顶张力立管涡激振动抑振装置性能比较

为降低甚至消除漩涡脱落引起的顶张力立管振动响应从而提高其疲劳寿命,设计了五种型式的涡激振动抑振装置,并在中国海洋大学物理海洋实验室对装有抑振装置的模型立管进行了实验研究.得到了模型立管在几种不同流速下顺流向和横向涡激振动应变时程曲线,同时为了对比分析也测量了没有安装抑振装置的裸管的响应曲线.对比分析了三种外流流速下抑振装置对立管涡激振动响应的影响,结果表明各种抑振装置对立管顺流向和横向涡激振动幅值和频率都有不同程度的降低,但其影响和有效性各不相同.     

来流角度对方柱流致振动的影响

方形结构由于存在几何棱角,在来流作用下会发生复杂的振动响应,是流致振动能量收集的理想结构。本文针对方柱流致振动开展数值模拟研究,分析不同来流角度下柱体的流致振动类型,揭示截面几何特征、来流角度对柱体振动响应、流体力及相位变化、尾流结构的影响。研究结果表明,来流角度是影响方柱振动响应和振动模式的重要因素,当来流角度为0°时,方柱会产生驰振响应,尾流结构发生斜向偏移且周期内漩涡脱落丰富,导致柱体呈低频高幅振动;来流角度在15°≤θ≤30°时,方柱产生涡激振动与驰振耦合的振动响应,来流角度为45°时,方柱发生涡激振动响应;从能量俘获角度,控制来流角度使方柱发生驰振响应,从而实现大范围流速下的海洋能量汲取。     

参激振动对顺应式垂直通路立管涡激振动的影响

顺应式垂直通路立管(CVAR)是目前处于研究阶段的一种新型的立管类型,在海流作用下产生涡激振动,在平台垂荡运动作用下产生参数激励振动。为了研究参数激励的影响,本文引入尾流振子模型模拟漩涡脱落对立管的作用,同时考虑浮式平台升沉运动产生的参数激励,建立了CVAR参激-涡激联合振动方程,获取联合作用下的动力响应,并与纯涡激振动响应进行对比。结果表明,在相同的流速下CVAR中部涡激振动幅值最大,流速的增大会导致涡激振动的频率增大,发生高阶锁振,高阶锁振振动幅值比低阶锁振振动幅值小。考虑参数激励之后,较纯涡激振动而言,立管的振动幅值增大;当参激频率与涡激振动频率接近时,立管的振动幅值最大。     

新型深吃水多立柱FDPSO变截面立柱涡激运动特性研究

文章采用FLUENT软件结合分离涡法对某新型深吃水多立柱FDPSO变截面立柱涡激运动特性开展了研究。将变截面立柱涡激振动系统简化为质量-弹簧-阻尼模型,引入雷诺平均应力模型求解不可压缩粘性Navier-Stokes方程,通过计算出流场作用于柱体的瞬时升力与阻力,并基于UDF程序求解运动微分方程同时运用动网格技术实现流场更新,实现了对变截面立柱涡激运动的数值模拟。对不同来流速度下变截面柱绕流和涡激运动特性进行了研究,分析了变截面柱阻力系数、升力系数、运动幅值和运动轨迹等,研究发现：在高雷诺数单柱绕流模拟中采用三维数值模型更具优势,变截面柱后方同一时间内可能有多个旋涡产生,旋涡之间相互影响,抑制了旋涡对柱体的升阻力作用;在折合速度6~9范围内,变截面柱未出现明显“锁定”现象;变截面柱涡激运动的横荡振幅峰值在Ur=4.5,约为1.2D;变截面柱流向平衡位置随着折合速度增加而增加;变截面柱运动轨迹出现了典型的“8”字形,但变截面柱的轨迹相对较紊乱。     

新型深吃水多立柱FDPSO变截面立柱涡激运动特性研究（英文）

文章采用FLUENT软件结合分离涡法对某新型深吃水多立柱FDPSO变截面立柱涡激运动特性开展了研究。将变截面立柱涡激振动系统简化为质量-弹簧-阻尼模型,引入雷诺平均应力模型求解不可压缩粘性Navier-Stokes方程,通过计算出流场作用于柱体的瞬时升力与阻力,并基于UDF程序求解运动微分方程同时运用动网格技术实现流场更新,实现了对变截面立柱涡激运动的数值模拟。对不同来流速度下变截面柱绕流和涡激运动特性进行了研究,分析了变截面柱阻力系数、升力系数、运动幅值和运动轨迹等,研究发现:在高雷诺数单柱绕流模拟中采用三维数值模型更具优势,变截面柱后方同一时间内可能有多个旋涡产生,旋涡之间相互影响,抑制了旋涡对柱体的升阻力作用;在折合速度6~9范围内,变截面柱未出现明显"锁定"现象;变截面柱涡激运动的横荡振幅峰值在U_r=4.5,约为1.2D;变截面柱流向平衡位置随着折合速度增加而增加;变截面柱运动轨迹出现了典型的"8"字形,但变截面柱的轨迹相对较紊乱。     

时间步长对低质量比圆柱涡激振动数值结果的影响

从圆柱涡激振动数值模拟结果的精度及可信度的角度出发,应用弱耦合算法分析时间步长选取对弹簧支撑低质量比圆柱涡激振动响应结果的影响.计算选取自激振动幅值分支的三个代表性流速,比较不同时间步长下响应结果.比较分析表明:在幅值响应的初始分支和下端分支段,存在最优的时间步长,使得计算效率最高,最接近实验现象;而在幅值响应的上端分支,数值结果要低于实验值,且相位角对求解时间步长非常敏感.     

细长海洋结构物涡激振动研究综述

随着世界范围内深海石油开采的需要,近年来关于海洋结构物涡激振动的研究越来越受到重视.虽然此问题在数值模拟和实验方面都已取得了一定的进展,但是还有许多问题尚待解决.同时,新型海洋结构物的引入给涡激振动的预报方法和抑振手段提出了新的挑战.因此,细长海洋结构物的涡激振动仍将是未来几年里备受关注的研究课题.本文在介绍有关涡激振动基本概念和理论背景的基础上,总结了近年来关于以深水立管为代表的海洋结构物涡激振动的研究与进展,包括对现有涡激振动分析工具的分类与评估;对柱体及海洋结构物涡激振动的实验研究;对深水立管与涡激振动相关的疲劳评估准则的研究;海洋结构物的横向、流向及轴向涡激振动的耦合作用研究;关于海洋结构物涡激振动的抑振措施和设备的理论及实验研究.本文着重介绍了计算流体力学方法在海洋结构物涡激振动研究中的应用和进展.最后,对海洋结构物涡激振动相关的研究热点的现状进行了总结并对今后工作提出了展望.     

波流联合作用下深海垂直杆件三维振动响应分析

本文研究了深海垂直杆件在波流联合作用下的波激-涡激-参激耦合振动特性.基于Hamilton原理,建立了垂直杆件的三维振动模型,考虑Morison力、涡激力和顶端变张力,对结构的波激-涡激振动和波激-参激-涡激联合振动进行数值模拟,求得杆件各点位移时历曲线,并针对时历曲线进行快速傅里叶变换得到能量频谱,从能量角度分析杆件振动特性.在此基础上,研究了振动幅值随流速、参激频率和参激幅值的变化规律.研究表明:在波流联合作用下,杆件振动出现非线性,轴向振动存在1/2和1/4亚频振动成分,拖曳力方向振动存在二倍波激频率成分;当涡泄频率接近杆件横向振动固有频率时,轴向振动和涡激振动振幅增加;存在参数激励时,杆件三个方向的振幅增大,振动对流速更加敏感;参激频率接近杆件固有频率时,轴向振幅和涡激振幅均增加,而当参激强度增加时,三个方向的振幅均增加,平衡位移不受影响.     

轴向板条对海洋立管涡激振动抑振的数值研究

涡激振动是一种在海洋工程领域普遍存在的流固耦合物理现象,易导致海洋立管等结构物发生疲劳损伤或失稳。本文为抑制涡激振动而提出一种附加轴向板条的方案,采用非定常流体数值计算方法求解分析不同分布形式下的轴向板条对海洋立管涡激振动特性的影响。首先定义轴向板条的分布形式;采用Newmark-β法求解立管双自由度振动方程并编写UDF,计算采用k-ω/SST湍流模型,并结合动网格技术模拟立管的振动过程。研究结果表明,轴向板条对海洋立管具有较好的抑振效果;当轴向板条数目n=20时,流向振动幅度减小78.57%,横向振动幅度减小58.10%。本文研究结果可为海洋结构物涡激振动的抑振提供参考。     

分隔板、控制杆及减振器对串联立管涡激振动抑制的试验分析

针对分隔板、控制杆和减振器3种抑振装置对串联立管涡激振动的抑制效果问题,在波流水槽中进行不同间距下串联立管的裸管试验以及抑振管涡激振动试验。试验结果表明,在同一流速条件下,附加抑振装置后立管的振动振幅与裸管相比明显降低,所采用的3种抑振装置可不同程度抑制海洋立管的涡激振动。对于横向振动最优抑制效果来说,控制杆的最优抑制效果最好;对于顺流向振动最优抑制效果来说,分隔板在上游立管中的最优抑制效果最好,控制杆在下游立管中的最优抑制效果最佳。综合比较各间距与振动方向的最优抑制效果,控制杆能够对串联立管横向与顺流向的振动起到不错的抑制效果。     

并联布置立管涡激振动抑制装置试验研究

针对分隔板、控制杆和减振器3种涡激振动抑制装置,在波流水槽中进行不同间距下并联布置立管的裸管试验以及抑振管涡激振动试验研究,对比分析3种抑制装置的抑制效果。试验结果表明:在同一流速条件下,附加抑振装置后立管的振动振幅与裸管相比明显降低,所采用的3种抑振装置在不同程度上均抑制海洋立管的涡激振动;从横向振动最优抑制效果来讲,控制杆的效果最好;从顺流向振动最优抑制效果来讲,控制杆和分隔板的效果好,减振器的效果较弱。综合比较不同工况下各个间距和振动方向的最优抑制效果发现,控制杆的最优抑制效果最好,能够对并联立管横向和顺流向的振动起到很好的抑制效果。     

串列双立管涡激振动抑制研究

实际工程中深海立管常以管群的方式出现,当立管彼此相互靠近时,会发生流场干涉效应。为研究立管间相互干涉作用及螺旋侧板抑制双立管涡激振动的效果,本文基于Ansys Workbench平台,采用双向流固耦合技术对Re=7800均匀来流下长径比为482的串列双立管进行三维数值模拟。结果表明,立管轴间距为5D时立管间有完整的涡旋脱落,下游立管在上游立管的尾流诱导下产生振动,双立管横向振动锁定在二阶模态,且振动方向相反。附加螺旋侧板能有效削弱双立管振动频率,降低上游立管横向振动幅值,但下游立管两向位移响应变化不大。     

计及海底井口影响的隔水管涡激振动响应特性试验

在靠近海底井口位置,隔水管周围流场受井口系统的影响发生变化,流固耦合下涡激振动可能诱发隔水管在横流向(CF方向)更为剧烈的振动。为了研究受管土装置影响的隔水管涡激振动响应特性,使用自主设计的管土装置模拟海底井口,采用8 m柔性立管,进行了均匀流下单管和受管土装置影响的涡激振动对比试验。试验通过FBG光纤应变片测得应变信息,使用模态叠加法、FFT变换处理分析试验数据,对比分析2组隔水管的主导频率、应变时历与幅值谱、无因次振幅以及激励力系数等参数沿管径的分布情况。结果发现管土装置影响下,隔水管主导频率减小;CF方向涡激振动增大,振幅沿径向呈非对称特征;涡激振动振幅更大,隔水管受流场的激励与阻尼更为剧烈。     

Effect of internal flow on vortex-induced vibration dynamics of a flexible mining riser in external shear current

Vortex-induced vibration (VIV) of flexible risers with both internal and external flows has received much attention recently. Hence, VIV dynamics of a fluid-conveying flexible riser subjected to external shear current is investigated. The effect of internal flow velocity and fluid density on VIV response is mainly examined and analyzed. A time domain model is introduced and elaborated. Then the finite element method is adopted to discretize the governing equations. Firstly, the model is validated based on the comparison between the numerical and experimental results. Then the influence of the internal flow velocity and fluid density on VIV dynamics is studied. The results show that multi-frequency response occurs when the flexible riser with various internal flow velocities and densities is subjected to external shear current. Under same shear current velocity, the IL mean deflection is enlarged with the increase of the internal flow velocity and fluid density. In addition, the internal flow velocity and fluid density have an evident effect on the vibrating frequency and the root mean square (RMS) displacement in both in-line (IL) and cross-flow (CF) directions. Moreover, mode and frequency transitions can be observed under different internal flow velocities and fluid densities.     

非粘结柔性立管静态分析

海洋柔性立管因材料和结构上的复杂性在设计分析中存在许多技术难题。本文在变形能原理和能量守恒的基础上,推导出了柔性立管各层的刚度矩阵。将各层刚度矩阵进行叠加,得到柔性立管总体刚度矩阵,并用总体刚度矩阵求解静载荷作用下立管变形响应。同时基于ABAQUS软件建立八层非粘结柔性立管有限元模型,并将有限元计算结果和刚度矩阵计算结果进行比较。结果分析表明：运用推导得到的刚度矩阵求解静态载荷下立管的变形是一种简便且准确的方法。     

LQR control on multimode vortex-induced vibration of flexible riser undergoing shear flow

Under the actions of ocean currents and/or waves, deep-sea flexible risers are often subject to vortex-induced vibration (VIV). The VIV can lead to severe fatigue and structural safety issues caused by oscillatory periodic stress and large-amplitude displacement. As flexible risers have natural modes with lower frequency and higher density, a multimode VIV is likely to occur in risers under the action of ocean currents, which is considered as shear flow. To decrease the response level of the VIV of the riser actively, a multimode control approach that uses a bending moment at the top end of the riser via an LQR optimal controller is developed in this study. The dynamic equations of a flexible riser including the control bending moment in shear flow are established both in the time and state-space domains. The LQR controllers are then designed to optimize the objective function, which indicates the minimum cost of the riser's VIV response and control input energy based on the Riccati equation of the closed-loop system under the assumption that the lift coefficient distribution is constant. Finally, the VIV responses of both the original and closed-loop systems under different flow velocities are examined through numerical simulations. The results demonstrate that the designed active control approaches can effectively reduce the riser displacement/angle by approximately 71%–89% compared with that of the original system. Further, for multimode control, the presented mode-weighted control is more effective than the mode-averaged control; the decrease in displacement is approximately 1.13 times than that of the mode-averaged control. Owing to the increase in flow velocity as more and higher-order modes are excited, the VIV response of the original system decreases slightly while the frequency response gradually increases. For the closed-loop system, the response becomes smaller and more complicated, and the efficiency of the controller becomes lower at a certain flow velocity.     

An integrated methodology for the design of mooring systems and risers

Traditionally, the design of mooring lines and risers of floating production systems (FPS) has been performed separately, by different teams, employing uncoupled analysis tools that do not consider the nonlinear interaction between the platform hull and the mooring lines and risers. Design processes have been focused on fulfilling the design criteria of the respective component (mooring/riser) alone, with few or no consideration to the other component, and little interaction between the design teams. Nowadays the importance of employing analysis tools based on coupled formulations is widely recognized, and analysis strategies have been proposed to consider feedback between mooring lines and risers within their respective design processes.In this context, this work details a proposal of one single and fully integrated design methodology for mooring systems and risers for deep-water FPS. In this methodology, the design stages of both risers and mooring lines are incorporated in a single spiral, allowing the full interaction of different teams; mooring design implicitly considers the riser integrity, and vice-versa, leading to gains in efficiency and cost reduction.Different analysis strategies are employed, taking advantage of uncoupled and coupled numerical models. The models generated at the initial/intermediate design stages can be reused in subsequent stages: simpler models are used in the initial stages, and more refined models are gradually introduced, to reach an ideal balance between computational cost and accuracy of results. In the advanced stages, the exchange of information between mooring/riser also allows the definition of criteria for the selection of governing/critical loading cases to be revised and verified in detail. This leads to the reduction of the original loading case matrix, allowing a feasible use of time-consuming fully coupled analysis.Results of a case study illustrating the application of some of the main processes of the methodology are included.     

深海立管涡激振动疲劳损伤影响因素分析

根据我国南海、墨西哥湾和西非海域的流速沿深度方向的分布规律,利用涡激振动预报程序计算了立管在不同参数下的动力响应.在此基础上计算了立管沿长度方向涡激振动引起的疲劳损伤.分别讨论了立管顶部预张力、管内流体密度、管外流速分布、立管外径、立管壁厚等参数的变化对疲劳损伤的影响.结果显示立管顶部预张力、管外流速分布、立管外径对疲劳损伤的影响非常明显,而管内流体密度和立管壁厚因其变化范围有限,对疲劳损伤的影响没有上述三个参数显著.     

台风条件下TLP串行立管系统碰撞分析

TLP立管系统以丛式方阵排列,台风条件下立管在波浪、海流及平台的联合作用下可能发生碰撞,有必要深入研究TLP串行立管系统的碰撞情况。文章基于DNV-RP-F203规范和Huse半经验尾流模型,提出台风条件下串行立管下游立管来流速度计算方法和立管系统碰撞分析方法,建立串行立管—井口—导管系统耦合有限元模型,研究台风条件下串行生产立管系统碰撞时的力学特性,在整体碰撞分析的基础上进行立管局部碰撞精细化分析,对比分析立管局部碰撞理论解和仿真解的不同。结果表明:下游立管来流速度的计算至少采用文中建立的方法迭代3次。串行立管发生碰撞时的最大应力发生在泥面导管处,碰撞位置应力发生了突变;立管发生碰撞的位置在水深100-120 m范围内。立管局部碰撞分析的理论解和仿真解基本吻合。