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1.
Unbonded flexible pipe is one of the important pieces of equipment in floating production systems for transport of oil and gas between floaters and subsea wells located in deep water. To assure safety over a long-term service period, analysis of fatigue behavior under alternative bending is a key requirement. An analytical model for prediction of bending behavior is essential for understanding the mechanism of the local stress distribution in the helical wires of the tension armor layers under alternative curvatures and rapid estimation of the service life of flexible pipes for designers in engineering practice. In this paper, seven analytical models available in the literature are selected and summarized. Although the experimental results reported in the literature are limited, a three-dimensional finite element model is developed for investigation of the seven models, and the validity and limitations of these models for different structural parameters of helical wire are discussed, i.e., the width-thickness ratio of the wire section and helical angle. The analytical model based on spring theory resulted in a satisfactory estimation of bending stress for most cases and is recommended as a tool for the basic design of the helical armor wire structures in flexible pipes. 相似文献
2.
Unbonded flexible pipes have superior fatigue performance as the internal armor layers are allowed to move relative to each other, leading to reduced structural loading. The main interactions between the internal layers are the contact forces and the frictional forces. Frictional interaction leads to a complex non-linear response of unbonded flexible pipes making prediction of cyclic bending fatigue a demanding task. Nevertheless, detailed understanding of local armor wire stresses and the related fatigue phenomena is of paramount importance as unbonded flexible risers are often operated close to their mechanical limits. This paper presents a method for calculating the tensile armor wire loading and the hysteresis effect on flexible pipes when subjected to tension, and non-symmetric cyclic bending. The effect of non-symmetric cyclic bending with different tensile armor lay angles, and frictional conditions are studied. The analysis uses an efficient repeated unit cell finite element model, allowing the analysis to be performed on a desktop computer. The study shows that the tensile armor wires gradually translate towards the compression side of the pipe bending plane, when the unbonded flexible pipe is subjected to combined tension and non-symmetric cyclic bending. In the analysis, cyclic bending is applied until steady-state in the bending response is achieved over a full bending cycle. The global bending response of the flexible pipe and the tensile armor wire loading conditions for fully stabilized non-symmetric cyclic bending become symmetric around the frictionless state for the mean cyclic bending curvature. An approximate analytic model for the tensile armor in the stabilized cycle, based on symmetric bending about the geodesic curve corresponding to the mean pipe curvature, is proposed. 相似文献
3.
基于3D FEMDEM方法建立三维原型尺度数值模型,模拟波浪荷载作用下斜坡上护面块体内部的应力分布。波浪作用下结构物的水动力荷载采用微幅波理论模拟,护面块体之间的运动、碰撞接触以及块体内部的应力变化采用3D FEMDEM方法模拟。块体之间的接触力采用基于势函数的罚函数法计算,有限元的变形采用中心差分的显式方法求解。应用该数值模型与ANSYS软件程序对自重作用下混凝土扭王字块的内部应力分布特性进行了比较分析,验证了数值模型应力计算的可行性和计算精度。通过数值模拟计算给出了波浪作用下斜坡上护面块体之间的相对运动和块体内部的应力分布及应力历时曲线,探讨了块体内部应力变化特性。 相似文献
4.
The current scenario of oil production in ultra deep waters challenges the design of flexible pipes since they have to withstand high pressures, temperatures and dynamic loads during operation. Amongst the known failure mechanisms in flexible pipes, armor wire lateral buckling is of uttermost importance as there is no undisputable model for its prediction. In this work, compressive failure load for tensile armor lateral buckling is calculated for a sample of 29 flexible pipes based on the resolution of a numerical model that considers force and moment equilibrium conditions and geometric compatibility relations from differential geometry concepts. The obtained results are fitted on an equation via symbolic regression. Thus, a simple empirical model to predict compressive failure load is proposed as a function of the radius of tensile armor, wire lay angle and torsional, normal and binormal bending stiffness of the wire cross section. The model assumes the absence of frictional distributed forces in the wire and curvature of the flexible pipe, therefore it provides conservative results. For the 29 flexible pipe sample, the mean absolute percentage error of the empirical results in view of the numerical results was 0.6%. 相似文献
5.
为解决现有深水连接器连接性能研究中力学分析建模不准确,且缺乏抗弯抗扭能力分析的问题,基于ABAQUS有限元分析软件对深水连接器进行三维模型动态仿真分析,对连接器的受力、密封性能以及在实际工程需求中不同内压下的抗弯及抗扭性能进行深入研究。结果表明:在安装及生产两种工况下,深水连接器各部件除密封环外受力均满足其强度设计要求,密封环接触表面发生合理塑性变形,满足密封要求;随着内压的增加,深水连接器的抗弯能力逐渐下降,抗扭能力则呈现增加的趋势;极限弯矩分别在0 MPa与35 MPa内压下的判定依据为密封失效,在14 MPa与52 MPa内压下的判定依据为下毂座屈服,而极限扭矩在不同内压下的判定依据均为密封失效。 相似文献
6.
Although the coupled horizontal–torsional vibrations of open ships have been investigated numerically for decades, the available experimental data in oblique seas seem rare. Model tests, considering natural frequencies of bending and torsional modes, have been conducted by the Centre for Ships and Ocean Structures (CeSOS) in the towing tank and ocean basin. A flexible backbone model was designed with five cut-outs on the top side of the aluminum beam to realize approximately torsional stiffness as well as vertical and horizontal bending stiffness. This paper mainly deals with measured bending and torsional vibrations in regular and irregular waves. The damping ratios, mode shapes, and modal moments were derived from experimental data, and a numerical model based on modal superimposition is established according to the measured hydroelastic properties. Some time-domain simulations are carried out considering the structural characteristics, and compared with measured results. The test data in regular waves are presented to show the possible factors of influence on the vibrations. The effect of bending and torsional vibrations on the extreme response values in irregular waves is estimated. The uncertainties in the experiments are discussed and conclusions are presented at the end of this paper. 相似文献
7.
采用卷管法进行海底管道铺设过程中,管道首先通过牵引作用上卷于卷筒进行储存。管道与卷筒发生非线性接触,可能会产生复杂的塑性变形和局部屈曲。通过全尺寸柔性管力学性能试验获得柔性管轴力—应变以及弯曲—曲率等非线性力学性能关系,将试验所得的非线性材料性能参数导入建立的两种柔性管上卷ABAQUS有限元模型（梁—实体单元模型与壳和桁架—实体单元模型）,实现柔性管较大轴向抗拉刚度和较小抗弯刚度的同步模拟以及管道与卷筒的非线性接触响应特征。通过对比分析两种有限元模型数值模拟得到的管道弯矩、弯曲曲率、管道轴力、管道与卷筒的接触压强等数据,发现在管道上卷过程中管道沿副法线方向的SM3弯矩占据其弯曲变形主导地位;管道与卷筒之间的摩擦效应对于管道轴力的影响较为显著;管道与卷筒的最大接触压强主要发生在卷管过渡段区域。 相似文献
8.
Jeom Kee Paik Anil K. Thayamballi P. Terndrup Pedersen Young Il Park 《Ocean Engineering》2001,28(8):51
For a ship hull with large deck openings such as container vessels and some large bulk carriers, the analysis of warping stresses and hatch opening deformations is an essential part of ship structural analyses. It is thus of importance to better understand the ultimate torsional strength characteristics of ships with large hatch openings. The primary aim of the present study is to investigate the ultimate strength characteristics of ship hulls with large hatch openings under torsion. Axial (warping) as well as shear stresses are normally developed for thin-walled beams with open cross sections subjected to torsion. A procedure for calculating these stresses is briefly described. As an illustrative example, the distribution and magnitude of warping and shear stresses for a typical container vessel hull cross section under unit torsion is calculated by the procedure. By theoretical and numerical analyses, it is shown that the influence of torsion induced warping stresses on the ultimate hull girder bending strength is small for ductile hull materials while torsion induced shear stresses will of course reduce the ship hull ultimate bending moment. 相似文献
9.
脐带缆螺旋滑移分析及力学性能研究 总被引：1，自引：0，他引：1
针对脐带缆内部螺旋层,应用Darboux标架建立螺旋结构空间坐标系,推导弯曲载荷下螺旋结构的局部变形和滑移。考虑螺旋构件间的接触和摩擦作用,建立螺旋结构的受力平衡偏微分方程,并研究螺旋角和摩擦系数对螺旋结构滑移的影响。基于同层螺旋结构本构关系相同假设,将所有螺旋结构力学性能线性叠加,拟合脐带缆整体弯曲刚度。运用建立的理论解析方法,对某双层铠装脐带缆的力学性能进行研究,并与数值模拟结果进行对比验证。对比结果表明,理论解析得到的螺旋滑移结果与数值模拟结果一致,理论解析得到的脐带缆弯曲刚度与数值模拟结果在全滑动阶段比较接近。 相似文献
10.
Owing to nonlinear contact problems with slip and friction, a lot of limiting assumptions are made when developing analytical models to simulate the behavior of an unbonded flexible riser. Meanwhile, in order to avoid convergence problems and excessive calculating time associated with running the detailed finite element （FE） model of an unbonded flexible riser, interlocked carcass and zeta layers with complicated cross section shapes are replaced by simple geometrical shapes （e.g. hollow cylindrical shell） with equivalent orthotropic materials. But the simplified model does not imply the stresses equivalence of these two layers. To solve these problems, based on ABAQUS/Explicit, a numerical method that is suitable for the detailed FE model is proposed. In consideration of interaction among all component layers, the axial stiffness of an eight-layer unbonded flexible riser subjected to axial tension is predicted. Compared with analytical and experimental results, it is shown that the proposed numerical method not only has high accuracy but also can substantially reduce the calculating time. In addition, the impact of the lay angle of helical tendons on axial stiffness is discussed. 相似文献
11.
正压冲固平台是一种采用短桩加固基础的新型海洋采油平台,对于这种新型的平台结构,在结构分析和构件强度校核中必须考虑其有限元模型的基础边界条件处理问题。本文提出了正压冲固平台有限元计算模型中基础边界条件的一种简化方法,将两个水平方向的扭转自由度简化为扭转弹簧边界元,其余自由度简化为固定约束。通过计算分析得到了不同的边界约束刚度系数的取值对平台总体位移和强度校核应力的影响及变化趋势。结论是,平台结构对约束刚度系数K的反应在10^4～10^4之间时比较明显,对K的敏感度最为强烈：在此范围之外,平台反应分别接近于简支约束情况和刚性约束情况。尤其对于接近约束边界的单元,其应力变化最敏感。 相似文献
12.
Wen-Bing Wu Guo-Sheng Jiang Shu-Hui Lü Bang-Hua Xie 《Marine Georesources & Geotechnology》2016,34(4):321-330
The dynamic response of a tapered pile (considering its construction disturbance effect) is investigated when the tapered pile is subjected to a time-harmonic torsional loading. For most engineering conditions, the surrounding soil may be weakened or strengthened owing to the construction disturbance effect of the tapered pile, resulting in the soil becoming radially inhomogeneous. In order to consider this problem, the circumferential shear complex stiffness transfer model is proposed to simulate the radial inhomogeneity of soil. Then, the governing equations of a tapered pile-soil system subjected to torsional dynamic loading are established. By virtue of the circumferential shear complex stiffness transfer method and the impedance function transfer method, the analytical solution of torsional dynamic impedance at the head of the tapered pile is derived. Based on the presented solution, the influence of the construction disturbance effect of the surrounding soil on the torsional dynamic impedance at the pile head is investigated within the low-frequency range concerned in the design of a dynamic foundation. The results show that, even if the hardening range and softening range of the surrounding soil vary within a smaller scale, the hardening effect and softening effect also have a notable influence on the torsional dynamic impedance at the pile head. 相似文献
13.
大型集装箱船（LCS）具有较大的甲板开口,抗扭刚度非常低。在恶劣海况下航行时,大型集装箱船可能会遭遇斜浪的作用,此时船体将受到三向载荷的联合作用,水平波浪弯矩和扭转波浪弯矩可能会接近甚至超过垂向波浪弯矩,船体可能因发生组合变形而破坏。因此有必要研究大型集装箱船在三向载荷联合作用下的结构可靠性。在研究三向载荷联合作用下各维度极限强度的相互关系的基础上,提出了大型集装箱船的极限承载能力的可靠性评估方法,并对目标船在各浪向角下的结构可靠性进行评估。结果表明：目标船在0°浪向角下的失效概率最高;考虑水平波浪弯矩影响后目标船的结构可靠性有所降低;扭转波浪弯矩对目标船船中剖面的结构可靠性影响较小。 相似文献
14.
低温柔性管道是海上浮式液化天然气装置系统(FLNG)的核心输运装备。针对低温柔性管道多材料、多层复合的结构设计难点,将其按照不同功能解耦成内衬层、抗拉铠装层以及辅助层三个关键结构层。基于神经网络模型(RBF)、Kriging模型以及响应面模型(RSM)三种建模方法建立了上述三个结构层响应分析的代理模型,并通过模型准确度的比较,发现RBF的误差均最小。在优化设计中,基于遗传算法分别对低温柔性管道上述关键结构层进行多目标优化设计。在内衬层结构的优化中,以质量及弯曲刚度最小为优化目标;在抗拉铠装层结构的优化中,以质量最小及拉伸刚度最大为优化目标;在辅助层结构的优化中,以质量、弯曲刚度及传热速率最小为优化目标。研究工作为低温柔性管道的结构提供了关键设计参数及理性的设计方法。 相似文献
15.
Metallic strip flexible pipes (MSFP), a relatively new style of unbonded flexible pipes, are considered as an attractive alternative to traditional submarine pipes. Pipelines will inevitably confront torsion load which may affect the integrity and safety during their installation and application. Throughout this paper, the mechanical behavior of MSFP subjected to pure torsion is investigated by both experimental and numerical methods. Results from these two methods are essentially in agreement with each other. The finite element method (FEM) can be adopted to predict the failure torque of MSFP under torsion and analyze the detailed stress conditions of each layer. In addition, the effects of boundary conditions, layout manners of steel strips, friction coefficients between contact surfaces, twist directions and tension loads are discussed. The obtained conclusions will benefit cross-section design of MSFP and relative practical engineering. 相似文献
16.
在工程设计中,通常采用模块化方式制造超大型浮式结构物,将巨大的单体结构分割成多个较小模块,后期通过合适的连接器拼装形成。为了明确多模块超大浮体在波浪作用下的水弹性响应,以两个相邻层合浮体（高刚度面板和低密度芯材）为研究对象,建立波浪作用下铰接层合浮体水弹性响应的高阶势流模型。采用匹配特征函数展开法求解流体运动的速度势,探讨了铰接处弹簧刚度对浮体的反射系数、透射系数、挠度、弯矩和剪力的影响规律。研究结果表明：迎浪侧浮体的存在可以有效降低背浪侧浮体的挠度、弯矩和剪力幅值;与垂直弹簧相比,扭转弹簧刚度的增加可以更加有效抑制铰接层合浮体的水弹性响应;当扭转弹簧刚度大于一定值时,继续增大弹簧刚度对浮体的动力响应不产生影响。 相似文献
17.
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. 相似文献
18.
The propulsive characteristics of auto-pitch wing-in-ground effect oscillating foil propulsors (APWIGs) were numerically investigated through an unsteady Reynolds Averaged Navier-Stokes solver. The kinematics of such a biplane configuration is characterized by the prescribed heave motion and flow-induced pitch motion restrained by a torsional spring for each foil. Based on the validated numerical model, the comparison of propulsive performance between APWIGs and single auto-pitch oscillating foil, as well as dual-foil heave-only configuration, was conducted at different advance speeds. Results show that APWIGs is advantageous in both thrust production and efficiency enhancement over other two configurations due to the resulting wing-in-ground effect and substantial reduction of flow separation by the flow-regulated pitch motion. Furthermore, the effect of torsional spring stiffness on the propulsion of APWIGs was studied under different loaded conditions. It was found that both the maximum pitching angle and phase difference of pitch with heave are dramatically affected by the spring stiffness, which has major contribution to the hydrodynamic behaviours of the foils. Under a certain operating speed, an optimal torsional spring stiffness that produces the best propulsive performance can be found. With respect to the parametric space in the current study, the APWIGs can achieve a constant high efficiency over 70% by employing an appropriate spring stiffness. 相似文献
19.
为了研究桩长对海底防沉板—桩复合基础在水平、弯矩和扭转荷载作用下承载特性的影响,以我国南海水深200 m的某工程实例为研究对象,利用Flac3D有限差分仿真软件建立了计算模型。研究了桩长为4 m、6 m和8 m的防沉板—桩复合基础在水平、弯矩和扭转荷载作用下的极限承载力和荷载传递机理。结果表明,桩长超过6 m时复合基础的水平承载力显著增长,在水平加载过程中,防沉板总是先达到极限状态而破坏,桩基础的贡献在加载后期体现,且桩长为4 m、8 m时,桩基础与防沉板的连接处弯矩最大;随着桩长的增加,复合基础的抗弯承载力大幅提高,桩基础对复合基础的抗弯承载力贡献增大,当桩长超过8 m,桩长的增加对提高复合基础的抗弯承载力意义不大;在弯矩加载过程中,桩长对于防沉板、桩基础的荷载分配有显著影响,桩长为4 m时,外荷载主要由防沉板承担,当桩长超过4 m时,外荷载主要由桩基础承担;当扭转荷载不超过2 100 k N·m时,防沉板承担主要荷载,直至防沉板达到极限状态而发生旋转,随后桩基础的承载力逐渐发挥;对于桩长为6 m、8 m的复合基础,其极限状态根据防沉板适用性准则确定。 相似文献