Wave impacts on a vertical breakwater

Abstract

Since waves have enormous power the design of structures to withstand this power is not easy. The history of breakwaters is one of many failures and damages. This has lead to continuously improving technology in marine construction. Over the years men made it possible to construct breakwaters with high stability against waves. The vertical breakwater is an ideal solution in deep water and in areas where the use of rubble stones is expensive or environmentally less acceptable. Furthermore a vertical breakwater with smooth vertical walls can be exposed to high wave loads, such as impulsive wave impacts. These impacts are characterised by very high pressure and a short duration time. It is believed that these impacts could well be essential to the failure of vertical breakwaters. The duration time of the wave impact is essential for the (dynamic) response of the caisson. For example if the wave impact duration is about the eigenfrequency of the vertical breakwater the response will reach a maximum, and the vertical breakwater could collapse. The objective of this graduation report is to investigate the assumption that wave impact is important with regard to failure of vertical breakwaters. Research has been carried out to investigate the time impact duration for vertical breakwaters and an analogy has been made of wave impacts with impulsive wave load on ships. Also, in order to investigate the (dynamic) response of vertical breakwater a computer model has been designed. With this model the response to the wave impact loads upon the Genoa Voltri breakwater can be estimated. The results of this graduation study is that wave impact do occur, but that the impact duration is much shorter than assumed in the past. The impact forces during these short duration result in little response of the vertical breakwater, since the impact duration is not in the range of the eigenfrequency of the vertical breakwater. It can therefore be concluded that wave impacts are not important for the stability of the Genoa Voltri breakwater.