Stochastic methods for the control of crane systems in marine applications

External excitations of oscillations which are caused by wind and waves are the main sources for disturbances in the task of load positioning by means of ship-mounted cranes in marine applications. These disturbances can be described with good accuracy by stochastic models. Although methods for the stability analysis of dynamic systems, which are subject to stochastic disturbances, are readily available, they are not widely used in practical applications. Instead, a control design is often performed for a nominal system model, while its robustness is commonly evaluated separately by numerous simulations (e.g. Monte-Carlo techniques) aiming at a quantification of the influence of disturbances. For this reason, methods are presented in this paper which are both applicable to the stability analysis of control and observer structures for ship cranes and to the enhancement of robustness properties by directly accounting for the stochastic nature of disturbances during control design. Suitable simulation results are presented which highlight the applicability of the presented methods for the trajectory control task of ship-mounted boom cranes.