Heerema Marine Contractors has been awarded contracts for the transport and installation of two ultra-heavy platforms — Arkutun Dagi and Wheatstone. The total transportation weight including deck support frame is about 45,000 mT for both of these projects. It requires the largest transportation and float-over barge in the world (H-851) and pushes it to the limit of its strength. A detailed study has been performed to verify the structural integrity of the barge. The design stresses have been determined using a spectral analysis, based on stress RAOs for each of the elements in the FEM model. All elements are tested against relevant code, looking at requirements for strength as well as buckling capacity. The advantage of the spectral strength analysis is that no assumptions need to be made about the most critical acceleration and the associated design wave. The method focusses directly on finding the critical stresses.
This paper explains the steps taken to perform a spectral strength assessment of a transportation vessel. It shows how stress RAOs are determined by combining results of a hydrodynamic analysis with a full scale FEM model. The stress RAOs are used to perform a strength and buckling verification using a full wave spectrum and results are related to the outcome of a design wave analysis performed by a third party. Explanations are provided based on Arkutun Dagi project.
