Non-propagating Waves and Behavior of Curtainwall-pile Breakwaters

Usually, evanescent modes or non-propagating waves are produced when a propagating incident wave impinges on an interface between two media or materials such as curtainwall-pile breakwater (CPB) at a subcritical angle and decay with distance from interface. To achieve an effective prediction of hydrodynamic performance of CPB and overcome the problem of underestimation of energy loss, the effect of non-propagating waves is considered. A numerical model was developed that can predict the interaction of irregular waves normally incident upon a CPB. The developed numerical model is based on an eigenfunction expansion method. The model utilizes a matching boundary condition nearby the vertical piles which accounts for energy dissipation. The accuracy and validity of the method were verified by comparison with results obtained by other authors. Furthermore, the nature of contraction coefficient is discussed and a new predictive formula is presented and compared with the former one suggested by Mei et al. (1974). The proposed contraction coefficient which comprises the hydrodynamic characteristics of waves enhances efficiency and effectiveness of estimation in comparison with other formulas. Non-propagating waves can affect wave propgation and scattering near permeable barriers. These effects have been analyzed and optimum number of necessary corresponding evanescent modes have been studied. Although, it is found that the first 5 evanescent modes strongly alter the results and stabilize them, greater reliability may be achieved by taking twenty waves into account.