海洋立管涡激振动频域和时域预报方法研究

发布时间：2017-12-30 19:07

本文关键词：海洋立管涡激振动频域和时域预报方法研究　出处：《上海交通大学》2014年硕士论文　论文类型：学位论文

【摘要】：随着海洋石油开采不断向深海发展，立管的安全性对于石油工业的发展以及海洋环境的维护至关重要。洋流中立管两侧交替泄涡引起的涡激振动现象是立管疲劳损伤的主要因素，严重威胁着立管的安全。因此，准确的估算立管在实际海洋环境中的涡激载荷及动力响应，不断优化立管的结构设计一直是海洋工程领域中的重要课题。本文首先开展了系列海洋立管模型实验，通过高雷诺数下刚性圆柱体强迫振荡实验研究，为频域和时域预报模型提供高雷诺数升力系数数据库，提高实尺度立管涡激振动响应预报精度；同时，通过柔性立管在均匀流和剪切流下自激振荡实验，研究立管主导模态的时域特性；然后利用频域方法对立管模型涡激振动响应进行预报、并与实验结果进行对比，探究频域方法的适用性和局限性；最后本文提出了一种半经验性的时域预报方法，期望解决立管遇到的变轴向力、立管-土壤耦合等非线性问题，并将时域预报结果与实验结果进行了对比。论文内容主要包括以下几个方面： 1.对均匀来流下刚性圆柱体做不同幅值和频率强迫振荡时的水动力特性进行了实验研究，得到了升力系数、阻力系数和相位角等与无因次振荡频率、振幅之间的关系曲线，从而为频域和时域预报模型提供高雷诺数升力系数数据库，提高实尺度立管涡激振动响应预报精度；并通过对比本试验数据与低雷诺数试验数据得到了在亚临界区域雷诺数对涡激振动特性的影响。研究发现，在亚临界区域，雷诺数对涡激振动特性的影响很小，因此用低雷诺数试验数据来预报实际海洋环境下的立管涡激振动是合理的，但只限于实际海洋环境的雷诺数处于亚临界区域的情况。 2.通过拖曳试验和旋转实验模拟了立管模型在均匀流和剪切流下的涡激振动响应情况，分别利用模态叠加法和小波方法对两种流场下立管在横向和流向上的幅值响应特性和主导频率的时域响应特性进行了分析；此外，本文还利用逆有限元方法将柔性立管位移响应作为输入条件计算出了附加质量系数在立管上的分布情况，期望能够对频域和时域经验模型中附加质量系数的选择提供科学依据。研究发现了一些有趣的现象，对于均匀流工况，虽然流向上的主导模态对应的固有频率并不是横向上2倍，但是两个方向上的锁定频率却总是呈2倍关系，原因可能在于流向和横向上的附加质量系数能够自己调整、直至两个方向上的主导模态对应的固有频率正好为2倍关系；此外，无论在均匀流还是在剪切流工况下，均发现了主导模态的“间歇”特性，在剪切流中该性质则更加明显，对于这种工况，频域方法已经基本不再适用。 3.对频域理论预报过程进行了详细的阐述，并利用频域方法对均匀流和剪切流工况下的柔性立管涡激振动进行了预报。与试验结果进行对比发现，对于剪切流下单模态涡激振动，频域方法十分适用，预报准确度很高；但是对于均匀流工况和剪切流下多频耦合工况，频域理论预报结果比较差。此外，本文还通过频域数值计算方法研究发现，轴向预张力对立管涡激振动的模态和幅值都会产生较大的影响，从而可以推断出涡激振动导致的轴向力变化会进行反馈、对涡激振动响应又产生影响，而且影响极有可能不可忽略；因此，对于剪切流单模态涡激振动宜采用频域方法，对于均匀流、剪切流多模态以及考虑变轴向力等非线性因素时，则需要研究新的时域预报方法。 4.通过研究发现，频域预报方法对于多频耦合响应因素的简化处理以及对于变轴向力因素的忽略，会导致较大的预报误差；因此本文提出半经验性的时域预报方法对立管在均匀流、剪切流和阶梯流下的涡激振动响应进行了预报，并与实验结果和频域预报结果进行了对比，，发现与实验结果吻合很好，从而证明了该时域预报方法的可行性和可靠性。理论上，这种时域预报研究方法基本上适用于解决海管中遇到的绝大多数非线性问题。
[Abstract]:With the continuous development of ocean oil exploitation to the deep sea, vertical pipe safety for the development of the petroleum industry, it is crucial to maintain the marine environment. The riser VIV currents on both sides of the turn of vortex shedding is the main factor caused by riser fatigue damage, a serious threat to the safety of the riser. Therefore, the accurate estimation of vortex shock load and dynamic response in real marine environment, constantly optimize the structure design of tube has been an important topic in the field of marine engineering.
This paper carried out a series of marine riser model experiment, through the high Reynolds number of rigid cylinder forced oscillation experiment, provide high Reynolds number of lift coefficient database for frequency domain and time domain prediction model, improve the real scale riser VIV response prediction accuracy; at the same time, through flexible risers in uniform flow and shear flow oscillation experiment self study, riser time-domain characteristics of dominant mode; then using frequency method of riser VIV response prediction model, and compared with the experimental results, the applicability and limitations of the method in frequency domain; finally this paper proposes a time domain prediction method of a semi empirical, expected to solve the variable axial force vertical pipe encountered the vertical pipe soil coupling nonlinear problems, and the time-domain prediction results are compared with the experimental results. The main research contents are as follows:
1. to do under the uniform flow rigid cylinder with different amplitudes and frequencies of the forced oscillation hydrodynamic characteristics are studied experimentally. The lift coefficient, drag coefficient and phase angle and the dimensionless oscillation frequency, the relationship between the amplitude of the curve, thus providing high Reynolds number database for the lift coefficient in frequency domain and time domain prediction model, improve full scale riser VIV response prediction accuracy; and the influence on the vibration characteristics of the vortex in the subcritical Reynolds number is obtained by comparing the regional test data and test data of low Reynolds number. The study found that in the subcritical region, the Reynolds number effect of vortex excited vibration is very small, so a low Reynolds number test data to predict the actual ocean environment of vortex induced vibration is reasonable, but only a Reynolds number of actual marine environment in the subcritical region.
2. by towing test and rotating experimental simulation of vortex induced vibration model in uniform flow and shear flow response, respectively, using the modal superposition method and the wavelet method of two kinds of flow in the horizontal and vertical pipe flow on the amplitude response characteristics of the time domain and the dominant frequency is analyzed; in addition, this paper also uses inverse finite element method of the displacement response of flexible riser as input to calculate the added mass coefficient in vertical distribution on the tube, expect that the added mass coefficients in frequency domain and time domain experience model selection to provide a scientific basis. The study found some interesting phenomena, for uniform flow conditions, although the dominant the corresponding flow mode natural frequency is not horizontal 2 times, but the frequency locking in two directions but always is 2 times, the reason may lie in the flow and the additional quality The amount of their natural frequency coefficients can be adjusted, the dominant mode corresponding to the two directions until just 2 times; in addition, both in uniform flow or in shear flow conditions were found in the dominant mode of "intermittent" characteristics, the nature is more obvious in shear flow, in this condition, the frequency domain method is no longer applicable.
3. of the frequency domain prediction process in detail, and the use of frequency domain method for uniform flow and shear flow conditions of the flexible riser vortex induced vibration was predicted. Compared with the experimental results showed that the shear flow for single modal vortex induced vibration, the frequency domain method is very applicable, the forecast accuracy is very high; but for uniform flow and shear flow conditions under multi frequency coupling condition, frequency domain theory prediction results are relatively poor. In addition, this paper also through the frequency domain numerical calculation method research found that the vortex induced vibration of axial pre tension riser mode and amplitude will have a greater impact, which can be inferred from the axial force changes of vortex induced vibration will lead to feedback, but also have an impact on the vortex induced vibration, and the impact is likely not to be ignored; therefore, the shear flow of vortex induced vibration of single mode should be adopted for the frequency domain method, uniform flow, shear flow It is necessary to study the new method of time domain prediction when multimodal and nonlinear factors such as variable axial force are considered.
4. through the study found that the frequency domain prediction method for multi frequency response coupling simplified factors and neglect of variable axial force factors, will lead to larger forecast errors; therefore this time prediction method of semi empirical in uniform flow in the riser, vortex induced vibration shear flow and step flow responses of the forecast, and compared with the experimental results and the frequency-domain prediction results, that are in good agreement with the experimental results, which proves the feasibility and reliability of the time domain prediction method. In theory, the time domain prediction research method basically applicable to solve pipe sea most nonlinear problems.

【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P742;P751

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