The permeability parameter of curtain-wall breakwaters

Abstract

A numerical model has been developed that can predict the interaction of regular waves on a single curtain-wall pile breakwater (CP B). The model is based on an eigenfunction expansion method and utilises a boundary condition close by the vertical piles that accounts for energy dissipation. Energy dissipation is modelled through the boundary condition via a permeability parameter. This parameter is a complex constant, so that the real part of it corresponds to the frictional resistance of the breakwater and the imaginary part is associated with the inertial resistance of the breakwater. The permeability parameter can be calculated by two different methods: one is advantageous because all the frictional and inertial related variables are known; the other requires the frictional resistance to be calculated by comparing the mathematical and experimental resultsThe purpose of this study is to compare the accuracy of the two methods in the case of CP Bs, and express the frictional resistance of the CP Bs as a function or a constant for the second method. Modelling is validated by comparison with previous experimental studies. The appropriate range for the porosity and relative draft of the breakwater is discussed and it is suggested that CP Bs can operate both effectively and efficiently in the draft range 0.15–0.75, although to achieve maximum energy, the porosity between 0.15–0.2 is recommended.