Research Of Weak Model Disturbance Compensation Control And Its Application In Stabilization Control Of High Performance Ships

To fulfill the fast increasing demands of ocean exploring, the development of new types of ships boost. These new ship designs break the conventional monohull concepts, extend it into the multihull era. Catamarans, trimarans and even M-type ships which have five hulls are invented. Non-displacement ships also become popular, such as hydrofoil ships, air cushion boats. To improve the seakeeping performance, small water plane concepts are also proposed. These high performance ships require development of related technology in marine engineering as well. The motion stabilization is right one of the aspects.The ship motion stabilization belongs to the ship motion control problems. It means that control the attitude of ships into a desired range via fins, rudders or any other stabilizers. In the conventional concept, the stabilization of ships mainly focuses on its roll reduction, since longitudinal motion is relatively small due to large pitch damping of conventional ships. When the story turns to high performance ships, things are quite different. For example, small water plane twin hull ships usually have a good seakeeping performance, however, in some particular situations, coupled roll and pitch motions produce an unacceptable motion sickness rate. To obtain a good control performance in this situation, multiple control surfaces are required, thus more complex controlalgorithm are required. The major disadvantages of conventional ship stabilization control are:Firstly, they are lack of multivariable control ability.Secondly, they have a strong dependency on the ship motion mathematical model. In other word, accurate knowledge of the hydrodynamics is require to obtain satisfactory control performance.Thirdly, they are lack of adaptive ability and difficult to handle control actuator constraints.To overcome there problems, a new control strategy named Weak Model Disturbance Compensation Control (WMDCC) is proposed. It has the following advantages: Firstly, it has little dependency on the model accuracy. In other words, it doesn't need accurate knowledge of the control object and even the disturbance, a little rough information is enough for its design. Thus, it is very suitable for the control of high performance ships which have complicated hydrodynamic characteristics. Secondly, it compensates the disturbance in a feed-forward channel, which means it has more quick response than the feedback mechanism.Thirdly, It combines both the advantages of predictive control and adaptive control, which make it have the ability to deal with constraints and adapt to the varying of sailing conditions.To verify the control performance of WMDCC, a new simulation model is extended based on the work of Bailey and Fossen. This simulation model combines the maneuvering and seakeeping models together thus makes it more accurate than the conventional simulation methods used in ship stabilization control research.Based on these work above, the author apply the WMDCC to a SWATH ship. Different kinds of controllers, including PID, MPC and WMDCC, are tested. The simulation results shows that WMDCC have much better performance than its counterparts.