Low-frequency Liner Wave Loads And Motion Response Of TLP

With the worldwide demand of the source of energy and with the development of ocean engineering, the oil and gas will be the main natural energy of source in the coming century. There are broad seas in China, it has been explored where there are plenty of gas and oil in Nansea. Therefore, it is very important to exploit the deepwater in our country. The Tension Leg Platform (TLP) has been found to be the most suitable type of platforms in large water depths due to its favorable motion characteristics and its cost. In this paper, proper mathematic model and software have been built to calculate the low frequency liner wave loads, hydrodynamic parameters and motion response of TLP. Some important conclusions are obtained which are useful to the theory study and designing of TLPs. The main parts of this paper are shown as follow:Low frequency (0.1-0.5rad/s) linear wave loads of TLP are accurate calculated .TLP can be simplified as an array of stationary, truncated circular cylinders. The individual circular cylinder's diffraction characters were determined by boundary progressive matching method. Since the wavelength of the low frequency linear waves is much larger then the distance between the cylinders, we can make some predigesting to calculate the wave loads of TLP. Software has been programmed to calculate the example of TLP to certify the solution. Some simplified formulas were found for the designing of TLPs.Added-mass and added-damping coefficients of TLP were calculated. The loads from the radiation wave of the cylinder were calculated by boundary progressive matching method, and the hydrodynamic parameters were obtained by separating the variables. Software has been programmed to calculate the example of TLP to certify the solution.Mechanic analysis of TLP is the important part of TLP research. Quasi-Static mechanic analysis has been used to calculate the relationship of offset, set-down, tendon tensions and horizontal forces in this paper. Meanwhile, the two dimension dynamic model of TLP was built to calculate TLP's dynamic response in this paper. Interaction of surge and heave and interaction of main part of TLP and tendons were considered. By programming software, surge and heave response and the velocity of TLP motion were presented, it can be seen that the motion response of TLP could be predicted precisely.Through analysis to the surge response, we can find that when the frequency of the incident wave is too low to the inhered surge frequency of TLP, very big displacement will take place. So dangers aroused by low frequency wave must be taken into account in the course of designing TLP. The problems about the diffraction and the radiation of second order difference-frequency incident waves were studied. The low-frequency second order difference-frequency diffraction and radiation loads were calculated by ring-source integral equation about Green's boundary panels in the free-surface method.All the theories and methods were created in this paper are precise and refined to the dynamics analysis of TLP. They will fill the research blank of TLP in our country .The conclusions are very useful to research and design TLPs.