Response Characteristics of Open-sea type Semi-submersible Type Very Large Floating Structure and its Mooring System

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A semi-submersible type Very Large Floating Structure (VLFS) is characterized by elastic response. Relations between major design parameters and response characteristics were investigated using simplified dynamic response model proposed by the authors. This model, a beam on elastic foundation, is simple but gives insight into relationship between dynamic response characteristics and major design parameters. Based on the design guideline obtained from this research, a conceptual VLFS is designed, and through a series of computer simulations and experiments, effectiveness of proposed design guideline was displayed. Hydroelasticity and hydrodynamic interactions is fully considered in the numerical analysis method proposed in this research.Lift force, an important load which has been less discussed so far, was investigated. Wind-wave tank experiments on semisubmersible type VLFS in regular progressive waves were conducted. The importance of lift force, especially at leading edge of deck, was verified from the experimental results : Lift forces and wind pressures were measured as a function of column diameter, unit number and wave conditions. The results showed that fluctuation in lift force caused by interaction between wind and wave was significantly large and can be comparable in magnitude to mean lift force in typhoon conditions. The lift force model consists of time averaged mean component and fluctuating component was proposed.General mooring characteristics of existing mooring systems were investigated. From this investigation, inclined tension leg mooring was proposed to makes horizontal motion pretically small. Progressive collapse behavior of inclined tension leg mooring system was studied in view of system safety. Experiments using 1/333 scale model were conducted. Time domain analysis program, in which in-plane response is modeled as a beam and out-of-plane response as a plate, was developed and experimental results were analyzed.