Wave-induced loads on fixed offshore structures: An assessment of ``wave-by-wave`` load variability and bias
- Shell Research, Rijswijk (Netherlands)
A theory is presented to estimate the characteristics of wave-loads on fixed offshore structures given the occurrence of a maximum of surface elevation time-series at some sensor location. The theory assumes a random Gaussian ocean environment, together with mixed inertia and drag loading defined according to the Morison equation. The analysis is based on the statistics of a Gaussian process near an extreme excursion of a different but related Gaussian process. The resulting software is used to explore the influence of wave field directionality (spreading) and sensor location on expected wave loads and their variability. Comparisons of theory with full-scale offshore measurements at the Tern structure in the northern North Sea indicate good agreement. It is demonstrated further that the standard interpretation of spreading as solely a velocity reduction factor in a unidirectional wave force calculation may not account correctly for the reduction in peak drag force on a fixed structure in spread seas. The extent of the inaccuracy is a function of structural dimensions; in general broadside loads are overpredicted and end-on loads slightly underpredicted. A set of calibration curves is included with which to estimate adjusted spreading values for use with standard fluid loading packages, which enables the effects of directional spreading to be estimated realistically.
- OSTI ID:
- 449716
- Report Number(s):
- CONF-9606279--; ISBN 0-7918-1490-4
- Country of Publication:
- United States
- Language:
- English
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