Transmission of Long Waves Induced by Short-Wave Groups Through a Composite Breakwater

Abstract

Theoretical findings and laboratory evidences are presented regarding the transmission of long waves induced by short-wave groups through the rubble base of an infinitely long composite breakwater. Multiple-scale perturbation method is applied in describing the long-wave fields in terms of velocity potential, and an analytical solution is derived for transmitted and reflected long waves induced by wave groups. Dependency of the reflection and transmission of free long waves on several parameters is examined through the numerical calculations. It is found that the linear friction factor, the rubble-base height and the modulation of short waves affect the transmission of free long waves significantly. Theoretical results are then compared with the results from laboratory experiments. It is shown that although the conventional rubble-mound breakwaters can reflect short wave energy efficiently, a significant part of the bound long-wave energy associated with shortwave groups is transmitted to the leeward side of the breakwater as free waves.