【作者】 林琳；

【导师】 王言英；

【作者基本信息】 大连理工大学 ， 船舶与海洋结构物设计制造， 2013， 博士

【摘要】 随着世界对石油需求量的逐年增加,石油短缺的矛盾越来越突出,为缓解该矛盾,人类逐渐从陆地钻井发展到海上钻井,并逐年加大了深海石油勘探、开发的力度。作为深海油气用开发系统结构的重要组成部分,海洋立管以其全新的形式、动态的特性以及高技术特点变得格外引人注目。海流、波浪及平台的运动不断作用于立管之上,尤其是当涡脱落频率接近立管的固有频率时,会引起立管的共振,发生所谓的“锁定”现象,严重时甚至会引起立管的疲劳损坏,缩短立管的使用寿命,因此在立管的设计过程中首先要考虑涡激振动的影响。本文的研究内容包括三大部分：一是绕圆柱湍流场计算尺度效应的研究及湍流场发展变化的研究；二是弹性支撑刚性圆柱体涡激振动的数值计算；三是立管在真实海洋环境下的非线性涡激动力响应研究。本文通过阐述我国海洋石油开采能力与世界先进水平的差距以及涡激振动对立管设计的重要性,论证了本文选题的理论意义和工程意义。分别从实验流体力学方法(EFD)、计算流体力学方法(CFD)和半经验方法(SEM)总结和归纳了涡激振动的研究进展,指出了当前涡激振动研究领域存在的一些亟待解决的问题。同时系统地阐述了涡激振动的机理、详细归纳了涡激振动的相关参数,并概述了求解湍流运动和流固耦合问题的数值方法。对雷诺数103～107范围内圆柱体的绕流场进行了大量细致的数值计算。应用雷诺平均纳维尔——斯托克斯方程(RANS),通过方程分析得到了有关湍动能和湍流耗散率这两个表征湍流脉动特性的相似数,用以衡量湍流计算的尺度效应,并给出相似数随雷诺数变化的规律。结果表明,在主流方向的尾流中心线上当Re≥3×106时,湍动能和湍流耗散率随着雷诺数的变化趋于平稳。而后研究了四种计算尺度下的湍流场及其发展变化(包括流向平均速度场、涡量场、湍流动能和湍流耗散率),并比较了不同计算尺度下圆柱湍流场的特征。最后,对Re≥3×106这一雷诺数范围的湍流场特征进行了详细的研究,给出湍流脉动量在下游的发展变化规律。采用雷诺平均纳维尔——斯托克斯方程(RANS),结合RNG k-ε和SST k-ω这两种不同的湍流模型,研究了低质量比弹性支撑刚性圆柱体的自激振动问题。从频率响应、振幅响应、对升力的谱分析、三个响应分支的水动力性能、尾涡模式和计算效率等方面比较了两种湍流模型的模拟效果,结果表明SST k-ω湍流模型在整体上优于RNG k-ε湍流模型。并对振动圆柱体的三个响应分支(初始分支、上端分支和下端分支)的湍流场(包括壁面压力系数、壁面切应力系数、流向平均速度、流向速度脉动值、横向速度脉动值和雷诺应力的分布)及其发展变化进行了研究,与同等雷诺数下固定圆柱体的湍流场进行了对比。建立了真实海洋环境下立管三维非线性涡激动力响应控制方程。采用Morison方程求解顺流力；Facchinetti改进的尾流振子模型求解横向升力,考虑了附加质量系数的变化：轴向力的计算考虑平台的升沉运动。在计算分析中考虑的非线性主要包括大变形引起的几何非线性、流体动力非线性和流固耦合非线性。在边界条件的处理上,综合考虑了波浪、海流、平台运动(升沉和纵荡运动)的影响,并且上下边界的处理考虑了转动刚度的影响。采用更新的拉格朗日方法(Updated Lagrangian Method)解决大变形引起的几何非线性问题,采用Newton-Raphson迭代法求解非线性方程组。在此基础上讨论了三维空间立管的非线性涡激动力响应的影响因素。同时,研究了高雷诺数剪切流条件立管的多模态涡激振动响应,讨论了剪切参数对立管涡激动力响应的影响,并比较了均匀来流和剪切流条件下不同的响应特征。更多还原

【Abstract】 In the oil and gas industry where the hydrocarbon drilling exploration and floating production activities move progressively towards deepwater areas with depths greater than1000meter or beyond, vortex induced vibration (VIV) of such key structures as drilling/production risers have become the subject of increasingly intense research investigation. In China, the key of ocean exploitation has turned into the South China Sea. Riser is the necessary device to connect the floater with oil well. Nevertheless, the prediction of deepwater riser VIV is very challenging owing to the fact that the incident flows are practically non-uniform and the associated fluid-structure interaction phenomena are highly complex. These result in a nonlinear coupled system which depends on several physical and mechanical parameters. Large amplitude oscillations occur when the vortex shedding and the structural vibration frequencies coincide, a condition referred to as ’lock-in’. The lock-in condition can occur over a range of oncoming flow velocities and the vortex shedding frequency can be driven relatively far from the Strouhal frequency which leads to increase in hydrodynamic loading and reduction in service life due to fatigue.This study contains three parts:the first one is investigation of scale effect for turbulence flow around a circular cylinder and development of turbulence flow around circular cylinder; the second one is numerical pridiction of vortex induced vibration of elastically supported rigid circular cylinder with low mass damping in a fluid flow and the last one is vortex induced dynamic response of marine riser under true ocean environment.The structures of this thesis are listed as follows:By analysis the state of art of VIV, the engineering sense of present study is proofed. Conclusions are made of current research status from the aspects of experimental fluid dynamics, computational fluid dynamics and empirical method. The basic theory of VIV and associated parameters are introduced.Numerical computation of flow parameters around a two-dimensional circular cylinder within Reynolds numbers range from103to107is accomplished. Velocity field, vorticity field, the fluctuation of turbulence flow and its development downstreams are discussed and comparisons of characteristics of turbulence flow at different scales are also made. In order to investigate the scale effect of turbulent flow around a circular cylinder, two items of simlarity criterion based on turbulent kinetic and turbulent dissipation rate which are associated with the fluctuation characteristics of turbulence wake are deduced by the equation analysis of Reynolds-Averaged Navier-Stokes equations (RANS). The result indicates that the fluctuations of turbulence flow along the center line in the wake of circular cylinder can never be changed with the increasing Reynolds numbers when Re≥3×106. Then characteristics of turbulence field when Re≥3×106are discussed specially and laws of fluctuations of turbulence downstreams are given.RNG k-ε and SST k-co turbulence models are adopted to predict transverse vortex induced vibration of elastically supported rigid cylinder with low mass damping in a fluid flow. By comparing the peak amplitude, response frequency and hydrodynamic coefficients as well as wake modes of three different response branches at two different turbulence models, analysis of differences between two turbulence models are presented. Results indicate there exisit significant differences between two turbulence models, and SST k-co model is better than RNG k-ε model on the whole. By comparing turbulence fields and developments of three different response branches with static cylinder at coequal Reynolds number, some differences are observed. Pressure coefficient on the wall, shear stress coefficient on the wall, mean streamwise velocity, streamwise velocity fluctuation, cross-flow velocity fluctuation and Reynolds shear stress of three branches are different from each other and from those of static cylinder.An investigation on the nonlinear dynamic response and vortex-induced vibration of marine riser subjected to waves and currents is performed. Three dimensional governing equations which considered nonlinearities including the geometrical nonlinearities, fluid dynamic and fluid-structure coupling nonlinearities are given. The in-line force is solved by Morison equation under combined waves, currents and platform movement while cross-flow force is solved by wake oscillator model which considered variation of added mass coefficient. The nonlinear governing equations are solved by Updated Lagrangian method(UL) and Newton-Raphson interation method in time domain. The influence of basic parameters on the dynamic response and vortex-induced vibration of marine riser were investigated. This research provides a basic foundation for practical design and theoretical analysis of marine riser. Since the vortex shedding frequency varies with flow velocity, a depth varying flow past a flexible cylinder will result in multi-frequency excitation. Depending on the range of velocity covered by the flow profile, many vibration modes of the structure can be excited. Understanding the vibration mechanisms of the structure in those cases is not a simple task. Based on this model, multi-mode excitation of riser pipeline in linear sheared flow, the effect of shear parameter on vortex induced vibration and dynamic response of riser pipeline are discussed, and the different responses in uniform and linearly sheared currents are compared. The results indicate that shear parameter has a significant effect on vortex induced vibration and dynamic response of riser pipeline. The multi-mode response of riser pipeline in linearly sheared flow differs from that in uniform current.更多还原