overall velocity level at V2 – 4 un

overall velocity level at V2 – 4 under Case 3 – 6 is 2.6 dB, 2.7 dB, 9.2 dB and 10.1 dB respectively. The vibration of flange is also reduced owing to the dissipation of transmitted energy by the damping material bonded on the web, although the flange is not covered by damping patches. From the comparison of Case 3 and 4, it is found that 1.0 mm thick damping layer has a similar reduction to the overall velocity level and the thin constraining layer can eliminate the vibration amplification at high frequencies which does not dominate the velocity. Case 5 with thicker constraining layer has a further reduction to the velocity level in the whole frequency range compared with Case 4. Case 6 achieves the highest reduction to the velocity level, but the total thickness of CLD is twice of Case 5.5.2.2 Noise MitigationThe measured waveforms of the normalised sound pressure