A New Method for Deriving Soliton Design Criteria

A new method for deriving extreme soliton current criteria for offshore engineering applications is described. The primary data source was site specific measurement close to the continental shelf break where metocean criteria were required. A dedicated oceanographic mooring was designed to quantify solitons, with rapidly sampled measurement of seawater temperature and velocities through the vertical. As described in two previous OMAE papers, quantification of soliton velocity profiles was achieved via temperature measurement and theory, with measured velocities playing a secondary role in critical validation. The previous methodology was extended in the present study, with separate contributions quantified from variations in soliton amplitude and water column density structure. The nonlinear Fourier techniques first described in OMAE 2017 were again used to reduce uncertainty in estimates of extreme soliton amplitude. In a new development, the long-term distribution of the density structure contribution was quantified using a calibrated hindcast of seawater temperature. Extreme conditions were defined at the boundary of a MITgcm model domain. This sophisticated model was then used to estimate extreme soliton velocities, through the water column and a few metres above the seabed, at a wide range of shallower target locations.