自升式海洋平台桩腿疲劳寿命研究

发布时间：2018-03-20 01:21

本文选题：自升式平台　切入点：管节点　出处：《江苏科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：自升式海洋平台其所处的工作环境极其恶劣,一旦出现安全性问题,往往造成巨大经济的损失,所以很有必要对平台进行疲劳寿命分析。本文以Super M2自升式平台为研究对象,结合波浪理论及相关环境载荷公式对其进行静力强度分析;然后,针对平台桩腿薄弱处即管节点位置,分析了该管节点在轴力作用下的沿焊缝周围的应力分布规律及其各几何参数对应力的敏感性;最后,基于两种疲劳理论对平台桩腿关键点进行平台的疲劳寿命分析并对其结果进行对比讨论。其具体的研究内容如下:(1)本文以Super M2自升式平台为研究对象,探讨了相关疲劳理论及环境载荷理论。通过合理的简化建立了平台的有限元模型,其中采用弹簧单元模拟平台与桩腿之间的连接关系,通过在定义的质量点上施加重力场的方式来模拟平台重物的分布。另外,考虑到桩靴与土壤连接的复杂性,采用Abaqus中有的线弹性模型进行处理,从而提高了自升式平台模拟分析的准确度。(2)设置合理的环境变量,采用斯托克斯5阶波波浪理论及Morision公式,并且考虑了波浪的动压力与静水压力所造成的浮力效应,分析计算了自升式平台在预压和风暴自存工况下的应力分布情况。并依据CCS规范进行强度校核,结果满足强度要求。(3)针对平台桩腿薄弱处即管节点位置,分析了该处在轴力作用下的沿焊缝周围的应力分布规律。然后结合正交试验理论,分析了管节点各几何参数对其应力影响的敏感性。(4)采用谱分析法对平台关键节点剩余寿命进行疲劳寿命分析,首先利用stokes fifth-order波浪理论来分析计算了不同浪向角及波浪频率下典型节点的热点应力传递函数,再结合中国南海波浪散布图以及疲劳理论,完成对桩腿各典型节点的疲劳强度评估。得出桩腿疲劳寿命为41.3年,其位于水面附近即为桩腿的飞溅区。(5)对裂纹尖端进行数值模拟分析,得出了其附近的应力场和位移场的分布情况。依据ABS设计规范,基于断裂力学对海洋平台桩腿危险点进行疲劳寿命计算,最终获得桩腿的使用寿命为33.2年,满足平台服役年限的要求。相比S-N曲线的疲劳设计的计算方法,裂纹扩展的计算方法考虑了结构件本身存在的焊接缺陷,因而使得其计算的疲劳寿命要短,更为保守。
[Abstract]:The working environment of jack-up offshore platform is extremely bad, once safety problems appear, it often causes huge economic losses, so it is necessary to analyze the fatigue life of the platform. This paper takes Super M2 jack-up platform as the research object. Combined with wave theory and related environmental load formula, the static strength analysis is carried out, and then, aiming at the weak position of the platform pile leg, that is, the position of the pipe joint, The stress distribution law and the sensitivity of the geometric parameters to the stress of the pipe joints around the weld under axial force are analyzed. Based on two kinds of fatigue theory, the fatigue life of platform is analyzed and the results are compared and discussed. The concrete research contents are as follows: 1) this paper takes Super M2 bootstrap platform as the research object. The related fatigue theory and environmental load theory are discussed. The finite element model of the platform is established by reasonable simplification, in which spring element is used to simulate the connection between the platform and the pile leg. The distribution of platform weight is simulated by applying gravity field to the defined mass point. Considering the complexity of the connection between the pile boots and the soil, the linear elastic model in Abaqus is used to deal with the problem. Therefore, the accuracy of simulation and analysis of the jack-up platform is improved. The reasonable environmental variable is set up. The Stokes' fifth order wave theory and Morision formula are adopted, and the buoyancy effect caused by the dynamic pressure and hydrostatic pressure of the wave is considered. The stress distribution of the jack-up platform under preloading and storm self-storage is analyzed and calculated. According to the CCS code, the strength of the platform is checked, and the results meet the strength requirements. 3) aiming at the position of the pipe joint where the pile leg is weak, the stress distribution of the platform is calculated under the condition of pre-loading and storm self-storage. The stress distribution around the weld under axial force is analyzed, and then the orthogonal test theory is used to analyze the stress distribution around the weld. The sensitivity of the geometric parameters of pipe joints to the stress is analyzed. (4) the residual life of the key joints of the platform is analyzed by spectrum analysis method, and the fatigue life of the key joints of the platform is analyzed by the method of spectrum analysis. In this paper, stokes fifth-order wave theory is used to analyze and calculate the stress transfer function of typical nodes at different wave angles and wave frequencies, and then combined with wave dispersion diagram and fatigue theory in the South China Sea. The fatigue strength of the typical joints of the pile leg is evaluated. The fatigue life of the pile leg is 41.3 years, which is located near the water surface as the spatter zone of the pile leg. (5) the crack tip is numerically simulated and analyzed. The distribution of stress field and displacement field in the vicinity is obtained. According to ABS design code, the fatigue life of pile leg is calculated based on fracture mechanics, and the service life of pile leg is 33.2 years. Compared with the fatigue design method of S-N curve, the calculation method of crack propagation takes into account the welding defects in the structure itself, which makes the fatigue life of the platform shorter and more conservative.
【学位授予单位】：江苏科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P75

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