附属圆柱对海洋立管涡激振动抑制效果研究

发布时间：2018-06-18 13:10

本文选题：涡激振动及其抑制 + 高速摄像技术　；参考：《西南石油大学》2017年硕士论文

【摘要】：海洋油气运输立管在复杂海洋环境中受到海流冲击,会导致立管发生涡激振动现象,而涡激振动是诱发海洋立管失效的重要原因之一。海洋油气输运工程中常常在立管周围布置或安装涡激振动抑制装置以增加其服役周期和降低失效概率。近年来,我国涡激振动及其抑制的研究虽然有所发展,但相比国外,大柔性、大长径比柔性管及相关抑制的研究工作还存在一定差距。随着我国对海洋资源的重视,海洋油气工程的飞速发展,柔性立管涡激振动及抑制研究工作亟待开展。本文基于有效利用海洋立管周围附属管缆的设想,针对柔性管涡激振动和附属圆柱对涡激振动抑制效果进行物理实验研究和数值模拟分析。对不同数量、不同安装位置的附属圆柱在不同流速下的抑制效果进行了探究。首先,对实验水槽进行流速测试,根据水流条件,建立柔性管模型实验,经过简单测试,对于无法达到实验条件的水槽进行改造。构建非介入测量——高速摄像技术应用于本文物理实验研究,以获取柔性管涡激振动位移。通过将裸柱和装有附属圆柱的柔性管置于不同流速的均匀流中,由于实验水槽的限制,约化速度范围只能达到一阶振动的下端分支,只观察到了一阶振动模态。由于呈现一阶振动状态,振幅最大处均为跨中,频率随约化速度增大而呈线性增加,流速范围内立管运动轨迹均为"8"字形,立管振动形态大多数以管道中点对称。附属圆柱能有效的抑制柔性管涡激振动响应,抑制效果最大达到90%。安装附属圆柱后柔性管振动频率变化规律基本不变,频率相比裸柱有所降低;附属圆柱会导致柔性管振动轨迹变得十分杂乱。附属圆柱设置在振幅峰值处抑制效果优于安装端部,非对称安装附属圆柱会使柔性管振形向安装一侧偏移。合理利用计算资源,对12inch(0.3048m)海洋立管进行了二维数值模拟。模拟实验均通过验证,验证参数采用物理实验测得参数,二维模拟结果更符合短直刚性圆柱振动变化规律。附属圆柱数量为8时,适应性最好,相比其余2个数量,抑制效果差异低于 30%。考虑到实验条件的限制,无法观察到物理实验柔性管尾部的旋涡形态和实时振动位形,利用CFX和Transient Structural对三维物理实验尺寸进行双向流固耦合模拟实验研究。相比二维模拟而言,三维模拟结果与物理实验结果更加接近,其取得一阶振动最大振幅对应的约化速度比二维相差更小。一阶共振区不同轴向距离能观察到不同尾流旋涡,两端呈2S,跨中附近为P+S和2P模式。安装附属圆柱的柔性管IL和CF振幅显著减小。可以明显观察到旋涡脱落受到了干扰。
[Abstract]:Marine oil and gas transportation risers are impacted by ocean currents in complex marine environment, which will lead to vortex-induced vibration of risers, which is one of the important reasons to induce the failure of marine risers. Vortex vibration suppression devices are often arranged or installed around risers in offshore oil and gas transportation projects to increase their service life and reduce failure probability. In recent years, although the study of vortex-induced vibration and its suppression has been developed in China, there is still a certain gap in the research work of large flexibility, large aspect ratio flexible tube and related suppression. With the rapid development of offshore oil and gas engineering in China, the research on Vortex induced vibration and suppression of flexible risers needs to be carried out. Based on the assumption of effective use of the attached pipe cable around the marine riser, the physical experimental study and numerical simulation analysis are carried out for the Vortex induced vibration of the flexible tube and the suppression effect of the attached cylinder on the vortex-induced vibration. The suppression effects of different numbers and different mounting positions of attached cylinders at different velocities were investigated. Firstly, the flow velocity of the experimental flume was measured, and the flexible tube model was established according to the flow conditions. After simple test, the flume that could not reach the experimental condition was reformed. Non-interventional measurement-high speed camera technique was constructed to obtain the Vortex induced vibration displacement of flexible tube. By placing the bare column and the flexible tube with an attached cylinder in a uniform flow with different velocities, the reduced velocity range can only reach the lower branch of the first order vibration due to the limitation of the experimental flume, and only the first order vibration mode is observed. Because of the first-order vibration state, the maximum amplitude is in the middle span, the frequency increases linearly with the increase of the reduced velocity, the trajectory of the riser in the velocity range is all "8" zigzag, and the vibration pattern of the riser is mostly symmetrical at the midpoint of the pipe. The attached cylinder can effectively suppress the vortex-induced vibration response of the flexible tube, and the maximum suppression effect is 90%. The vibration frequency of the flexible tube after installing the attached cylinder is basically unchanged and the frequency is lower than that of the bare column, and the attached cylinder will cause the flexible tube vibration trajectory to become very chaotic. The suppression effect of the attached cylinder at the peak amplitude is better than that at the end of the installation, and asymmetric installation of the attached cylinder will make the vibration of the flexible tube move to one side of the installation. Two dimensional numerical simulation of 12inchus 0.3048m ocean riser is carried out by using calculation resources reasonably. The experimental results show that the parameters are measured by physical experiments, and the results of two-dimensional simulation are more suitable for the vibration variation of short straight rigid cylinders. When the number of attached columns was 8, the adaptability was the best, and the difference of inhibition effect was lower than that of the other two. Considering the limitation of the experimental conditions, it is impossible to observe the vortex shape and the real time vibration configuration of the tail of the flexible tube in the physical experiment. The bidirectional fluid-solid coupling experimental study on the three-dimensional physical experimental size is carried out by using CFX and transient structure. Compared with the two-dimensional simulation, the three-dimensional simulation results are closer to the physical experimental results, and the reduction velocity corresponding to the maximum amplitude of the first-order vibration is smaller than that of the two-dimensional simulation. Different wake vortices can be observed at different axial distances in the first order resonance region. The amplitudes of IL and CF for flexible tubes with attached cylinders are significantly reduced. It can be observed that the vortex shedding is disturbed.
【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】：TE973.92

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