Ocean Space Utilization Using Very Large Floating Semi-Submersible

Very Large Floating Structures (VLFS) are highly specialized floating structures with variety of applications in the civil engineering of ocean. Their economic design is based on their hydro-elastic behavior due to wave environmental forces. VLFS are extra large in size and mostly extra long in span in the design feature for their applications. For that reason they are mostly modularized into several smaller structures and joined together in the site. The critical problem is the longitudinal bending moment of the long floating vessel in severe wave environment. With the result of that the present available VLFS designs become not economical for applications in hostile-ocean. This paper presents ocean space utilization using an innovative VLFS with truss pontoon concept. The concept uses a strong deck with strong longitudinal beams to take care of the needed bending moment of the vessel for the survival, standby and operational conditions of the ocean environment. At the submerged bottom just above the keel-tank top, a simple open-frame truss-structure is used instead of a heavy shell type pontoon. The truss-pontoon provides the necessary flow transparency for the reduction of the wave exciting forces and consequently reduces heave amplitude of motions and the vertical acceleration. Each individual columns of the truss pontoon semi-submersible is tuned to have heave-period over 22 sec, independently, such that minimum hydrodynamic-motions are obtained for the overall structure. The VLFS is designed with minimum heave for the extreme storms unlike the conventional column stabilized semi-submersible unit with conventional pontoon. The paper proposes a new VLFS concept which is feasible for applications in harsh environment. Most importantly cost effective VLFS is achieved. This paper presents the details of the VLFS design, stability, motion, and experimental verification from the physical wave-tank with the scaled-down model. At the end of the paper, a few comprehensive example applications are illustrated.