Experimental Investigation of 3D Reflection in an Ocean Basin

Abstract Traditionally, wave basins are equipped with wave generators and absorbers, the efficiency of the latter being typically described by frequency-dependent reflection coefficients. The definition of the reflection coefficient usually assumes a two-dimensional wave field only composed of an incident and a reflected wave component. This study presents an experimental investigation of the 3D aspects of wave reflection across a wave basin. For that purpose, a series of tests were conducted in the Ocean Basin at SINTEF Ocean. They were performed with regular long-crested waves, and the free-surface elevation was measured over a large area of the basin. Linear wave theory and constant water depth were assumed. The incident and reflected wave components were first split in the time domain based on the group velocity, and at a finite number of positions in the basin. Then, two different methods were used to reconstruct the whole wave fields from these point measurements, thus yielding a mapping of the reflected waves over an extensive area of the basin. First, the two methods were applied to synthetic wave fields for which the three-dimensional incident and reflected fields were known. Then, the reflection of regular waves generated in the Ocean Basin was analysed for two different beach configurations and with the two methods. The amplitude of the extracted reflected waves was compared to the reflection coefficient obtained through traditional techniques. It was found that the reflected waves were multidirectional and inhomogeneous, and that both methods made it possible to identify the main sources of reflection in space.