考虑海底管线初始侧向变形的低阶模态

温度应力下海底管线的整体屈曲是海底管线设计中的关键问题之一,不埋或半埋的海底管线较易发生水平向整体屈曲。海底管线会因为制造的缺陷或铺设的原因而具有初始变形,即初始侧向变形。研究了初始侧向变形对海底管线整体屈曲的影响,应用小变形理论建立了单拱侧向变形和反对称双拱侧向变形管线发生低阶模态水平向整体屈曲的理论分析方法,结合工程实例分析了初始侧向变形形态、侧向变形幅值以及地基土体强度特性对管线水平向整体屈曲的影响。结果表明,初始侧向变形的存在使管线更易发生整体屈曲;而反对称双拱侧向变形比单拱侧向变形更易引起管线整体屈曲;随初始侧向变形幅值的增加管线发生整体屈曲所需要的温差降低,且整体屈曲变形形态有所改变管土间摩擦系数的增加会提高管线发生整体屈曲的温差,从而提高管线抵抗整体屈曲变形的能力。     

浮力装置触发深海管道水平向整体屈曲效果的数值模拟研究

海洋油气资源的运输主要通过海底管道进行,管道在工作时受到较大的温度荷载,会产生整体屈曲变形。深海管道设计中常采用人为装置触发一定程度的水平向整体屈曲变形,来释放轴向的温度应力,浮力装置是常用的触发方式之一。本文通过数值模拟研究,分析了不同浮力大小和不同浮力施加范围下,管道水平向整体屈曲的临界屈曲力,得出临界屈曲力随浮力大小和施加范围变化的情况;并研究了不同土体阻力下,浮力装置触发整体屈曲的效果。研究表明,水平向土体阻力较大时,浮力装置触发水平向整体屈曲的效果较好。浮力装置的触发效果对轴向土体阻力不敏感。     

海底管线整体屈曲过程中塑性变形研究

海底管线是海洋油气工程中主要的输送手段。在工作状态下,受高温高压的影响,深海管线可能会发生水平向整体屈曲。随海洋油气作业水深的增大,施加于管线的温度和压强也逐渐增加,导致管线产生较大的屈曲位移和截面应力,使得截面产生塑性应变。本文采用数值模拟方法,对海底管线整体屈曲过程中塑性区的分布及其与整体屈曲影响因素的关联性、塑性变形对水平向变形的影响和塑性变形造成的截面椭圆度的变化规律进行分析,研究塑性变形对整体屈曲过程影响的规律。     

双拱初始缺陷海底管线水平向整体屈曲数值模拟分析

为了研究具有双拱反对称初始缺陷海底管线的整体屈曲特性,采用模态分析法将最可能出现的缺陷形态引入数值分析模型中。针对管线在高温高压作用下发生整体屈曲的动态变形特征,运用显式动力数值模拟方法研究了管线整体屈曲过程中水平向变形与轴向变形随温度和内压的变化规律,建立了在整体屈曲过程中屈曲管段与滑动管段轴力的变化过程与初始缺陷形态的关系。将数值模拟结果同经典解析解和室内模型实验结果进行对比,验证了本方法的可靠性。工程算例的分析结果表明,管线整体屈曲的发生是一个由低阶向高阶发展的过程,具有双拱缺陷的管线首先发生二阶模态的整体屈曲,而后过渡到四阶模态;管线整体屈曲的变形包括屈曲段的水平向变形和滑动管段的轴向缩进,其中水平变形释放了管壁内的轴力,轴力的释放量随初始缺陷尖锐程度的降低而增大;轴向缩进变形由于受到地基土的摩阻力使滑动管段内的轴力发生累积,轴力的累积量随初始缺陷的尖锐程度的降低而增加。以上研究成果对指导实际工程具有现实意义。     

正压冲固平台结构分析中基础边界条件的影响

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。     

A general model for analysis of sound radiation from orthogonally stiffened laminated composite plates

A general theoretical model is developed to investigate the sound radiation from an infinite orthogonally stiffened plate under point excitation force. The plate can be metallic or composite, and fluid loading is also considered in the research. The first order shear deformation theory is used to account for the transverse shear deformation. The motion of the equally spaced stiffeners is examined by considering their bending vibrations and torsional movements. Based on the periodic structure theory and the concepts of the equivalent dynamic flexibility of the plate, the generalized vibro-acoustic equation of the model is obtained by applying the Fourier transform method. The generalized model that can be solved numerically is validated by comparing model predictions with the existing results. Numerical calculations are performed to investigate the effects of the location of the excitation, the spacing of the stiffeners, the plate thickness, the strengthening form and the fiber orientation on the sound radiation characteristic of the orthogonaUy stiffened plate, and some practical conclusions are drawn from these parameter studies.     

Lateral Global Buckling of Submarine Pipelines Based on the Model of Nonlinear Pipe–Soil Interaction

With the increasing development and utilization of offshore oil and gas resources, global buckling failures of pipelines subjected to high temperature and high pressure are becoming increasingly important. For unburied or semi-buried submarine pipelines, lateral global buckling represents the main form of global buckling. The pipe–soil interaction determines the deformation and stress distribution of buckling pipelines. In this paper, the nonlinear pipe–soil interaction model is introduced into the analysis of pipeline lateral global buckling, a coupling method of PSI elements and the modified RIKS algorithm is proposed to study the lateral global buckling of a pipeline, and the buckling characteristics of submarine pipeline with a single arch symmetric initial imperfection under different pipe–soil interaction models are studied. Research shows that, compared with the ideal elastic–plastic pipe–soil interaction model, when the DNV-RP-F109 model is adopted to simulate the lateral pipe–soil interactions in the lateral global buckling of a pipeline, the buckling amplitude increases, however, the critical buckling force and the initial buckling temperature difference decreases. In the DNV-RP-F109 pipe–soil interaction model, the maximum soil resistance, the residual soil resistance, and the displacement to reach the maximum soil resistance have significant effects on the analysis results of pipeline global buckling.     

Numerical analysis of cross-section ovalization in the deep-sea pipeline lateral buckling process

Abstract

The deep-water pipeline is the main means of transportation in offshore oil and gas development engineering. The deep-water pipeline may incur lateral global buckling due to the high temperature and pressure that are applied on the pipeline to ensure the contents’ liquidity. With the increasing operating water depth, a higher temperature and pressure are applied to the pipeline, causing large lateral deformation and a large bending moment. Due to the inhomogeneous distribution of the bending moment on the cross-section, different points on the cross-section will deform differently. This kind of deformation causes the cross-section to turn into an oval ring. The cross-section ovalization caused by global buckling was rarely analyzed in former engineering practice since the load is relatively low. With the increase in operation water depth and operation load, the ovality caused by global buckling is noticeable. This article analyzed cross-section ovalization caused by pipeline lateral global buckling with a numerical simulation method. The pipelines with different initial cross-section shapes were simulated, and the influence of several impact factors, including load, pipeline and soil factors on the ovality of the cross-section, were analyzed. The results show that the initial cross-section shape type has little effect on the pipeline ovalization pattern. The initial ovality of the pipeline with an oval ring cross-section shape has little influence on the residual ovality. Among all the factors analyzed in this paper, the pressure difference is the primary factor that should be considered in a pipeline ovalization check.     

双层自行式施工平台结构强度评估

以一种适合港口施工作业的新型自行式施工平台为研究对象,介绍了该型平台特点与工作流程。根据其工作行走状态及载荷特点,使用有限元方法分析多工况下平台的结构屈服强度,并根据规范进行平台和桩腿结构屈曲评估。该平台由上下两层平台组合而成,针对此平台上下层接触的特点,探讨了不同类型MPC,ABAQUS接触分析的结构强度计算结果。研究对自行式海洋平台设计具有借鉴意义,并对平台结构强度计算研究提供了一定参考。     

Ultimate Strength of Ship Plating under Axial Compression

The failure of a ship hull girder is governed by buckling and plastic collapse of the deck, bottom and side shell steel stiffened plates. The stiffened steel plating in ships is generally subjected to both in-plane and out-of-plane loading and is more important to understand the characteristics of these panels under buckling. Tests are reported on the collapse load of stiffened plates with and without cutout and with reinforced cutout under uniaxial compression. A generalized computer program for the semi-analytical solutions proposed by various investigators based on strut approach and orthotropic plate approach, and a finite element analysis program based on orthotropic plate approach are developed. The panels are also analysed using the finite element analysis software ANSYS. An approximate method based on strut approach is proposed to calculate the collapse load of stiffened plates with cutouts and initial imperfections. The reduction in strength of the panels due to the presence of square cutout, rectangular cutout and increase in strength due to reinforcement around rectangular cutout are calculated based on the test results. Comparisons are made between the test results and predictions based on semi-analytical solutions and finite element analyses, and the uncertainty parameters calculated are discussed. Based on this study it is concluded that the cutout can be reinforced with a maximum increase in strength up to 19% for plate initiated failures.     

An empirical model for flexible pipe armor wire lateral buckling failure load

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%.     

Experimental and finite element study on lateral global buckling of pipe-in-pipe structure by active control method

Offshore oil and gas exploration are gradually heading toward the deep sea and even the ultra-deep sea. According, the working temperature and pressure intensity of subsea oil and gas pipelines have increased by a considerable degree. This situation is accompanied by the global buckling problem in deep sea pipelines, which has become increasingly common. Meanwhile, ordinary single-layer pipelines cannot last for a long time under harsh deep-sea working conditions. Thus, multilayer pipelines, such as the pipe-in-pipe (PIP) structure and bundled pipelines, have gradually become top choices. However, the global buckling mechanisms of these multilayer pipelines are more complicated than those of single-layer pipelines. The sleeper–snake lay pipeline, which is an active control method for global buckling, was used in this study. The change and development laws of global buckling in a PIP structure at different wavelengths and amplitudes were determined through an experimental study. A dynamic solution method that considers artificial damping was adopted to establish finite element global buckling models of a PIP structure with initial imperfections. The effects of various factors, such as pipeline laying shape, sleeper–pipe function, and seabed–pipe function, on global buckling were analyzed. By the result of finite element method analysis, the initial imperfection, and sleeper–pipeline friction were determined to be the key factors that influenced critical pipeline buckling force. Accordingly, a reference for the design of PIP structures is presented.     

On the formulation of a finite element method for the stiffened multi-layered airfoil/hydrofoil structure: Post buckling analysis for the wings of underwater gliders

A finite element method is developed for the stiffened multi-layered airfoil/hydrofoil structure for the large deformation and finite strain problem. The kinematics of the airfoil/hydrofoil is set up. The Consistent Orthogonal Basis Function Space is applied for the airfoil/hydrofoil structure. Given the airfoil/hydrofoil configuration and boundary conditions, the basis function space can be uniquely determined, such that the diagonal mass matrix is obtained accurately and the basis functions are very identical with the mode shape functions of the structure. In order to satisfy the displacement compatibility condition between adjacent layers of the airfoil/hydrofoil, the traction degree-of-freedom is also induced.The post buckling analysis is presented for the wing (hydrofoil) structure of the underwater glider. The water pressure is applied on the outer surface and the critical buckling pressure is calculated. The post buckling equilibrium path is also given. The results are verified with ANSYS. The present study of the buckling analysis of the airfoil/hydrofoil under water pressure is helpful to the design of underwater glider.     

考虑翘曲应力的半潜平台扭转极限强度计算方法研究

半潜平台由于结构和受力复杂,目前主要采用非线性有限元整体模型计算其扭转极限承载力,存在建模和计算时间较长、精度较差和不易收敛等问题。一方面进行半潜平台的整体有限元模型的简化研究,提高其计算效率和收敛性;另一方面基于薄壁杆件理论,将该半潜平台截面简化为单壁室截面计算其翘曲应力,提出了基于一跨模型且考虑翘曲应力影响的半潜平台约束扭转极限强度计算的简化增量迭代方法,并编制了相应的计算程序。计算结果表明,所提简化增量迭代方法计算精度较高,能很好地反应翘曲应力对半潜平台约束扭转极限强度的影响,大幅减少了计算约束扭转极限强度的时间,可用于半潜平台的设计。     

Settlement Mode Analysis for An Immersed Tube Tunnel Considering A Nonuniform Foundation Under Tidal Load

Immersed tube tunnels are usually placed on soft soil layers in cross-sea tunnelling engineering. Owing to the influence of stratum conditions and slope design, the longitudinal distribution of substratum layers is generally uneven. Thus, the inhomogeneous deformation of the element-joint becomes the key factor in the failure of the immersed tube tunnel. Therefore, a corresponding calculation method for joint deformation is needed to explore the deformation law of immersed tube tunnels. By constructing a three-section immersed tube tunnel analysis model (TTM), the relationship between the two types of deformation of the immersed tube tunnel structure in a longitudinal nonuniform soft soil foundation is described, and the deformation characteristics of the immersed structure under different boundaries are discussed. Based on the mechanical behaviour of the joint and foundation, according to the Timoshenko beam on the Vlasov two-parameter foundation (VTM), considering the tidal cyclic load during the operation and maintenance period, an example analysis is given. Moreover, the deformation characteristics and development trend of the immersed tube tunnel under the influence of different soil layers are discussed. The obtained results have a certain guiding significance for the deformation calculation of immersed tube tunnels.

     

Small- and large-scale model tests on the buckling property of slender pile

Slender piles embedded in soft ground or liquefied soil may buckle under vertical load. In this paper, both small- and large-scale model tests are conducted to investigate the buckling mechanisms of a slender pile and the lateral earth pressure acting on the pile. To observe the buckling of a slender pile, the strain-controlled loading method is adopted to apply a vertical load. When the two ends of a slender pile are hinged, the buckling mechanisms of small- and large-scale model tests are same. It should be noted that this applies only to a system with a small ratio of pile bending stiffness to soil bending stiffness. An applied vertical load increases with an increasing pile head settlement until it reaches the critical buckling load. By further increasing the pile head settlement, the measured load approaches the critical buckling load. In the large-scale model test, the measured lateral earth pressure (i.e., active and passive) acting on the slender pile varies linearly with the lateral pile displacement when the measured range is 3–5?m beneath the ground. A critical buckling calculation method has been adopted to compare with the conventional “m” method. The two-sided earth pressure calculation method can achieve more approximate results with the model test.     

浮式风机气动—水动—气弹性耦合响应数值模拟

随着海上风电产业的快速发展,大型浮式风机逐渐从概念设计走向工程应用,但仍面临较大的挑战。一方面,在风、浪等环境载荷的作用下,浮式风机的气动载荷和水动力响应之间存在明显的相互干扰作用;另一方面,风力机大型化使得叶片细、长、薄的特点愈发突出,叶片柔性变形十分显著,这会影响到浮式风机的耦合性能。基于两相流CFD求解器naoe-FOAM-SJTU,结合弹性致动线模型和等效梁理论,建立了浮式风机气动—水动—气弹性耦合响应计算模型,并对规则波和剪切风作用下Spar型浮式风机的气动—水动—气弹性耦合响应进行了数值模拟分析。结果表明,风力机气动载荷使得叶片挥舞变形十分显著,而叶片的扭转变形会明显降低风力机的气动载荷。此外,风力机气动载荷会增大浮式平台的纵荡位移和纵摇角,同时,浮式平台运动响应会导致风力机气动载荷产生大幅度周期性变化。进一步地,叶片结构变形响应会使得浮式风机尾流场的速度损失和湍动能有所降低。     

Static Analysis of Collision Strength of Offshore Platform

In this paper a numerical analysis method combining FEM incemental technique with limit analysis concept is proposed for the study of the static strength of offshore platform in collision. Large deformation and plasticity are accounted for and the limit yield surface expressed by generalized stress for a tubular section is derived. The modified stiffness matrix of space beam element is formulated by Plastic Node Method. The buckling behavior of beam columns can also be taken into account. It can trace the generation of plastic hinges during loading and finally the ultimate strength of offshore platform against collision is obtained.     

Viscous model of plate tectonics for the Black Sea region (in relation to the problem of the late Cenozoic evolution of the Black Sea basins)

A numerical model of the Black Sea region (Northeastern Mediterranean) is presented in which it is regarded as a part of the mosaic plate ensemble consisting of the fixed East European platform; the active Arabian, Adriatic, and Pannonian plates; and passive East and West Black Sea and Mysian microplates, which are embedded in a plastically deformable regional orogenic matrix. The fields of displacements, stresses, and deformations in the region are calculated by means of the finite element method within the framework of a linear-viscous rheology approach to a system with nonhomogeneous viscosities. The velocity field obtained is in good agreement with published data of direct observations of plate displacements in the region. In the pressure field, areas of low pressure and decompression are established in the western part of Black Sea and in the south of the Mysian microplate. The poles of rotation of the East and West Black Sea microplates and of the Mysian microplate are computed. For the latter two microplates, significant rotational components are suggested. The East Black Sea microplate acts mostly as indenter, which transmits the collisional motion from the Arabian plate to the southern edge of the East European platform including the Crimea. According to the geodynamical model, the rates of the Cenozoic sedimentation in the Black Sea depression at the collision stage (Oligocene-Pliocene) result from the greater compression of the East Black Sea microplate as compared to the West Black Sea microplate, which, probably, experienced a kind of extension.     

海洋结构薄板承载性能的裂纹群体效应

大型海洋结构长期服役中构件裂纹不可避免,结构承载性能必然随之弱化。针对含非均匀分布裂纹的薄板,以有限元方法对小变形状态下其极限承载能力进行计算,得到裂纹数量、长度、分布等因素对薄板屈曲临界应力的影响规律。发现裂纹不仅改变截面的有效承载面积,同时改变局部结构的变形状态,多种因素共同作用使板的承载性能非单调变化,即多裂纹对板承载性能的影响具有一定的"群体"效应。