海洋立管内部气液段塞流动特性及其流致振动研究

发布时间：2018-02-11 17:09

本文关键词： 柔性立管段塞流流致振动自由悬挂高速摄像 CFD　出处：《西南石油大学》2017年硕士论文　论文类型：学位论文

【摘要】：海洋立管作为海洋油气生产中的重要枢纽,被誉为海洋石油中的生命线。立管在外部洋流与内部油气两相流的共同作用下,其振动特性变得极其复杂。国内外学者对外流作用下的立管涡激振动已经做了大量的研究,这方面的成果已经相当丰富成熟,但气液段塞流作为海洋立管中最常见的流型,由它诱发的管道振动不可忽视,目前少有对自由悬挂的柔性立管的内流规律与振动规律的同步研究。因此,本文针对气液两相内流作用下的柔性立管内部段塞流流动机理及其诱发的立管振动问题,综合运用实验和数值模拟方法,探究内流作用下的柔性立管振动和内部流体流动规律。首先,基于相似比尺模型设计了实验尺寸下的柔性立管模型,利用高速摄像机捕捉内流形态与立管位移,压力传感器捕捉立管底部压力变化,开展了共30组不同气液速度下的立管两相流及流致振动实验,通过分析发现实验组次共可分为三种流型:拟严重段塞流、水动力段塞流和过渡流;立管振动呈现一定的周期性,且随液体速度增大,立管位移总体上呈现出逐渐减小的趋势;立管空间位形上的均方根振幅曲线反映出立管在x方向振动存在一个波峰,在z方向上振动存在两个波峰,一个波谷;在振动过程中有多个频率共同参与。立管在不同位置的振动轨迹形状相异,在立管底部振动轨迹为"1字"形,中部为"纺锤"形,上部以"长条"形为主;立管底部压力变化与管内流体分布规律有关,液体流速越大,平均压力越大,压力波动幅度越小;不同组次的管内流体分布明显相异,液体速度越大,液塞长度越短,液塞运移速度越大;拟严重段塞流的四个周期能在实验组次中明显观察到。对比固定立管条件下的气液内流实验发现,立管固定后引起底部压力波动幅度变小,压力平均值呈现小幅度的上下波动;管内长液塞被气体分割成多个短液塞,这也是造成压力值变化规律存在差异的直接原因。利用计算流体力学软件,基于双向流固耦合技术,建立了三维柔性立管气液两相流及流致振动数值模拟方法,模拟计算结果与实验值变化规律吻合,但在数值上有一定差异,最大平均误差为30%。数值模拟可以展现出立管表面在振动过程中的等效应力分布,表明立管上下端固定点是应力值最大位置。数值模拟结果很好地解释和补充了实验结果。
[Abstract]:As an important hub in offshore oil and gas production, marine riser is regarded as the lifeline of offshore oil and gas. The vibration characteristics have become extremely complicated. Scholars at home and abroad have done a lot of research on the vortex-induced vibration of risers under the action of outflow. The results in this field have been quite rich and mature, but the gas-liquid slug flow is the most common flow pattern in marine risers. The pipe vibration induced by it can not be ignored. At present, there are few researches on the internal flow and vibration law of the flexible riser with free suspension. Aiming at the mechanism of slug flow in flexible riser and the induced vibration of riser under the action of gas-liquid two-phase internal flow, the experimental and numerical simulation methods are used synthetically in this paper. The vibration and internal fluid flow of flexible riser under the action of internal flow are investigated. Firstly, the flexible riser model with experimental dimensions is designed based on the similarity scale model, and the internal flow pattern and riser displacement are captured by high speed camera. The pressure sensor captured the pressure change at the bottom of the riser and carried out 30 experiments of riser two-phase flow and flow-induced vibration under different gas-liquid velocities. Through analysis, it was found that the experimental group could be divided into three types of flow patterns: pseudo-serious slug flow. The riser vibration presents a certain periodicity, and the riser displacement decreases gradually with the increase of liquid velocity. The root-mean-square amplitude curve on the spatial configuration of the riser shows that there is a wave peak in the vibration of the riser in the direction of x and two peaks and a trough in the direction of z. In the process of vibration, there are many frequencies participating together. The vibration trajectory of riser in different positions is different. The vibration track is "1 word" at the bottom of riser, "spindle" in the middle, and "long strip" in the upper part. The variation of the pressure at the bottom of the riser is related to the distribution of fluid in the tube. The larger the liquid velocity, the greater the average pressure, the smaller the pressure fluctuation, the more different the fluid distribution in different groups, the larger the liquid velocity, the shorter the slug length. The four periods of pseudo-serious slug flow can be observed obviously in the experimental group. Compared with the gas-liquid flow experiment under fixed riser condition, it is found that the pressure fluctuation at the bottom becomes smaller when the riser is fixed. The average value of pressure fluctuates in a small range, and the long plug in the pipe is divided into several short plugs by gas, which is also the direct cause of the difference in the law of pressure change. Using computational fluid dynamics software, based on bidirectional fluid-solid coupling technology, A numerical simulation method for gas-liquid two-phase flow and fluid-induced vibration in flexible riser is established. The simulation results agree with the experimental values, but there are some differences in numerical value. The maximum average error is 30. The numerical simulation can show the equivalent stress distribution of the riser surface during vibration, indicating that the fixed point of the upper and lower end of the riser is the largest position of the stress value. The numerical simulation results explain and supplement the experimental results well.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE952

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