The Study Of Intact Stability Analysis Of Asymmetric Semi-Submersible Platform

As floating offshore industry equipment,the semi-submersible platform has one most basic characteristics of intact stability,which has direct influence on the safety and performance of the platform.The stability analysis of the platform is essentially to study the shape and position of the GZ curve in order to check whether the platform is safe enough for operation.Compared with the conventional symmetric semi-submersible platform,the asymmetric semi-submersible platform has obvious advantages.The asymmetry of deck arrangement can be achieved by designing an asymmetric pontoon.This makes the arrangement of the platform completely dominated by the function without having to be limited by the center of gravity.Therefore,the general arrangement of the platform can be very flexible.Also the platform can achieve more functions and improve the work efficiency.The effect of twist axis on the intact stability of semi-submersible platform has been discussed here based on a real semi-submersible lifting and living platform.Firstly,the relative position of the center of buoyancy and the center of gravity for slender and sy,the dynamic righting arm surface and the residual dynamic righting arm surface should be obtained,and weakest axis is selected based on minimum residual energy.Secondly,an intensive study of wind moment calculation for semi-submersible platform and specifications for intact stability has been performed here.The comparison and analysis of requirements which formulated by IMO,DNVGL,ABS and CCS has been carried out and the similarities and differences between these rules and specifications have been analyzed and summarized.Aiming at the "Greta" asymmetrical semi-submersible lifting platform,the hydrostatic model and wind moment model of stability analysis have been established by using NAPA software.The heeling moment calculation of platform under 100 knots wind has been carried mmetrical floating body with unidirectional inclination has been discussed.However,the form of semi-submersible platform is usually non-symmetric and non-slender body,whose motion is usually not inclined in one direction,so torsional motion in 3d space with inclining moment.In order to accurately evaluate the anti-capsizing ability of the platformout for typical loading cases.Asymmetric platform is not a traditional centrally-symmetric platform.The differences of overturning moment in different directions and different inclination angles are studied to understand the characteristics of wind overturning moment.At the same time,under normal operating and storm survival conditions,DP is normally in working condition.The existence of DP will lower the center of lateral of the platform,and increase the overturning moment,and quantitative study of influence on the wind heeling moment has been performed.The selected asymmetric semi-submersible platform is unlike traditional ship type.During the heeling process,the lower pontoon will come out of the water and the upper deck will be immersed in sea water where it is complex process.The study of static hydraulic characteristic during transverse heeling process to have a clearer and intuitive understanding of static hydraulic characteristics and cause and effect on the platform stability.In the process of gradually heeling,two kinds of calculation modes are freely twist axis and fixed twist axis.For the conditions with different draught and the center of gravity height,the dynamic righting arm surface,the residual dynamic righting arm surface and the area ratio have been respectively calculated by the two kinds of calculation methods.The influences of draft and center of gravity height on the intact stability of the platform are obtained,and the differences of the stability of the platform at various azimuth angles can be intuitively observed,to provide theoretical guidance for the optimal design of the platform.