Probabilistic description of the (quasi-static or dynamic) response of offshore structures to random wave and current loading, may require the estimation of the first four moments of its probability density function. The existing models for determination of these moments are computationally very demanding; Consequently, the distributed wave loading on the structure must be idealised by a relatively small number of point loads, which is not adequate for representation of the continuous loading on (complex) structures with many structural elements. The application of random sampling technique in the derivation of these moments can potentially lead to significant reductions in computational effort so that the loading can be idealised more realistically by a large number of point loads.
For an offshore structure, wind, wave, current and gravitational forces are all important sources of loading. The dominant load, however, is normally due to wind-generated waves. Therefore, the accurate estimation of the response of the structure to wave-induced loading is essential for design purposes. An offshore structure must be designed so that the probability of any response exceeding its assumed failure threshold (the risk of first-excursion failure) during the service life of the structure be acceptably small. In addition, the accumulated fatigue damage due to stress reversals associated with the passage of each wave must not cause failure. For some applications, a third criterion is to reduce the down-time period to an acceptable minimum (Inglis et al, 1985). To meet the design criteria, the response of the structure to wave loading must be established. This can be achieved by deterministic or probabilistic methods. In the deterministic method, the structure is considered to be exposed to a range of regular waves whose heights and periods are determined from the long-term probability distribution of the waveheights and their associated periods at the site.
