A dynamic model for lifting heavy modules between two floating offshore structures

The installation of new topside modules on existing floaters in deep water poses new cha llenges, as both the crane vessel and floater move independently. Installing even a relatively light module on a moving target with existing
topsides needs careful consideration. This paper describes the development of a numerical dynamic model to simulate an offshore installation of two modules on a Floating Production Unit (FPU) from a dynamically positioned crane vessel. The main reason for the development of this model was to prevent damage to both the existing equipment and the new modules and to optimise the installation procedure. The numerical model is based on an existing time domain simulation program extended with a dedicated user interface. The approach of this project was to tune and validate the numerical model using the results of an extensive model test program. The methodology of tuning will be presented in this paper along with a comparison between the results of the tuned numerical simulations and the model tests. As a next step in this approach the validated numerical model was used to do Monte Carlo simulations to derive and verify design input. Subsequently operational limits could be determined for all possible sea states and wave directions. Finally, this paper highlights some optimised aspects of the installation procedure.