A MECHANICAL FILTER CONCEPT FOR CONTROL OF NON-LINEAR CRANE-LOAD OSCILLATIONS

Abstract

In this article, results obtained through analytical and numerical investigations into the control of planar, large-amplitude crane-load oscillations are presented. A novel concept called a mechanical filter is proposed and described. In the context of ship crane-load oscillations, this concept is implemented on the basis of the premise that by controlling the pivot point about which the load oscillates, one can effectively suppress crane-load oscillations. Ship-roll-induced load oscillations are considered and a “mechanical filter” is introduced at the pivot to control these oscillations. The pivot is constrained to follow a circular track in the considered filter. The governing non-linear dynamical systems for the cases with and without the filter are presented. Transfer functions are determined for the linearized dynamical systems and the filter performance characteristics are discussed. The non-linear dynamics of the systems with and without the filter is studied with respect to quasi-static variation of different scalar control parameters. Static feedback laws for actively controlling the pivot motions are also considered and the dynamics in the controlled cases is compared with the dynamics in the corresponding uncontrolled cases. It is shown that the presence of the filter helps in eliminating some of the subcritical bifurcations that may arise in the crane-load response during periodic ship-roll excitations. The presence of feedback control also allows us to effectively suppress transient crane-load oscillations.