Naoya Umeda

Estimation of Parametric Roll in Random Seaways

This chapter attempts to provide a guideline for quantifying the magnitude of parametric roll of a ship in irregular seaways. First, in the light of physical model experiments with a scaled ship model in irregular water waves, it is shown that parametric roll of this ship model is a practically nonergodic process. Second, a guideline is developed by randomly sampling time series from the measured records. It is tentatively recommended that we should conduct physical and/or numerical experiments of more than 12-realizations and more than 360 excitation cycles for accurately estimating the magnitude of parametric rolling. The results of parametric roll estimation sufficiently above the threshold should be used for practical stability assessment. Finally, a container ship example is used to compare the numerical results with physical data.