Hydrodynamic Performance Analysis Of Mini-platform In Deeper Water

Spar platform is a kind of light-duty platforms working in deepwater, which has good motion performance in waves and less cost in construction. It is playing an important role in exploitation of petroleum in deepwater.In this paper, some hydrodynamic problems with 2-dimension for Spar platform with mooring system in waves are discussed from the ocean engineering point of view. Typical model of Spar platform is simplified, and the equations of three segments of the mooring line are derived. Limited tension analysis for the mooring line for given example is carried out in this paper. The verification of the hawser's strength in survival condition is also checked.The keystone of this paper is to investigate how to restrict the motion for the platform in waves from mooring system. Wind and current loads are neglected. Horizontal wave force and the wave moment are calculated by Morison equation. Vertical forces are composed by frictions and the perpendicular component of Morison force. As the hydrodynamic coefficients in the motion equations are changed with time and the generalized displacement of the platform, generalized displacement response in 3 degrees-of-freedom of spar platform while it is in single regular wave are calculated by solving motion equation in time domain. The JONSWAP spectrum with the significant wave height of 18m is analyzed as input spectrum to get displacement response spectrum, by which the characteristics of motions and loads of spar platform both in free condition and moored condition are forecasted.In this paper, the forces of the regular wave in each frequency segments are calculated by spectrum analysis directly. Transform spectrum are calculated later to get response spectrum. It is different from the usual method, which response spectrum is calculated by encounter spectrum that transformed from wave spectrum.Some approximations and assumptions are applied in this paper to solve motion equations and other calculations. The feasibility of these assumptions and approximations are also discussed.The restriction effect to the motion of spar platform by the mooring system is analyzed in this paper. The results show that the restriction by anchoring system is remarkable while spar platform in surge, and is slight while it is in pitch or heave. When spar platform is in pitch or heave, it is effective to restrict the platform by tension legs system (TLS).