Theory 27/Offshore & Marine Engineering
Riser Vibration Locks On
The claim
Vortex-induced vibration of a riser becomes large when the ratio of shedding frequency to natural frequency approaches one, so current speed matters only through that ratio.
01Mechanism
Lock-in occurs when shedding synchronises with structural motion; outside the ratio, the response is small regardless of current.
02Predictions
- P1Response should peak at the ratio.
- P2Current speed alone should mispredict.
03Refutation
Response tracking current speed would remove the lock-in.