"Assessment of the effect of Infragravity waves on the reliablity of the moorings of a floating coastal structure".
Traditionally, moored systems (LNG tanker, offshore wind structure, floating wave energy converter), which have low frequency resonant responses, are designed in taking into account non-linear forces (linear+second order) due to waves. When free low frequency waves (>60s) are present, the linear forces induced by these waves are added to the non-linear ones in the same low-frequency band, which amplifies the resonant response of the structure. Joint statistics of such free low frequency waves Infra-Gravity (IG) with “high frequency” waves are then necessary and must be included in the assessment of the mooring reliability. Statistics on the IG from numerical hindcast wave models permit to estimate statistics of the strains in the moorings. In one part, probabilistic methods were developed at Ifremer to calculate the statistics of a floating structure non-linear response knowing the spectral density of the waves in a sea-state (see for example ). In another part, databases of sea-state wave spectra have been constructed from numerical hindcast modelling  and a simple model of IG has been validated in a recent thesis .
The aim of these work is to couple these databases and IG model with the probabilistic tools to assess the reliability of a mooring from the long term statistics of a structure response. The sensitivity to the presence of IG will be evaluated.