Study on wave-induced motions of a turning ship in regular and long-crest irregular waves

A 6 degrees of freedom (DOF) maneuvering and seakeeping unified model is developed and validated for the accurate simulation of wave-induced motions of a turning ship (S175) in regular and long-crest irregular waves. In the model, a 3DOF surge-sway-yaw maneuvering model and a 5DOF sway-heave-roll-pitch-yaw seakeeping model are coupled weakly based on the unify theory. Maneuvering and seakeeping time steps are determined to balance between the time efficiency and accuracy. Numerical simulations of the S175 turning in regular and irregular waves under different wave lengths and directions are performed. In regular waves, the simulated turning trajectory, speed and wave-induced pitch, and roll motions are compared with free-running experimental results. It is found that the simulation model can capture general trends of motion characteristics while the ship turning in waves. Considerably good agreements are observed for the ship speed and pitch motion especially for cases with long wave length lambda/L-pp >= 0.70, while reasonable agreements of the turning trajectory and roll motion can also be observed. In irregular waves, ship turning motions are simulated under different wave patterns with the same spectrum. It is found that spectrums of pitch and roll motions under different wave patterns have large discrepancies.

Automated summary

A 6 degrees of freedom ship motion model has been developed to accurately simulate wave-induced motions in both regular and irregular waves. The model shows good agreement with experimental results in regular waves, especially for ship speed and pitch motion. However, large discrepancies in pitch and roll motion spectra were observed under different wave patterns in irregular waves.