自升式平台桩腿动力响应及疲劳分析研究

发布时间：2018-02-01 14:34

本文关键词： 自升式平台波浪载荷动力响应疲劳分析　出处：《华南理工大学》2014年硕士论文　论文类型：学位论文

【摘要】：桁架式的自升式平台，其自身柔性较大，在复杂多变的海洋环境载荷的作用下，平台结构动力响应明显而复杂，特别是在波浪载荷这一主要控制载荷的长期作用下，平台桩腿容易出现裂纹，甚至发生疲劳失效，因此，对自升式平台桩腿进行动力响应研究和疲劳分析，并预测其疲劳寿命，对于自升式平台的安全使用是非常必要的。本文采用海洋工程专业软件SACS，对自升式平台桩腿进行动力响应和疲劳分析研究。首先，对作业工况进行模态分析，对比其固有频率与波浪频率，判断其共振的可能性；然后，在此基础上，进行平台结构的波浪动力响应分析；最后，考虑动力放大效应和应力集中的影响，采用直接确定性方法和动态谱分析方法进行平台桩腿的疲劳寿命预测。本文的主要工作如下： 1)阐述海洋环境载荷、疲劳分析的基本理论和方法，介绍基于SACS的疲劳分析流程等； 2)采用海洋工程软件SACS建立自升式平台的三维有限元模型，考虑桩-土非线性边界条件的影响，，研究船体与桩腿结构的连接方法以及采用弦杆模型的等效方法解决桩腿水动力问题，并对平台桩腿结构进行强度校核和桩基承载力校核；应用模态分析方法计算平台的固有频率，并与设计波浪频率进行对比分析，判断发生共振的可能性；另外，还对平台结构进行波浪动力响应分析，将波浪载荷下的动力响应与准静态分析结果进行对比； 3)采用频域分析方法中的直接确定性方法和谱分析方法分别对自升式平台进行疲劳分析研究，并考虑结构动力放大效应和应力集中系数的影响，对平台桩腿进行疲劳寿命预测。采用直接确定性方法进行疲劳分析时，选取一年期波浪散布图中发生频次较高的24组波浪，进行平台桩腿的疲劳寿命预测，疲劳寿命较短的区域集中在桩腿飞溅区的左舷位置及桩腿与主船体连接处；采用谱分析方法预测在波浪交变载荷作用下平台的疲劳寿命时，以北海-BeryFrig地点处的一年期波浪散布图为海况条件进行研究，通过计算应力传递函数，求得管节点的结构响应谱密度函数，再根据S-N曲线和Miner线性累计损伤理论，求得平台桩腿的疲劳寿命。通过分析上述两种方法的计算结果可知，直接确定性方法的计算精度虽不如谱分析方法的计算精度高，但该方法计算简单易行，在初步进行自升式平台疲劳分析时，可先用直接确定性方法确定较为危险的管节点，再使用谱分析方法做进一步的疲劳分析，该方法的结果满足海洋平台疲劳分析的精度要求； 4)分别就S-N曲线的选择、常见波浪谱密度（P-M谱等）、管节点应力集中系数SCF的计算方法以及波浪散布图等因素对自升式平台桩腿结构谱疲劳分析结果的影响进行探讨，并给出了合理的选择范围和方法。
[Abstract]:The truss self-lifting platform is flexible, and the dynamic response of the platform structure is obvious and complex under the complex and changeable marine environment load. Especially under the long-term action of wave load, the pile leg of platform is prone to crack and even fatigue failure. Therefore, the dynamic response and fatigue analysis of the platform pile leg are carried out. It is necessary to predict its fatigue life for the safe use of bootstrap platform. In this paper, the marine engineering professional software SACSS is used to analyze the dynamic response and fatigue of the pile leg of the jack-up platform. Firstly, the modal analysis is carried out to compare the natural frequency with the wave frequency. Judging the possibility of resonance; Then, on this basis, the wave dynamic response of the platform structure is analyzed. Finally, considering the effect of dynamic amplification and stress concentration, the direct deterministic method and dynamic spectrum analysis method are used to predict the fatigue life of the platform pile leg. The main work of this paper is as follows: 1) the basic theory and method of marine environmental load and fatigue analysis are introduced, and the fatigue analysis flow based on SACS is introduced. 2) the three-dimensional finite element model of jack-up platform is established by using marine engineering software SACS, and the influence of pile-soil nonlinear boundary condition is considered. The connection method between the hull and the pile leg structure and the equivalent method of the chord model are studied to solve the hydrodynamic problem of the pile leg, and the strength check and bearing capacity check of the platform pile leg structure are carried out. The natural frequency of the platform is calculated by using the modal analysis method, and compared with the design wave frequency, the possibility of resonance is judged. In addition, the wave dynamic response of the platform structure is analyzed, and the dynamic response under the wave load is compared with the quasi-static analysis results. 3) the direct deterministic method and spectral analysis method in frequency domain are used to analyze the fatigue of the jack-up platform, and the influence of dynamic amplification effect and stress concentration factor are considered. The fatigue life of platform pile leg is forecasted. When fatigue analysis is carried out by using direct deterministic method, 24 groups of waves with high frequency in the wave scatter map of one year are selected to predict the fatigue life of platform pile leg. The area with shorter fatigue life is concentrated in the port side position of the splashing zone of the pile leg and the joint between the pile leg and the main hull. In order to predict the fatigue life of the platform under the action of wave alternating load, the one-year wave dispersion map at Beihai BeryFrig site is used to study the sea condition when the spectrum analysis method is used. By calculating the stress transfer function, the structural response spectral density function of the tubular joints is obtained, and then according to the S-N curve and the Miner linear cumulative damage theory. The fatigue life of the platform pile leg is obtained. By analyzing the calculation results of the above two methods, it can be seen that the calculation accuracy of the direct deterministic method is not as high as that of the spectral analysis method, but this method is simple and feasible. In the initial fatigue analysis of jack-up platform, the more dangerous pipe joints can be determined by direct deterministic method, and then further fatigue analysis can be done by using spectrum analysis method. The results of this method can meet the precision requirements of offshore platform fatigue analysis. 4) the selection of S-N curve, the common wave spectrum density and P-M spectrum, etc. The calculation method of stress concentration factor (SCF) of pipe joints and the influence of wave scatter diagram on the spectrum fatigue analysis results of pile leg structure of jack-up platform are discussed, and the reasonable selection range and method are given.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P751

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