Analysis And Research On Scale Effect Of Anti-motion Structure Of Cylindrical FPSO

Floating Production Storage and Offloading(FPSO)plays a pivotal role in the process of offshore oil and gas resources extraction,which is a multifunctional oil recovery platform integrating production,storage,loading and offloading.The cylindrical FPSO has good isotropic characteristics among them,but a large swing motion amplitude will be produced under the survival sea condition,and the increase in the bottom of the anti-motion structure is beneficial to improve the heave motion performance of the cylindrical FPSO.Therefore,it is a great of engineering importance to study the structure.In this thesis,the cylindrical FPSO is the main object of study,and the following aspects are studied by adding an anti-motion structure at its bottom and conducting motion response analysis:(1)Based on the three-dimensional potential flow theory,the six configurations of anti-motion structure of the cylindrical FPSO are selected and designed.The wave period of5～64s with an interval of 1s is selected,and the hydrodynamic performance analysis is carried out by AQWA to obtain the additional mass and motion response transfer function of the drogue motion,and the mooring cable design is calibrated.The results show that the mooring cable design meets the requirements,and the suppression performance of heave motion is best for configuration Ⅰ(annular rectangular anti-motion structure).(2)STAR-CCM+ was used to numerically simulate two types of cylindrical FPSO with and without the anti-motion structure,and analyzing the heave motion suppression mechanism of the anti-motion structure in terms of water mass fraction,vortex motion,velocity change and interface pressure.In addition,a three-dimensional model with a scaling ratio of 1:77.8 is used to analyze the influence of different heights of the extended cylinder based on the theory of similarity,the change of height and width of the anti-motion structure,and the different connection forms between the anti-motion structure and the extended cylinder on the heave motion performance of the cylindrical FPSO.The results show that the increase of the anti-motion structure and the extended cylinder can significantly increase the intrinsic period of the cylindrical FPSO and keep it away from the once-in-a-century spectral peak period in the South China Sea.The optimal scale of the anti-motion structure is 11 m in height and 12 m in width,and the distance from the bottom of the extended cylinder is +1m,when the cylindrical FPSO has an optimal vertical motion performance.(3)The JONSWAP spectrum is selected to analyze the kinematic response of the cylindrical FPSO in the operating and survival conditions in the South China Sea,and the optimal scale range of kinematic performance is explored by changing the diameter of the main cylinder and the width of the anti-motion structure.The results show that the diameter of the extended cylinder is designed below 78 m and the width of the anti-motion structure is designed around 11.5m to produce a better heave motion suppression effect.