A N 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-Jensen 1*, Sergey Sorokin et al 2 1 Minus10dB Stokrosevej 29, 8330 Beder, Denmark 2 Department of Mechanical Engineering, Aalborg University Pontoppidanstraede 101, Aalborg East, DK 9220, Denmark RASD July 20101

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 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 20103

Background RASD July Red: Motor spectrum Blue: impact spectrum Varying speed drive Operating range: 20 to 60 Hz shaftspeed Example: 38 Hz

Pipe with highly damped termination RASD July 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 Pipe with highly damped termination Effect of damping Undamped Damped

Beam with reflecting termination RASD July Måling og analyse i 6 frihedsgrader

Theory: Boundary equations RASD July 20108

Experimental Insertion Loss RASD July , 2 and 1 blocks3: Heavy, light, medium blocks

RASD July Comparison Insertion Loss

Background 6 Degree of freedom measurement RASD July 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 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 – verticalxx – bending horizontal plane – Y – horizontalyy- bending vertical plane – Z – longitudinalzz –torsion longitudinal

RASD July Setup7: 0 blocks - 3 block1 47 g

RASD July Setup7: 0 bloks - 3 block5 203 g

RASD July 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