'Ringing' of offshore structures - observations and challenges to offshore wind
3. oktober 2011
Professor John Grue, Mechanics Division, Department of Mathematics, UiO:
'Ringing' of offshore structures - observations and challenges to offshore wind power extraction
SUMMARY: We review wave basin recordings of so-called ringing response observed on models for the Heidrun TLP and Draugen monopile, revealed during their construction phase in 1993. Both platforms had to be reinforced in order to keep an acceptable safety level. We also review perturbation methods of third order loads and their comparison to experiments. Of particular relevance to columns intended to support wind turbines in shallow waters, is a data set for the Draugen monopile made available by Saga Petroleum. This shows the presence of a secondary load cycle for wave slope down to 0.18 and wavenumber times the diameter of 0.22, which is a cause of the 'ringing-load', and may contribute to fatigue. Accurate predictions of the force governed by gravity effects are lacking.
Location: 'Foredragssalen', Geophysical Institute, UiB.
Reference: Grue and Huseby, Higher-harmonic wave forces and ringing of vertical cylinders. Applied Ocean Research (2002), 24:203-214