Observer-Lagrangian-based controller applied to two dynamically controlled vessels

The application of the Observer-Lagrangian-based controller for a typical offshore system comprised of two dynamically controlled vessels connected by a hawser in tandem configuration is investigated. The control law is obtained by introducing some virtual constraints in the Lagrangian control model. The virtual constraints are defined in terms of the relative position and heading between the vessels. The state variables (position, heading and velocities) and the external forces of the system required by the controller are estimated through a nonlinear observer based on the passivity approach. The closed-loop dynamics is proved to be exponentially stable in the sense of the Lyapunov stability theory. Some results of dynamical simulations have indicated a very good performance of the controller.