Study On Mooring Performance And Thrust Allocation Strategy Of Hybrid Positioning System

Nowadays,the world’s ocean oil and gas development trend is gradually moves towards the deep sea.More and more people are focusing on deep-sea engineering.The semi-submersible platform has the advantages of a small waterline surface and a large variable deck load.It has been widely used in the development of offshore oil and gas resources.Under the combined action of wind,waves,and current,the semi-submersible platform moves in six degrees of freedom.The mooring positioning system and the dynamic positioning system serve as platform positioning and motion restraint systems,which limit the platform’s movement within the operating allowable range,thereby ensuring the semi-submersible platform safety under operating conditions and harsh sea conditions.In this paper,the semi-submersible platform HYSY 982 with a working water depth of 1500 meters is used as the object to study the hydrodynamic analysis and positioning system performance.The main research contents of the paper include the following aspects:The hydrodynamic performance of semi-submersible platforms is calculated.The hydrodynamic model of the semi-submersible platform is established.After meshing,classic AQWA is used to perform a hydrodynamic analysis of the platform to analyze its hydrodynamic performance under the action of regular waves.The calculation is based on the three-dimensional potential flow theory.By calculating the frequency domain motion response under the action of regular waves,the additional mass and damping coefficient of the platform at each frequency,the motion response amplitude operator,and the first order at each direction and frequency are obtained.Hydrodynamic parameters such as wave force and second-order wave force.Through the numrical simulation,the hydrodynamic parameter library of the platform in the frequency domain is obtained,and the relevant laws of the platform’s movement performance in six degrees of freedom are analyzed in detail.Research the positioning performance of semi-submersible platform mooring positioning system performance.In order to study the influence of static characteristics of the buoys on the mooring line of the mooring system,establish static analysis model of single anchor line and anchor system.Based on the static analysis of the single mooring line and the mooring system,the sensitivity analysis of the position and buoyancy of the series buoys in the mooring line is performed,the influence of buoys with different positions and buoyancy on the static characteristics of the mooring line under fixed interference.Later,in order to analyze the influence of the buoys on the dynamic characteristics of the mooring system.On this basis,a time-domain coupling analysis is performed to establish a finite element model of the anchoring system at a water depth of 1500 meters,under different conditions of operation and survival in the South China Sea,and the six-degree-of-freedom motion response of the platform and the force of the mooring system are compared.It was found that series buoys in the mooring line can effectively reduce the tension of the mooring line,but reduce the positioning ability of the mooring system.Study on thrust allocation strategy for semi-submersible platform dynamic positioning.For the thrust optimization design of the "over-drive" dynamic positioning system,based on the principles of minimum energy consumption and reduced thrust wear,establish a reasonable mathematical model for thrust distribution.At the same time,in order to avoid the hydrodynamic loss caused by the thruster interference,four different methods of thrust restricted area treatment were compared.Analyze the difference between the four methods in the system energy consumption,thruster wear and thrust error in the direction of sway,surge and yaw,and finally a suitable treatment method was found.Among them,the dynamic setting of the feasible region has obvious advantages in reducing the thruster wear and reducing the thrust error.Adopt the method of setting thrust forbidden zone to keep the thruster running outside the thrust forbidden area,so that the system energy consumption is minimized.