Blocked Force Determination Explanation and Examplesvac.engr.uky.edu/.../01_VAC_Web_Meeting_Blocked_Force_Analysis.pdf · Blocked Force Determination • 14 blocked force input points

Blocked Force DeterminationExplanation and ExamplesVibro-Acoustics Consortium Web Meeting

University of Kentucky

Vibro-Acoustics Consortium

April 16, 2020


Overview

• Transfer Functions and Superposition

• What are Blocked Forces?

• Similar Approaches

• Example: Small Compressor attached to Structure

• Example: Engine Cover attached to Plate

• Example: Acoustic Duct

• Future Work

2

Vibro-Acoustics Consortium 3

Transfer Functions

𝐹

𝑣

𝑣 𝐻 𝐹

𝐹𝑣 𝐻 𝐹


Linear Systems and Superposition

𝐹

𝑣

𝐹 𝐹

𝑣 𝑣 𝑣 𝑣 𝑣

𝑣 𝐻 𝐹 𝐻 𝐹 𝐻 𝐹𝑣 𝐻 𝐹 𝐻 𝐹 𝐻 𝐹

𝑣 𝐻 𝐹 𝐻 𝐹 𝐻 𝐹⋮

𝑣 𝐻 𝐹


Overview







• Future Work

5


What Are Blocked Forces?

𝐹 𝑇 𝜔𝑣

𝑣


Infinitely Stiff Bed Plate

7


𝜔𝑣 𝐹 𝑇

𝐹



𝜔𝑣 𝐹 𝑇

𝐹

𝑣 0



𝐹

𝑣

Input Forces Removed



𝐹

Blocked forces are independent of the receiver.


Blocked Force Analysis

𝐹

𝑣


Overview







• Future Work

12


Classical Transfer Path Analysis

𝐹

𝑣


Pseudo Force Analysis

𝐹

𝑣


Force Identification Approaches

Measured Transfer FunctionsSource is “off”

Indicator ResponsesSource is “on”

Unknown Blocked ForcesInverse least squares


Summary

Method Transfer Function Measurement

Inverse Force Locations

Can Inverse Forces be Used with Modified Receiver?

Classical TPA Remove Source Interface between Source and Receiver

If Source is well Isolated

Blocked Forces Include Source Interface between Source and Receiver

Yes

Pseudo Forces Include Source User Decided Maybe


Overview







• Future Work

17


Source and Test Structure

Indicator response Target response

1.6 mm Steel

Air CompressorCompressor

0.6 m x 0.6 m

• Classical TPA, pseudo force and blocked force methods are used to predict target response.

18


Compressor

Blocked Force Locations


Input Force Locations

Compressor 20.5 cm 9 cm

22.5 cm

29.5 cm

10 cm

3.5 cm

10 cmClassical TPA Blocked Forces

• For Classical TPA, transfer functions are measured with compressor removed from steel plate.


Input Force Locations

001 002003

004 005 006

X

Y

Z

Compressor

• For pseudo force method, 6 input force points should capture all 3 translational and 3 rotational motions of compressor.


Acceleration Target Comparison

-80

-60

-40

-20

0

20

4012

.5 16 20 2531

.5 40 50 63 80 100

125

160

200

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

Acce

lera

tion

(dB)

Frequency (Hz)

MeasurementClassical TPA8 Blocked Forces4 Blocked ForcesPseudo Forces


Baseline Modified

Modification Added Mass

Compressor

Steel Plate

Steel Frame

Compressor

5 kg Mass

23


Measurement Case Target Comparison

24

-80

-60

-40

-20

0

20

4012

.5 16 20 2531

.5 40 50 63 80 100

125

160

200

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

Acce

lera

tion

(dB)

Frequency (Hz)

Measurement ModifiedMeasurement Baseline


Measurement Case Results Comparison

25

-80

-60

-40

-20

0

20

4012

.5 16 20 2531

.5 40 50 63 80 100

125

160

200

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

Acce

lera

tion

(dB)

Frequency (Hz)

Measurement Modified

Blocked Force Modified

Classical TPA Modified

Pseudo Force Modified


Recommendations

• A spacing (𝑠) of 𝑠 0.5𝜆 is recommended along an interface for plate and shell structures where 𝜆 is the bending wavelength. This spacing has been validated using FEM analyses.

26


Overview







• Future Work

27


Engine Cover

• Engine cover (receiver) is bolted on a plastic plate (source)

0.65 m

0.2 m

0.1 m

2.5 mm thick


Measurement Setup

Foam

Shaker

Engine Cover

Plastic Plate

• Electromagnetic shaker is used to excite plastic plate.• Assembled system is placed on foam to simulate free-free boundary

condition.


Blocked Force Determination

• 14 blocked force input points are chosen on the bolts in normal direction.• 21 indicator points are evenly spaced on engine cover.• 7 target points are chosen on engine cover

Blocked force input points

Target response points

101102103104105106107108

109

110 111 112 113 114


Correlated Single Target Comparison

-80

-60

-40

-20

0

20

0 500 1000 1500 2000

Acce

lera

tion

(dB)

Frequency (Hz)

MeasurementBlocked Force


Correlated Target Average Comparison

Average acceleration level of 7 target points is compared between measurement and blocked force prediction.

0.01

0.10

1.00

10.0050 63 80 10

012

516

020

025

031

540

050

063

080

010

0012

5016

0020

0025

0031

50

Acce

lera

tion

(m/s

2 )

Frequency (Hz)

Measurement14 Blocked Forces11 Blocked Forces8 Blocked Forces5 Blocked Forces2 Blocked Forces


• Phase is not included in the calculation.

Uncorrelated Blocked Force

𝑎 𝐻 𝐹


0.01

0.10

1.00

10.0050 63 80 10

012

516

020

025

031

540

050

063

080

010

0012

5016

0020

0025

0031

50

Acce

lera

tion

(m/s

2 )

Frequency (Hz)

Measurement14 Blocked Forces11 Blocked Forces8 Blocked Forces5 Blocked Forces2 Blocked Forces

Uncorrelated Target Average Comparison

34


Measurement Case Modification

• Cylinder shaped mass is glued on engine cover to reduce acceleration level.• The added mass is about 1/4 of the engine cover.• Can uncorrelated blocked forces be used to predict the effect of a modification?

35


Uncorrelated Averaged at Targets

0.01

0.10

1.00

10.00

50 63 80 100

125

160

200

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

Acce

lera

tion

(m/s

2 )

Frequency (Hz)

Measurement BaselineMeasurement Modified

0.01

0.10

1.00

10.00

50 63 80 100

125

160

200

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

Acce

lera

tion

(m/s

2 )

Frequency (Hz)

8 Blocked Forces Baseline8 Blocked Forces Modified

36


Recommendations

• A spacing (𝑠) of 𝑠 0.5𝜆 is recommended along an interface for plate and shell structures where 𝜆 is the bending wavelength. This spacing has been validated using FEM analyses.

• Once 𝑠 0.5𝜆 , it is recommended to use uncorrelated forces.

37


Overview







• Future Work

38


Acoustic Blocked Source Analysis

Transfer Functions

Output Response Pressure Volume Velocities - Acoustic Blocked Forces


Reconstructed Input Source Layer

0.1 m 0.1 m 0.2 m 0.2 m

Output Response Pressure Layers

40

• Input source layer has 6 reconstructed sources• Each output response layer has 6 indicators and 1 target.

Acoustic Duct

Source Room


Measurement Case Baseline Setup

0.7 m 0.7 m 1.2 m


Transfer Function Measurement

0.3 m

• Reciprocity method is used to calculate transfer function.• A reference microphone is placed 0.3 m away from the volume source

to calculate the volume velocity.

0.3 m 0.3 mPoint Source


Correlated Targets Comparison

30

40

50

60

70

80

90

100

110

50 63 80 100

125

160

200

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

4000

5000

6300

8000

Soun

d Pr

essu

re L

evel

(dB)

Frequency (Hz)

Measurement5 Blocked Sources3 Blocked Sources1 Blocked Sources


Uncorrelated Targets Comparison

30

40

50

60

70

80

90

100

110

50 63 80 100

125

160

200

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

4000

5000

6300

8000

Soun

d Pr

essu

re L

evel

(dB)

Frequency (Hz)

Measurement5 Blocked Sources3 Blocked Sources1 Blocked Sources


Modification Lined Duct

• A lined duct (5 cm fiberglass) is connected to the baseline case• Reconstructed acoustic blocked forces for baseline will be used to

predict sound pressure level for modification case

1 m


Correlated Targets Comparison

30

40

50

60

70

80

90

100

11050 63 80 10

012

516

020

025

031

540

050

063

080

010

0012

5016

0020

0025

0031

5040

0050

0063

0080

00

Soun

d Pr

essu

re L

evel

(dB)

Frequency (Hz)

BaselineModified5 Acoustic Blocked Sorces3 Acoustic Blocked Sorces1 Acoustic Blocked Sorces


Uncorrelated Targets Comparison

30

40

50

60

70

80

90

100

11050 63 80 10

012

516

020

025

031

540

050

063

080

010

0012

5016

0020

0025

0031

5040

0050

0063

0080

00

Soun

d Pr

essu

re L

evel

(dB)

Frequency (Hz)

BaselineModified5 Acoustic Blocked Sorces3 Acoustic Blocked Sorces1 Acoustic Blocked Sorces


Summary

• A spacing (𝑠) of 𝑠 0.5𝜆 is recommended along the cross-section where 𝜆 is the acoustic wavelength.

• Once 𝑠 0.5𝜆 , it is recommended to use uncorrelated acoustic sources.


Overview







• Future Work

49


Future Work

• Use response measurements for source diagnostics.

𝐹

𝑣

50


Future Work

𝑣

Machine Under Test

51


Future Work

• Blocked forces characterize a source with its isolators irrespective of the receiver substructure.

𝐹

𝑣

52


References

• Moorhouse, A. T., Elliot, A. S., and Evans, T. A., “In-situ Measurements of the Blocked Force of Structure-Borne Sound Sources,” Journal of Sound and Vibration, Vol. 325, No. 4-5, pp. 679-685 (2009).

• Lennström, D., Olsson, M., Wullends, F., and Nykänen, A., “Validation of the Blocked Force Method for Various Boundary Conditions for Automotive Source Characterization,” Applied Acoustics, Vol. 102, pp. 108-119 (2016).

• Chen, K. and Herrin, D. W., “Technical Note – Blocked Force Determination on Plate Structures using an Offset Interface,” Applied Acoustics, Vol. 158, Paper No. 107044 (2020).

• Chen, K., Herrin, D. W., and Baker, J. R., “Determination of Correlated and Uncorrelated Blocked Forces on an Engine Valve Cover,” Noise-Con 2019, San Diego, CA, August 26-28 (2019).

53

Documents

Blocked Force Determination Explanation and Examplesvac.engr.uky.edu/.../01_VAC_Web_Meeting_Blocked_Force_Analysis.pdf · Blocked Force Determination • 14 blocked force input points