SIMULATION OF EXTREME EVENTS OF OBLIQUE WAVE INTERACTION WITH POROUS BREAKWATER STRUCTURES

Abstract

This paper introduces a numerical approach for the analysis of extreme events of wave interaction with coastal and marine structures. The method is exemplified by investigating oblique wave interactions with a rubble mound breakwater structure. The use of numerical models for analysis of wave-structure interaction is seen more often. For many applications a two-dimensional approximation is valid, however, for investigating complex structural details or e.g. oblique wave interaction with coastal structures, a three-dimensional simulation is required. One challenge for a practical use of three-dimensional simulations is the computational cost. For extreme event analysis it is necessary to determine the characteristics of the extreme events which will occur during an irregular sea state of a given duration. Therefore the complete irregular sea state must be simulated. A three-dimensional simulation of a full irregular sea state with duration of e.g. 3 hours will be a large computational burden. The present work proposes a methodology where the analysis is performed in two steps. 1) A two-dimensional simulation of a full 3 hour irregular sea state is performed including the breakwater structure. The extreme events are observed in terms of loads on the super-structure. 2) The extreme events are reproduced in a three-dimensional model as oblique waves by short realizations. The method was validated by comparing the surface elevation and sea-wall forces from a full irregular sea state to the short reproduction sequences. Good agreement was found for both surface elevation and horizontal sea-wall forces. The short reproduction of extreme events was applied in a three-dimensional setup for investigating the effect of oblique waves. For an incident wave angle of 30° a reduction of the peak impact load of 25-50 % was found for the tested extreme events.