| As a typical deepwater platform, with its ability to resist the wind, to adapt to the wide scope of work depth, drilling capability, and many other advantages, semi-submersible platform has been widely used in offshore oil exploration and development. Different from shallow fixed jacket platform, deep water floating platform complying with the function of the Marine environment, the platform in the Marine environment has very complicated motion response characteristics, and the motion response of the floating platform is directly related to the personnel safety, equipment safety, normal production and drilling methods. Therefore, accurate prediction of hydrodynamic and motion response of semi submersible platform has vital significance on platform drilling work.This paper uses software AQWA based on potential flow and software FINE / Marine based on viscous flow to analyze the hydrodynamic performance,motion responses and air gap of the semi-submersible platform. The retrofit design and optimization are carried out with the vertical displacement of semi-submersible platform as the main target.The LINE module of the software AQWA is used to make frequency domain analysis on hydrodynamic force of the semi-submersible platform in order to get the added mass, radiation damping and the amplitude response operator under different wave angles, first order wave force and the two order wave force and other hydrodynamic coefficients. FINE/Marine software is used to realize the platform’s forced sinusoidal motion. By observing the motion curve of the platform and the force curve on the moving direction, the viscous quality and damping of the platform are obtained by mathematical model conversion.With the application of DRIFT module of AQWA software, numerical simulation of motion response of semi-submersible platform is carried out under seven kinds of sea condition, five Angle of wave to a total of 35 kinds of working conditions to get the duration curve of six degrees of freedom motion and acceleration of the platform and the calculation results of 35 kinds of working conditions are classified and analyzed according to the wave direction Angle and wave parameters. The results show that the platform surge and yaw performance can meet the requirements of specification. The platform heave motion amplitud is large and the maximum value reached 15.7m which exceeds the standard requirement.The platform roll extreme reached 28 degrees and bow wave reached 12 degrees which are both more than 10 degrees of the norm and pitching performance of the platform can meet the specification requirements.The platform sway acceleration reaches 1.5m/s2 and surge acceleration reaches 1.7m/s2, transverse acceleration is relatively large which can cause the discomfort of human labor and the heaving motion acceleration is in line with the requirements of specification.The viscous damping of the semi submersible platform is obtained by the method of free attenuation numerical simulation.With the viscous dampingadded to the potential flow software AQWA artificially, the motion response of the platform is predicted and the viscous damping and the influence of Viscous damping and potential flow damping on semi-submersible platform are analyzed. The results show that with viscous damping increasing,surge motion decreases 6% and transverse motion decreases 26% and heave motion decreased 16% in average, roll motion decreases 68% and pitch motion decreases 23% and yaw motion decreases 20% in average. This shows that the influence of viscous damping can not be ignored.Based on viscous flow and potential flow software, the air gap of the semi submersible platform is analyzed and compared with the self compiled program. In order to observe the variation of the air gap of the semi-submersible platform under various operating conditions easily, 34 observation points are arranged on the platform and the observation points are mainly located at the edge of the platform and the surrounding of the column. Results show that the negative gap occurs mainly at the edge of the platform deck, and negative clearance of the semi-submersible platform based on viscous flow calculation is generally greater than the potential flow theory results.According to the heave motion formula and relevant experience of the semi-submersible platform, with the platform vertical displacement and acceleration as the main target, the amplitude and acceleration of the rolling and pitching are considered comprehensively and relevant retrofit scheme of the platform is proposed.The movement performance of each scheme is analyzed and compared with the prototype and the optimal scheme is selected finally.The hydrodynamic performance, hydrostatic decay and viscous athletic performance are researched for the optimal modification scheme.The results of the movement response all comform to the standard. |
PDF Full Text Request