| People begin to focus on deep-sea resources because of the shortage of land energy,and the safety performance of deep-sea valve pipeline system in oil and gas transmission system arises more attention.But the underwater environment is complex,wave force and ocean current force will not only change the dynamic characteristics of the valve pipeline system,but cause pipeline resonance and increase the probability of instability,which will seriously affect the safety and service life of the valve pipeline system.Based on the research on the dynamic response and vortex-induced vibration of underwater structures under the action of wave and current force at home and abroad,this paper explored the distribution of wave-current force,and studied the dynamic response and vortex-induced vibration of the deep-sea valve-pipeline system under the action of simple harmonic dynamic load.The specific work is as follows:(1)The main background and significance of this study were described.It briefly introduced the research status of ocean wave force,ocean current force and vortex-induced vibration at home and abroad.The linear wave theory,Morison formula method for calculating wave force and ocean current force,as well as the calculation process and theory of pre-stressed modal analysis and harmonic response analysis were introduced.(2)Combined the linear wave theory with Morison formula method,the numerical values of wave force,wave-current interaction force and ocean current force at different water depths were calculated by using visual mathematical software MATLAB,and the curves were drawn and compared according to the data.Comparisons showed that they were all harmonic loads.With the increase of water depth,the wave force decayed quickly.And when it reached a certain depth,the wave force could be neglected.In addition,the comparative data of the same water depth showed that the wave force had a great influence on the wave force when the wave force under the influence of ocean currents.Therefore,it was necessary to consider the effect of wave and current interaction on the valve pipeline system.(3)Shallow water wave and current force have a great impact on the structure.The pre-stressed modal analysis and harmonic response dynamic analysis of the valve pipeline system were carried out by using Fluent software and ANSYS Workbench software.It was found that the natural frequencies in the pre-stressing mode were slightly higher than those in the dry mode.The main reason was that the stiffness of the structure increased to a certain extent because of the pre-stressing force.The harmonic response frequency curves showed that the peak acceleration of the str ucture was achieved at the fourth,fifth and sixth frequencies,i.e.41Hz,61Hz and 68Hz.(4)Further explored the influence of ocean currents,and two-dimensional flow around a cylinder was analyzed with the method of LES and FFT transformation.The vortex shedding diagram displayed the whole cycle of the vortex shedding,and the lift curve was a harmonic curve with periodic distribution.The discharge frequency of the vortex could be obtained from the power spectral density curve,and it was found that there was no risk of resonance in the valve pipeline system.(5)The phenomenon of vortex-induced vibration under critical span length of subsection support in valve pipeline system was investigated.It was found that the critical span length calculated by dynamic and static methods varies with the way of support mode,the longest was when fixed at both ends and the shortest was when simply supported.The valve pipeline system would not resonate at the critical span length under the calculation of f_s<0.7f_p. |
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