海底管道与桩柱受力特性数值模拟

发布时间：2018-01-04 19:01

本文关键词：海底管道与桩柱受力特性数值模拟　出处：《浙江大学》2015年硕士论文　论文类型：学位论文

【摘要】：海底滑坡等地质灾害是引起海洋结构物(海底管线、桩柱等)破坏的主要原因之一。海底油气管道是深海油气输运的重要生命线,由于海底管道长距离输运,经历的海底地形崎岖、起伏变化大,海底管道容易形成局部悬跨段,而这些悬跨段所在的海沟、海槽等低洼区域往往是海底滑坡泥流的主要输运通道,严重威胁着管道的在位稳定性。海底滑坡泥流的流速极快,改变了周围水域的流动,极易造成影响区域内的海洋结构物的破坏。由于海洋结构物(桩柱)的存在,对水流的阻流作用,其周围流场发生改变,形成桩前水流下降、马蹄涡以及尾涡等现象,这些现象造成桩柱周围海床的局部冲刷,因此,对桩柱的稳定性提出了更高的要求。目前关于地质灾害对海洋结构物影响的研究主要以模型试验和数值模拟(CFD)为主,其中模型试验是在岩土力学和流体力学两大理论的指导下研究流体与结构的相互作用,而数值模拟作为技术手段再现模型试验的结果,相互验证其可靠性和适用性。本文的研究主要是以有关文献的模型试验结果为依据,从数值模拟角度研究了海洋结构物与流体的相互作用,并将数值分析结果与实验结果进行了对比分析。本文关于海洋结构物(海底管线、桩柱)与流体相互作用方面完成了以下工作： 1.在数值计算中采用赫巴模型模拟海底滑坡泥流,得到了与实验相近的结果,证明了计算模型的合理性,进一步优化了无量纲拖曳力系数与非牛顿流体雷诺数之间的关系,得到了管道拖曳力系数随非牛顿流体雷诺数的增大而减小的规律,研究了不同悬跨高度下管道拖曳力系数的变化,发现管道拖曳力系数随着管道悬跨高度的增大而增大,最后保持稳定；在Renon-Newtonian一定的情况下,存在临界悬跨高度比(H/D)Critical,在小于此值时,管道拖曳力系数随之增大,大于此值时,管道拖曳力系数保持稳定；给出了海底管道法向拖曳力系数与管道悬跨高度之间的关系,提出了更为合理的管道拖曳力计算方法； 2.采用三种湍流模型对桩柱周围流场的变化做了数值模拟分析,得到了与前人研究相近的结果,证明了计算模型和湍流模型的合理性,详细分析了群桩桩间距、湍流模型、床面类型及粗糙度、水流速度变化及其水深变化对桩柱周围流场变化的影响,得出以下结论：桩间距S/D4时,桩柱周围流场变化的相互影响越小；湍流模型对桩周流场分布影响较大；光床时桩周流速要比粗床时的大；床面粗糙度D/Ks越小,对桩周靠近床面附近的流场分布影响越大；来流速度越大,桩前下降水流速度增大,桩前马蹄涡现象有增强趋势,桩前形成顺压梯度区；桩侧流速增大,发生流动分离,桩柱两侧分离角向后移动；桩后流速减小,形成逆压梯度区；桩前出现马蹄涡现象,桩前0.5D范围内受到马蹄涡的影响。
[Abstract]:Submarine landslide and other geological hazards are one of the main causes of damage to marine structures (submarine pipelines, piles, etc.). Submarine oil and gas pipeline is an important lifeline of deep sea oil and gas transportation, because of long distance transportation of submarine pipeline. The undersea topography is rugged and fluctuating greatly, and the submarine pipeline is easy to form local overhanging section, and the trench and trough in which the overhanging section is located are often the main transport channel of the submarine landslide mudflow. It is a serious threat to the stability of pipeline. The velocity of mud flow in submarine landslide is very fast, which changes the flow of surrounding waters. It is easy to cause the damage of ocean structure in the affected area. Because of the existence of the ocean structure (pile column), the flow field around the water flow changes and the flow in front of the pile drops. The phenomena such as horseshoe vortex and wake vortex cause the local erosion of the seabed around the pile column, so the stability of the pile column is required higher. At present, the research on the influence of geological hazards on marine structures mainly consists of model test and numerical simulation (CFDs). The model test is based on the two theories of rock and soil mechanics and fluid mechanics to study the interaction between fluid and structure, and numerical simulation is used as a technical means to reproduce the results of the model test. The research in this paper is mainly based on the model test results of relevant literature and studies the interaction between ocean structures and fluids from the point of view of numerical simulation. The numerical results are compared with the experimental results. In this paper, the following work has been done on the interaction between ocean structures (submarine pipelines, piles and columns) and fluids: 1. In the numerical calculation, the Herba model is used to simulate the mudflow of submarine landslide, and the results are close to those of the experiment, which proves the rationality of the calculation model. The relationship between the dimensionless drag force coefficient and the Reynolds number of non-Newtonian fluid is further optimized, and the law that the drag force coefficient decreases with the increase of the Reynolds number of non-Newtonian fluid is obtained. The variation of towing force coefficient under different suspended span heights is studied. It is found that the towing force coefficient increases with the increase of the suspended span height of the pipeline and remains stable at last. In the case of Renon-Newtonian, the critical ratio of suspended span to height is H / D critical, and when it is less than this value, the drag coefficient of the pipeline increases. When the value is greater than this value, the drag force coefficient of the pipeline remains stable. The relationship between the normal drag force coefficient and the suspended span height of the pipeline is given, and a more reasonable method for calculating the towing force of the pipeline is put forward. 2. Three kinds of turbulence models are used to simulate the flow field around the pile column, and the results are similar to those of the previous researches, and the rationality of the calculation model and the turbulence model is proved. The influences of pile spacing, turbulence model, bed surface type and roughness, flow velocity and water depth on the flow field around the pile column are analyzed in detail. The following conclusions are drawn: when the pile spacing is S / D _ 4. The interaction of the flow field around the pile column is smaller; The turbulence model has a great influence on the distribution of flow field around the pile. The velocity of pile circumference in bare bed is higher than that in thick bed. The smaller the bed roughness D / Ks, the greater the influence on the distribution of the flow field near the bed surface. The larger the velocity of flow is, the greater the velocity of descending flow in front of pile is, and the phenomenon of horseshoe vortex in front of pile is increasing, and the gradient region is formed in front of pile. The flow separation occurs when the velocity of the pile side increases, and the separation angle moves backward on both sides of the pile column. The velocity of flow behind the pile decreases and the inverse pressure gradient zone is formed. The horseshoe vortex appears in front of the pile and is affected by the horseshoe vortex in the range of 0.5 D in front of the pile.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P756.2;TU470

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