1

AN INVESTIGATION OF A PERIODIC STRUCTURE TO SUPPRESS THE TRANSMISSION OF ENERGY IN AN ELASTIC TUBE, AND EXPERIMENTAL 6 DOF TECHNIQUES TO DETECT IT

 Ole Holst-Jensen1*, Sergey Sorokin et al2

 1Minus10dBStokrosevej 29, 8330 Beder, Denmark

ole.holst@minus10db.dk 

2Department of Mechanical Engineering, Aalborg UniversityPontoppidanstraede 101, Aalborg East, DK 9220, Denmark

svs@ime.aau.dk

RASD July 2010

Periodic beam structures• Organisation: Makunet 

– Machine acoustic network– Major Danish industrial partners– Institute of Mechanical Engineering at Aalborg 

University Denmark

• Purpose of this project– Use periodic structures to control pipe vibration in 

pipes and plates– Develop engineering tools for the design of periodic 

structures• Theoretical optimisation tool• Measurement tool

RASD July 2010 2

• Background• Experimental setups

• Pipe with highly damped termination• Beam with reflecting termination

• Theory• Results with damped termination• 6 degree of freedom experimental 

technique • Application to beam with reflecting 

termination• Conclusion

Transmission control

RASD July 2010 3

4

Background

RASD July 2010

0 40 80 120 160 200 240 280 320 360 400[Hz]

300u1m3m

10m30m0.10.3

1[rad/s²]

PLF - z_rotation (Real) \ FFTPLF - z_rotation Mark 1 (Real) \ FFT

Red: Motor spectrum

Blue: impact spectrum

Varying speed driveOperating range:20 to 60 Hz shaftspeedExample: 38 Hz

Pipe with highly damped termination

RASD July 2010 5

• Tube ø 34 / 27, steel• Length: 4000 mm• Blocks: 75 x 75 mm h: 220 mm• Block weight: 4000 g• Damping stiffening: 19 x 19 mm

RASD July 2010 6

Pipe with highly damped terminationEffect of damping

Frequency Response H1(Signal 5,Signal 1) - Mark 1 (Magnitude)FRF : 4m tube 0 damp o blk : Input : FFT Analyzer

0 200 400 600 800 1k 1.2k 1.4k 1.6k 1.8k 2k

100m

300m

1

3

10

30

100

300

[Hz]

[(m/s²)/N] Frequency Response H1(Signal 5,Signal 1) - Mark 1 (Magnitude)FRF : 4m tube 0 damp o blk : Input : FFT Analyzer

0 200 400 600 800 1k 1.2k 1.4k 1.6k 1.8k 2k

100m

300m

1

3

10

30

100

300

[Hz]

[(m/s²)/N]

Frequency Response H1(Signal 5,Signal 1) - Mark 2 (Magnitude)FRF : 4m tube w damp 0blk : Input : FFT Analyzer

0 200 400 600 800 1k 1.2k 1.4k 1.6k 1.8k 2k

100m

300m

1

3

10

30

100

300

[Hz]

[(m/s²)/N] Frequency Response H1(Signal 5,Signal 1) - Mark 2 (Magnitude)FRF : 4m tube w damp 0blk : Input : FFT Analyzer

0 200 400 600 800 1k 1.2k 1.4k 1.6k 1.8k 2k

100m

300m

1

3

10

30

100

300

[Hz]

[(m/s²)/N]

Undamped

Damped

Beam with reflecting termination

RASD July 2010 7

• Måling og analyse i 6 frihedsgrader

8

Theory: Boundary equations

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RASD July 2010

Experimental Insertion Loss

PeritubeInsertion Loss: 10*log10({no blocks}/{3 blocks})

-30

-20

-10

0

10

20

30

40

50

0 200 400 600 800 1000 1200 1400 1600 1800 2000

f Hz

IL d

B

IL 0blk 3blk IL 0blk 2blk IL 0blk 1 blk

RASD July 2010 9

PeritubeInsertion Loss: 10*log10({no blocks}/{3 blocks})

-30

-20

-10

0

10

20

30

40

50

0 200 400 600 800 1000 1200 1400 1600 1800 2000

f Hz

IL d

B

IL 0blk 3blk IL 0blk 3 blk01 IL 0blk 3blk02

3, 2 and 1 blocks 3: Heavy, light, medium blocks

RASD July 2010 10

Comparison Insertion Loss

11

Background6 Degree of freedom measurement

RASD July 2010

•Simple method of separating modes •Torsional modes are  often not recognized in simple measurements•Evolution of vibration measurements:

• One axis• Three axis• 6 axis

•Mulitchannel digtal techniques makes realtime 6 DOF possible

Test setup

RASD July 2010 12

• Comparison of plain beam and beam with three blocks• Two types of blocks

– Aluminium 10 x 10 x 100mm beam with thread– Block 1:   47 g weight on top– Block 5: 156 g weight on top

• Axes – X – vertical xx – bending horizontal plane– Y – horizontal yy- bending vertical plane– Z – longitudinal zz –torsion longitudinal

RASD July 2010 13

Setup7: 0 blocks - 3 block1 47 g

0 50 100 150 200 250 300 350 400 450 500[Hz]

2u

10u

50u

200u

1m

5m20m

[m/s²]

PLF - x_ave (Magnitude) \ FFT \ W2 0blkPLF - x_ave Mark 1 (Magnitude) \ FFT \ W2 3blk1 glue 100mm S:500mm

0 50 100 150 200 250 300 350 400 450 500[Hz]

2u

10u

50u

200u

1m

5m20m

[m/s²]

PLF - y_ave (Magnitude) \ FFT \ PLF - y_ave Mark 1 (Magnitude) \ FFT \

0 50 100 150 200 250 300 350 400 450 500[Hz]

2u

10u

50u

200u

1m

5m20m

[m/s²]

PLF - z_ave (Magnitude) \ FFTPLF - z_ave Mark 1 (Magnitude) \ FFT

0 50 100 150 200 250 300 350 400 450 500[Hz]

5u

20u

100u

500u

2m

10m

50m[rad/s²]

PLF - x_rotation (Real) \ FFTPLF - x_rotation Mark 1 (Real) \ FFT

0 50 100 150 200 250 300 350 400 450 500[Hz]

5u

20u

100u

500u

2m

10m

50m[rad/s²]

PLF - y_rotation (Magnitude) \ FFTPLF - y_rotation Mark 1 (Magnitude) \ FFT

0 50 100 150 200 250 300 350 400 450 500[Hz]

5u

20u

100u

500u

2m

10m

50m[rad/s²]

PLF - z_rotation (Real) \ FFTPLF - z_rotation Mark 1 (Real) \ FFT

RASD July 2010 14

Setup7: 0 bloks - 3 block5 203 g

0 50 100 150 200 250 300 350 400 450 500[Hz]

2u

10u

50u

200u

1m

5m20m

[m/s²]

PLF - x_ave (Magnitude) \ FFT \ W2 0blkPLF - x_ave Mark 1 (Magnitude) \ FFT \ W2 3blk5 glue loose 100mm S:500mm

0 50 100 150 200 250 300 350 400 450 500[Hz]

2u

10u

50u

200u

1m

5m20m

[m/s²]

PLF - y_ave (Magnitude) \ FFT \ PLF - y_ave Mark 1 (Magnitude) \ FFT \

0 50 100 150 200 250 300 350 400 450 500[Hz]

2u

10u

50u

200u

1m

5m20m

[m/s²]

PLF - z_ave (Magnitude) \ FFTPLF - z_ave Mark 1 (Magnitude) \ FFT

0 50 100 150 200 250 300 350 400 450 500[Hz]

5u

20u

100u

500u

2m

10m

50m[rad/s²]

PLF - x_rotation (Real) \ FFTPLF - x_rotation Mark 1 (Real) \ FFT

0 50 100 150 200 250 300 350 400 450 500[Hz]

5u

20u

100u

500u

2m

10m

50m[rad/s²]

PLF - y_rotation (Magnitude) \ FFTPLF - y_rotation Mark 1 (Magnitude) \ FFT

0 50 100 150 200 250 300 350 400 450 500[Hz]

5u

20u

100u

500u

2m

10m

50m[rad/s²]

PLF - z_rotation (Real) \ FFTPLF - z_rotation Mark 1 (Real) \ FFT

RASD July 2010 15

Conclusions• Pipe with highly damped termination

– Eigenfrequencies match theory– Insertion loss show agreement between theory and experiment with stop 

bands, when using energy and acceleration levels• Beam with reflecting termination

– 6 DOF measurement on rigid body termination can separate modes– Eigenmodes are suppressed

• Further investigations: – Parametric studies– Application to industrial setting