Physical and numerical modelling of extreme wave conditions

This paper presents the results of an experimental and numerical investigation into the generation of realistic model scale extreme waves for survivability testing of offshore structures. The objective of this investigation was to develop a numerical method to accurately model the maximum wave height (Hmax) and wave spectrum of a realistic focused wave group that was embedded into an irregular sea state. The sea state selected for this investigation was based on extreme conditions recorded during a Tropical Cyclone. The sea state was experimentally modelled using NewWave theory and was subsequently replicated in a computational fluid dynamics (CFD) numerical wave tank. The wave component amplitudes and phase angles were derived from the experimental data, which were then used to generate a polychromatic wave in CFD. The NewWave formula was then modified by applying an exponential function which intended to explicitly amplify the largest waves in the wavefield while applying minimal amplification to the remainder of the waves. This technique reduced the difference between the experimental and numerical Hmax while maintaining a level of spectral similarity. The methodologies presented in this paper are appropriate for modelling realistic extreme sea states for model scale survivability testing of offshore structures.