Experimental Investigation of Extreme Waves - Comparison With Analytical Models and CFD

Abstract

The study of extreme sea states and predictions of associated wave kinematics form the basis for the design and re-assessment of offshore structures. This paper compares analytical and numerical models with scaled wave flume experiments that were carried out at the University of Aberdeen, UK, to measure surface elevation profiles and the velocity beneath extreme crests. Focused wave groups representing the extreme events were generated at a given point in space and time. The input amplitude spectra for the flap-type wave maker were derived using Tromans’ NewWave theory which corresponds to the autocorrelation of the surface spectrum. The sea states in the experiments were chosen to represent extreme waves in the North Sea and Australian waters. The effects of nonlinear wave-wave interactions, which shift the actual focus point and focus time from the linear position, are analyzed and discussed. The results from second order NewWave theory and higher order stream function waves are compared with the experimental results to evaluate the validity range of these analytical models. CFD simulations are also conducted and the results are compared with the experimental values.