characterisation of vibratory, pulsation and noise … · cav april 2017 0/20 characterisation of...
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CAV April 2017 0/20
CHARACTERISATION OF VIBRATORY,PULSATION AND NOISE SOURCES
Goran PavićINSA Lyon, France
CAV April 2017 1/20
scope
Objectives: predict the transmission source → surroundings allow meaningful specs formulation troubleshoot the causes of excessive levelsDifficulty: source excitation depends on its environment !Challenge: independent source characterisation.Problem: no norms / standards !
Industrial techniques: sound power vibration level p-p pulsations
Academic techniques: holography inverse BEM beamforming
assemblerNVH design
supplier
supplier supplier
subsuppliersub
supplier
subsupplier
CAV April 2017 2/20
source needs a double descriptor
circuit current ic
open-loop voltage VS
load resistance RL
=
source resistance RS
+
Source → 2 descriptors: driving potential coupling capacity
Receiver → 1 descriptor: coupling capacity
Mechanical / acoustical:coupled velocity Vc
blocked excitation Eb
receiver impedance ZRsource impedance ZS
coupled impedance: RSc ZZZ +=
simplemultiple Vc = Eb
Zccoupling: -1
CAV April 2017 3/20
vibration
blocked excitation Fb ? source impedance ZS ?
Difficulties: forces and moments translations and rotations multiple coupling points.
=wrench
=screw
How to get Fb ? Vc FbZc-1= How to get ZS ? Zc ZS ZR= −–
To make this work: a convenient calibration receiver is needed !
The coupling (operational) forces transmitted to any surroundings of impedance Z will read: bSc FZZZF 1)( −+=
CAV April 2017 4/20
smart receiver
Fb = ZcVc ZS = Zc – ZR Solid block 6-DOF screw sensor 6-DOF wrench sensor
Fit 6 simple sensors !
Excitation by 6 external forcesMeasurement in running conditions
Source coupled
Source removedExcitation by 6 external forces:
The block measures both source descriptors in all DoF
coupling pointvibration characterisation:
smart receiver
soft mount source footsolid block
source
CAV April 2017 5/20
equivalent force approach
Example:4 connection points
=4 wrenches(24×1 vector)
impedance (24×24 matrix)
4 screws(24×1 vector)
eq. force(6×1 vector)
impedance (6×6 matrix)
eq. screw(6×1 vector)=
equivalent force: resultant of interface wrenches !equivalent screw: mean of interface screws!vibration characterisation:
equivalent force
CAV April 2017 6/20
measurement practice
water pumpcompressorhydromotor
CAV April 2017 7/20
equivalent force application: electro-pump
characterisation
prediction
vertical
lateral
CAV April 2017 8/20
equivalent force application: compressor
3D force sensor
Source characterisation
blocked charact.operat. measuredoperat. predicted
lateral
verticalblocked charact.operat. measuredoperat. predicted
CAV April 2017 9/20
insertion of resilient mounts
Blocked forces
boltedmounts
Operational forces:
lateral
vertical
CAV April 2017 10/20
pulsation
Difficulties: impedance measured with the source operating blocked pressure impossible to measure directly
blocked pressure impedance
1.1m1 2
CAV April 2017 11/20
multiple load technique
pulsation characterisation:multiple load
coupled pressure pc
SLS
Lc P
ZZZP+
=
blocked source pressure pS
≥2 different loads: ZL1, ZL2…
CAV April 2017 12/20
laboratory measurement: gear pump
measuredpredicted
5b, 600 rpm(gear meshing: 150 Hz)
10b, 1500 rpm(gear meshing: 375 Hz)
CAV April 2017 13/20
industrial measurement: vane pump
measuredpredicted
5b, 2000 rpm
3b, 1000 rpm
7b, 3000 rpm
CAV April 2017 14/20
airborne noise
blocked pressure impedance
Difficulties: source coupled to receiver through a surface physical surface of source extremely complex source power depends on the surroundings.
define an interface surface S. separate into source space and receiver space identify blocked pressure of running source Pb identify impedance of idle source space ZS
source space receiver space
CAV April 2017 15/20
dummy source: principle
1. build a simple dummy similar to original source2. fit the dummy with K small drivers3. measure source noise in N control points4. replace the source by the dummy5. establish TRF drivers / control points
P (N×1)
T (N×K)6. compute driver strengths Q out of P = T Q Q (K×1)
Source model: applicable to any receiver environment !
Q2
Q1
…Qk
QK
airborne noise characterisation:dummy source
CAV April 2017 16/20
dummy source: demonstration
200 Hz
1000 Hz
CAV April 2017 17/20
dummy source: vibrating box
Semi-anechoic spacetransfer functions →
analytical computation
CAV April 2017 18/20
dummy source: excavator
CAV April 2017 19/20
equivalent source approach
Ω0
Ω
vn
real source → set of monopoles reproduce normal boundary velocity diffraction disregarded (small
sources)
The normal vibration velocity can be measured by an accelerometer array.
airborne noise characterisation:equivalent source
CAV April 2017 20/20
Field computed using: equivalent source method mirror image principle
application to a loudspeaker cabinet
measuredpredicted
CAV April 2017 21/20
summary
source characterisation methods → industrial applications dual source descriptor → blocked excitation and impedance best way to characterise a source → measurement unified approach to vibration, pulsation and noise
vibration: smart receiver **** equivalent force method ***
pulsation: multi-load method **
noise: dummy source method *** equivalent source approach ** coupling surface method *****
* simple ***** difficult
CAV April 2017 22/20
CAV April 2017 23/20
how to define surface impedance ?
original field
expand into N eigenfunctions
….
discretize into N patchesIn either case:p, v : N×1 vector
Z : N×N matrix
p = Z v
CAV April 2017 24/20
coupling using patches: examples
62 patches 142 eigenfunctions62 patches
142 eigenfunctions
patch size < λ/3
CAV April 2017 25/20
steel block, 70 kgL 400mmW 280mH 80mm
calibration block impedance
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