URANS study of Delft catamaran total/added resistance, motions and slamming loads in head sea including irregular wave and uncertainty quantification for variable regular wave and geometry

A methodology is assessed for uncertainty quantification (UQ) of resistance, motions and slamming loads in variable regular wave representing a given sea state, and compared to irregular wave (benchmark) and deterministic regular wave studies. UQ is conducted over the joint distribution of wave period and height; the irregular wave inlet boundary condition is based on the wave energy spectrum; deterministic study is conducted at the most probable condition. Application to the high-speed Delft Catamaran at Fr=0.5 and sea state 6 is presented and discussed. Deterministic regular wave study shows an average error for design optimization-related quantities (expected value of resistance, motions amplitude and slamming loads) equal to 25%. Variable regular wave UQ shows an average error close to 6%, providing in addition output distributions. Extension to uncertain design through Karhunen-Loève expansion is presented and discussed; variable geometry studies show a potential reduction of 6.5% for calm water resistance and 3.9% for resistance in wave, with small variations in motions amplitudes; an increase of 6.4% in maximum slamming load is experienced by the reduced-resistance geometry, revealing a trade-off between performances and loads. UQ with metamodels reveals ordinary Kriging and polyharmonic spline as the most effective metamodels overall.