Study On Fluid - Solid Coupling Dynamic Model Of Deep Water Test String And Its Application

In the process of deepwater hydrocarbon test, the pressure fluctuation of oil and gas fluid and the operation of the control system cause the motion state change of fluid and the free vibration of pipe system. The free vibration reaction on fluid intensified pipe vibration effects. The interaction of fluid flow, pressure fluctuation and pipe vibration is called fluid-structure interaction (FSI).Affected by the internal and external motivation, the deepwater testing pipe is prone to vibration easy with the action of FSI. This vibration mode is mainly reflected in three aspects:First, when valve was emergency shut down, the velocity of gas and oil to zero at the mouth of well, which caused hoopstrain of testing pipe. It will lead to fluid pressure pulsation and testing stress wave. Second, if the external frequency equal to testing pipe frequency, which will cause sympathetic vibration of testing pipe system. Third, if the fluid flow in testing pipe exceeds critical velocity, it will cause testing pipe vibration in horizontal direction, resulting flutter instability of testing pipe. The three kinds of vibration caused by interaction between fluid and testing pipe will affect the performance of pipe. It can cause the destruction of testing pipe structure. So, in order to avoid testing pipe failure which caused by fluid-structure interaction, the interaction between fluid and pipe must be considerated before designing testing pipe.This paper based on Timoshenko beam theory firstly, established the static equation of testing string system in marine environment, combined with the boundary conditions of deepwater testing pipe, and using the finite difference method to calculate lateral deformation of testing pipe. Secondly, combined with the deformation characteristics of deep water testing pipe, the time domain analysis and the frequency domain analysis were used to establish different modeling theory by adopting straight instead of curved pipe, and calculated stress strain curve and free vibration of deepwater testing pipe in fluid-structure interaction. Finally, through the VISUAL BASIC and FORTRAN programming technology, we developed a deepwater testing pipe dynamics analysis software by using FSI theory to realize its application in engineering.In the process of analysis of fluid-structure dynamic interaction to deepwater testing pipe, this paper use different computation models to analyze pipe dynamic response. In time domain analysis, starting from the structure constitutive relation and the elastic, we establish the mechanical model of14equations of testing pipe under consideration of Poisson coupling and Junction coupling. After using the method that replacing curve by straight to simplifies testing pipe mechanics boundary, the dynamic response curve of testing pipe are calculated using characteristic line.For deepwater testing pipe system, The results of study have an important theoretical significance and the practical significance to take measures to inhibit or reduce the vibration of the system in the process of design deepwater testing pipe. They also can guarantee operation effective of testing pipe by analysis of coupled vibration characteristics of pipe and the prediction of the vibration response of system.