Abstract: The exceedance probability of wave applied loading is a critical environmental inputs for the design/reassessment of marine structures. With attention often focused on structural reliability, and in some cases survivability, the largest loads arising at the smallest exceedance probabilities, said to be located in the tail of a distribution, are of primary interest. This seminar outlines a new method by which the tail of the loading distribution can be accurately estimated using the surface elevation profiles of a relatively small number of deterministic wave events. This avoids the need to explore the entire distribution using very long (and expensive) random wave simulations.
To achieve this, the nonlinear effects that underpins the evolution of the largest random waves are investigated using a large set of experimental data. Two primary nonlinear changes are identified: a nonlinear crest height amplification beyond second-order prediction and a downstream shift of the spatial wave envelope. Based upon these discoveries, a new method is proposed by which the tail of the crest height distribution can be defined using a relatively small number of deterministic wave events. The new approach allows both an extension of the distribution to smaller exceedance probabilities and a concentration on the largest most design relevant crest heights. This seminar demonstrates that the associated confidence intervals of the largest crest heights can also be accurately and efficiently defined. Having addressed the tail of a crest height distribution, attention is turned to wave-in-deck (WID) loads that arise from the waves with the largest crest heights. The important wave properties that affect the magnitude of the applied WID loads are identified using experimentally collected data. The relevant analysis follows a data-driven procedure. It was found that WID loading is primarily a momentum-driven process. As such, the magnitude of the loads are affected by the incident water volume and the associated water particle kinematics. Based upon this discovery, a data-driven model was established that enables an accurate prediction of the WID loading distribution using the free-field incident wave profiles. The focus of the seminar lies in improved design calculations, based upon the nonlinear dynamics of extreme waves and the nature of the WID loading process in realistic seas.