海底管道在不平整海床上的高温屈曲及液化稳定性研究

发布时间：2019-05-24 00:52

【摘要】：随着海洋油气资源的不断开采,海底管道的铺设力度也不断加强,其运行的稳定性直接关系到整个输送系统的连续性与安全性。由于海管所处的环境非常复杂,在受到波浪、流、地震、高温、高压等荷载作用下很容易出现失稳现象,海床的不平整性也是造成海底管道失稳的原因之一。当海床液化时,海底管道会发生很大的上浮位移,严重影响海底管道的安全性。对于埋设于海床中的海底管道,其失稳方式主要为竖向屈曲。本论文以Ansys程序为平台,提出海底管道在不平整海床上的竖向屈曲模拟方法。模型中以非线性弹簧模拟管土相互作用,弹簧刚度采用ASCE规范中的定义方法,该方法考虑了土壤粘聚力、内摩擦角、上覆土压力、管线直径等因素。因此本论文主要讨论海底管道搁置在不平整海床上时,海床不平整度、轴向摩擦系数、内压、土壤类别和以上几种因素对其整体稳定性的影响。对于处于液化海床中的海管,在液化土壤中会受到浮力作用而发生较大的上浮位移,因此本论文从减小海管上浮位移和应力的角度出发,提出了三种方法使海管保持稳定。三种方法分别为间隔回填不易液化材料、间隔锚固、间隔设置简单门式框架。有限元模型中考虑了海管的几何与材料非线性。计算结果表明,海床不平整度、粘聚力和内摩擦角对海管的竖向屈曲过程影响较大。内压大小不会改变屈曲发生的突然性。而轴向摩擦系数对海底管道屈曲前的位移和屈曲安全温度的影响微乎其微,但对海管屈曲后的竖向位移影响较大,对于保持海底管道屈曲后的稳定性有重要影响。对于液化海床下三种保持海管稳定的措施中,三种方法均能有效的减小海管的上浮位移,但间隔锚固措施不能有效的减小海管应力。因此建议采用间隔回填和间隔设置简单门式框架来保持海底管道的稳定性。
[Abstract]:With the continuous exploitation of offshore oil and gas resources, the laying strength of submarine pipeline is also strengthened, and the stability of its operation is directly related to the continuity and safety of the whole transportation system. Because the environment of sea pipe is very complex, it is easy to appear instability under the action of wave, current, earthquake, high temperature, high pressure and so on. The unevenness of sea bed is also one of the reasons for the instability of submarine pipeline. When the sea bed is liquefied, there will be a great floating displacement of the submarine pipeline, which will seriously affect the safety of the submarine pipeline. For the submarine pipeline buried in the seabed, the instability mode is mainly vertical buckling. In this paper, based on Ansys program, the vertical buckling simulation method of submarine pipeline on uneven sea bed is proposed. In the model, the nonlinear spring is used to simulate the interaction between pipe and soil, and the spring stiffness is defined by ASCE code. This method takes into account the factors of soil cohesion, internal friction angle, overlying earth pressure, pipeline diameter and so on. Therefore, this paper mainly discusses the effects of seafloor roughness, axial friction coefficient, internal pressure, soil type and the above factors on the overall stability of seafloor pipelines when they are shelved on uneven seafloor. For the sea pipe in the liquefied sea bed, the floating displacement will occur due to the buoyancy in the liquefied soil. Therefore, from the point of view of reducing the floating displacement and stress of the sea pipe, three methods are proposed to keep the sea pipe stable. The three methods are interval backfilling not easy liquefaction material, interval anchoring, interval setting simple door frame. The geometry and material nonlinear of sea tube are considered in the finite element model. The calculation results show that the unevenness of the sea bed, cohesion and internal friction angle have great influence on the vertical buckling process of the sea tube. The magnitude of internal pressure does not change the sudden occurrence of flexion. However, the influence of axial friction coefficient on the displacement and safety temperature of submarine pipeline before buckling is minimal, but it has a great influence on the vertical displacement after buckling of submarine pipeline, and has an important influence on maintaining the stability of submarine pipeline after buckling. Among the three measures to keep the sea pipe stable under the liquefied sea bed, the three methods can effectively reduce the floating displacement of the sea pipe, but the interval anchoring measure can not effectively reduce the stress of the sea pipe. Therefore, it is suggested that interval backfilling and interval setting simple door frame should be used to maintain the stability of submarine pipeline.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P756.2

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