Structural Optimization on Topside Supports for Ship-Shaped Hulls

PROJEMAR S. A., a naval and offshore design company at Brasil has developed several conversion projects of FPSO’s to operate at Campos Basin. This way, PROJEMAR faced some interface difficulty in the structural design of the topside supports, mainly for the vessel reinforcement. The structural analysis of the cargo region, when performed together with the topside supports and loads, introduces significant buckling and fatigue problems in the main transverse and longitudinal structure of the vessel. The solution adopted in first instance is to reinforce the transverse structure and longitudinal bulkheads of the cargo tanks just below the topside supports. This reinforcement is expensive and takes a lot of time to be done, as hundreds of buckling bars should be installed. In order to avoid this work inside the cargo region, PROJEMAR evaluated this study to minimize the steelwork inside the cargo region, and to optimize the steel weight for topside supports. PROJEMAR analyzed three different concepts of topside supports: two transverse bulkheads supporting each topside module, two sets of strong brackets supporting each topside module, and sets of pillars supporting each topside modules. The results present the amount of steelwork inside and outside the cargo tanks, the total amount of steel reinforcement after the evaluation of stress, deflection, buckling and fatigue verification. The conclusions present cost and benefit for each solution, and some discussions on the time acceleration for the conversion.