|Alternative Title||Sliding-rolling Mechanism and Analysis Model for the Lateral Instability of the Pipeline in Currents|
|Place of Conferral||北京|
Previous studies on the lateral instability of the pipeline seldom paid attention to the rolling motion at the pipe-soil interface, while in the detailed lateral breakout process of submarine pipelines under ocean currents, the sliding and the rolling motion could be coexistent. In this thesis, the mechanical loading tests, hydrodynamic tests were carried out to investigate the sliding-rolling mechanism in the process of lateral instability of the submarine pipelines. Eventually an analysis model for pipeline sliding-rolling instability is established.
A series of mechanical loading tests were carried out to investigate the characteristics of the soil resistance and the pipeline motion in the lateral instability of submarined pipelines. The test results indicate that the ultimate lateral soil resistance of the pipeline increases with the increase of the dimensionless submerged pipeline weight, but the corresponding dimensionless soil resistance coefficient decreases gradually and finally approaches a stable value. When the dimensionless submerged weight of the pipeline remains unchanged, the ultimate lateral soil resistance and its dimensionless coefficient increase with the increase of the ratio of the initial pipeline embedment to the diameter of the pipeline. Meanwhile, a series of hydrodynamic tests were conducted in a large fluid-structure-soil interaction flume. The results indicate that under ocean currents, the critical Froude number of the pipeline instability increases with the increase of the dimensionless submerged pipeline weight and the ratio of the initial pipeline embedment to the diameter of the pipeline.
In mechanical loading and hydrodynamic tests, it is found that the sliding and the rolling exist simultaneously at the pipe-soil interface in the lateral instability of submarine pipelines. The sliding-to-rolling ratio was introduced to characterize the sliding-rolling motion in the process of the pipeline lateral instability. On the basis of the dimensional analysis, the variation of the sliding-to-rolling ratio with the relative lateral displacement, the dimensionless submerged weight, the ratio of the initial embedment to the diameter of the pipeline was discussed. When the lateral displacement is small, the sliding dominates, and then the pipeline gradually tends more to roll. With the development of relative lateral displacement, the sliding-to-rolling ratio shows a nonlinear decreasing trend. There exists a positive correlation between the sliding-to-rolling ratio and the dimensionless submerged weight, or the ratio of the initial embedment to the diameter of the pipeline.
The numerical method was used to simulate the quasi-static process of the pipeline lateral instability, and the plastic zone of seabed soil and displacement increment vector field in the process of the pipeline lateral instability were further investigated. The numerical model was verified by the results of the mechanical loading test. On the basis of the rolling friction mechanism and the principle of quasi-static torque balance, the prediction model for the pipeline lateral rolling instability is given. On the basis of the interfacial sliding friction mechanism and the principle of quasi-static force balance, the prediction model for the pipeline lateral sliding instability is given. Making the correlation analysis, an analysis model for the pipeline sliding and rolling instability is established.
|徐凯. 海流作用下海底管道侧向失稳滑滚机制及分析模型研究[D]. 北京. 中国科学院大学,2019.|
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