Wave-forces on structures in deep water may be estimated by Morison's equation and linear wave theory. However, for shallow water waves at or near to breaking, there is difficulty in deciding the correct wave theory to use to predict particle velocities and accelerations, and crest heights. Also, near to breaking it is necessary to include the contribution of impact forces. The evaluation of such impact forces has been investigated elsewhere; here the method is generalised by dimensional analysis to deal with post-breaking waves. Linear interpolation was found to be satisfactory to deal with waves very close to breaking. The probability of high waves is normally assessed by extrapolation of the probability of smaller waves. However breaking will curtail the probability of larger waves, depending upon their period, so the conventional extrapolation is unduly conservative. The preliminary assessment of a realistic design case suggests that design total forces and moments (for a typical 50 year return period) are substantially reduced when probability curtailment is considered. The proper design methodology for quantity production offshore wind turbine structures would be to balance investment cost against failure (or insurance) cost.
Design wave forces for offshore structures
Konstruktionswellenkraefte fuer Offshore-Bauten
1982
8 Seiten, 6 Bilder, 27 Quellen
Conference paper
English
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