Influence Of Dynamic Water Pressure On Deep-sea Valve Pipeline System Under Earthquake Load

With the continuous progress of offshore oil and gas development technology.The world has made remarkable progress in deep-sea oil and gas development.The national technical investment in deep-sea oil recovery equipment is increasing continuously.As a key part of subsea oil and gas production system.Deep-sea valve pipeline system has proposed a higher demand for its safety and stability in complex deep sea environment.Under seismic load.The interaction of deep-sea valve pipeline system with seawater produces hydrodynamic pressure,which not only changes the dynamic characteristics and dynamic response of the system,but also increases the probability of system failure.The safety and service life of the system are tested severely.In this paper,the methods of modal analysis and seismic response analysis of underwater structures considering fluid-structure coupling at home and abroad are summarized.The wet modal vibration characteristics and fluid-structure coupling seismic response of deep-sea valve rigid structure and deep-sea valve pipeline flexible system are discussed.The research work is as follows:1.The research background and significance of this subject are introduced.The research status of wet modal vibration analysis and seismic response analysis of underwater structures and the analysis and calculation method considering the interaction between fluid and structure are described.The basic theory of acoustic finite element method and Morison formula method for calculating the hydrodynamic pressure of underwater structure is explained.2.Taking the finite element analysis software ANSYS Workbench as the simulation platform.The acoustic finite element method and Morison formula method are used to calculate the wet modal vibration characteristics and seismic response of deep-sea valve rigid structure.The results show that the natural frequency of the wet modal of the deep-sea valve is less than the natural frequency of the dry modal.The existence of water causes the structure to be unsafe under external dynamic excitation.The acoustic finite element method and the Morison formula method are similar and consistent in the calculation of low order wet modal of structures.Under the action of different types of seismic waves.Earthquake hydrodynamic pressure increases the dynamic response of the structure.3.Taking into account the actual engineering conditions.In order to ensure that the deep-sea valve pipeline system will not undergo static damage and vortex-induced vibration during installation and operation.The critical span length of deep-sea valve pipeline system is calculated by dynamic and static method.At the same time,it verifies the independence of the current force.Taking a deep-sea valve pipeline system with overhanging length as an analysis object.The acoustic finite element method and Morison formula method are used to study the characteristics of wet modal vibration and seismic response of the system.The results show that the existence of water significantly reduces the natural frequency of the system,and the wet modal analysis is more accurate than the low-order natural frequency.Different from the seismic response analysis results of deep-sea valve rigid structure.The effect of earthquake hydrodynamic pressure on the dynamic response of flexible system is obvious.The horizontal displacement and the acceleration response of the middle valve body node are obviously increased.The acoustic finite element method and the Morison formula method are similar in seismic response analysis.The influence of earthquake hydrodynamic pressure on underwater flexible structures can not be ignored in earthquake-prone sea area.4.The influence of span length and support mode on seismic response of deep-sea valve pipeline system is discussed.The results show that the longer the span length,the more obvious the dynamic response of the system.The greater the dynamic response of the system under the condition of both ends.