Generation of rogue waves at model scale

Abstract

The study of rogue waves is becoming increasingly important, as the offshore oil and gas, as well as renewable energy industries, expand. The unpredictability of such disastrous waves poses a significant risk to floating and fixed structures, making it necessary to develop methods capable of recreating rogue waves for model testing purposes. In this paper, an investigation into the useability of the NewWave theory, a theoretical formula for producing focused waves, was conducted in model test facilities with a wavemaker. The numerical modelling of rogue waves was performed using MATLAB codes developed to create several types of wave packets. The success of the numerical generation of design rogue waves was dependent on the number of wave components used during construction such that a suitable rogue wave (Hmax/Hs > 2.0) could be created using 400 or more components. It was found that the NewWave technique could construct and physically generate design rogue waves within a close range of the predicted height provided the main wavemaker stroke was smooth enough (at around 0.8 s trough-crest for the tested model scale). The measured rogue waves were found to be complex; highly non-linear in amplitude with the behaviour of up to the 3rd order. Furthermore, it was observed that rogue waves, created based on a 100-year sea state, were very similar to the New Year Wave confirming that such extreme waves, approximately 25–27 m high at full scale, can indeed occur in severe sea states.