Robust Control Allocation of Overactuated Ships; Experiments with a Model Ship

This paper adresses the problem of nonlinear control allocation applied to marine vessels. An energy optimal solution combining a static and a dynamic non-recursive algorithm is proposed. Ships equipped with azimuth (rotatable) and tunnel ((xed) thrusters are considered. The static-solution gives the optimal orientation of the thrust forces corresponding to minimum use of power, whereas the dynamic-solution provides dynamic capabilities. The dynamic-solution uses the Damped Least-Squares pseudo inverse of the Jacobian matrix about the static-solution. This guarantees singularity robustness, i.e. bounded solutions in all singular points. The combined solution (static and dynamic allocation) gives a 37% reduction in thrust compared to the pure static solution when simulated on a supply vessel. Experiments with a model ship are also reported.