This paper on "Simulation of Dynamic Behaviour of an Offshore Crane on a Floating Production Vessel" was presented at the NAFEMS World Congress on The Evolution of Product Simulation From Established Methods to Virtual Testing & Prototyping - 24-28 April 2001, The Grand Hotel, Lake Como, Italy.

Abstract

Lifting operations on a FPSO (Floating Production, Storage and Offloading vessel) are 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 waves and strong winds, the crane is subjected to additional dynamic forces as well as swinging loads.
This present paper deals with numerical simulation of the dynamic behaviour of the "Norne" offshore cranes during lifting operation. The simulations are performed by FEDEM - a general non-linear dynamic analysis program for flexible multibody systems. The pedestal, the revolving crane superstructure called crane king, and boom are flexible links modelled by shell finite elements and connected together by different joints. Linear and non-linear spring and damper elements are used to model the hoisting rope and the hydraulic cylinders. A hydraulic control system is implemented in the model, making it possible to control the movement of the boom and the winch to compensate for the relative motion between the ship and the supply vessel and to keep the load in rest relative to the vessel. Simulation examples are shown for sealift from supply vessel.
Besides giving necessary stress data for design verification against overload and fatigue, the presented model can be used to optimise the operation procedure, determine the maximum allowable load for various sea states and to calculate the required power to control the motion of the load.