The overall motion induced interruptions in seakeeping optimization analysis

The paper presents an optimization technique to improve hull forms in a seaway by a new index, namely the Overall Motion Induced Interruptions OMIIs, defined as the mean MIIs value on ship main deck and chosen as single-objective function to be minimized. Parametric hull modelling is used to generate, by the Lackenby method, several ship variants, with some modified hull form parameters. Despite of classical optimization techniques, mainly based on heave, pitch and roll RAOs peak values minimization in regular head seas, all heading angles are considered, accounting for the probability of occurrence of each sea state, derived by the wave scattering diagram for the Mediterranean Sea. The method is applied to the hull form optimization of the round bilge NPL series. Optimum hull is finally derived and OMIIs indexes are compared, as well as heave, pitch and roll RAOs at various and relevant speed polar plots.