CABLE VIBRATION
The analysis models take the site specific, main system parameters, including the cable properties, the cable protection system design, and the monopile dimensions into account.
FORCED SINUSOIDAL EXCITATION STUDY
The forced sinusoidal excitation study applies a sinusoidal displacement-time history to the hang-off deck (to which the cable is fixed). A range of displacement magnitudes, directions, and frequencies are investigated.
Specialised post-processing software enables plots of estimated fatigue damage as a function of excitation frequency and residual cable tension. This robust analytical approach for determining the free hanging cable resonant frequencies is superior to a typical ‘eigenvalue analysis’ which does not consider that the hang-off deck is moving.
FOUNDATION FATIGUE ANALYSIS The foundation fatigue analysis provides the hang-off deck displacement-time histories resulting in the full vibration induced fatigue life assessments. These would cover all anticipated operational conditions at the wind farm.
The simulations are post-processed using the Rainflow count algorithm, and BPP- Cables cable stress analysis tools. The output is an estimated cable fatigue life for all the metallic components of the cable.
SENSITIVITY STUDIES
Sensitivity studies should be employed to assist in the interpretation of the main effects that different modelling parameters have on the predicted fatigue life.
CONCLUSIONS
The conclusions from all the analyses performed show that vibration in free- hanging cables needs to be addressed and studied to minimise the risks.
Mitigation measures may include changes and/or additions of bespoke hang-off stiffeners.
Richard Langdon & Adrien Montfort BPP-Cables
Click to view more info = Click to view video
www.windenergynetwork.co.uk
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