Feed forward control of U anti-roll tanks

Feed forward control of U anti-roll tanks: Research on the effect of using a wave prediction system for the control of an active U anti-roll tank on the workability of an SOV operating at zero speed

Immink, Leon (TU Delft Mechanical, Maritime and Materials Engineering)

Lombardi, C. (graduation committee)
Naaijen, P. (mentor)
Hopman, J.J. (graduation committee)
van Wingerden, J.W. (graduation committee)
Schreier, S. (graduation committee)

Delft University of Technology

2021-03-19

Within this thesis an attempt is made to improve the seakeeping of a Service Operation Vessel (SOV) by means of an active anti-roll tank (ART). It is researched if the addition of a wave prediction system can improve the ART’s performance. As the seakeeping of the SOV is most important for the installed motion compensated gangway, the workability is assessed for different control methods based on the design criteria of the gangway. The computations have been made in frequency domain. A one directional model is used with two degrees of freedom: the ship roll angle and the tank’s fluid angle. Due to the presence of a wave prediction system, a feed forward loop can be introduced in the control system. It is found that if the pump moment leads the wave excitation moment, the tank’s fluid will oscillate in a less power demanding way. This is caused by the better interaction of the action and reaction forces that are caused by the pump. The action force on the ship’s structure will always oppose the wave moment, but the force acting on the tank’s fluid will only stabilise the vessel at certain frequencies. To obtain a robust model, the feed forward loop is combined with a feedback controlled model. The stability of the models’ feedback loop is assessed using Nyquist plots and sensitivity plots. It is found that for the damping factor belonging to the ART of the SOV, the feedback loop is unconditionally stable. On topic of the powers related to the active ART the dissipated and actual power are analysed. Based on the dissipated powers it is found that for the same amount of dissipated power by the pump, the feed forward controlled model causes a lower root mean square value of the ship’s roll in comparison with the feedback controlled model. This is explained by the better interaction of the forces generated by the pump. Based on the obtained RAO for the roll motion, the workability of the SOV is assessed for a significant wave height of 3m. It is found that even though the seakeeping of the vessel increases because the roll response decreases, the gangway motions aren’t significantly affected by the active control of the ART. The reduction in roll response is not proportional to the reduction of the gangway motions since other vessel motions such as heave and sway also effect the gangway’s motions. All in all, it is concluded that adding a feed forward loop to a feedback controlled model improves the seakeeping of the SOV. However, to improve the workability of the SOV it is recommended to include a passive ART in the design, instead of an active ART. This is because the active control has little impact on the gangway’s motions compared to the passive ART.

Workability
Anti-roll tank
Seakeeping
Frequency domain
ART
Roll damping
Service Operation Vessel
Motion compensated gangway

http://resolver.tudelft.nl/uuid:8b3f3b77-260c-4883-887d-b6ae842b4d3a

2021-03-19

Student theses

master thesis

© 2021 Leon Immink