| The South China Sea is enriched with abundant oil and gas resource, which is over 33% of the total in China. As the demand of oil and gas increase, the exploitation of them in oceans has attracted much attention in the recent years. However, as the lack of the technology, the exploitation of ocean oil and gas in our country only is limited to the Bohai Sea and Beibu Gulf, but can not reach the South China Sea. Because of the great water depth, the fixed platform can't be economically constructed. The concept of the compliant platform has been introduced, and has become a research focus.The study and application of compliant platform started in the 1960s, and has formed a comprehensive technology in the advanced countries. However, in our country, the development of compliant platform techonology is still in its infancy, which hampers the oil and gas exploitation in deep water. Consequently, study on the compliant platform is very important for the development of China ocean industry, which will produce the enormous economic benefits and social benefit.In this dissertation, the motion performance of the semi-submersible platform subject to wind and wave has been studied, and the methods to decrease the heave motion of the platform have been discussed.The main contents of this dissertation can be demonstrated as follows:Firstly, the main types of the compliant platform used for ocean oil and gas exploitation, such as TLP, Spar, FPSO and semi-submersible platform, have been summarized, their structure feathers and developmental process have been demonstrated, and several new types of the compliant platform have been presented. Meanwhile, the studies on the compliant platform have been reviewed.Secondly, the wind loads and wind pressures acting on the semi-submersible platform have been studied by numerical and experimental simulation. In the numerical simulation, the N-S equation, 3-D steady implicit solver, 2nd order upwind discretization and sst k-ωturbulence model have been chosen for the calculation. Meanwhile, in the experimental simulation, two models, with the scale of 1:100 and 1:150, have been measured for wind loads and wind pressure distribution in wind tunnel respectively. By comparing the numerical and experimental results, the shape factors and wind pressure distribution of the platform have been studied, and the influence of platform pitch (roll) motion on the wind loads has been analysised.Thirdly, the motion performance of the semi-submersible platform subject to wind and waves has been studied by numerical and experimental simulation. In the numerical simulation, the wind loads are got from the results in the second chapter, the wave force is calculated by boundary element method, and the mooring force is calculated by piecewise extrapolating method. In the experimental simulation, the model with the scale of 1:100 has been used in the joint laboratory of wind tunnel and wave flume. By comparing the numerical and experimental results, the horizontal motion of the platform under different conditions has been studied, and the influence of wind loads on platform horizontal motions has been analysised.Fourthly, the air gap response of the semi-submersible platform has been studied by numerical and experimental simulation. In the numerical simulation, the platform motion and wave surface function have been calculated by boundary element method in time domain, and the air gap response of the points on deck downward surface have been calculated. In the experimental simulation, the model and laboratory are the same as them used in the third chapter. By comparing the numerical and experimental results, the air gap response of the points on the deck down surface have been studied, and the deck downward surface, where is possibly slapped by waves, has been analysised.Fifthly, based on the TMD concept, the conceptual design of a moveable heave-plate semi-submersible (MHS) platform has been put forward. The heave motion RAO of MHS platform has been calculated by iteration method, the connect stiffness between MHS hull and heave-plate has been optimized, and the platform pitch (or roll) motion has been decreased by enlarging the pontoon volumn.Lastly, based on the structure feature of Truss-spar platform, the conceptual design of Truss-spar-buoy platform used for wind tubine has been put forward. By numerical simulation, the influence of wind loads on platform has been studied, and the motion performance of the platform has been analysised in time and frequent domain respectively. Meanwile, to decrease the platform motion response, a position system with two groups of mooring line has been put forward.
|
PDF Full Text Request