Robust Dynamic Positioning of Offshore Vessels using Mixed-μ Synthesis Part II: Simulation and Experimental Results

This paper is a follow-up of a companion paper by Hassani et al. (2012b) on a control design methodology for Dynamic Positioning (DP) of marine vessels and offshore rigs subjected to the influence of sea waves, currents, and wind loads using mixed-μ synthesis. The present paper describes the results of a design exercise in which robust controllers were designed for a representative vessel. Its main focus is on the discussion of the results of numerical simulations and experimental model-testing of a set of robust DP controllers operating under different sea conditions: calm, moderate, high, and extreme seas. The robust DP controllers were first evaluated in a high fidelity nonlinear DP simulator, illustrating the efficiency of the design. To bridge the gap between theory and practice, the results were experimentally verified by model testing of a DP operated ship, the Cybership III, under different simulated sea conditions in a towing tank equipped with a hydraulic wave maker.