Evaluation of Roll Damping Characteristics of U-Tube Tanks in Regular Wave Conditions

Ships in turbulent seas suffer a lot of unstable motions which results in discomfort of crew members and passengers, as well as creating unfriendly working environment on the main deck for the crew members. U-tube tank was designed and introduced to damping the roll motion in other to stabilize the ship in one-degree-of-motion. The U-tube tank has a different port and starboard sides connected by a channel between them. The U-tube tank acts as a damper to quickly mitigate roll motion of the rolling ship. The damping ratio is usually tuned through the size and shape of a valve in the connecting channel of the U-tube. When the tank is turned off the response amplitude operator (RAO) reaches a peak value of 12 at a frequency of 0.1 Hz and the RAO remains constant at the value of 0 as the wave encountered frequency increases when the tank is turned on. Effective control of ship roll motion can be achieved with a U-tube water tank as actuator. For the predictive control, system identification is applied to update the parameters of the linear ship roll model with a U-tube tank when the ship dynamics changes.