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.

Local buckling of thin plate on tensionless elastic foundations under interactive uniaxial compression and shear

This paper uses a mathematical method to develop an analytical solution to the local buckling behaviour of long rectangular plates resting on tensionless elastic Winkler foundations and under combined uniform longitudinal uniaxial compressive and uniform in-plane shear loads. Fitted formulas are derived for plates with clamped edges and simplified supported edges. Two examples are given to demonstrate the application of the current method： one is a plate on tensionless spring foundations and the other is the contact between the steel sheet and elastic solid foundation. Finite element （FE） analysis is also conducted to validate the analytical results. Good agreement is obtained between the current method and FE analysis.

Submarine Pipeline Lateral Global Buckling and Buckling Failure Critical State Discussion

Due to high temperature and pressure,unburied or shallow buried submarine pipelines experience lateral global buckling. Excessive bending caused by uncontrolled deformation may threaten the safety of the pipeline system. Thus,the integer of a post-buckling pipeline section should be assessed under design temperature and pressure differences. This study focuses on the post-buckling pipeline safety assessment.First,a series of model tests based on sand obtained from Bohai Gulf were proposed,and soil resistance to pipelines with different embedment are measured. A dynamic soil resistance model with varying pipeline embedment and lateral displacement was established. The influence of embedment on peak soil resistance and residual soil resistance was analyzed. Second,the critical buckling forces of pipelines with different imperfections were analyzed. A"critical force range"was proposed to evaluate whether the pipeline exhibits lateral global buckling or not. Third,the limit state of a post-buckling pipeline in an engineering case was assessed. The assessment was proposed based on both load control condition and displacement control condition. Further comparisons show that pipelines reach their limit state according to load control condition far more quickly than according to displacement control condition.

A THEORETICAL MODEL OF MAGNETOELASTIC BUCKLING FOR SOFT FERROMAGNETIC THIN PLATES

As an essential model of magnetoelastic interaction between magnetic field and mechanical deformation, the study on magnetoelastic buckling phenomenon of soft ferromagnetic plates in a magnetic environment has been conducted. One of the key steps for the theoretical prediction of the critical magnetic field is how to formulate magnetic force exerted on the magnetized medium. Till today, the theoretical predictions, from theoretical models in publications, of the magnetoelastic buckling of ferromagnetic cantilevered beam-plate in transverse magnetic field are all higher than their experimental data. Sometimes, the discrepancy between them is as high as 100%. In this paper, the macroscope formulation of the magnetic forces is strictly obtained from the microscope Amperion current model. After that, a new theoretical model is established to describe the magnetoelastic buckling phenomenon of ferromagnetic thin plates with geometrically nonlinear deformation in a nonuniform transverse magnetic field. The numerical method for quantitative analysis is employed by combining the finite elemental method for magnetic fields and the finite difference method for deformation of plates. The numerical results obtained from this new theoretical model show that the theoretical predictions of critical values of the buckling magnetic field for the ferromagnetic cantilevered beam-plate are in excellent agreement with their experimental data. By the way, the region of applicability to the Moon-Pao's model, or the couple model, is checked by quantitative results.

Analytical determination of non-local parameter value to investigate the axial buckling of nanoshells affected by the passing nanofluids and their velocities considering various modified cylindrical shell theories

We analytically determine the nonlocal parameter value to achieve a more accurate axial-buckling response of carbon nanoshells conveying nanofluids. To this end, the four plates/shells' classical theories of Love, Fl ¨ugge, Donnell, and Sanders are generalized using Eringen's nonlocal elasticity theory. By combining these theories in cylindrical coordinates,a modified motion equation is presented to investigate the buckling behavior of the nanofluid-nanostructure-interaction problem. Herein, in addition to the small-scale effect of the structure and the passing fluid on the critical buckling strain,we discuss the effects of nanoflow velocity, fluid density(nano-liquid/nano-gas), half-wave numbers, aspect ratio, and nanoshell flexural rigidity. The analytical approach is used to discretize and solve the obtained relations to study the mentioned cases.

Interaction formulae for buckling and failure of orthotropic plates under combined axial compression/tension and shear

An interaction function was constructed based on the axial compression/tension and shear loads of orthotropic plates.The coefficients of the polynomial function were determined by uniaxial test results.Buckling interaction and failure interaction formulae under combined axial tension/compression and shear loads were established.Based on the uniaxial load test results of orthotropic plates,the buckling load and bearing capacity under any proportion of the combined loads could be predicted by using the proposed interaction formulae.The buckling interaction curves and failure envelopes predicted by the proposed interaction formulae were in excellent agreement with the test results.

K6型单层球面网壳整体交互耦合屈曲行为

采用有限元数值模拟,基于K6型单层球面网壳的屈曲与后屈曲性态,提出整体屈曲的判别准则,并首次从变形特征角度分析两种整体屈曲模态交互耦合的发生机理及对屈曲承载力的削弱效应。研究结果表明,K6型单层球面网壳的稳定性易受整体交互耦合屈曲影响,且可导致屈曲极限承载力的显著削弱及不稳定后屈曲;其变形模式从屈曲阶段的最低阶整体屈曲模态主导,演化为初始后屈曲阶段的整体交互耦合屈曲模态主导,及最终的次低阶整体屈曲模态主导,是交互耦合屈曲产生的原因;缺陷幅值也会影响整体交互耦合屈曲对K6型单层球面网壳屈曲极限性能的主导作用。

预应力撑杆构件交互屈曲与承载力智能估计方法

预应力撑杆构件造型优美、省材高效,但由于其柔度较大,易产生多个屈曲模态交互耦合即“交互屈曲”模式的破坏,且交互屈曲对其极限承载力、屈曲性能影响显著。研究了交互屈曲对预应力对称、不对称撑杆构件在轴压、压弯作用下屈曲性能、极限承载力的影响,并据此采用基于回归算法的人工神经网络(ANN)建立了其极限承载力估计模型。研究结果表明,对于预应力撑杆构件,模态交互易造成不稳定后屈曲,且对其极限承载力有显著的削弱效应;该削弱效应是否会产生影响由结构几何参数与参与交互的模态屈曲荷载决定,其削弱程度受结构撑杆不对称性、预应力水平影响;所建立的极限承载力ANN预测模型可考虑交互屈曲的影响,且准确、可靠、适用范围广泛。研究可为后续开发预应力撑杆构件智能设计软件平台提供基础,满足工程设计的需求。

砂土对埋设管线约束作用的模型试验研究

屈曲剧变是海底管线失稳破坏的重要形式之一。运营中的高温、高压是导致海底管线发生屈曲剧变的直接条件,而地基土体对管线的约束作用是导致管线屈曲的根本原因。研究表明地基土对管线作用力的大小决定着管线发生屈曲变形的形态。采用取自渤海湾的细砂进行了室内管土相互作用试验,研究不同直径、不同埋深的管线竖直向上运动、水平向运动以及轴向运动时土体抗力的发挥过程。试验结果表明土抗力的发挥过程与管线的埋置率有关;埋深相同的管线水平向运动时受到的抗力比竖直向运动时大2倍以上;结合试验结果提出了适于计算渤海湾砂土地基对埋设管线约束力的经验公式。

考虑筋/板相互作用的环肋圆柱壳屈曲强度分析

环肋圆柱壳是潜艇耐压壳体的一种主要结构形式。环肋圆柱壳的失稳破坏主要表现在肋骨间的壳板失稳和总体失稳。在计算肋骨间的壳板失稳时,传统方法认为肋骨为壳板提供简支边界,忽略了在边界上肋骨和壳板的相互影响。在实际结构中,由于肋骨提供扭转刚度,壳板在与肋骨相交的边界上将存在弯矩,并非自由支持边界。因而,壳板失稳时,筋/板产生相互影响,提高了壳板的屈曲强度。本文的主要目的是,推导考虑筋/板相互影响的环肋圆柱壳壳板屈曲强度的理论计算方法,分析筋/板的相互关系。通过本文的算例表明,本文推导的计算方法以及所编制的计算程序是可靠的,可以用于工程设计。

复合材料层合板条的流固耦合动力屈曲分析

导出置于液面上的复合材料层合板条变形时流体作用力的解析表达式;由Hamilton原理建立考虑横向剪切变形及流固耦合效应时迭层板的非线性动力屈曲控制方程;采用差分方法求解了轴向面内加载时板条的流固耦合动力屈曲;讨论了铺层角度、铺层数目、流场深度、加载形式以及初始几何缺陷等因素对动力屈曲的影响.

薄壁结构局部-整体相关屈曲研究现状

薄壁结构因屈曲而丧失承载能力的现象日益突出,局部屈曲与总体屈曲的相互作用成为必须考虑的问题。本文综述了薄壁结构局部-整体相关屈曲研究若干重要方面的理论发展和现状,并试图对进一步研究提出建议。

不锈钢焊接箱形截面柱轴心受压相关稳定试验研究

不锈钢的非线性材料特性使其构件承载性能不同于普通钢结构构件,需要开展专门的研究。通过焊接加工8个不锈钢箱形截面柱,包括奥氏体型S30408和双相型S22253两种牌号,在试件两端铰接的约束条件下开展轴心承压加载试验。试验中对板材力学性能、试件的局部与整体几何初始缺陷、纵向焊接残余应力分布和加载初偏心进行了测量。加载试验得出了板件的局部屈曲承载力与构件的相关稳定承载力,展示了从组成板件局部屈曲到构件整体弯曲屈曲的渐变失效形态。将试验结果与欧洲不锈钢规范EN 1993-1-4、直接强度法和中国冷弯薄壁型钢结构技术规范GB 50018的计算公式进行比较表明,由于欧洲规范和直接强度法没有考虑不同牌号不锈钢材料力学性能的差异,对双相型S22253构件的承载力计算偏于保守,而奥氏体型S30408构件的计算承载力偏于不安全;而中国规范GB 50018没有考虑焊接残余应力、几何缺陷和材料非线性的不利影响,高估了构件的相关稳定承载力。所得到的试验结果将为后续的数值分析与理论研究提供数据支撑。

高强等边角钢轴压杆局部-整体相关屈曲分析

采用ANSYS有限元软件,考虑初始缺陷和双重非线性,对25根高强等边角钢轴压杆的局部-整体相关屈曲进行了数值分析,得到其局部-整体相关屈曲的极限承载力。分析了不同的肢件宽厚比及屈服强度对局部-整体相关屈曲的极限承载力的影响,利用相关屈曲法推导了高强等边角钢轴压杆的相关屈曲建议公式。分析结果表明:相关屈曲建议公式具有合理性,可为今后的工程设计提供参考。

Ⅰ形轴压构件中板件的相关屈曲及宽厚比

采用有限条法分析了Ⅰ形轴心受压构件中翼缘和腹板的相关屈曲 ,推导了翼缘和腹板的宽厚比限值公式。分析中考虑了屈曲系数的变化以及残余应力、初弯曲等的影响 ,在弹塑性阶段采用了有效模量。最后 ,讨论了现行规范GBJ17—

薄壁柱相关屈曲分析的混合有限元模型

提出了一种用于薄壁柱局部屈曲与整体屈曲相互作用问题的新的分析模型──混合有限元模型，模型特平面壳单元、杆单元和线单元联合应用于薄壁柱的非线性反应分析，考虑了柱子的各种初始缺陷的影响．计算分析表明，文中提出的分析模型精确、高效，并且具有广泛的适用性．

冷弯型钢局部屈曲的相关性和卷边板件的有效宽度

在已有弹性相关屈曲成果的基础上讨论了现行规范（ＧＢＪ１８—８７）规定的适用性，又对受弯的卷边槽钢作了有限条法相关屈曲分析，阐明受弯构件中的卷边翼缘按现行规范计算其有效宽度偏于保守，在卷边尺寸适当的情况下可以考虑按两边支承板对待。

变截面工形柱平面内稳定极限承载力研究

基于非线性板壳有限元结构分析方法,对门式刚架变截面工形柱平面内稳定极限承载力进行了大挠度弹塑性分析研究。在考虑壁板局部屈曲和构件整体屈曲相关作用的同时,对影响稳定承载力的几何参数包括腹板宽厚比、翼缘宽厚比、构件楔率和构件长细比等进行了系统的分析和研究,并与现行《门式刚架轻型房屋钢结构技术规程》进行了比较,获得的结论对工程设计具有参考价值。

穿越平移断层海底埋地管道屈曲失效分析

长输海底管道常不可避免地穿过地震断层,地震断层活动可能导致管道发生扭曲、皱折甚至断裂,极大威胁管道安全。采用创新性的向量式有限元方法 (VFIFE)分析穿越地震断层海底管道屈曲失效行为,首先推导考虑材料非线性的VFIFE空间壳单元计算公式,提出适用壳单元的非线性管土耦合模型,然后重点解决了海底管道屈曲及屈曲传播过程中存在的内壁自碰撞接触问题,编制了Fortran计算程序和相应后处理程序。通过文献对比证明了模型的正确性。开展了平移断层作用下空载状态海底管道屈曲失效过程模拟,分析了穿越角度、土体性质和水压大小对海底管道屈曲失效行为的影响,结果表明:海底管道径厚比小,用钢等级高,周围土体强度低,具有更高的抵抗断层位移载荷能力;较低外压和平移断层联合作用下,管道变形呈S形,屈曲失效由断层位移引起的过度弯曲主导,失效模式是第二个弯曲处或者两个弯曲处的受压侧出现明显内陷,截面变形呈椭圆形;穿越角度越小,屈曲失效的临界断层位移越小;周围土体强度越高(砂土>黏土>淤泥夹砂),管道弯曲变形越严重,屈曲失效的临界断层位移越小;较高外压和平移断层联合作用下,屈曲失效由外压主导,主要模式是第一个弯曲处或者第二个弯曲处首先出现压溃,然后发生屈曲传播现象;不同水压和平移断层位移组合下海底管道破坏程度不一,压溃位置、屈曲传播方向和范围、截面变形呈现不同模式。结果可用于指导穿越地震断层海底管道抗震设计和止屈防护研究。

钢结构稳定设计的新进展

本文介绍了近年来框架和冷弯型钢构件稳定承载力计算的新问题和新方法,包括框架先进分析法的实用化,当前广泛应用的计算长度法的改进,弱支撑框架和半刚性连接框架的稳定,大跨度框架无侧移失稳的可能性和计算方法,陡坡山形门式刚架的稳定,冷弯薄壁型钢板件局部相关屈曲,开口截面的畸变屈曲,以及局部和整体的相关屈曲。