Dynamic Non-Linear Analysis of Offshore Jacket Type Platforms Under Extreme Wave Loads

Abstract

Regular wave theories such as Airy and 5th order Stokes are widely employed to compute wave loads on offshore platforms. These deterministic approaches are based on certain wave heights and frequencies, so, it does not suitably account for the randomness of the sea state. The most accurate methods for estimating extreme responses are based on time domain but they need long duration’s storm inputs and are computationally very time consuming. NewWave theory offers a different time-domain approach for the extreme response evaluation. By constraining a NewWave with a pre-determined height within a completely random background Constrained NewWave is generated. Constrained NewWave allows for the easy and efficient evaluation of extreme response statistics; achievable without the need to simulate many hours of real time random seas. In the present study the extreme response of a Jacket offshore platform has been evaluated using a 5th order Stokes wave; long duration random reproduction of the sea surface; and a Constrained NewWave method. In general, it has been found that the Constrained NewWave method provides reasonably accurate results, as compared to those from long duration random reproduction of the sea surface, with significantly lower computational time.