陡波型柔性立管浮力块参数优化及应用

浮力块分布和外径等参数直接影响柔性立管在环境载荷作用下的动力响应,对某深水柔性立管进行陡波型布置,开展时域内的整体动态有限元分析,得到浮力块分布和外径对柔性立管动力响应的影响规律,表明浮力块参数是陡波型柔性立管整体设计的一个重要因素。立管动力响应是弯曲加强器的设计载荷,根据上述规律,构造具有不同浮力块参数的柔性立管模型,进行多工况动态分析,通过对比弯曲加强器设计载荷对(T,θ)的散点图,得到弯曲加强器设计载荷优化方法及最优设计载荷。     

非黏结柔性立管疲劳损伤特性分析

对柔性立管的疲劳损伤特性进行分析,探究抗拉层与抗压层的疲劳特性,并分析弯曲加强器的存在与否对柔性立管疲劳损伤的影响。研究表明:柔性立管最内层抗拉层上的疲劳损伤最大,从内到外,抗拉层的疲劳损伤依次减小;抗压层受到的疲劳损伤远小于抗拉层的疲劳损伤;弯曲加强器的存在可以减小立管的疲劳损伤,并改变抗拉层疲劳危险点的位置。     

组合载荷作用下深海非粘结柔性管力学性能对比分析

建立深海非粘结柔性管新型力学数值分析模型,分析其在复合载荷工况下的力学性能。深海非粘结柔性立管是深水资源开发的关键设备,安装成本低,适用于恶劣深海环境。然而,由于非粘结柔性管本身的结构型式复杂以及层与层之间的摩擦、接触等诸多强非线性特性,使其局部力学性能分析面临众多挑战。研究针对非粘结柔性立管特殊的结构型式,建立一个高效的数值分析模型,对其刚度进行数值求解并与实验结果进行对比,探讨了内压和拉伸、扭转、弯曲的组合载荷工况和拉扭组合载荷工况对非粘结柔性立管刚度的影响。研究表明,本文所建立的简化模型计算结果与实验结果吻合较好。此外,柔性立管所受到的内压可以在一定程度上增加非粘结柔性立管的刚度;拉扭组合载荷工况使非粘结柔性立管的拉伸刚度降低明显,而使其扭转刚度少量增加,总体上较单一载荷工况更加危险。     

基于有限元方法的柔性立管防弯器疲劳寿命分析

防弯器是柔性管系统中的一个关键附件,其与柔性立管相互作用带来的非线性问题使得预测其疲劳寿命十分困难。以南海某油田柔性立管防弯器为例,采用ABAQUS建立了柔性立管与防弯器的“管中管”分析模型,模型中考虑了两者之间的间隙和滑动摩擦,以及材料非线性和接触非线性等因素。在加载方式上利用“位移”载荷取代传统的“力—角度”载荷,更符合工程实际。利用防弯器材料的ε-N疲劳试验曲线,结合防弯器的应力分析结果,得到危险截面的疲劳寿命。考虑材料非线性的管中管模型和疲劳寿命的计算方法,可为今后运动监测数据的利用和防弯器的优化设计提供借鉴。     

非粘结柔性立管螺旋键缠绕角度敏感性分析

非粘结柔性立管结构形式复杂,层与层之间涉及摩擦、接触等非线性特性,使其数值模拟方面很难同时保证效率与精度。针对柔性立管特殊的结构形式,本文建立不同角度螺旋键的非粘结柔性立管高效分析简化模型,通过Ansys workbench软件分析非粘结柔性立管在内压和拉伸、扭转、弯曲的组合荷载工况下螺旋键缠绕角度对其刚度的影响。结果表明:本文所建立的立管简化分析模型与立管原型的力学性能吻合较好,并且可以提高计算效率;螺旋键缠绕角度越大,立管的扭转刚度越大,拉伸刚度与弯曲刚度越小;内压的施加对拉伸刚度、扭转刚度和弯曲刚度是有利的,内压对于弯曲刚度有较明显的增加,对拉伸刚度和扭转刚度有较小程度的增加。     

深水无粘结柔性管抗拉伸层屈曲问题研究进展

随着我国海洋石油工业不断向深水发展,深水柔性管即将获得广泛应用。深水柔性管结构形式复杂,其抗拉层螺旋钢缆在铺管安装和弯曲过程中可能受到轴向压载荷,产生鸟笼现象和侧向屈曲失效,是当前柔性管开发中的研究热点。介绍了国外在柔性管抗拉层钢缆受压载荷失稳的数值模拟和试验研究现状,为我国开展柔性管开发提供参考。     

海洋电缆弯曲加强器参数化设计与

为建立海洋电缆弯曲加强器参数化设计方法,使用有限元模型进行了弯曲加强器设计参数研究。基于海缆及其弯曲加强器的几何结构及受力特点,建立了基于多相耦合梁单元的平面有限元模型,可以计算并分析海缆及其弯曲加强器在一定角度的张力作用下的形变与等效应力分布。通过多个案例系统性地分析了弯曲加强器的主要设计参数,即根部直径、锥体段长度及材料弹性模量,对海缆弯曲挠度、曲率及等效应力分布的影响。原创性地提出了弯曲加强器组合设计参数φ (t, L, E)。通过定量分析确定了其与海缆最大曲率之间的近似线性关系,并由此设计了参数化的弯曲加强器设计流程。通过设计实例验证了组合参数与海缆最大曲率之间关系的准确性和参数化设计流程的有效性。     

基于能量竞争载荷模型的海洋立管双向涡激振动时域预报方法研究

海洋立管是深海油气开发中用于连接海底井口和水面浮体的唯一通道。立管在洋流作用下极易发生涡激振动（vortex-induced vibration,简称VIV）,发展快速经验性涡激振动时域预报方法对立管的安全设计具有重要意义。通过柔性立管模型试验,结合载荷重构方法和最小二乘法,识别建立了能量竞争载荷模型下的经验水动力载荷系数模型。应用识别建立的经验水动力载荷系数模型,发展形成了海洋立管顺流向及横流向双向涡激振动时域预报方法。将预报结果与试验结果对比,结果表明：基于能量竞争载荷模型的海洋立管双向涡激振动预报方法能够有效预报海洋立管涡激振动主导模态、主导频率、流向平均位移响应和涡激振动位移响应等力学行为特性。研究成果对发展更为有效的涡激振动预报手段具有有益参考。     

海洋电缆弯曲加强器参数化设计与分析

为建立海洋电缆弯曲加强器参数化设计方法,使用有限元模型进行了弯曲加强器设计参数研究.基于海缆及其弯曲加强器的几何结构及受力特点,建立了基于多相耦合梁单元的平面有限元模型,可以计算并分析海缆及其弯曲加强器在一定角度的张力作用下的形变与等效应力分布.通过多个案例系统性地分析了弯曲加强器的主要设计参数,即根部直径、锥体段长度及材料弹性模量,对海缆弯曲挠度、曲率及等效应力分布的影响.文中原创性地提出了弯曲加强器组合设计参数φ(t,L,E).通过定量分析确定了其与海缆最大曲率之间的近似线性关系,并由此设计了参数化的弯曲加强器设计流程.通过设计实例验证了组合参数与海缆最大曲率之间关系的准确性和参数化设计流程的有效性.     

非金属柔性立管在海洋潮流下的动力响应特性研究

针对海洋柔性立管在服役期间,整体性能和运动响应受潮流影响较大的问题,本文在海上试验的基础上,采用OrcaFlex对长细比为448的非金属柔性立管模型进行了数值模拟。研究了潮流作用下,流速和流向的改变对于非金属柔性立管受力情况、涡激振动(VIV)响应特性和控制模态的影响。研究结果表明:潮流流向对立管顶张力、曲率和立管整体VIV响应有着显著影响,随着流速增加呈现不同变化规律。柔性立管悬垂段在高流速下更容易激发高阶模态,并呈现出明显的行波特性;立管的悬挂点和触底点为危险区域,随着流向改变易发生疲劳破坏。研究结果对海洋柔性立管总体布置设计具有参考意义。     

Nonlinear bend stiffener analysis using a simple formulation and finite element method

Flexible marine risers are commonly used in deepwater floating systems.Bend stiffeners are designed to protect flexible risers against excessive bending at the connection with the hull.The structure is usually analyzed as a cantilever beam subjected to an inclined point load.As deflections are large and the bend stiffener material exhibits nonlinear stress-strain characteristics,geometric and material nonlinearities are important considerations.A new approach has been developed to solve this nonlinear problem.Its main advantage is its simplicity;in fact the present method can be easily implemented on a spreadsheet.Finite element analysis using ABAQUS is performed to validate the method.Solid elements are used for the bend stiffener and flexible pipe.To simulate the near inextensibility of flexible risers,a simple and original idea of using truss elements is proposed.Through a set of validation studies,the present method is found to be in a good agreement with the finite element analysis.Further,parametric studies are performed by using both methods to identify the key parameters and phenomena that are most critical in design.The most important finding is that the common practice of neglecting the internal steel sleeve in the bend stiffener analysis is non-conservative and therefore needs to be reassessed.     

深海采矿立管在波流载荷下的弯矩响应分析

采矿立管是深海采矿系统的重要组成部分，立管的弯矩分析是确保立管正常使用的重要指标。立管所处海洋环境复杂，且立管底部的自由边界条件使得立管弯矩特性难以分析。本文基于波浪理论，使用Abaqus 有限元软件建立海洋采矿立管的模型，运用Abaqus中的AQUA海洋工程模块，考虑立管在轴向力、自重、浮力、波浪载荷、海流载荷及模拟海上平台水平和升沉运动共同作用下，对采矿立管进行弯矩分析，计算了提升泵不同安装位置、不同中继仓重量变化对弯矩的影响，结果表明：提升泵会增大安装位置的弯矩幅度，且安装在不同位置对立管弯矩会产生叠加影响；中继仓重量的增加提高了立管整体稳定性，但会使提升泵处弯矩波动产生向中部延伸的不利影响。     

Nonlinear Behaviour of Coflexip Risers

A modified Newton-Raphson iterative technique is formulated for obtaining the static configuration of the Lazy "S" flexible marine riser between the floater and mid-arch buoy under its submerged self weight and the applied top tension. The geometrically non-linear problem is solved by finite difference with the above technique. The problem is formulated as a regular boundary value problem with specified moments and deflections at both ends. Usually the bending stiffness of the flexible riser made of Coflexip pipe is very low. By use of the above analysis, several flexible riser configurations are analyzed and their characteristic behaviors are investigated. Also, changes in the riser characteristics due to quasi-static motion of the floater end are estimated for the safety of the riser layout.     

An inverse problem methodology for multiple parameter estimation in bend stiffeners

The flexible riser top connection is a critical region for lifetime assessment due to large tension/curvature variations and modeling uncertainties. The bend stiffener polyurethane mechanical response not only presents a nonlinear loading rate and temperature dependency but is also subjected to weather ageing during operation, which may affect its mechanical behavior over time. The top tension, employed for riser local cross-section stress calculation, is usually obtained from global dynamic analyses performed under selected environmental conditions, if direct measurement is not available. As a consequence, both the bend stiffener effect on the curvature distribution and the top tension time series present inherent uncertainties for riser lifetime (re)assessment. In the present work, a proposed monitoring approach composed by gyrometers installed along flexible riser/bend stiffener top connection system length combined with an inverse problem methodology is numerically investigated to estimate the following parameters: (i) polyurethane hyperelastic response and (ii) effective top tension. The top connection system is modeled using a large deflection beam bending model and the parameters are estimated using a damped least-square minimization approach with the Levenberg–Marquardt algorithm. For the preliminary feasibility investigation, the gyrometer experimental data is numerically estimated through Monte Carlo simulations. A case study is carried out to investigate the influence that the number of sensors, sensors arrangement, loading conditions and top connection model have on the inverse parameters estimation. The results indicate that the proposed monitoring approach and inverse parameter estimation methodology may effectively reduce flexible riser lifetime calculation uncertainties.     

A nonlinear viscoelastic bend stiffener steady-state formulation

Bend stiffeners are essential components of a flexible riser system, employed to ensure a smooth transition at the upper connection and to protect the riser against over bending and from accumulation of fatigue damage. The highly nonlinear rate dependent behavior of these structures directly affects the integrity assessment of the riser in one of its most critical regions, the top connection. A steady-state formulation (disregarding inertial forces) and numerical solution procedure is developed in this work employing the perturbation method for a nonlinear viscoelastic bend stiffener large deflection beam model subjected to harmonic loading conditions. For stochastic loading conditions, the response is calculated employing the superposition principle by summing up the steady-state result of a number of individual frequency components. A time domain formulation is also derived employing the state-variable approach for the numerical solution of the resulting hereditary integral in the governing equations. A case study is presented for the top connection system of a 4″ ID flexible riser using relaxation and tensile experimental data obtained from a typical class of bend stiffener polyurethane. Harmonic and stochastic input loading conditions are employed for time and frequency domain model comparison/validation and to assess loading history and frequency influence in the curvature response.     

A variational formulation for three-dimensional analysis of extensible marine riser transporting fluid

This paper presents a model formulation for static and dynamic analysis of three-dimensional extensible marine riser transporting fluid. A variational model formulation is developed based on the principle of virtual work-energy and the extensible elastica theory. The virtual work-energy functional is composed of the virtual strain energy due to axial stretching, bending, and torsion and the virtual work done by the external and internal fluid. The governing dynamic equilibrium equations are derived in the Cartesian coordinate. The finite element method is used to obtain the numerical solutions. The numerical examples are provided to demonstrate interesting effects of fluid transportation and axial deformation on large displacements and dynamic properties of the three-dimensional extensible marine riser.     

海洋立管综合环境条件设计标准研究

首先用有限单元法推导海洋输液立管在外界环境荷载条件下的侧向振动微分方程。对渤海某海区的15次风暴过程作了抽样分析，得到以波高为主时的波高、流速序列和以流速为主时的波高、流速序列，并对其进行了Weibull、Gumbel、Lognormal等适线分析，以确定各序列的最优分布形式及相应的特征值。用重点抽样法进行随机模拟得到联合概率为百年一遇的波高的流速。针对线海固定式平台铰接的海洋输液立管，以最大应力为控制条件确定其联合设计标准，并与其它方法作了比较，得到一些有益的结论。     

Dynamic response of marine risers by single wave and spectral analysis methods

This paper uses the Galerkin method in the solution of the marine riser differential equation and compares the dynamic bending stresses in a tension-leg-platform riser calculated by the linearised single wave and linearised spectral analysis methods.The results show that it is possible to make some rational assessment of approximate peak values of bending stress in the spectral method.The analysis methods are applicable to any riser system subject to horizontal exciting forces due to fluid and vessel motion.