| COSCO Shipping has built four deep-water cylindrical floating drilling platforms in the past 10 years,three of which have been put into use and are currently serving in the Gulf of Mexico,Brazil and other sea areas.In this paper,the fourth cylindrical platform is taken as the research object,and its hydrodynamic performance is analyzed and studied according to the sea conditions in the South China Sea.The significance of this study is that the advent of cylindrical drilling platform provides a new choice for oil and gas exploration and development in deep water areas of South China Sea.The research on the applicability of this kind of platform in the South China Sea can provide theoretical basis and technical support for relevant departments,and it is also conducive to the development of hydrodynamic theory and the accumulation of data in China.Based on the three-dimensional potential flow theory,the hydrodynamic performance of the cylindrical floating drilling platform in the South China Sea is analyzed by combining numerical calculation with physical model test.The main contents of this paper are as follows: 1)platform stability analysis;2)numerical calculation of overall hydrodynamic performance of the platform;3)physical model test;4)preliminary design of tensioned mooring system;5)analysis of influence factors of platform coupling motion and optimization of mooring system scheme.The main conclusions are as follows:(1)Due to its special waterline and main hull shape,the cylindrical drilling platform has a high initial metacentric height and a large restoring arm.Under 100 knots strong winds,the platform can still meet the requirements of the rules with relatively high margin.(2)Based on the three-dimensional potential flow theory,the motion response of cylindrical drilling platform under waves is calculated.The natural period of platform heave is 15.93 seconds,the natural period of rolling and pitching is 26.82 seconds,and the short-term prediction of platform response is made.In the case of a 1000 yrp sea condition,the significant amplitude of platform surge is 6.326 m,the significant amplitude of heave is 6.610 m,and the significant pitch amplitude is 4.31 degrees.(3)The hydrodynamic performance model test of the cylindrical drilling platform in the South China Sea was carried out.The results show that the significant amplitude of surge is 1.996 m,the significant amplitude of heave is 0.994 m,and the significant amplitude of pitch is 3.16 degrees under the circumstance of 1yrp operation sea condition,and the significant amplitude of surge is 6.762 m,the significant amplitude of heave is 6.580 m,and the significant amplitude of pitch is 5.39 degree under the circumstance of 1000 yrp extreme sea conditions.It is found that the numerical calculation of vertical motion is in good agreement with the model test results,while the numerical calculation of pitch is 20.0% smaller than the experimental value,and the surge is 6.4% smaller than the experimental value.(4)A set of tension mooring positioning system is preliminarily designed and its hydrodynamic performance is numerically simulated in time domain.It is found that surge,heave and pitch are the main motion responses of the cylindrical drilling platform due to its axisymmetry.Under storm conditions,the maximum surge is 45.16 m,which is 3.0% of the water depth.This shows that the horizontal motion response of the platform is well controlled.The maximum heave response of the platform is 9.29 m and the maximum pitch response is 15.93 degrees,which indicates that the vertical motion of the platform is obvious under storm conditions and is not suitable for drilling operations.By calculating the force of mooring cables under environmental loads of 0 and 180 degrees,it is found that mooring cables are more dangerous in the direction of 0 degrees.No.6 and No.7 mooring cables,which bear the main mooring pull force,bear the greatest force 6905 KN,with a safety factor of 1.85,which just meet the requirements of the rules.(5)By analyzing the relevant factors affecting the coupled motion of cylindrical drilling platform,it is found that when the angle between mooring cable and sea surface becomes larger,the force of mooring cable will continue to increase,while the surge will decrease first and then increase;when the initial length of mooring cable decreases,the pre-tension and maximum pulling force of mooring cable will increase,and the horizontal motions of platform will increase.When the length of the mooring chain at both ends increases,the force of the mooring cable increases and the motion response does not change significantly.By comparing the three different combinations,it is found that the mooring cable is divided into three groups,with four in each group having the best results.In order to reduce the force of mooring cable,the scheme is optimized.After optimization,the maximum force of mooring cable is reduced by about 14.8%.Based on the optimization scheme,the calculation under normal drilling conditions is carried out,and the results show that the surge of the platform is 31.90 m,about 2.1% of the water depth,the maximum heave of the platform is 3.10 m,and the maximum pitch of the platform is 6.02 degrees,which basically meets the requirements of normal drilling.Finally,the calculation of the cable force and platform motion response under the condition of a broken mooring cable is carried out.The maximum force of the mooring cable is 7315 KN,the safety factor is 1.75,and the surge response is 72.99 m,which is about 4.9% of the water depth.All of these can meet the requirements of the rules. |
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