海底管线的冲刷极限与动力调整研究

The submarine pipeline is the most important transport tool of oil & gas in ocean resource exploitation. Because the ocean environment is very complicated, the submarine pipeline break caused by erosion and free span can always be discovered from newspapers and other media , so it is an incomputable amount for its economic loss and environmental pollution caused by pipeline destroy. The wave and tide current directly lead to scour and erosion of submarine pipeline, however, the extreme weather is an sudden change factor of pipeline broken,so that we carry on the study on the scouring limit and dynamic adjustment of submarine pipeline will have very high science value and engineering application prospect. . Field investigation and non-lineal theory analysis as well as system models tests will be used to study the stable erosion hole size and extreme scouring one of submarine pipeline under the condition of normal weather and extreme weather in this proposal project, respectively. The inner relation between normal erosion size and extreme scouring one and their mechanism will be found, and a forecast model for calculating extreme scouring depth and width will be set up too. On this basis, in order to perfect the erosion theory of all weather environment and innovation of erosion calcualtion method and dynamic adjustment design for pipeline safe working.The effect of dynamic adjustment on the extreme scouring hole will be further studied, and the size of flexible plate fixed on the pipeline will be established by all kinds of comparasion experimental data.

海底管线是海洋油气资源传输的重要方式，由于复杂的海洋动力环境所造成的冲蚀-悬空-破坏屡见报端，其经济损失与环境污染无法估量。波与流是引起海底管道局部冲刷的直接动力；而极端天气是导致海底管线冲刷积累达到极限冲刷破坏的突变因素。开展极端天气环境下的海底管线局部冲刷极限与动力调整研究，不仅具有很高的学术价值，而且具有广阔的工程应用前景。本课题拟采用野外调查、非线性理论分析、系列物理模拟试验相结合的方法，重点开展正常天气环境中的海底管线稳定冲刷尺度与极端天气环境下的冲刷累积导致的极限冲刷尺度的研究，找出两种冲刷深度的内在累加关系，弄清海底管线冲刷破坏的复杂动力耦合机制，建立管线极限冲刷尺度的预测模型。在此基础上，探讨柔性导流板对海底管线极限冲刷破坏的减灾效果，确立最优导流控制尺度，实现海底管线全天候冲刷理论的丰富与完善。

海底管线是油气传输的主要方式，因复杂的海洋动力环境所造成的冲蚀悬空破坏屡见报端，其经济损失与环境污染无法估量。波与流是引起海底管道局部冲刷的直接动力，而极端天气产生的复杂动力环境是导致管线冲刷积累达到极限冲刷破坏的诱导因素,开展复杂动力环境作用下的海底管局部冲刷极限与动力调整研究，不仅具有很高的学术价值，而且具有广泛的工程应用前景。本课题借助于动力分析和非线性理论推导，建立了海底管线冲刷的临界压差、动休止角、冲止流速和稳定冲刷深度的计算公式，以及管线冲刷演变过程的非线性关系；利用波流水槽和大型波浪水池中的系列物理模型试验手段，对不同浪向的单个管线冲刷与动力叠加效应、以及子母管线的冲刷机理和动力耦合效应做了机理研究和动力响应分析；基于紊流模型、泥沙起动和输运模型的二次开发，成功模拟了海底单个管线、子母管线的冲刷演变过程，以及动力参数随环境动力变化的响应机制；同时，利用导流板、管线沟槽和管线表面柔性体对海底管线动力调整做了数值模拟研究，得到了能有效改变管线前后压差和局域压力分布的调控效果。应用有限体积法和VOF方法对恒定流作用下水下管道局部绕流流场进行了数值模拟分析，得到了考虑水面变化时的管线周围床面压力分布情况，讨论了水深、单向导流板及双向导流板长度对压差的影响。在此基础上，基于多孔介质假设，通过修改动量方程对管道周围海床的渗流场进行了数值求解计算，分析了导流板长度对水力梯度分布的影响，并对导流板的临界长度进行了研究分析。