Infragravity waves and moored floating structures

Up to this day, design recommendations or practices for floating structures, such as DNVs RP-C205 and F205 for example, do not account for the existence of low frequency free Infragravity (IG) waves. These are low-frequency water waves which represent an additional excitation for (moored) floating structures. In this study, the influence of free IG waves on moored floating structures response is investigated and compared to second-order low-frequency wave forces, as the standard low frequency excitation, for two selected important free IG events in 2013 and 2014 at the SEM-REV (Site d'Experimentation En Mer - Recuperation de l'Energie des Vagues) test site near Le Croisic, Pays-de-la-Loire, France. The wave forces and motion response for two example floater-mooringsystems are calculated and compared for the different frequency ranges separately and combined. Using the latest developments in the wind-wave framework WAVEWATCHIII®, e.g. the parameterized implementation of free IG sources at the reflecting boundaries, directional wave spectra including the low-frequency IG wave band are used. This study has been conducted between November 2014 and October 2015 in the scope of the axis 7 «Sea motions and interaction with marine structures» of the cluster of Excellence LabexMER A changing ocean .