CHARACTERISATION OF VIBRATORY, PULSATION AND NOISE SOURCES

Transcription

1 CHARACTERISATION OF VIBRATORY, PULSATION AND NOISE SOURCES Goran Pavić INSA Lyon, France CAV April /20

2 scope Objectives: predict the transmission source surroundings allow meaningful specs formulation supplier troubleshoot the causes of excessive levels supplier Difficulty: source excitation depends assembler on its environment! sub Challenge: supplier independent source characterisation. NVH design Problem: no norms / standards! sub sub supplier supplier Industrial techniques: Academic techniques: sound power holography supplier vibration level inverse BEM p-p pulsations beamforming CAV April /20

3 source needs a double descriptor source resistance R S open-loop voltage V S load resistance R L Mechanical / acoustical: blocked excitation E coupled circuit velocity current V c i b c = source impedance Z S + receiver impedance Z R Source coupled impedance: 2 descriptors: c driving potential coupling capacity Receiver multiple simple coupling: 1 descriptor: coupling capacity Z = Z + S V c = E b Z c -1 Z R CAV April /20

4 vibration blocked excitation F b? source impedance Z S? Difficulties: forces and moments translations and rotations multiple coupling points. = wrench = screw -1 How to get F b? V c = Z c F b How to get Z S? Z c = Z S Z R The coupling (operational) forces transmitted to any surroundings of impedance Z will read: F c = Z( Z S + Z) 1 F b To make this work: a convenient calibration receiver is needed! CAV April /20

5 smart receiver Solid block 6-DOF screw sensor 6-DOF wrench sensor F b = Z c V c Z S = Z c Z R Fit 6 simple sensors! Source coupled Excitation by 6 external forces Measurement in running conditions vibration characterisation: smart receiver coupling point source Source removed Excitation by 6 external forces: The soft block mount measures solid both block source source descriptors foot in all DoF CAV April /20

6 equivalent force approach Example: 4 connection points equivalent force: resultant of interface wrenches! equivalent vibration screw: characterisation: mean of interface screws! 4 wrenches (24 1 vector) eq. force (6 1 vector) = equivalent force = impedance (6 6 matrix) eq. screw (6 1 vector) 4 screws (24 1 vector) impedance (24 24 matrix) CAV April /20

7 measurement practice water pump compressor hydromotor CAV April /20

8 equivalent force application: electro-pump characterisation vertical prediction lateral CAV April /20

9 equivalent force application: compressor Source characterisation lateral 3D force sensor blocked charact. operat. measured operat. predicted vertical CAV April /20

10 insertion of resilient mounts Blocked forces lateral Operational forces: bolted mounts vertical CAV April /20

11 pulsation blocked pressure impedance Difficulties: impedance measured with the source operating blocked pressure impossible to measure directly 1 1.1m 2 CAV April /20

12 multiple load technique blocked source pressure p S coupled pressure p c P c = Z S Z + L Z L P 2 different loads: Z L1, Z L2 S pulsation characterisation: multiple load CAV April /20

13 laboratory measurement: gear pump 5b, 600 rpm (gear meshing: 150 Hz) 10b, 1500 rpm (gear meshing: 375 Hz) measured predicted CAV April /20

14 industrial measurement: vane pump 3b, 1000 rpm measured predicted 5b, 2000 rpm 7b, 3000 rpm CAV April /20

15 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 P b identify impedance of idle source space Z S source space receiver space CAV April /20

16 dummy source: principle Q k Q 2 Q K Q 1 airborne noise characterisation: dummy source 1. build a simple dummy similar to original source 2. fit the dummy with K small drivers Source model: applicable to any receiver environment! 3. measure source noise in N control points 4. replace the source by the dummy 5. establish TRF drivers / control points P (N 1) T (N K) 6. compute driver strengths Q out of P = T Q Q (K 1) CAV April /20

17 dummy source: demonstration 200 Hz 1000 Hz CAV April /20

18 dummy source: vibrating box Semi-anechoic space transfer functions analytical computation CAV April /20

19 dummy source: excavator CAV April /20

20 equivalent source approach Ω The normal vibration velocity can be measured by an accelerometer array. Ω 0 airborne noise characterisation: equivalent source v n real source set of monopoles reproduce normal boundary velocity diffraction disregarded (small sources) CAV April /20

21 application to a loudspeaker cabinet Field computed using: equivalent source method mirror image principle measured predicted CAV April /20

22 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 /20

23 CAV April /20

24 how to define surface impedance? expand into N eigenfunctions original field. In either case: p, v : N 1 vector Z : N N matrix p = Z v discretize into N patches CAV April /20

25 coupling using patches: examples 142 eigenfunctions 62 patches 142 eigenfunctions 62 patches patch size < λ/3 CAV April /20

26 calibration block impedance steel block, 70 kg L 400mm W 280m H 80mm CAV April /20