Many problems occur when the protected setting is in deep water. Many new systems were created like floating caissons, immersed flags, caissons fixed on piles, ARION systems, AGRIPEL absorbers…In this paper, we show that these breakwater types can present resonance phenomena developing when the protected setting is not totally absorbing. A simple calculation technique of these phenomena is described and applied to the « Fixed water wall » phenomenon developed by caissons fixed on piles. Introduction The system studied in the open sea (when the distance is great between the breakwater and the setting) behaves as a pass band filter (immersed flags for example) or a low pass filter. In a range of periods the amplitude of the swells strongly decreases behind the breakwater. The comportment of this type of breakwater can be characterized by the swell transmission coefficient Kt : Kt=Ht/Hi. Ht is the swell amplitude transmitted behind the breakwater and Hi is the incident swell amplitude. When we study the different papers relating to this type of structure, we observe that the breakwater is tested as if the port side was an infinite surface. For the fact of using a perfect absorber beach (real or numerical) at the end of the wave flume, simulates the phenomenon, but is not representative of the reality. For a good understanding of the phenomenon, we must consider the protected setting. This study must show the interaction between the protection systems and strongly reflecting settings like a steeply sloping sea bottom. (Monaco for example), or a large boat moored near the breakwater.
To understand the phenomenon, we must divide the zone where the breakwater is built into three parts. The port part is considered as an excited water body (oscillator).