Modelling 3D dynamics of offshore lattice jib cranes by means of the rigid finite element method

Abstract

Offshore cranes require particularly careful design due to the difficult environmental conditions in which they work. This paper presents a 3D model of the dynamics of an offshore crane with a truss jib formulated by means of the rigid finite element method. The inertial features of the truss members are assigned to nodes whose rotational and translational displacements are degrees of freedom. Flexible features of the truss members are modelled by massless and dimensionless spring–damping elements (sde). The computer programme developed on the basis of the model is verified and validated, and good correspondence of the authors’ own results with those obtained using commercial FEM package is achieved. Computer simulations are carried out for the light crane used on the wind platforms. The influence of the base movements (sea waves) on the system are also investigated. Lifting a load from a supply vessel and the load on the system during rotational movement of the crane are simulated too. Finally, conclusions concerning the influence of the movement conditions on the overload coefficient and deflections of the crane boom are formulated.