Hydrodynamic Analysis And Lifting Research Of Submersible Dismantling Platform

With the plunge of international oil price,the exploitation of oil resources begin to slow down and the market demand for offshore platforms remain weak.In this paper,the number of decommissioning projects of offshore oil and gas facilities increases remarkably.According to investigation,there will be more than 600 offshore oil and gas facilities demolition project into service in the next 5 years,and the offshore scrapping industry market is approaching to a new peak of.Meanwhile the dismantling platform which undertakes the task of dismantling the abandoned platform appear.This research is based on three dimensional potential flow theory,and aims on target platform through ANSYS-AQWA.This essay analyzes the hydrodynamic performance of platform and studies the coupling problem of lifting and weight on its gravity center.The focuses are followed:(1)This section summarizes the past study of platform hydrodynamic analysis and lifting weight which are both national and international.Their researches cover mooring,dynamic response,crane load,platform load and so on.(2)Author interprets common mooring types,mooring theory,wave theory and wind flow empirical formula in this section,and then goes through the AQWA Catenary mooring and wind flow formula which are verified by simple calculation examples.(3)The platform geometry and mesh is built by ANSYS.Calculations on platform hydrodynamic performance which are including mass,radiation damping,amplitude response operator,wave force are done through AQWA,What’s more,the content mentioned above provides the basis for the subsequent dynamic response calculations about semi-submersible under the compound of complex wind and wave circumstance.Results of calculations turn out that the hydrodynamic performance of the platform is better than contrast group when the wave period is longer than 20s,which means the influence of steady force and radiation damping on the platform asymmetric structure is greater.(4)Based on the results of frequency-domain analysis in section(3),catenary mooring,tension mooring and dynamic position are analyzed as 3 different method through AQWA in order to calculate the degree of freedom of motion under different environmental loads on the platform and stress on the mooring line.The results show that under the restrain of 4×2 catenary,the motion response of the disassembled platform is small and the force stays in tolerable rank.However,yaw amplitude is quite large,the force of the mooring line exceeds the allowable range when authortest the tension type mooring line,the dynamic positioning yaw is small but the pitch and roll are large under such circumstance.So the catenary arrangement is proved to be the best option.(5)After taking catenary mooring arrangement into account,author focuses on the dynamic response of the platform under the impact of environmental load in a wide water area.In order to make the conclusions convincible,this essay concludes analysis of 72 environmental load cases with different angles.The results show that six degree of freedom dynamic response is relative small and flow direction almost has no effect on the mooring line stress.But the wave direction has greatest matter.Among the 72 samples,XB-27 is the most dangerous working condition.Under su ch condition,the wind direction is 90°,the wave direction is 90°,and the flow direction is 135°.(6)The operation model of platform lifting is established to measure the inf luence of tide on the platform movement under light lifting load in the last section.The results show that when the platform is lifted from underwater to certain a height,rotation angle of the crane is mainly affected by its sway.In the aspect of tide analysis,the motion response of the platform has a strong relation with ebb.Last but not the least,the case assumes lifting object is at a height and the lifting load is constant in order to calculate the motion response of the disassembly platform.The result shows that at condition of great lifting load,when the rotation angle of the boom is 90°,the mooring line is under the greatest tension.When the same environment load is lifted lightly,maximum stress cable turns into the opposite direction cable of environment load.The influence of large lifting load on dynamic response has taken over the environmental load.