Abstract

Surface water waves are a dominant feature of most marine environments, including both deep-water offshore and shallow-water coastal locations. Their description forms the basis of numerous environmental models and the loads they impart dictate the design and safe operation of all manner of marine structures and vessels. Within severe storms, the occurrence of extreme waves has long been recognised and our ability (or inability) to model them the subject of much research. In recent years attention has been focused on the most extreme waves; the occurrence of so-called freak or rogue waves representing events that lie outside accepted statistical predictions.

The seminar will present the results of a new laboratory study investigating the existence of these extreme events and will outline new modelling procedures capable of describing the evolution of abnormally large waves. These models allow deterministic engineering calculations and also provide guidance as to those sea states in which unexpectedly large waves may occur. The key factors are found to be the nonlinearity (or steepness) of the sea state, its directional spread and the underlying spectral bandwidth. Confirmation of the importance of these effects is provided by laboratory observations of both large individual wave events and long random wave simulations. The seminar will conclude by considering the practical implications of these waves for both fixed and floating structures, including evidence of unexpectedly large loads, the occurrence of wave impacts and green water inundation.