海底滑坡过程数值模拟及其对管线的作用

发布时间：2018-07-01 10:07

本文选题：海底滑坡 + 泥石流　；参考：《大连理工大学》2014年硕士论文

【摘要】：长时间降雨或暴雨过后,在山区很容易见到泥石流和滑坡。滑坡、泥石流不仅在陆地上会发生,在水面下(海底)也会发生。与陆地滑坡不同,在极缓的坡度下(0.5-3°),海底滑坡都能发生。大规模的海底滑坡滑移距离往往长达数百公里,这会严重损坏海洋平台、海底管线、电缆等海底设施,并造成严重的经济损失。为了避免灾害和降低经济损失,研究和预测海底滑坡的滑动过程及海底滑坡对海底管线的作用有重要意义。论文第一部分内容为模拟海底滑坡的滑坡过程。运用流体力学基本方程,如边界层近似理论、连续方程、动量方程、纳维-斯托克斯方程等,推导了Herschel-Bulkley及双线性(Bilinear)流变模型的控制方程及其差分格式。这些方程验证了一维海底滑坡模拟软件BING程序的准确性。之后,用ANSYS CFX与BING两款软件模拟了海底滑坡的运动过程,发现当泥浆抗剪强度越大时两款软件模拟的结果越接近。由于BING计算速度很快(普通计算仅需1～2分钟),对于抗剪强度大的泥浆,便可用BING模拟,这样可大大提高工作效率。第二部分内容是研究海底滑坡对海底管线的作用。准确的预测海底滑坡对海底管线的作用力是海洋工程师关心的问题。海底滑坡对管线的冲击力通常采用传统的流体力学的阻力系数来描述。Zakeri (2009)使用计算流体动力学(Computational Fluid Dynamics-CFD)方法,数值模拟了5种冲击角度下,富含粘土的海底泥石流对管线的冲击。并且,Zakeri提出了任意冲击角度下,计算管线所受的法向阻力和纵向阻力的方法。Randolph和White (2012)用土力学的方法,对Zakeri(2009)的数值结果重新进行了分析处理,提出用一条失效曲线来计算任意冲击角度管线所受的冲击力。本文采用CFD数值分析重新模拟了Zakeri (2009)的计算工况,并增加了更多工况。根据模拟的结果,发现冲击角度对法向阻力系数影响很大,但对纵向阻力系数影响甚微。接着得到了改进的近似公式,该公式能更准确的估算任意冲击角度悬浮管线受到的法向和轴向冲击力。用土力学的方法对这些数值模拟结果也进行了重新分析,得到了新的失效曲线。土力学方法预测的力与CFD计算的力结果很接近。
[Abstract]:Debris flows and landslides are easy to see in the mountains after long periods of rain or heavy rain. Landslides and mudslides occur not only on land, but also below the surface. Different from land landslides, submarine landslides can occur at a very slow slope (0.5-3 掳). Large scale landslides often slip hundreds of kilometers away, which can seriously damage offshore platforms, pipelines, cables and other submarine facilities, and cause serious economic losses. In order to avoid disasters and reduce economic losses, it is important to study and predict the sliding process of submarine landslide and the effect of submarine landslide on submarine pipeline. The first part of the thesis is to simulate the process of submarine landslide. The governing equations of Herschel-Bulkley and Bilinear rheological models and their difference schemes are derived by using the basic equations of fluid mechanics, such as boundary layer approximation theory, continuum equation, momentum equation, Navier-Stokes equation and so on. These equations verify the accuracy of the one-dimensional submarine landslide simulation software ing program. Then, ANSYS CFX and ing are used to simulate the movement of submarine landslide. It is found that when the shear strength of mud increases, the simulation results of the two software are closer. Due to the fast calculation speed of ing (only 1 / 2 minutes for ordinary calculation), the mud with high shear strength can be simulated by ing, which can greatly improve the working efficiency. The second part is to study the effect of submarine landslide on submarine pipeline. It is the concern of marine engineers to predict accurately the action force of submarine landslide on submarine pipeline. The impact force of submarine landslide on pipeline is usually described by traditional resistance coefficient of hydrodynamics. Zakeri (2009) using Computational fluid Dynamics-CFD method, numerically simulates the impact of clay rich debris flow on pipeline under five kinds of impact angles. And Zakeri proposed a method for calculating the normal and longitudinal resistance of pipelines at any impact angle. Randolph and White (2012) used the method of soil mechanics to reanalyze the numerical results of Zakeri (2009). A failure curve is proposed to calculate the impact force of the pipeline at any impact angle. In this paper, the computational conditions of Zakeri (2009) are resimulated by CFD numerical analysis, and more conditions are added. According to the simulation results, it is found that the impact angle has a great influence on the normal drag coefficient, but has little effect on the longitudinal resistance coefficient. Then an improved approximate formula is obtained, which can more accurately estimate the normal and axial impact forces on the suspension pipeline with any impact angle. The numerical simulation results are also reanalyzed by soil mechanics method, and a new failure curve is obtained. The force predicted by the soil mechanics method is very close to that calculated by CFD.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P756.2;P642.22

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