Simulation of Dynamic Behaviour of a FPSO Crane

Lifting operation on a FPSO (Floating Production, Storage and Offloading vessel) is much more demanding for the crane and the crane driver than similar operations on a fixed offshore platform. Due to the motion of the FPSO in heavy sea and strong wind, the crane is subjected to additional dynamic forces as well as swinging loads. The present paper deals with numerical simulation of the dynamic behaviour of the Norne offshore crane during lifting operation. The simulations are performed by FEDEM - a general nonlinear dynamic analysis program for flexible multibody systems. The pedestal, "king" and boom are flexible links modelled by shell finite elements and connected together by different joints. The hoisting rope and the hydraulic cylinders are modelled by linear and nonlinear spring and damper elements. A control system is implemented in the model making it possible to control the movement of the boom and the winch to compensate for the ship motion. Examples are shown of calculated natural frequencies and mode shapes as function of rope length and boom angle. Furthermore, ex