Research On Networked Control Of Course-keeping For Ships

Ship navigation safety is always a great concerned topic around the world. To the disaster of mounting piracy threat, how to avoid being hijacked and the emergency treatment after ships'being hijacked have become issues of interested in the field of shipping industry. That not only affects the nomal operation of ships, but also seriously threatens the personnel security. In addition, with the deepening study of Unmanned Surface Vehicle (USV), ships without any sailor on board in the future would be capable to navigate to the destination automatically by employing the remote control system. Once there is no sailor on board, more cargo can be carried and resulting in greater profit. In the other side, accidents caused by human errors would be greatly reduced, e.g., pirates will be helpless in the face of USV. At present, the modern integration of ship and shore monitoring system, an essential instrument in the future USV, has been more and more in favor of shipping companies. That will provide more effective protection for the shipping safety, in order to improve operational efficiency. Once ships encounter hijack and other emergency situations, the shore station center can receive real-time data from ships to implement remote control by virtue of the integration of ship and shore monitoring system. However data exchange through the communication network is inevitably faced with inherent problems of networked control system (NCS), such as time delay and packet loss.In the paper, adverse impacts of system stability and performance caused by time delay in NCS are processed to implement the ship course-keeping remote control. The time delay and packet loss performance of the Internet and maritime satellite communications networks are real-time tested and analyzed, and then a new robust adaptive neural network control scheme is developed to compensate for the uncertain time delay. In this scheme, Backstepping method is utilized to vertical transmit nonlinear terms in each step to the n sub-system, and then radial basis function neural network (RBFNNs) is introduced to compensate for stabilization. A simulation is also carried out. The scheme is with advantages of simple form, easy to implement in practice and so on.In order to simultaneously handle the system adverse impacts caused by time delay and packet loss in NCS, an auxiliary model estimation (AME) method is introduced. The characteristic model is firstly identificated from the ship maneuvering trial as an auxiliary model, and its output substitutes the estimated value of the plant in case of packet loss situation, while combining Pade approximation technique with closed-loop gain shaping algorithm (CGSA) to design ship course-keeping concise robust controller considering time delay. Finally, a simulation is carried out. The method has advantages of simple design process, easy engineering implementation, simple model structure, satisfying control performance and so on.In order to implement the simulation experiment of the proposed schemes, the ship course-keeping control test platform based on maritime satellite communications is designed and realized by using the Visual Basic programming language, which is more practicable than the single digital simulation. Combined with the proposed approach for the time delay in NCS, the comparison test between maritime satellite communications and Internet communications are conducted, and the feasibility of ship course-keeping remote control through maritime satellite communications and the practicability of platform are illustrated.In the paper, from view of improving emergency response processing capability when ships encounter hijack and other emergency situations, the strategy of utilizing shore station center by satellite communications network is proposed and achieved to realize ships'networked control, which including to impair impacts of time delay and packet loss in the NCS, and the ship course-keeping control test platform based on maritime satellite communications is designed and realized. Therefore, the research work has provided the possibility for implementing the ships'remote control.