Research On The Multi-body Coupling Dynamics Of The Subsea Manifold Based On The Sheave Installation Method

With the development of offshore oil industry from shallow water to ultra-deep water,as well as increasing weight and size of subsea equipment,the sheave installation method,as one of the methods for installing subsea equipment in ultra-deep water,was applied in Brazil offshore oil and gas development project due to its advantages of better bearing performance,deeper water depth and higher safety.The application of the sheave method is still blank in China.Therefore,it is necessary to study the dynamic response of installing the subsea manifold by the sheave method.In this paper,a kind of subsea manifold is taken as the research object.Based on the relevant data and literature obtained from the investigation,the sea conditions in the northern continental slope area of the South China Sea and the process flow of the sheave method for installing subsea manifold are sorted out.The hydrodynamic coefficients of the subsea manifold is calculated by using Morrison’s equation.Based on the coupling model of the cable and the manifold,the mechanical characteristics of the coupling motion of the cable and the manifold are solved by using the simultaneous Morrison equation and the catenary equation.The numerical model of vessel-cable-manifold is established to solve the problem of excessive structural offset,large angle turnover and cable breakage that may occur during the lowering process.By means of simultaneous equations of Morrison equation,catenary equation and basic equation of vessel motion,the motion posture and dynamics response of a single model under environmental conditions are obtained.And the response characteristics of vessel-cable-body coupled motion are obtained by using the lumped method and applying the same boundary conditions.By theoretical research,numerical calculation and comparison study,the results of the effect about current speeds and wave heights on coupled motion between wire ropes and manifold can be obtained,which is of great engineering guiding significance for improving the safety reliability,positioning accuracy of the manifold,as well as the development of offshore oil and gas in the northern continental slope area of the South China Sea.