For offshore structures the common design procedure against failure is to expose the structure to a range of regular waves whose heights and periods are detemined from the long-term probability distribution of the waveheights and their associated periods at the side. However, in reality these structures are exposed to random wave-induced forces in the ocean environment, and hence it is inherently much more satisfactory to account for the randomness of the loading by establishing the probabilistic properties of the loading and the resulting responses. The major obstacle is the nonlinearity of the drag component of Morison's wave loading which results in non-Gaussian distributions for both loading and response. In this paper, progress made to data towards a systematic probabilistic analysis of fixed jacket-type offshore structures will be reviewed. Concluding remarks: a) it has been shown that the probalistic approach has many advantages over the deterministic approach; b) the short-term probability distribution of the nonlinear Morison loading is of Pierson-Holmes (P-H) type and is fully expressed by its first four moments; c) due to the linear nature of the relationship between response and loading for fixed jacket-type quasi-static offshore structures, the short-term probability distribution of response is also a Person-Holmes type and hence, subject to certain restrictions, is fully defined by its 2nd and 4th statistical moments; d) due to excessive computational effort, the computer model developed by Burrows (1983) for the moments of response can only be applied to structures where loading can be idealized to a low number of loads (40). Other coorelations in the model have led to significant reductions in run-time, therefore the number of nodal loads can be increased to about 85 and 2oo; e) the long term distribution of peaks, needed for fatigue analysis, and the distribution of the extreme value during the service life of the structure, needed for failure analysis, can be obtained by convoluting their corresponding short-term distributions.
A review of the probabilistic description of Morison wave loading and response of fixed offshore structures
Überblick über die probabilistische Beschreibung der Morison-Wellenlast und das dynamische Verhalten von fixierten Offshore-Strukturen
Journal of Fluids and Structures ; 9 , 6 ; 585-616
1995
32 Seiten, 14 Bilder, 49 Quellen
Aufsatz (Zeitschrift)
Englisch
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