Dynamic Analysis Of Complaint Vertical Access Riser

In recnet years,with the advancement of science and technology,the offshore oil exploration and exploitation have been approached from shallow water to deepwater and even to the ultra-deepwaster.As the main artery of offshore oil and gas production,riser system plays an important role in the offshore oil exploration and exploitation.The main types of riser currently used in deepwater platforms include top tension riser,steel catenary riser and flexible riser.The applied depth is limited due to poor adaptability for top tension riser,the fatigue problem of the steel catenary riser is serious,as for the flexible riser,the cost of manufacture is expensive and can’t be adapted to the production conditions of high temperature and high pressure,so it is urgent to find a new type riser.Complaint vertical access riser(CVAR)is one of forms whose realative research just starts,it not only has the good adaptability,but also because of its vertical connection to the wells,various operations on the well can be performmed directly from the floating platform,and so greatly reducing the cost of operations.Based on the principle of virtual work and variational principle,this paper firstly adopts the updated Langelang coordinate system,fully considers the geometric nonlinearity of the riser,and introduces the high temperature and high pressure fluid action inside the riser into the mechanical model,creating a CVAR mechanical model.The Newton Iterative Method was used to compile the CVAR static analysis finite element program,and the program was used to analyze the static force of CVAR and propose a new improved configuration.After further correcting the buoyancy factor,the Newmark-β method was used to analyze CVAR dynamics in the time domain,and the sensitivity of the CVAR dynamic parameters was analyzed.Finally,a dynamic experiment of CVAR physical model is carried out by using the wave-flow combined sink and non-contact displacement measuring system,and the experimental results are compared with the numerical simulation results.The calculation results show that CVAR,as a new type of riser,demonstrates its excellent mechanical properties and unique operational advantages in both static analysis and dynamic analysis.The existence of the transition section plays a important role,inhibiting the vibration of the riser caused by the movement of the platform and the waves,ensuring the safety of the lower pipe section,and making the CVAR riser more adaptable to the extreme sea conditions.Through static analysis,it can be seen that the new configuration proposed in this paper has more operational advantages than the original configuration,which reduces the number of buoyancy moduls but effectively reduces the bending moment of the riser,making the upper and lower parts of the riser closer to vertical.According to the dynamic response analysis,the position of the platform has a great influence on the overall performance of the riser,so the appropriate platform position is particularly important.If the buoyancy moduls are placed too high,the bend moment of lower part will be too large and unstable.Increased fluid density can adversely affect the riser configuration.Reasonable buoyancy moduls arrangement can make the riser model realize CVAR configuration in the water tank.The test results are basically consistent with the numerical simulation results,and qualitatively verify the advantages of CVAR risers system.