考虑跨肩管土作用的悬跨管道涡激振动特性研究

海底悬跨管道涡激振动是一个复杂的流场-管道结构-跨肩土体耦合问题,其发生机理和振动特性十分复杂,特别是两端跨肩处管土作用对涡激振动的影响有待深入讨论。为此,文章引入了P-y曲线描绘跨肩处管土耦合作用,提出了基于管道位移和速度的新非线性土体弹簧模型,根据能量平衡原理计算土体阻尼,采用尾流振子模型模拟悬跨管段流固耦合作用,建立了考虑流—固—土多场耦合作用的海底悬跨管道涡激振动预报模型,并重点研究了考虑跨肩管土作用时,悬跨管道涡激振动的诸多特性。     

大坡度海底管道悬跨及疲劳分析

针对大坡度海底管道的悬跨和疲劳问题,基于DNV规范和线性疲劳累积损伤理论,分析管道顺流向和横向涡激振动的特点,并根据实例计算了大坡度海底管道不同水深处的最大悬跨长度和管道的疲劳寿命。结果表明:悬跨长度越长,管道的涡激振动现象越明显,即跨长对VIV疲劳损伤的影响较大;该管道的设计参数满足疲劳要求,其中大坡度海底管道出现最大疲劳损伤的位置为管道与斜坡底端的触地点处。     

非线性管土耦合条件下悬跨管道涡激振动响应时域预报

海底悬跨管道与海床耦合呈现高度非线性,使得发展一种时域预报方法成为需要.文章运用有限元法对输液张紧悬跨管道进行空间离散,并应用Facchinetti等改进的尾流振子模型和切片假定模拟每个有限单元上的涡激振动水动力,发展了一种悬跨管道-海床-流场多场耦合的非线性时域预报方法.在合理选取尾流振子模型附加水动力阻尼参数的基础上,时域预报了线性、理想塑性和张力截断弹簧模型下悬跨管道的涡激振动响应.研究结果表明,基于尾流振子的时域预报方法能够合理地描述非线性管土耦合边界下VIV响应;非线性边界条件下,锁定产生的最大响应幅值低于线性结果.     

悬跨海底管道安全评估和风险分级

为确定不同程度悬跨海底管道的安全性,以避免涡激共振为控制条件对不同振动方向和不同边界条件下海底管道悬跨临界长度计算方法进行分析,发现悬跨海底管道的安全长度与约化速度和边界条件具有正相关性;提出以不同条件下得出的临界悬跨长度值作为分级依据的悬跨海底管道风险分级方法,案例分析结果表明,该方法可识别出亟需治理的悬跨段,使有限的资源得到最优的分配。     

悬跨管道功能载荷对涡激振动响应的影响(英文)

在海底悬跨管道安装和操作过程中会产生的高轴向力和高压力,功能载荷对管道涡激振动的影响小可忽略.本文首先基于Hamilton原理,推导并求解了简单支撑的输液张力管道自由运动方程,在此基础上利用DNv.RPl05规范评估悬跨涡激振动响应,对悬跨管道受不同功能载荷(特别是有效轴向力和内流流速)进行计算.结果显示功能载荷通过改变管道的固有频率来影响涡激振动响应,而且由于实际内流流速一般不高,其影响较有效轴向力要弱.结果可以为悬跨管道的许用长度选取提供参考.     

考虑不同管土作用模型的海底多跨管道动力特性

当前,海底多跨管道涡激振动分析多将管土段简化为固支或简支边界.针对此问题,采用3种更为复杂的土体模型,研究对比不同管土作用对多跨管道涡激振动特性的影响.采用尾流振子模型模拟流-固耦合作用,构建考虑流-固-土多场耦合的悬跨管道涡激振动预报模型,分析不同土体模型下的管道动力学规律.研究结果表明:不同的管土模型会对管道振动产生不同程度的影响,且管土非线性作用会明显制约管道的振动特征,使最大位移幅值和局部应变等发生改变.     

图解法预报悬跨管道涡激振动响应

利用水动力经验模型,用简易的图解法预报不同功能载荷和边界条件下的深水悬跨管道涡激振动响应频率和振幅.分析内流流速、阻尼和管土耦合作用等因素对涡激振动响应及锁定范围的影响.指出对于低流速内流,特别是有效张力比较大的时候,内流流速对结构固有频率影响很小;管土耦合边界对悬跨振动响应的主要作用在于减小结构固有频率和提高阻尼,有利于减少疲劳累积损伤预报值.     

海底多跨管道涡激振动疲劳简化分析

多跨管道由于其自振频率低且相邻模态频率临近,容易在低流速下产生多模态涡激振动.针对长期作业的海底多跨管道,考虑遭遇海流流速变化以及涡激振动响应本身的随机性,多模态响应采用单频响应的等效组合,利用 N-S曲线和Miner线性累积损伤准则进行悬跨涡激振动疲劳损伤简化预报,为深水悬跨管道初始设计提供参考.通过一输气多跨管道的疲劳累积损伤度的影响因素分析,结果表明:疲劳损伤对土壤刚度选取敏感;DNV RP-105规范中多模态响应缩减系数较振幅权重形式更保守;用Rayleigh分布描述涡激振动响应进程计算的疲劳损伤要高于恒幅稳态振动描述.     

弹性支承约束下海底管线允许最大跨长的计算方法

直接铺设于海底的管道在服役期间,由于海流的冲刷作用,海底管道的某些管段会逐渐地裸露出来形成悬跨段。悬空管道在浪、流等外部条件作用下,极易产生振动并引起较大动应力,从而引起结构疲劳,严重时会导致管道疲劳断裂。文中将管道入土端等效为线弹簧和转角弹簧,对悬空管道允许悬跨长度进行了初步分析,并对某海域典型管道进行分析,为悬跨管道的治理和安全隐患排除提供技术支持。     

稳定流作用下海底悬跨管线涡激振动研究

讨论了目前用于海底悬跨管线涡激振动预报的主要数值模型,针对海底管线悬跨段涡激振动问题编制了有限元分析程序,程序采用梁单元模拟管跨结构,动力响应计算方法采用VIVANA模型,模型控制方程采用Newton-Raphson迭代算法求解。采用Larsen,Koushan等人(2002)和Larsen,Baarholm等人(2004)给出的两组不同的用于确定升力曲线的参数曲线进行计算,将计算结果与Tsahalis(1984,1987)的模型实验结果进行了比较。结果表明本文的涡激振动模型能够预报间隙比e/D=∞时海底悬跨管线的涡激振动响应;采用Larsen,Koushan等人(2002)参数曲线得到的计算结果与间隙比e/D=∞时的实验结果符合较好,Larsen,Koushan等人(2002)参数曲线较Larsen,Baarholm等人(2004)参数曲线更适合于海底悬跨管线的涡激振动预报。     

Experimental and theoretical studies on lateral buckling of submarine pipelines

Global buckling of a submarine pipeline during high pressure/high temperature (HP/HT) operation results in a loss of pipeline stability that is similar to a bar in compression; this phenomenon constitutes one of the key factors affecting pipeline integrity and design. To intuitively study the buckling response, a test system was designed that can account for thermal loading and pipe-soil interactions, and this system was used to perform a series of small-scale model tests on the lateral buckling of submarine pipelines with different initial imperfections. Based on the hat-shaped buckling profiles of the test pipelines, a new buckling mode called "hat-shaped buckling" was proposed. In an attempt to study the conditions under which the pipeline exhibits this hat-shaped buckling mode, the changing law of the buckling mode was investigated through finite element analyses of pipelines with different parameters, including the length of the pipeline and the amplitude and wavelength of the initial imperfection. Subsequently, an analytical solution for calculating the buckling amplitude of a pipeline with a hat-shaped buckling profile was proposed. The theoretical solution was compared to the experimental data, which verified the feasibility of the model in calculating pipeline buckling deformation. The experimental data, the buckling mode based on these data and the corresponding analytical model discussed herein may provide a reference for future experimental studies of pipeline buckling.     

海洋悬空管道非线性振动稳定性分析

以海洋悬空管线为研究对象，根据海洋悬空管道的主要特征，将海洋悬空管道简化为两端简支梁力学模型．涡激升力简化为简谐荷载。在考虑管道非线性因素下，建立悬空管道的横向振动方程，并采用谐波平衡法对方程求解。可得出洋流涡激作用下海洋悬空管道横向振动失稳的双尖点突变模型，由此导出悬空管道失稳条件。根据失稳条件分析发现．海洋悬空管长度对稳定性影响起主导作用，并在假定其他条件不变的情况下，分析影响悬空管道稳定性的因素和悬空段临界长度之间的关系。分析结果表明：随着外流流速、管内流流速、管内压强的增加，悬空管道的临界长度减小：随着材料弹性模量、管外直径的增大．悬空段的临界长度增加：其他影响因素相比较而言可以忽略．     

Time domain approach for coupled cross-flow and in-line VIV induced fatigue damage of steel catenary riser at touchdown zone

Existing VIV prediction approaches for steel catenary riser (SCR) typically employ truncation model without considering the interaction between the SCR and soil, and only allow for cross-flow (CF) VIV. In this study, a time domain approach accounting for the SCR-soil interaction is proposed to predict the CF and in-line (IL) VIV induced fatigue damage of a SCR at touchdown zone (TDZ). The hydrodynamic force resulting from the vortex shedding is modeled using the forced oscillation test data of a rigid cylinder and an empirical damping model, which are defined as functions of the non-dimensional dominant frequency and amplitude of the SCR response. Due to the coupling effect, the IL VIV force is magnified based on the CF VIV amplitude. By combining a linear hysteretic interaction model with a trench shape model, some particular phenomena during the vertical SCR-soil interaction are captured and qualitatively discussed, while for the horizontal direction, the seabed is simplified as nonlinear spring model. Based on these models, parametric studies are conducted to broaden the understanding of the sensitivity of VIV induced fatigue damage to the seabed characteristic. The results indicate trench depth, vertical and lateral stiffness, and clay suction are significantly affect the VIV induced maximum fatigue damage at TDZ.     

Laboratory tests and thermal buckling analysis for pipes buried in Bohai soft clay

Upheaval buckling of submarine pipelines occurs due to relative movement of pipeline and surrounding soil and is often triggered by high operational temperature of the pipeline, initial imperfection of the pipeline, or a combination of both. Since buckling can jeopardize the structural integrity of a pipeline, it is a failure mode that should to be taken into account for the design and in-service assessment of trenched and buried offshore pipelines. In this study, a series of vertical (uplift) and axial pullout tests were carried out on model pipe segments buried in soft clay deposit similar to that present in Bohai Gulf, China. Pipe segments with three different diameters (= 30 mm, 50 mm and 80 mm) were buried in different depth-to-diameter ratios ranging from 1 to 8. Based on the results of laboratory tests, nonlinear force–displacement relations are proposed to model soil resistance mobilized during pipeline movement. The proposed nonlinear soil resistance models are employed in finite element analysis of buried pipelines with different amplitudes of initial geometric imperfections. Thermal upheaval buckling behavior of pipelines operating at different temperatures is studied. Results show that the capacity of pipeline against thermal buckling increases with the burial depth and decreases with the amplitude of initial imperfection.     

顶张力对深水刚性立管涡激振动及疲劳损伤的影响

分析讨论顶张力对深水刚性立管在剪切流中的涡激振动响应和疲劳损伤的影响。从理论上分析张力对刚性立管固有特性的影响,并利用OrcaFlex软件建立数值模型,模拟不同顶张力系数下立管于剪切流中的涡激振动响应,同时采用S-N曲线法计算立管疲劳损伤。结果表明,顶张力对立管的影响直接体现在刚度上,立管刚度随着张力的增大而增大,因此顶张力对降低立管疲劳损伤有一定积极作用。但是随着顶张力的增大,其对降低疲劳损伤的贡献越来越小,而对立管强度储备的危害却逐渐增大。     

Fatigue damage induced by vortex-induced vibrations in oscillatory flow

Vortex-induced vibration (VIV) of a flexible cylinder in oscillatory flow was experimentally investigated in an ocean basin. An intermittent VIV was confirmed to have occurred during the tests. The fatigue damage caused by VIV was calculated based on rainflow counting and a standard S–N curve. There are 3 main observations for fatigue damage from VIV in oscillatory flow: 1) the damage varied significantly with the KC number, which is a unique feature for VIV in oscillatory flow. 2) Fatigue damage at small KC number cases was found to be larger compared to those at large KC numbers owing to the fact that number of vortex shedding cycles per half of the motion cycle is low, and damping within half of the motion cycle will hence become low. The fact that vortices from the previous cycle still are active during the next may also contribute to the large response at small KC numbers. 3) ‘Amplitude modulation’ and ‘mode transition’, two specific features for VIV in oscillatory flow, were found to have a strong influence on fatigue. Fatigue damage has also been calculated by an empirical VIV prediction model assuming that all cases have steady flow at an equivalent velocity. Finally, a simplified method for calculating fatigue damage from VIV in oscillatory flow based on steady flow conditions is proposed. A modification factor diagram is presented, but the scope of the present study is too limited to provide a good basis for a general model for this factor. A general model for how to apply results from constant current analysis to predict fatigue in oscillatory flow will therefore need further research.     

海底管线悬空振动的研究现状

海底管线管跨段的涡激振动,是引发海底管线疲劳失效的主要因素之一。介绍了管跨段的形成原因,总结国内外关于管跨段临界长度的计算方法,探讨了近年来对涡激振动问题理论及实验研究的研究现状,提出了在今后的管跨段研究中有待解决的问题。