
90
35
45
55
65
75
85
dB
Pa
100.00
20.00
dB
[0-20480Hz]
Pa
A L
Challenges with high frequency acoustic excitationHousing radiation
The monopole source should excite the acoustic environmentwith the noise that is emitted at the nozzle only.
Noise radiation from tubing or housing should be avoided
Compact driver design
Reinforced tubing
Double sealed driver connection
Nonlinear tube acoustics make radiating
noise uncorrelated and therefore not critical
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
11/29
11
Challenges with high frequency acoustic excitationNonlinear tube acoustics
At low source output level, the emitted noise is symmetric.
At maximum output level, the time signal of the reference sensor is deteriorated. The
pressure in the tube is in the range where nonlinear acoustics apply.
Symmetric waveform
Asymmetric waveform
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
12/29
12
Challenges with high frequency acoustic excitationStable sound source strength measurement
Volume acceleration as a quantity for sound source strength is more independent of acousticenvironment, compared to sound power calculation based on pressure measurements.
Volume acceleration reference sensor infree-field and in an engine bay showconsistent source strength quantification.
Pressure reference sensor in free-field andin an engine bay show variable soundsource strength in function of acousticenvironment.
Q& p
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
13/29
13
Challenges with high frequency acoustic excitationHigh frequency reciprocal FRF measurement
As isolation performance increases with frequency, so do the noise levels of the sourceneed to increase. This triggered LMS to develop a special version of the current sourcewhich allows a higher noise level at frequencies above 3kHz.
2 versions exist:
A normal mid high frequencysource with 4 meter tube
A wide frequency range mid highfrequency source with a 2 meter tubethat can be extended to a 6 meter tube.
200-10000Hz 150-10000HzHigher noise level
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
14/29
14
Challenges with high frequency acoustic excitationNoise level - Q-MHF vs Q-MHF-WIDE(long&short tube)
1500050 100 1000 1000060 70 80 90 200 300 400 500 600 700 800 2000 3000 4000 5000 6000 7000
Hz
-10
-60
-50
-40
-30
-20
-55
-45
-35
-25
-15
-58
-53
-48
-43
-38
-33
-28
-23
-18
-13
dB
(m3/s2)2/Hz
F PSD VOLACC:S SHORT TUBE MAX SPECTRA 500-10kHz MAX AMPLI RUN 2
F PSD VOLACC:S LONG TUBE MAX SPECTRA 150-2kHz MAX AMPLI RUN 2
F PSD VOLACC:S STANDARD TUBE MAX SPECTRA 200-2kHz MAX AMPLI RUN 2
Q-MHF-WIDE: Long tubeQ-MHF-WIDE: Short tube
Q-MHF standard
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
15/29
15
Challenges with high frequency acoustic excitationNoise level - Q-MHF vs Q-MHF-WIDE(long&short tube)
Accelerometer reponse:MOUNT:ENGINE:-Z
The long tube at lowfrequencies a significantgain is obtained instructural response.
13000100 1000200 300 400 500600 800 2000 3000 4000 6000 8000
Hz
-50.00
-110.00
-100
-90
-80
-70
-60
-105
-95
-85
-75
-65
-55
dB
(m/s2)2/Hz
F PSD LONG:0001:+Z NORMAL_burst100%_han_500avg_200-10kHz
F PSD LONG:0001:+Z WIDE_LONG_burst100%_han_500avg_150-3kHz
13000100 1000200 300 400 500 700 2000 3000 4000 6000
Hz
1.00
0.00
Amplitud
e
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
16/29
16
Challenges with high frequency acoustic excitationNoise level - Q-MHF vs Q-MHF-WIDE(long&short tube)
Accelerometer reponse:MOUNT:ENGINE:-Z
With the short tube athigh frequencies asignificant gain isobtained in structuralresponse and an
improvement incoherence. 13000.003000.00 100004000 5000 6000 7000 8000 9000
Hz
-70.00
-120.00
-110
-100
-90
-80
-115
-105
-95
-85
-75
dB
(m/s2)2/Hz
F PSD LONG:0001:+Z NORMAL_burst100%_han_500avg_200-10kHz
F PSD LONG:0001:+Z WIDE_SHORT_burst100%_han_500avg_400-10kHz
13000.003000.00 100004000 5000 6000 7000 8000 9000
Hz
1.00
0.00
Amplitude
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
17/29
17
Challenges with high frequency acoustic excitationNoise level - Q-MHF vs Q-MHF-WIDE(hort tube)
Curve: Coherence FRF interior mic to microphone in engine compartment
Comparing the coherence of a microphone near engine compartment shows ansignificant improvement.
120003000 4000 5000 6000 7000 8000 9000 10000 110003500 4500 5500 6500 7500 8500 9500 10500
Hz
1.00
0.00
Amplitude
/
3000.00 10000.00
Curve Average Hz
0.38 /
0.58 /
F Coherence ENCO:frnt:S/Q_NORMAL:S
F Coherence ENCO:frnt:S/Q_WIDE:short:S
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
18/29
18
Challenges with high frequency acoustic excitationNoise level - Q-MHF vs Q-MHF-WIDE (short tube)
FRF interior mic to microphone inengine compartment
To obtain a full bandwidth FRF, thetwo FRF sets can be easily mergedwithin LMS Test.Lab environment.
10000.001.00 Hz
0.10
100e-9
Lo
g
Pa/(m
3/s2)
180.00
-180.00
FRF ENCO:f rnt:S/Q_WIDE:long:S
10000.000.00 Hz
1.00
0.00
Amp
litude
F Coherence ENCO:frnt:S/Q_WIDE:long:S
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
19/29
19
Overview
Challenges with acoustic excitation
Noise level
Directivity Sensor freq response
Housing radiation
Challenges with structural excitation
Accessibility
Mass loading
Sensor freq response
Housing radiation
Reproducability
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
20/29
20
Challenges with high frequency structural excitationaccessibility
The LMS Qsources shakers are based on the inertiaprinciple making it possible to excite structures without anyexternal support.
Shakers are self aligning making the test efficient.
Internal force and acceleration sensors reduce space
constraints and alignment work.
The uncoupled mass is kept to a minimum.
Shakers allow testing from a safe location.
Frequency range: 20-2000Hz
50-5000Hz
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
21/29
21
Challenges with high frequency structural excitationMass loading
Reference accelerometer with added weights
Four types of transfer functions withvolume source excitation wereperformed:
No added weight With added weight close to the
response point of the accelerometer :8.3g , 132.3g, 950 g
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
22/29
22
Challenges with high frequency structural excitationMass loading
For every weight added you can see a peak in the FRF and the level drops justafter this peak.
Each peak corresponds to the local mode of the added mass on a spring with thestiffness of the metal sheet of the body.
For 800Hz we have a stiffness of around 5e7 N/m. If we calculate the resonance fora 132g mass, it will be around 1000 Hz.
5000.002.00 Hz
-20.00
-110.00
dB
(m/s
2)/(m3/s2)
180.00
-180.00
800.00 3067.95
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
23/29
23
Housing radiationInfluence of airborne noise emitted by minishaker
_Normally attached
_Insulated all around with foam
_ Decoupled (on foam)
100002000 Hz
70.00
-30.00
dB
Pa/N
180.00
-180.00
FRF Mic:S/Q-MSH:+X Run 1
FRF Mic:S/Q-MSH:+X Run 3_w ith_insulationFRF Mic:S/Q-MSH:+X Run 6_decoupled
100002000 Hz
1.00
0.00
Amplitude
/
FRF
Coherence Functions
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
24/29
24
Challenges with high frequency structural excitationfrequency response internal force sensor
The frequency response of the internalforce sensor is flat up to 5kHz.
820050 1000 2000 3000 4000 5000 6000 7000
Hz
1000.00
1.00
Log/
F FRF accelerometer:-Z/Force cell:+Z
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
25/29
25
Challenges with high frequency structural excitationBlocked force spectrum vs floornoise
Setup:
Shaker mounted to rigid base
max output voltage: 2.5V
Amplifier level:+16dB
Red curve:maximum force level in 1/3 octaves
Excitation frequency range: 50-5000Hz
Green curve: maximum force level in 1/3 octaves
Excitation frequency range: 50-600Hz
Black curve: Background noise during no excitation.
10.00 10000.00Hz
100e-6
1.00
Log
N
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
26/29
26
Challenges with high frequency structural excitationForce level - example
100000 2000 4000 6000 8000Hz
1.00
0.00
Amplitude
/F Coherence Mic:S/shaker:+X
100000 2000 4000 6000 8000
Hz
90.00
0.00
d
B
Pa/N
180.00
-180.00
2000 4000 6000 8000 10000
2893.18 5262.82
FRF Mic:S/Force Cell:+X Shaker_on_force_cell Run 1
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
27/29
27
27 copyright LMS International - 2005
LMS Qsources Integral ShakerVery high data accuracy and reliability
Typical operator variation:
Hammer worst repeataiblity
Q-ISH best repeatability resulting in high data accuracy and confidence in themeasurement results.
Integral shakerModal hammerConventional shaker
Exact excitation position andorientation is critical in highaccuracy measurements.
Following comparison has beenshows that the Integral Shakeris most robust in operatorreproducability and repeatability.
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
28/29
28
28 copyright LMS International - 2005
Challenges with high frequency structural excitationReproducability
Typical operator variation:
Q-ISH: Positioning error
Misalignment errorRepeatability
A comparison between
Integral shaker
Conventional shaker Modal hammer
Q-ISH shows a minimumvariation in vibro-acoustic
FRF on a passenger car.
35.00
70.00
dB
Pa/N
35.00
70.00
dB
Pa/N
200 600300 400 500220 240 260 280 320 340 360 380 420 440 460 480 520 540 560 580
Hz
35.00
70.00
dB
Pa/N
Misalignment of conventional shaker5degrees
Positioning error of ring on structure2mm
Reproducability of 10 persons with modal hammer
-
7/30/2019 LMS Webex - Supporting High Frequency Noise Analysis
29/29
29
Overview
Challenges with acoustic excitation
Noise level
Directivity Sensor freq response
Housing radiation
Challenges with structural excitation
Accessibility Mass loading
Sensor freq response
Housing radiation
Reproducability
Questions?