Hull Structural Analysis of Turret-Moored FPSOs Considering Hull–Turret Interaction

Abstract

For turret-moored ship-type offshore structures such as floating production storage and offloading (FPSO) units, the hull structure is affected by mooring and riser loads that are transferred through turret systems, in addition to environmental loads on the hull itself. Moreover, the existence of turret structures has an influence on the structural behavior of the hull around the turret system. In the structural design of FPSOs, the turret structure and its loads are considered in a direct analysis of hull structure for a realistic strength assessment of FPSOs. This paper investigates several specific techniques for hull structural analysis considering the interaction with the turret system. The linear gap function is utilized to represent the nonlinear contact behavior between the hull and turret structures. The linear superposition of structural responses is also adapted, and its validity is demonstrated in the case of hull–turret contact problems. These studies conclude that the hull structures with turret systems that involve contact nonlinearity in their interface can be assessed using the conventional hull strength assessment based on linear analysis. Moreover, by including the turret model directly in hull structural analysis, the uncertainty arising from hull–turret interface loads can be reduced, and a robust and adaptive design procedure can be set up in the detailed engineering stages.