Vibration Analysis And Suspended Control Of Suspended Pipeline In Seafloor

Submerged pipelines are the lifeline of the offshore oil field. But it is significant toanalysis and control the suspended pipeline, because the ocean environment of the submarinepipeline is complicated and variable especially the suspended pipeline caused by many kindsof factors, such as the current scour, the construction of the residual stress and so on, whichincreases the operation risk of the pipeline. In this paper, the main research object is thesuspended pipeline in seafloor, the types and the reasons of the suspended pipeline,taking theinfinitesimal section of the pipeline, the inner fluid and the pipe wall in the section are forceanalyzed respectively,list the vibration differential equation of the deformation pipeline by thegravity action and the force analysis of the submarine pipeline by the current scour aresystems introduced.The first ten natural frequencies under the different length and thevibration mode of suspended pipeline of the pipeline in Chendao sea area are researchedthrough the ANSYS Workbench software.Because of the vortex-induced vibration caused bythe resonance of the long free span, we should check the pipeline in time in order to preventthe pipeline being broken in actual engineering.The natural frequencies of the two ends of thefree span under the different stiffness are simulated by the software,we find that the differentconstraints of the two ends of the free span have an effect on the natural frequencies of thepipeline and the bigger stiffness is, the bigger the natural frequencies are.That is to say, thesafety and the service life of the pipeline are easily affected when the resonance of thesuspended pipeline easily happened because of the hard interface in seafloor, such as rock andso on. In order to further explore the suspended pipeline affected by the current scour, thestress of the suspended pipeline in seafloor is analyzed, the displacement of the verticaldirection at the middle part of the suspended pipeline, which under the different length andthe different velocity of the current scour and the stress distribution of the whole suspendedpipeline are stimulated through the ANSYS Workbench software and the stress distribution ofthe pipeline and the variation curve of the middle part are obtained.The determination methodof the maximum allowable length of the suspended pipeline was proposed taking the criticalreduced velocity for standard, and the maximum allowable length of the suspended pipeline inthe environmental parameter of the paper was calculated using this method.The generalapplied methods are given for the management of the target area suspended pipeline andtreated as the reference for the design and construction of the special pipeline in seafloor.