Maximum wave force and run up on the curtain wall-pile breakwaters

A perforated wall breakwater consisting of a perforated front wall, a solid back wall and a waveabsorbing chamber between them was initially proposed by Jarlan (1961). As is well known, theperforated wall breakwater has two main advantages. One is to dissipate the incident wave energy and reduce the wave reflection from the breakwater, and the other is to reduce the wave force acting on the structure. The interaction of the water waves with perforated wall breakwaters have been studied for a longtime by different researchers. Most of the studies have focused on the reflection coefficient ofthe perforated wall breakwater. The horizontal force on the perforated wall structures has also been investigated by some researchers.In some instances, a permeable barrier, such as slotted vertical barrier made from timber planks, may be used. For example, this may be selected in an effort to reduce unwanted wave reflectionson the upwave face of the barrier. Thus the prediction of wave interaction with a permeable orslotted thin vertical barrier is also of interest. Classical inviscid solutions are available for a thin slotted vertical barrier extending from the free surface to the seabed {e.g., Lamb [4] and morerecently Martin and Dalrymple [5]}. However, these solutions do not account for the energy loss within the barrier due to viscous effects and therefore they overestimate wave transmission in comparison with the experimental results. An approximate solution was given by Wiegel (1961) in an attempt to include the energy loss within the barrier, but this was found to underestimate the wave transmission because the effectsof wave reflection were neglected. More generalized formulations that explicitly account for thewave energy absorption have been developed for wave interaction with permeable structures extending from the free surface to the seabed {e.g., Bennet et al. [6]; Kakuno and Liu [7]; Yu[8]}. Most such formulations assume that the velocity through the porous medium is proportionalto the pressure gradient, with a complex proportionality constant that accounts for possible phasedifferences between the velocity and pressure gradient. This description can be related to thephysics of the flow within the structure on the basis of frictional and inertial effects. Comparisonwith the experimental measurements of transmission and reflection coefficients has been carriedout for rows of vertical cylinders {e.g., Kakuno and Liu [7]} and slotted barriers {e.g., Bennet etal. [6}}, and these generally exhibit satisfactory agreement. However these works has not beenextended to partially submerged barriers.This paper outlines the numerical calculation of wave runup and wave forces on the upwave face of the curtain-wall breakwater (CBP) using circular piles. Numerical results compare well with available experimental measurements of the wave transmission, reflection coefficients andindicate that the numerical model is able to account adequately for the maximum wave force and wave run up. The effects of the porosity, relative draft of curtain-wall are discussed.

Keywords:

Breakwaters , Curtain Walls , Eigenfunction Expansion Method , Evanescent Modes , Wave Run Up , Wave Force