A mechanical filter concept for control of non-linear crane-load oscillations

In this article, results obtained through analytical and numerical investig ations into the control of planar, large-amplitude crane-load oscillations are presented. A novel concept called a mechanical filter is proposed and d escribed. In the context of ship crane-load oscillations, this concept is i mplemented on the basis of the premise that by controlling the pivot point about which the load oscillates, one can effectively suppress crane-load os cillations. Ship-roll-induced load oscillations are considered and a "mecha nical 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 t he filter are presented. Transfer functions are determined for the lineariz ed dynamical systems and the filter performance characteristics are discuss ed. The non-linear dynamics of the systems with and without the filter is s tudied with respect to quasi-static variation of different scalar control p arameters. Static feedback laws for actively controlling the pivot motions are also considered and the dynamics in the controlled cases is compared wi th the dynamics in the corresponding uncontrolled cases. It is shown that t he presence of the filter helps in eliminating some of the subcritical bifu rcations that may arise in the crane-load response during periodic ship-rol l excitations. The presence of feedback control also allows us to effective ly suppress transient crane-load oscillations. (C) 1999 Academic Press.