Hydrodynamic Modelling for Dynamic Positioning and Maneuvering Controller Design

In this paper we present a new approach for mathematical modeling of hydrodynamic drag and lift forces and moment of marine vessels for the purpose of model-based control in the horizontal plane spanned by the surge, sway and yaw degrees of freedom (DOFs). Simplified low-fidelity models are proposed satisfying strict real-time computing requirements. The proposed control plant models are particularly suitable for the use in real-time simulation-based design and testing of dynamic positioning (DP) and maneuvering control systems. Moreover, the proposed equations may be suitable for a wider range of both underwater vehicles and surface vessels. The main idea is to employ conventional rudder theory, consider the vehicle as a large lifting surface similar to slender body theory, and, finally, transform the equations into the body-fixed reference frame. It will be shown that only moderate modifications to standard rudder equations are needed to derive the total hydrodynamic damping in surge, sway and yaw. Full scale experimental test results are presented showing that the proposed drag and lift models match the actual forces to a large extent.