Towards an improved critical wave groups method for the probabilistic assessment of large ship motions in irregular seas

A novel approach for the systematic construction of wind-generated, high probability, wave groups, is presented. The derived waveforms originate from a Markov chain model allowing for the incorporation of cross-correlations between successive wave heights and periods. Analytical expressions of the transition probability distributions are provided in terms of copulas. Rank correlations are estimated from an envelope-process-based approach. The Karhunen–Loève theorem is employed in order to construct the continuous analogs of discrete height and period successions. The method seems to predict well the expected wave heights. The period predictions are conservative, yet they follow the trends of simulated wave trains. Comparisons with predictions of the “Quasi-Determinism” theory for very high runs indicate good coincidence. The derived wave groups are intended to be used for the assessment of ship stability in irregular seas.