Motions Assessment Using a Time Domain Approach for a Research Ship in Antarctic Waters

An approach combining frequency and time domain analysis is introduced in this study for ship motions assessment. The open-source NEMOH code is utilized to compute the excitation forces and the hydrodynamic coefficients, while heave and pitch motions time histories are determined by solving the Cummins equations in the time domain. The study compares the numerical outcomes for the heave, pitch, and vertical acceleration at the center of gravity with data obtained from a smartphone onboard during an oceanographic expedition in the Antarctic Ocean in early 2020 on the "Laura Bassi" research vessel. In order to validate the proposed method, weather forecast data from the global-WAM (GWAM) model are utilized. The comparison reveals a good agreement between numerical results and onboard measurements, with differences in motion values remaining below 10% and accelerations below 15%. Therefore, the developed code, taking into account its future improvements, represents an initial step towards creating a promising tool for an accurate estimation of ship motions and accelerations.