| The top tensioned riser(TTR)system is a common riser form on the tension leg platform(TLP),which connects the subsea wellhead and the TLP to serve as the channel of oil and gas transmission.Therefore,ensuring the integrity of the TTR system in the complex and changeable marine environment is one of the research hotspots in the ocean engineering field.The top tensioner and wellhead connector,which are the core equipment of the TTR system,connect the TTR to the TLP and subsea wellhead to form a complete riser system for oil and gas production.However,the technology of the top tensioner and wellhead connector of the TTR system is monopolized by European and American countries,and domestic research is still in its infancy.With the implementation of China’s deep-sea strategy,mastering the key technology of the top tensioner and wellhead connector of the TTR system is of vital significance to break the monopoly of foreign technology and realize the independent exploitation of deep-sea oil and gas resources in China.A structural configuration of the top tensioner system and wellhead connector for the top tensioned riser system of the TLP in water depth of 405 m applied to a sea area in the South China Sea is designed and proposed in this paper.The drag force and inertia force of the wave on the TTR are obtained by the Morison formula,which also applied to the calculation models of the riser top tension and axial external load of the top of wellhead connector.Study the selflocking property of wellhead connector locking structure and the sealing performance of the sealing structure;derive the relation between axial preload and contact stress of the sealing structure.The axial external load and bending moment load of the wellhead connector are studied and provide a reference for the sealing design of the bottom wellhead connector.A top tensioner tension variation model with piston and piston rod masses and pipe losses is established to meet the need for the top tensioner system to provide stable tension to the TTR during operation;Based on Taylor first-order approximation method and Laplace method,a frequency domain model of the top tensioner tension variation is obtained,and then models of stiffness coefficient,natural angular frequency and damping ratio of the top tensioner system is derived;Through numerical simulation,the laws of the effect of the initial pressure and volume of the high-pressure accumulator,the initial pressure and volume of the low-pressure accumulator,the diameters of the piston and piston rod,the length and inner diameter of the oil pipe,etc.on the stiffness coefficient,natural angular frequency and damping ratio of the top tensioner system are studied,thus,the performance analysis of the top tensioner system can be realized.In order to study the dynamic bending moment load on the wellhead connector caused by the movement of the TTR riser,the contact of the metal sealing ring is established by analyzing the mechanical transfer relationship between the parts of the wellhead connector under preloading conditions and working conditions.The mathematical model of stress is used to obtain the relationship between the axial preload force,seal contact stress,driving pressure,and internal oil and gas pressure.The influence of bending moment load on the contact position of the metal seal ring is analyzed.And it is proved that the tension-compression effect generated by the bending moment lead to the decrease of the axial preload of the metal seal gasket on the tension effect side and the increase of that on the compression effect side,which causes the decrease of the contact stress of the metal seal gasket on the tension effect side and the increase of that on the compression effect side.Finally,the finite element simulation verification is carried out.A thermal-structural coupling stress analysis is carried out to research the problem that the sealing performance of the wellhead connector changes under fluctuating internal oil and gas pressure and temperature loads.Based on the theory of elasticity,the complex thermal stress function and Fourier’s law are used to solve the thermal stress for the steady-state and the transient heat conduction process.Based on the Lame formula and the coordinate system conversion method,the mathematical model of the three-dimensional stress caused by the internal pressure load and the contact is unified.The numerical simulation method is used to analyze the sealing contact characteristics and mechanical properties of components of the wellhead connector under different working conditions under steady-state and transient temperature fields.The temperature pressure cycle test is used to verify the sealing performance of the wellhead connector after thermal-structural coupling loading. |
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