局部火灾作用下焊接导管架海洋平台的失效分析

发布时间：2018-03-27 22:26

本文选题：导管架海洋平台　切入点：管节点局部柔度　出处：《烟台大学》2017年硕士论文

【摘要】：焊接导管架海洋平台因其结构简单、适应性强、安全可靠等优点已成为我国浅海地区的主要油气开采平台。作为建造导管架海洋平台的主体建筑材料,钢材的弹性模量及屈服强度在高温下都会有较大程度的下降,严重威胁导管架海洋平台在火灾条件下的安全性能及生存能力。目前导管架海洋平台火灾条件下的有限元研究主要有以下两种方式,一是通过实体单元或壳单元建立海洋平台整体模型进行抗火分析,二是将导管架海洋平台简化为空间梁单元,弦管与支管视为刚结,不考虑管节点的局部变形。前者精度较高但耗时长、代价高昂,后者分析快,但无法准确反映节点的局部柔性效应。本文在局部柔度的基础上,提出了一种抗火虚拟梁单元,并将其引入导管架海洋平台的有限元分析模型中进行局部火灾作用下的失效分析。首先,在管节点局部柔度的基础上,提出了抗火虚拟梁单元的概念。抗火虚拟梁单元设置于弦管与支管相交处,方向垂直于弦管轴线,长度为弦管的半径。将节点区域隔离出来,分别以钢材在不同温度下对应的本构关系曲线进行材料定义,建立节点区域的有限元静力分析模型。通过将分析得到的不同温度下的荷载变形曲线进行转换,得到抗火虚拟梁单元在高温下的应力应变曲线。对5个T型节点平面管桁架及3个Y型节点平面管桁架分别建立了壳单元瞬态有限元模型、传统刚结瞬态有限元模型及引入了抗火虚拟梁单元的FBE瞬态有限元模型。对三种模型分析得到的加载点温度位移曲线进行了对比,结果表明传统的刚结模型不能准确地反应管桁架的在火灾作用下的位移,且会过高的估计结构的抗火能力。采用了抗火虚拟梁单元的FBE模型分析所得的温度位移曲线则与壳单元模型分析结果吻合较好,其对于管桁架的结构失效温度的预测与刚结模型相比也更加接近壳单元模型的分析结果。针对于管桁架结构,选取了不同火灾工况,对抗火虚拟梁单元在局部火灾条件下的适用性进行了研究。采用抗火虚拟梁单元对胜利油田CB25A井组中的井口平台进行了局部火灾作用下的失效分析,针对不同的火灾工况,对平台的结构响应进行了研究,为焊接导管架海洋平台的抗火设计提供了依据。
[Abstract]:Welding jacket offshore platform has become the main oil and gas exploitation platform in shallow sea area of China because of its simple structure, strong adaptability, safety and reliability. The elastic modulus and yield strength of steel will decrease to a large extent at high temperature. The safety performance and survivability of jacket offshore platforms under fire conditions are seriously threatened. At present, the finite element analysis of jacket offshore platforms under fire conditions mainly includes the following two ways. First, the integral model of offshore platform is established by entity element or shell element for fire resistance analysis; second, the jacket offshore platform is simplified into a space beam element, and chord and branch tubes are regarded as rigid junction. The former has high precision, long time consuming and high cost, but the latter can not accurately reflect the local flexibility effect of the joints. Based on the local flexibility, a fire resistant virtual beam element is proposed in this paper. It is introduced into the finite element analysis model of jacket offshore platform for failure analysis under the action of local fire. Firstly, based on the local flexibility of pipe joints, The concept of fire resistant virtual beam element is put forward. The fire resistant virtual beam element is arranged at the intersection of chord and branch, perpendicular to the axis of chord, and the length is the radius of chord. The finite element static analysis model of the joint region is established by defining the constitutive relation curves of steel at different temperatures, and the load deformation curves at different temperatures are transformed by the finite element static analysis model. The stress-strain curves of fire resistant virtual beam elements at high temperature were obtained. The transient finite element models of shell elements were established for five T-joints planar tube trusses and three Y-joint planar tubular trusses. The traditional rigid-junction transient finite element model and the FBE transient finite element model with fire resistant virtual beam element are introduced. The results show that the traditional rigid-junction model can not accurately reflect the displacement of pipe truss under fire. The temperature displacement curve obtained by the FBE model of fire resistance virtual beam element is in good agreement with the shell element model. The prediction of failure temperature of pipe truss structure is closer to the analysis result of shell element model than rigid junction model. Different fire conditions are selected for pipe truss structure. The applicability of anti-fire virtual beam element under local fire condition is studied. The failure analysis of the wellhead platform in CB25A well group in Shengli Oilfield under local fire condition is carried out by using the anti-fire virtual beam element, and the failure analysis is carried out under different fire conditions. The structural response of the platform is studied, which provides the basis for the fire resistance design of the welded jacket offshore platform.
【学位授予单位】：烟台大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE95

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