| With the development of China’s offshore oil industry and the increase of service time of submarine pipelines,the submarine pipelines in various sea areas are suspended to varying degrees.Different from the buried pipeline,the constraint state of the suspended section of the pipeline changes and it is directly exposed to the ocean environment under the joint action of wave and current,which increases the risk to failure.Meanwhile,due to the existence of the rugged topography of the seabed,it is very common for the elastic laying pipeline with elastic bending deformation to be suspended,but the existing research is mostly focused on the suspended straight pipeline.Due to the existence of elastic bending deformation,the structure of elastic laying pipeline is no longer symmetrical,and its vibration characteristics are no longer the same as that of straight pipeline.Therefore,it is necessary to study the suspended section of elastic laying pipeline,this paper has done the following work:(1)Based on the sea condition of Bohai Sea,the mechanical analysis of the suspended section of submarine pipeline is carried out.Combined with Morison formula and Airy wave theory,the load of wave induced vibration on the suspended section is obtained,and the load of vortex induced vibration is obtained based on the analysis of vortex discharge process.(2)In order to accurately characterize the interaction between pipeline and seabed soil and avoid the error caused by the setting of pipeline-soil contact length in the model,a 3D model with pipeline-soil coupling is established by using the finite element software ABAQUS.The infinite element is introduced to characterize the "infinite range" constraint effect of seabed soil on pipeline.Based on the model,modal analysis is carried out on the suspended section of the elastic laying pipeline.The effects of elastic bending deformation,suspended length and pipeline diameter on the natural frequency of pipeline are studied,and the safe frequency range to avoid resonance is determined.(3)In this paper,the wave induced vibration and vortex induced vibration of the suspended pipeline in different water depths are analyzed considering the coupling effect of the loads in the directions of in-line and cross-flow.In this paper,the fatigue life of the suspended section of elastic laying pipeline is predicted,and the effects of the suspended length,pipeline diameter,flow velocity and other factors on the vibration response and fatigue life are discussed.It is found that due to the existence of elastic bending deformation,the vibration response of the suspended section of the pipeline no longer shows symmetry,and the dangerous point of fatigue failure appears in the edge location of pipeline-soil contact area.It is helpful to prolong the fatigue life of pipeline to reduce the length of suspension and select larger diameter pipeline.(4)Based on the treatment measures and failure maintenance technology of submarine suspended pipeline at home and abroad,the innovative maintenance scheme is put forward,and the stress analysis of its construction condition is carried out.The mechanical analysis of interference installation in connector maintenance technology is carried out,and the prediction formula of installation load for connector installation is obtained. |
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