Torsional Response Analysis of Flexible Pipe Based on Theory and Finite Element Method

As key components connecting offshore floating production platforms and subsea imports, offshore flexible pipes play significant roles in oil, natural gas, and water injection. It is found that torsional failure is one of the failure modes of flexible pipes during transportation and laying. In this paper, a theoretical model(TM) of a flexible pipe section mechanics is established, in which the carcass layer and the pressure armor layer are equivalent to the orthogonal anisotropic layers due to its complex cross-section structure. The calculation results of the TM are consistent with those of a finite element model(FEM), which can accurately describe the torsional response of the flexible pipe.Subsequently, the TM and FEM are used to discuss the influence of boundary conditions on the torsional response.The structure of the flexible pipe is stable when twisted counterclockwise. However, limiting the top axial displacement can improve the axial and radial instability of the tensile armor layer when twisted clockwise. Finally, it is recommended that the flexible pipe can be kept under top fixation during service or installation to avoid torsional failure.

Prediction of Load-Displacement Curve of Flexible Pipe Carcass Under Radial Compression Based on Residual Neural Network

The carcass layer of flexible pipe comprises a large-angle spiral structure with a complex interlocked stainless steel cross-section profile, which is mainly used to resist radial load. With the complex structure of the carcass layer, an equivalent simplified model is used to study the mechanical properties of the carcass layer. However, the current equivalent carcass model only considers the elastic deformation, and this simplification leads to huge errors in the calculation results. In this study, radial compression experiments were carried out to make the carcasses to undergo plastic deformation. Subsequently, a residual neural network based on the experimental data was established to predict the load-displacement curves of carcasses with different inner diameter in plastic states under radial compression.The established neural network model’s high precision was verified by experimental data, and the influence of the number of input variables on the accuracy of the neural network was discussed. The conclusion shows that the residual neural network model established based on the experimental data of the small-diameter carcass layer can predict the load-displacement curve of the large-diameter carcass layer in the plastic stage. With the decrease of input data, the prediction accuracy of residual network model in plasticity stage will decrease.

Analytical and Numerical Modeling for Flexible Pipes

The unbonded flexible pipe of eight layers, in which all the layers except the carcass layer are assumed to have isotropic properties, has been analyzed. Specifically, the carcass layer shows the orthotropic characteristics. The effective elastic moduli of the carcass layer have been developed in terms of the influence of deformation to stiffness. With consideration of the effective elastic moduli, the structure can be properly analyzed. Also the relative movements of tendons and relative displacements of wires in helical armour layer have been investigated. A three-dimensional nonlinear finite element model has been presented to predict the response of flexible pipes under axial force and torque. Further, the friction and contact of interlayer have been considered. Comparison between the finite element model and experimental results obtained in literature has been given and discussed, which might provide practical and technical support for the application of unbonded flexible pipes.

Axial mechanical experiments of unbonded flexible pipes

Axial structural damping behavior induced by internal friction and viscoelastic properties of polymeric layers may have an inevitable influence on the global analysis of flexible pipes.In order to characterize this phenomenon and axial mechanical responses,a full-scale axial tensile experiment on a complex flexible pipe is conducted at room temperature,in which oscillation forces at different frequencies are applied on the sample.The parameters to be identified are axial strains which are measured by three kinds of instrumentations:linear variable differential transformer,strain gauge and camera united particle-tracking technology.The corresponding plots of axial force versus axial elongation exhibit obvious nonlinear hysteretic relationship.Consequently,the loss factor related to the axial structural damping behavior is found,which increases as the oscillation loading frequency grows.The axial strains from the three measurement systems in the mechanical experiment indicate good agreement,as well as the values of the equivalent axial stiffness.The damping generated by polymeric layers is relatively smaller than that caused by friction forces.Therefore,it can be concluded that friction forces maybe dominate the axial structural damping,especially on the conditions of high frequency.

A Finite Element Model for the Instability Analysis of Flexible Pipes Tensile Armor Wires

The instability of the tensile armor wire of flexible pipes is a failure mode associated with deep and ultra-deep water applications. Real compressive forces acting on the pipe are necessary to trigger this process. The loss of stability may be divided into two distinct processes, according to the main direction of the wire＇s displacement： radial or lateral instability. This study aims at proposing a numerical tool for predicting lateral and radial critical buckling loads for the tensile armor wires of flexible pipes. A simple finite element model, based on springs and beams elements, was developed in ABAQUS~ to deal with this problem in an efficient and reliable manner. A parametric study was conducted concerning the behavior of the critical load when the laying angle, the initial curvature and the total pipe length are varied. The results were consistent with previously published literature data and analytical expressions, proving its applicability to pipe engineering projects. It also has the advantage of approaching the problem three-dimensionally, which allows further modelling modifications, such as including friction effects.

The development of studying flexible pipe bend reinforced by Kevlar fibers

The flexible pipe bend can not only reduce the structural vibration and fluid noise in pipeline, but also realize the flexible connection of a horizontal line and a vertical line and compensate the displacement of three dimensions produced by the shock or vibration of pipeline in the special situations. Up to now, little attention has been paid to study the flexible pipe bend applied in the pipeline of medium or high pressure, because no appropriate framework materials can be used to reinforce it which must endure the burst pressure higher than 10 MPa. The investigation shows that it is possible to produce the flexible pipe bend of medium or high pressure if such fibers with high performance as Kevlar fibers are used to be its reinforced materials. However, its structural designing theory, manufacturing technology and measuring techniques aren't yet perfect and systematic, which leads to the instability of the performance of products. Furthermore, few references about its research can be seen. Therefore, it is necessary to systematically and thoroughly develop the structural designing theory, manufacture technology and measuring techniques of flexible pipe bend.

An Analytical Approach for Assessing the Collapse Strength of an Unbonded Flexible Pipe

This paper presents an analytical scheme for predicting the collapse strength of a flexible pipe, which considers the structural interaction between relevant layers. The analytical results were compared with a FEA model and a number of test data, and showed reasonably good agreement. The theoretical analysis showed that the pressure armor layer enhanced the strength of the carcass against buckling, though the barrier weakened this effect. The collapse strength of pipe was influenced by many factors such as the inner radius of the pipe, the thickness of the layers and the mechanical properties of the materials. For example, an increase in the thickness of the barrier will increase contact pressure and in turn reduce the critical pressure.

Mode Transitions in Vortex-induced Vibrations of a Flexible Pipe near Plane Boundary

A pipe model with a mass ratio（mass/displaced mass） of 4.30 was tested to investigate the vortex-induced vibrations of submarine pipeline spans near the seabed.The pipe model was designed as a bending stiffness-dominated beam.The gap ratios（gap to diameter ratio） at the pipe ends were 4.0,6.0,and 8.0.The flow velocity was systematically varied in the 0-16.71 nondimensional velocity range based on the first natural frequency.The mode transition between the first and the second mode as the flow velocity increases was investigated.At various transition flow velocities,the research indicates that the peak frequencies with respect to displacement are not identical along the pipe,nor the frequencies associated with the peak of the amplitude spectra for the first four modes as well.The mode transition is associated with a continuous change in the amplitude,but there＇s a jump in frequency,and a gradual process along the pipe length.

Parameter sensitivity analysis of the axial stability for a marine flexible pipe

Marine unbonded flexible pipes serve as the most essential equipment in offshore oil and gas exploration and exploitation.Axial compressive loads during installation or in service in the complex marine environment usually lead to buckling failure.A flexible pipe is a composite structure with multiple functional layers,of which the tensile armor layer plays a key role with regard to the response of the pipe subjected to axial loads.In this paper,a simplified three-dimensional finite element model is developed,focusing on the tensile layer and replacing the carcass layer,pressure sheath layer,and pressure armor layer by a cylindrical rigid body to reduce computational expense.By using this model,the buckling failure modes of the tensile armor layer(in particular the birdcaging phenomenon)are analyzed.Several key parameters that affect the stability of the flexible pipe under axial compression and torsion are emphasized,and their effects on its axial and torsional stiffness are compared and discussed.The results show that both the lay angle of the steel wires and the interlayer friction coefficient have a significant influence on the axial and torsional stiffness of the pipe,whereas the damaged length of the outer sheath has virtually no effect.

Fiber-Reinforced Polymer Bridge Design in the Netherlands： Architectural Challenges toward Innovative, Sustainable, and Durable Bridges

This paper reviews the use of fiber-reinforced polymers （FRPs） in architectural and structural bridge design in the Netherlands. The challenges and opportunities of this relatively new material, both for the architect and the engineer, are discussed. An inventory of recent structural solutions in FRP is included, followed by a discussion on architectural FRP applications derived from the architectural practice of the author and of other pioneers.

海洋复合管缆设计关键技术与挑战

海洋复合管缆是海洋资源开发的重要装备之一,广泛应用于海上油气开发、深海采矿、海上风电等。海洋复合管缆具有弯曲性能好、质量轻、强度高、耐腐蚀和耐高低温等优点,能满足海洋资源开发不断向深水进发的需求。然而,海洋复合管缆相较于传统均质管道结构设计更加复杂,力学特性和使用寿命的准确预测更加困难。结合相关规范对海洋复合管缆设计的常规方法进行介绍,并归纳总结海洋复合管缆设计中需要进一步考虑的结构优化技术、材料非线性问题、几何非线性问题和界面非线性问题(界面强度、界面疲劳、界面摩擦)等关键技术。研究结果可为海洋复合管缆的设计研究提供指导。

深海采矿柔性管力学性能及加工工艺研究综述

海洋蕴藏着储量丰富的矿产资源,深海矿产资源开发逐渐成为学术界和工程界的研究热点。管道提升式开采方案是目前公认的最具商业前景的海洋矿产开发方案。矿产输运管道作为连接海底中继舱和海上采矿平台的纽带,需要承受恶劣的风、浪、流环境载荷和复杂作业工况的工作载荷,其设计制造和力学性能分析一直备受关注。相比于刚性管道,柔性管道的弯曲刚度小、便于安装与回收、使用寿命较长。然而,柔性管道的结构复杂,各层之间相互影响,金属柔性管道由于自身结构的限制,在深海采矿行业中难以广泛应用,人们开始把目光放在非金属柔性管的设计与应用上。本文回顾了柔性管的发展历程,总结阐述了柔性管设计及加工制造中的力学性能分析方法和力学特性,并对柔性管设计制造的未来发展提供力所能及的展望。

层间摩擦系数对非黏结柔性管抗拉铠装层轴压屈曲失效模式的影响研究

在柔性管运输、铺设安装和服役过程中,由于其抗拉铠装层钢带为柔性细长螺旋结构,当外部载荷超过临界值时,抗拉铠装层钢带容易发生屈曲失效。考虑非线性材料、几何大变形、层间接触和摩擦等非线性效应的影响,运用ABAQUS有限元软件建立了63.5mm典型非黏结柔性管8层完整结构模型,研究了在抗拉铠装层不同层间摩擦系数的情况下,非黏结柔性管在轴向压缩载荷作用下的力学性能和屈曲失效模式。研究结果表明,层间摩擦系数对非黏结柔性管的抗压刚度和抗拉铠装层屈曲失效模式有较大影响,层间摩擦系数以0.1和0.2为分界点,抗压刚度和屈曲失效模式均呈现出“三段式”变化规律。研究成果可为海洋非黏结柔性管的结构设计和屈曲失效评估提供技术参考。

LNG螺旋骨架复合耐超低温柔性管道拉伸性能分析研究

LNG螺旋骨架复合耐超低温柔性管道采用了以螺旋骨架支撑,多层复合材料缠绕的非粘接结构形式,这类结构的力学性能分析中涉及到几何大变形、超低温环境、复杂层间接触等难题。传统的柔性管道拉伸理论模型不再适用于这类结构形式。本文针对12英寸(1英寸=0.025 4 m)口径的低温柔性管道开展了常、低温拉伸性能实验研究,建立了低温柔性管道的精细数值模型,并通过实验进行了模型修正。基于所建立的数值模型开展了温度、支撑层参数对管道拉伸性能的敏感性分析。结果表明,低温环境下管道的抗拉伸性能提高了12.69%,支撑层螺距增大50%将导致管道的抗拉伸性能降低52.36%。本文的研究为LNG螺旋骨架复合耐超低温柔性管道的设计和优化提供了一定的参考和指导。

均匀流作用下柔性悬垂管涡激振动响应特性试验研究

温差能发电是近年海洋可再生能源研究的热点,悬垂取水管作为温差发电装置中提取深层冷海水的关键结构,其涡激振动响应特性尚不明确。本文开展了均匀流下悬垂管的涡激振动水池模型试验,利用光纤光栅应变传感器测量涡激振动应变响应,通过模态分析法、小波变换等数据处理方法研究悬垂管的幅值和频率特征。分析试验结果发现:均匀流作用下,悬垂管的涡激振动位移响应最大幅值主要位于悬垂管底部;柔性悬挂立管IL(in-line)和CF(cross-flow)主导频率基本满足二倍频关系,但是在模态转换的流速工况下会出现IL和CF方向主导频率相同的现象,同时伴随着明显的“行波”、“多频响应”以及“时间共享”特征;处理得到背景洋流作用下悬垂管的CF和IL方向斯特哈尔数分别为0.15和0.30,略小于以往两端铰支柔性立管试验结果,该值将为悬垂输水管涡激振动预报研究提供参数输入。

弯管内可控万向铰接柔性管动力学特性研究

针对弯管内可控万向铰接柔性管随机动态接触问题,以弯管和可控铰接柔性管为研究对象,采用哈密顿原理结合多体系统动力学理论,引入刚体运动坐标系描述可控铰的运动约束,以管-管接触模型描述可控万向铰接管和弯管的动态接触,建立了弯管内可控万向铰接柔性管多体系统接触非线性动力学的数值计算方法。以超短半径水平井造斜段柔性钻具为例,根据贝克休斯公司的钻具动力学特性标准,对柔性钻杆的振动特性进行了评价,研究了不同转速和不同钻压对柔性钻杆动力学特性的影响。研究结果表明:横向振动是导致柔性钻具可能失效的主要因素;柔性钻杆的横向振动剧烈程度随着转速的增加而减小,随着钻压的增加而增大。

螺旋缝埋弧焊管铣边机的应用与改进

介绍了铣边机在螺旋缝埋弧焊管生产中的发展和应用情况,详细分析现有铣边机结构在应用中存在的问题。针对这些问题以及铣边机的发展方向,提出了铣边机下托辊整体式调整、分体式仿形随动组合机构、重力和柔性防飞溅组合等改进方案,为部分国产铣边机的升级改造提供了可借鉴的有益思路。

内压载荷下输氢复合柔性管力学性能研究

中国氢能产业正随着碳中和愿景的不断推进而快速发展,由于氢气在钢管中容易引发“氢脆”现象,使用钢管输送氢气存在较大挑战,纤维增强复合柔性管作为一种非金属管道在氢气输送领域备受关注,其结构设计及强度分析是产业化应用的瓶颈。为探讨内压工况下输氢复合柔性管的结构响应,考虑不同层材料的各向同性及各向异性,基于三维各向异性弹性力学,建立了纤维增强输氢复合管道在内压作用下的力学理论模型,并采用数学方法求解管道位移微分方程,进而获得了N层缠绕增强层输氢复合管道在内压作用下的应力应变解析解,计算结果与内压作用下13层输氢复合柔性管的数值计算结果相符。管道的环向应力最大值出现在防渗透层,输氢软管的增强层承担约70%的载荷作用,径向应力绝对值大小随距离管道截面中心点的距离增大而减小。提出的力学行为分析模型及求解方法为设计输氢复合柔性管提供了重要的理论支撑。

柔性复合管在油田服役后的性能

为评价柔性复合管在油气田地面集输系统中的应用效果,采用宏观观察、微观分析、水压爆破试验、气密封性能测试、结构组成分析、热分析、红外光谱分析、力学性能测试等方法对两条柔性复合管进行分析,以确定其在不同工况下的适用性。结果表明:在经过一段时间的服役后,两条柔性复合管结构层保持完整,未发现明显缺陷,内衬层颜色加深;两条管道的失效形式均为管体爆破,其中1号试样因长期高温运行,其爆破压力不满足标准要求;两条管道的内衬层分别为交联聚乙烯和普通聚乙烯,增强层分别为芳纶纤维和涤纶纤维,热分解温度分别为580℃和440℃,但芳纶纤维的抗拉强度明显小于涤纶纤维。

基于自整定模糊PID的柔性管道加热控制系统研究

针对传统温度控制器调节控制精度低、超调量大的缺点,设计了一套模糊控制策略+比例积分微分(PID)控制方法+物联网云平台技术的柔性管道加热控制系统。该系统可实现过程实时监控、温度检测和闭环控制功能,使输气管道在加热过程中的温度控制稳定、温度调节响应速度快、超调量小。通过对控制过程的可视化,可实时分析系统运行状况,从而实现对加热过程和气体输送过程的动态监控。该系统具有加热及温度控制、运行状态实时监测功能。适用于管道加热系统的柔性管道加热控制系统对半导体企业降低生产能耗、提高生产效率、过程监控、保证输送系统安全和平稳运行有重要意义。