Offshore crane control based on adaptive external models

An adaptive controller for cranes employed in heavy-lift offshore marine operations is presented. The control objective is to reduce the hydrodynamic slamming load acting on a payload at water entry of moonpool operations, while letting the payload track a given velocity profile. The adopted solution relies upon the use of an adaptive observer and two adaptive external models of the disturbance, employed to recover the unavailable information about the error to be regulated. As a result, the closed-loop system is rendered adaptive with respect to both the plant parameters and the frequencies of the harmonic disturbances affecting the system. A certainty-equivalence controller which makes use of the estimated parameters and the reconstructed tracking error is proposed, and the performance of the overall scheme is verified experimentally on a scale-model. Results show a remarkable improvement over a previous approach based on an observer-based internal model control of fixed structure.