The buckling of plastic oblate hemi-ellipsoidal dome shells under external hydrostatic pressure

The paper presents a theoretical and an experimental investigation into the buckling of seven oblate hemi-ellipsoidal dome shells under external hydrostatic pressure. Four of the shells were made in glass reinforced plastic and three were made from a thermosetting plastic called solid urethane plastic. All the vessels were tested to destruction. The theoretical study was made with the aid of a non-linear finite element solution, where both geometrical and material non-linearity were allowed for. Good agreement was found between experiment and theory for all the vessels. The very oblate domes failed axisymmetrically. Theoretical convergence was good for the more oblate domes but it was not as good as for the less oblate domes. This may have been because the less oblate domes did not fail in a classical axisymmetric manner as was expected. This work is of much importance in ocean engineering.     

The buckling and vibration of tube-stiffened axisymmetric shells under external hydrostatic pressure

The paper reports on a theoretical and an experimental investigation into the buckling and vibration of prolate hemi-ellipsoidal tube-stiffened domes under external water pressure. The theoretical analyses were via the finite element method, where both the fluid and the structure were modelled with finite elements. The dome was modelled with a varying meridional curvature element and with eight displacement degrees of freedom and the water was modelled by solid annular elements where each element had eight pressure degrees of freedom in its cross-section. Comparison was good between experiment and theory.     

不同径厚比的海底管道压溃屈曲研究

为了探索不同径厚比海底管道的压溃屈曲特性,本文分别采用挪威船级社（Det Norske Veritas,DNV）规范、有限元模拟和深海压力舱模型试验,研究不同径厚比海底管道承载外部水压的能力,并就DNV规范压溃屈曲计算公式对不同径厚比管道的适用性进行了讨论,优化了小径厚比海底管道压溃屈曲的设计方法。研究表明：小径厚比管道的压溃屈曲临界压力对管道径厚比的变化更敏感;DNV规范计算小径厚比管道的压溃屈曲临界压力偏小,在进行深海管道的压溃屈曲设计时,建议采用模型试验结合有限元模拟的方法,计算管道实际可提供的压溃屈曲承载力。     

Inelastic buckling of thick-walled circular conical shells under external hydrostatic pressure

The paper reports on a theoretical and an experimental study into the collapse of three thick-walled circular conical shells, which were tested to failure under external hydrostatic pressure. All three vessels failed by plastic non-symmetric bifurcation buckling. Two theoretical analyses were carried out, both based on the finite element method. One of the theoretical analyses was based on inelastic non-symmetric bifurcation buckling and the other analysis was based on plastic axisymmetric buckling. Both of these theoretical analysis and the experimental observations appeared to indicate that there is a link between plastic non-symmetric bifurcation buckling and plastic axisymmetric buckling.     

Numerical study on lateral buckling of pipelines with imperfection and sleeper

Lateral buckling is an important issue in unburied high-temperature and high-pressure (HT/HP) subsea pipelines systems. The imperfection–sleeper method is one of the most well-known methods used to control lateral buckling of HT/HP pipelines. Pipelines–sleeper–seabed numerical models are established and verified to analyze the buckling behavior of pipelines using the imperfection–sleeper method. The influence of six main factors on lateral buckling behavior is investigated in details based on the numerical results. Equations of buckling displacement (buckling displacement is defined by the final displacement of the middle point of the pipelines), critical buckling force, and buckling stress (Mises stress) are proposed using the gene expression programming technique. These equations show good accuracy and can be used to assist in the design of sleepers and assess the compressive and stress levels of pipelines.     

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.     

屈曲利用因子约束下船体板架结构优化设计方法

船体板架结构在屈曲约束下的优化问题具有变量多和约束多的特点,且屈曲计算需借助有限元分析,属于大规模耗时优化问题,运用常规优化方法求解需要较高的计算成本。这里提出一种适用于屈曲约束下船体板架快速优化方法,该方法利用板格屈曲利用因子具有局部性的特点,对板格厚度自变量空间进行降维处理;利用板格屈曲利用因子对板格厚度具有单调性的特点,采用牛顿迭代方法求解其达到目标值的板格厚度;同时比较板格在相同重量增量下,加筋叠加板厚与仅加板厚对屈曲利用因子改善程度的大小决定是否加筋;通过两阶段的迭代寻优,快速获得最优的板厚以及防屈曲筋布置方案。某油船双层底优化结果显示,该方法能够在30步之内完成优化计算,优化效率高;优化方案相比原始方案减重达17.63%,绝大部分板格屈曲利用因子取值在0.9～1.0之间,材料得到充分利用。     

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。     

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.     

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63.5 mm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。     

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。     

Impact Buckling and Post-Buckling of Elasto-Viscoplastic Cylindrical Shell Under Torsion

The dynamic torsional buckling and post-buckling of elasto-plastic circular cylindrical shell isstudied.By the usage of the Bodner-Partom constitutive relation,the present visco-plastic problem is treat-ed as an orthotropic elastic problem.Based on the nonlinear large deflection shell therory,the governingdynamic buckling equation is solved by the Runge-Kutta method,and the critical buckling stress is deter-mined by the B-R criterion.The present paper is mainly focused on the imperfection sensitivity,the strainrate sensitivity,and the dynamic post-buckling characters for the shell loaded dynamically with a constantshear strain rate.Numerical results show that the critical shear stress and imperfection sensitivity will in-crease with the increase of strain rate.It is found that the elastic buckling stress is more sensitive toimperfection than the visco-plastic buckling.The present research also reveals some dynamic post-bucklingcharacters for the cylindrical shell,and it is shown that the shell will vibra     

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。     

海底管道整体屈曲的枕木-浮力耦合法研究

不埋海底管道在高温高压作用下,易发生水平向整体屈曲。实际工程中,常通过在管道路由上设置整体屈曲触发装置,实现对水平向整体屈曲的有效控制,其中以枕木法的成功应用最为多见。本文分析了枕木法的主要影响因素并验证了采用枕木法会出现管道屈曲段应力集中的现象,对比了枕木法、分布浮力法和枕木-浮力耦合法对管道整体屈曲变形规律的影响,采用数值模拟方法系统研究了枕木及浮力参数对管道水平向屈曲和后屈曲的影响规律。研究表明,在枕木两侧设置浮力段的人工触发装置可有效触发管道整体屈曲,同时促使管道虚拟锚固点间轴力的释放,降低了管道中屈曲段的应力,相较枕木法,枕木-浮力耦合法可将管道中的最大应力降低23%。     

管道热屈曲动力过程数值模拟

运输高温高压油气的海底管道会发生整体热屈曲现象。管道热屈曲过程中可能会产生平衡状态的跃迁(snapthrough),且这样的跃迁过程必然会伴随着动力响应。管道热屈曲动力过程中侧向弹出的速度以及轴向缩进的速度对管土相互作用参数的取值有很大影响,然而关于管道热屈曲动力过程的研究却很少。本文给出了数值模拟过程中管道系统阻尼值和升温速率的确定方法,研究了管道初始几何缺陷以及海床参数对管道热屈曲动力过程的影响。     

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。     

含初始缺陷海底管道侧向屈曲临界力的参数解

未埋设的海底管道在高温高压运行条件下可能发生侧向屈曲,情况严重时影响海底管道的结构安全。侧向屈曲临界力作为判定海底管道发生侧向屈曲的重要依据,主要影响因素有初始缺陷、管土相互作用等。现有关于侧向屈曲临界力的公式并未考虑管土相互作用、缺陷不平直度和管道自身材料特性对侧向屈曲临界力的综合影响。建立含有通用几何初始缺陷海底管道的数值模型,使用Riks算法进行参数分析以研究极限侧向土壤阻力、管道缺陷不平直度和截面几何尺寸对海底管道侧向屈曲的具体影响。基于量纲分析法和多元线性回归,推导出海底管道侧向屈曲临界力关于上述3个影响参数的一般公式,并对该公式进行了检验,结果表明文中推导的公式在参数涵盖的研究范围内有效。     

Mechanisms of mud extrusion on the Mediterranean Ridge Accretionary Complex

 Drilling two mud domes on the Mediterranean Ridge during ODP Leg 160 has demonstrated that the eruption of mud breccia began at least 1.5 Ma ago. An evolution through extrusive building of a cone, followed by successive eruptions of clast-bearing mud debris flows and subsequent subsidence can be deduced for both domes. Results from permeability and shear strength tests, grain size analyses, sedimentary textures, and clast provenance provide clues concerning the mechanism of mud volcanism. The collision of Africa with Eurasia resulted in backthrusting of the evaporite-dominated accretionary wedge against a rigid backstop. This allowed egress of overpressured fluid-rich mud of presumed Messinian age from the décollement, although many of the clasts may have originated from the overlying accretionary wedge.     

Upheaval buckling of surface-laid offshore pipeline

Offshore pipelines operating under high pressure and temperature are subjected to upheaval buckling. Pipeline behaviour in upheaval buckling depends on a number of factors including the shape of pipeline imperfection, installation stresses, loading types, seabed sediment behaviour and the flexural stiffness of the pipe. Current method of predicting upheaval buckling is based on simplified shapes of pipeline imperfection developed for idealized seabed conditions. To account for the effect of internal pressure, the pressure load is represented using an equivalent temperature. However, the applicability of these idealizations on the prediction of upheaval buckling has not been well-investigated. In this paper, the three-dimensional finite element modelling technique is used to investigate the applicability of idealized shapes and their effects on the upheaval buckling of pipeline for a seabed condition at offshore Newfoundland in Canada. The finite element model is then used to conduct a parametric study to investigate the effects of installation stress, loading types, seabed parameters and the flexural stiffness of the pipe. Finally, a design chart is developed to determine the optimum height of seabed features to manage pipeline stability against upheaval buckling under different temperature and pressure loadings.     

非对称局部壁厚减薄海底管道的屈曲分析

在深海环境中,海底管线不仅承受较高外压,还会因为海水及运输介质的常年侵蚀而形成腐蚀缺陷,而腐蚀缺陷往往会导致管道的外压承载力下降。基于壳体稳定性理论,建立了含有非对称局部壁厚减薄管道在外压作用下的屈曲压力理论公式。公式具有广泛的适用性,当内、外局部壁厚减薄深度相等时,可用于计算含有对称局部壁厚减薄管道屈曲压力,而当内部或外部缺陷深度为零时,便可用于计算只含外部或者内部腐蚀缺陷的管道屈曲压力。通过有限元分析验证了该公式的正确性,结果表明公式可以准确预测不同缺陷位置及尺寸时管道的屈曲压力。详细研究了局部壁厚减薄缺陷位置、长度和深度等参数对屈曲压力的影响。研究表明,局部腐蚀对管道的屈曲压力产生重要影响,尤其当腐蚀角度和深度较大时,在腐蚀形成初期就会造成管道的承载力急剧下降,并且管道的屈曲压力与缺陷的径向位置有关,腐蚀缺陷位于管道外侧时的屈曲压力明显大于其位于管道内侧时的屈曲压力。