双腐蚀缺陷海底管道的有限元分析研究

硕士学位论文双腐蚀缺陷海底管道的有限元分析研究Finiteelementanalysisandresearchofsubmarinepipelinewithdoublecorrosiondefects-I-摘要基于腐蚀缺陷对海底内压管道应力的重大影响及海底管道由于腐蚀缺陷破坏带来危害的严重性，本文针对含有腐蚀缺陷内压管道，结合国内外学者的研究，讨论了有关内压作用下含有双腐蚀缺陷管道的诸多问题，为工程中判断管道应力水平提供了依据。为了确定两个或多个腐蚀缺陷的相对位置对于管道整体应力水平的影响，文中应用有限元数值计算方法，并考虑了材料非线性和几何非线性，对含有两个不同径向夹角和不同轴线间距的腐蚀缺陷的内压钢制管道进行了应力集中系数变化与影响的分析计算。并拟合得到了腐蚀缺陷在不同角度下的“极限影响距离”公式，用于判断腐蚀缺陷之间是否发生相互影响作用，进而估计管道上的应力水平。同时，对不同相对腐蚀深度条件下，含有两个类似的腐蚀缺陷内压管道也进行了应力集中系数计算分析和“极限影响距离”公式拟合，并把各相对腐蚀深度条件的计算结果做了比较分析。对含有腐蚀缺陷的海底管道在复合荷载（弯矩及内压、轴力及内压）联合作用下的应力情况也应用有限元软件ANSYS进行了等效应力计算，依据计算结果对其特点进行了研究，分析了弯矩、轴力、内压三者对等效应力的影响。基于静力分析基础，对海底管道进行了水平方向和竖直方向的稳定性分析。并应用有限元数值计算方法，对含腐蚀缺陷管道作了模态分析，从而得到了管道的固有频率与振型，分析了含蚀缺管道发生共振的可能性和破坏方式。模态分析包括无损伤管道、含有单个缺陷管道和含有多个缺陷管道，同时考虑了液固耦合现象，并对其计算结果进行了分析比较，得出了管道上的腐蚀缺陷与模态的关系。并采用有限元方法对管道进行了疲劳分析，估算管道疲劳寿命。关键词：有限元分析；腐蚀缺陷径向夹角；腐蚀缺陷轴间距；应力集中系数；极限影响距离双腐蚀缺陷海底管道的有限元分析研究-II-FiniteelementanalysisofsubmarinepipelinewithdoublecorrosiondefectsAbstractBasedonthesignificantimpactonstressinthesubmarinepipelinebycorrosiondefectsandseverityofdamageduetothecorrosiondefects,thispaperaimsattheinjuredpipelinewithinside-pressure,anddiscussesissuesrelatedtopressurizedpipelinewithdoublecorrosiondefectsandfurthermoreprovidesfeasiblesolutiontothestressleveljudgmentinengineeringmakingreferencetoresearchbothhomeandabroad..Inordertomakecertaintheinfluenceontheoverallstresslevelofpipelinecausedbytwoormorecorrosiondefectstotheoverallstresslevelofpipelineinrelativelydifferentlocation,finiteelementmethod(FEM)consideringmaterialandgeometricnonlinearityisemployedtoanalyzethechangeandinfluenceofthestressconcentrationfactorinaninside-pressuredsteelpipelinewithtwocorrosiondefectsdifferentinradial-angleandaxis-distance.Itisshownthattheangleandtheaxis-distancearecouplingparametersinstressconcentrationfactorcalculating.Therefore,aformulaofCriticalInfluenceDistanceconsideringthesetwoparametersisobtainedthroughFEManalysisandcurvefitting,whichcanbeusedinjudgingthepossibilityofdefectsinteractionandthenestimatingthestresslevelofsteelpipelines.Acomparativeanalysis,consideringdifferentcorrosiondepths,isalsocarriedoutontheresultsobtainedthroughstressconcentrationfactoranalysisandformulacurvefittingofpipelineswithsimilardefects.Meanwhile,finiteanalysisofequivalentstressofdefectivepipelinesbyANSYSunderthecomplicatedloads(bendingmomentsandinsidepressure,axialstressandinsidepressure)jointeffectisconductedforitsstresscharacteristicsanalysis,arrivingattherelationofmoments,axialstressandinside-pressuretoequivalentstress.Stabilityanalysisofpipelineinhorizontalandverticaldirectionisadoptedbasedonthestaticanalysisofsubmarinepipeline.Withtheapplicationoffiniteelementmethodandconsideringthefluid-solidinteractionphenomenon,modalanalysisofpipelines,includingnon-damagedpipeline,pipelinewithasingledefectanddoubledefectsiscarriedouttoeducethenaturalfrequencyandvibrationmode,whichcouldbeusedtodeterminethepossibilityofthepipelineresonanceanddestructionalforms.Finiteelementmethodisusedinthecurrentpapertoconductthefatigueanalysisofpipelinesandthefatiguelifeofpipelinesisthereforeestimated.-III-KeyWords：finite element analysis; corrosion defects radial‐angle; corrosion defects axis‐distance; stress concentration factor; Critical influence distance 双腐蚀缺陷海底管道的有限元分析研究-IV-目录摘要.....................................................................................................................................IAbstract.....................................................................................................................................II1绪论......................................................................................................................................61.1本课题背景及意义...................................................................................................61.2相关领域国内外研究概况.......................................................................................81.3本文主要内容...........................................................................................................92有限单元法理论................................................................................................................112.1有限元法简介.........................................................................................................112.2本文所用有限元软件（ANSYS）及非线性概述................................................132.2.1ANSYS简介及分析流程............................................................................132.2.2非线性基本理论与本文涉及内容................................................................143双腐蚀缺陷海底管道分析计算........................................................................................163.1含腐蚀缺陷管道计算理论简介.............................................................................163.1.1单个腐蚀缺陷管道计算理论........................................................................163.1.2多个腐蚀缺陷管道计算理论........................................................................173.2典型管道模型有限元计算.....................................................................................193.2.1计算模型及参数..................................................