Numerical And Experiment Study On Ship Parametric Rolling In Oblique Seas

Parametric rolling in longitudinal seas is a research focus, however,when ship in oblique seas, roll motion stands both external force and parametric force, which may lead to large roll under parametrcially forced action.First, this paper proves the existence of parametric roll in oblique seas though ship model experiment and then proposes a new method to calculate restoring force considering the relative positions and the coupling of ship motion, thus forming a set of MATLAB program to calculate ship motion based on the method. After checking the correction of the program on getting ship restoring force, use it to calculate C11in oblique seas and compare the numerical results with the experiment results. The comparison shows the program is reliable.Next, use the numerical program to do the following researches:through safe basin research in oblique seas to find that parametric rolling in oblique seas hardly causes capsizing and the safe areas by linear and nonlinear method are almost the same though roll by nonlinear method was obviously larger; through ship nonlinear roll research under all wave directions to find that roll in longitudinal seas and oblique seas is larger than that in beam seas if parametric roll happens when wave amplitude is not so big, and that roll in beam seas is larger when wave amplitude is big enough; through parametric roll research on different ship in longitudinal seas to find that the container ship is sensitive to parametric rolling while other ships are not,due to the ship shape as well as the position center of gravity.At last, ship roll in random seas considering nonlinear restoring force is studied, to find that in the calculated wave condition ship roll increases with the wave significant height but it won’t increase obviously when the significant height exceeds some value.