Study On Heave Suppression Of Deepwater Semi-submersible Platforms

The heave suppression of semi-submersible has always been of great concern to engineers.Good heave characteristics allow platforms to withstand harsh marine environments,increase their continuous operating time,and reduce the risk of damage to their riser system.This paper fully investigated the semi submersible heave inhibition status and development trend,the results show that the present stage of semi-submersible platform heave suppression focus on increasing draft,arrangement of Heave Plate,double floating body,optimization design and new concept design in five aspects.First,this paper takes A platform under the southern sea as the target platform and selected heave plate,waterline area,draft and displacement totally four parameters to carry on the discussion.The results show that: 1)the heave plate can increase the natural period of heave motion,and they can suppress the heave motion only when they were installed in deep water area;2)increase the waterline area and the draft both can inhibit the heave motion,but increase the waterline area will reduce the natural period of heave;3)3)the increase of the displacement has little influence on the heave motion,but it can obviously increase the natural period of heave.After that,we put forward the RVPA method on the basis of the field experience and the hydrodynamic theory,the advantage of this method is the structure of the existing platform to achieve less modification.The results of AQWA software simulation show that the RVPA method can significantly reduce the heave motion of the semi submersible platform,but also slightly reduce the natural cycle of the platform heave motion.Finally,according to domain analysis results,we put forward 5 sets scheme of semi submersible platform heave suppression.The effectiveness of these 5 schemes was verified by the frequency domain and time domain analysis.The results showed that these five schemes can suppress the heave motion,and except for the program A,the other programs reduce the heave response of work conditions,under the once a year,once in a decade,once in a hundred years sea conditions by more than 25%.