A non-intrusive and continuous-in-space technique to investigate the wave transformation and breaking over a breakwater

Simone Ferrari,Giorgio Querzoli,Maria Grazia Badas

doi:10.1051/epjconf/201611402022

Abstract

To design longshore breakwaters, the evaluation of the wave motion transformations over the structures and of the energy they are able to absorb, dissipate and reflect is necessary. To characterize features and transformations of monochromatic wave trains above a breakwater, both submerged and emerged, we have designed and developed a non-intrusive and continuous-in-space technique, based on Image Analysis, and carried out an experimental campaign, in a laboratory flume equipped with a wave-maker, in order to test it. The investigation area was lighted with a light sheet and images were recorded by a video-camera. The working fluid was seeded with non buoyant particles to make it bright and clearly distinct from dark background and breakwater. The technique, that is based on a robust algorithm to identify the free surface, has showed to properly work also in prohibitive situations for traditional resistive probes (e.g., very shallow waters and/or breaking waves) and to be able to measure the free surface all over the investigation field in a non-intrusive way. Two kind of analysis were mainly performed, a statistical and a spectral one. The peculiarities of the measurement technique allowed to describe the whole wave transformation and to supply useful information for design purposes.

Highlights

Longshore breakwaters are extensively used as littoral or harbour protection systems and, more recently, as devices for wave energy conversion ([2])
The origin of abscissa X is put in the middle of the obstacle longitudinal section; the origin of the wave height H is put at the hydrostatic level
A non-intrusive and continuous-in-space technique, based on Image Analysis, has been developed to overcome the limits of traditional resistive probes, usually employed to investigate wave transformation caused by a breakwater

Summary

Introduction

Longshore breakwaters are extensively used as littoral or harbour protection systems (see, for instance, [1]) and, more recently, as devices for wave energy conversion ([2]). The estimation of the wave motion transformations over the breakwater and of the amount of energy this structure is able to absorb, dissipate and reflect, is necessary, as stated in [3]. The proper design of longshore breakwaters for littoral protection requires that wave motion in the sheltered area is within certain limits, so laboratory experiments can be carried out to determine reflection and dissipation of the energy of trains of monochromatic waves above a breakwater, as in [4]. As a consequence, using traditional probes the breakwater results as a “black box” and it is not possible a direct comprehension of the physical phenomena determining the wave evolutions

Methods

Results

Conclusion