Spectral simulation of non-breaking wave forces up to the second order on immobile vertical walls

Spectral simulation of non-breaking wave forces up to the second order on immobile vertical walls

De Jong, R.

Civil Engineering and Geosciences

Hydraulic Engineering

2001-01-01

Induced by a rapid increase of ship sizes in the last decades, the demand for deeper waterways emerged and so did the demand for higher breakwaters. The scale of land reclamation projects has also increased concomitantly. This means they extend such projects now further offshore into deeper water, requiring higher watersheds. In this deeper water environment caissons become an economic alternative for the triangular shaped rubble mound breakwaters and the conventional dikes, whose volumes are proportional with their heights squared. So there is much potential for vertical wall breakwaters, both as breakwaters and as watersheds for reclamation projects. The hydraulic loads on these breakwaters cannot yet be predicted in a satisfying and generally accepted way. For this reason, the use of vertical breakwaters, especially in Europe is stilI very limited. Two types of hydraulic loads can be distinguished: 1. wave impact forces, which are short, high pressure impacts caused by waves, which are breaking at the moment they hit the construction and 2. quasi-static loading as a result of standing or partly standing nonbreaking waves. At this moment the method proposed by Goda is most frequently used to estimate the quasi-static wave forces. This method is based on the linear wave theory and uses one (significant) wave height and one characteristic wave period as input. Many empirical parameters are used, resulting in conservative predictions for this type of wave force. The aim of this work is to provide a more sophisticated model, which approximates the changeable water surface by the sum of a large number of sinusoids, each having its own amplitude and period. During the design of the Oosterschelde storm surge barrier, such a description of the water surface was used in combination with the linear wave theory. It turned out that second order effects, caused by interaction between the waves are important in relatively shallow water (in comparison with the wavelength of about 100-150 m), where the caissons are placed. Therefore all interactions between (first order) waves should be taken into account. This report provides a theoretical model for the irregular wave forces up to the second order on an immobile vertical wall supposing a horizontal foreshore and unidirectional waves. The input for this model is a first order wave incident wave spectrum.

linear wave theory
water surface
vertical wall breakwater

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Student theses

master thesis