超大型浮式结构在复杂环境载荷作用下的疲劳强度评估

发布时间：2019-03-29 19:28

【摘要】：超大型浮式结构物是一种尺度巨大的海洋工程平台,可布置在预定海域供飞机起降和人员驻扎,对保障海洋安全和开发海洋资源有着重要作用。超大型浮式结构物一般由多个模块连接而成,尺度在千米以上,将承受复杂的海洋环境载荷。其关键节点将承受弯扭剪等组合载荷,可能会产生严重的疲劳问题。目前,S-N曲线法已在船舶与海洋工程结构的疲劳评估中得到了广泛应用,但复杂应力状态下的疲劳损伤评估在船舶与海洋工程领域内还没有统一的标准。因此,本文对超大型浮式结构物纵向撑杆形式的单模块的撑杆接头进行多轴疲劳估,为超大型浮式结构的设计和建造提供依据,也可供船舶与海洋工程结构多轴疲劳寿命评估方法研究进行参考。超大型浮式结构物单模块在波浪中的载荷与其结构形式有密切关联。本文先计算了其在规则波中的弯矩传递函数,并分析了下浮箱中心距对垂向弯矩的影响情况。然后通过商业有限元软件计算了撑杆接头的应力响应,给出其幅值和相位分布情况,以进一步分析接头处应力的多轴程度。应力幅值和相位决定了主应力方向的变化程度,本文通过对撑杆接头处在规则波以及短期海况下的应力响应的分析,给出了其主应力方向的变化程度,为对其进行多轴疲劳评估提供基础。然后,本文根据整理的多轴疲劳试验结果,对目前常用的简单多轴疲劳准则下临界面选取方法进行了分析和比较,并据此讨论了比例和非比例应力状态对多轴疲劳寿命影响,为选择多轴疲劳准则进行谱疲劳分析提供依据。最后,本文建立了复杂应力状态下,使用多轴疲劳准则对结构进行疲劳谱分析的具体方法,给出应力谱变换和常用的多轴疲劳准则的谱分析形式;通过短期与长期预报,比较了结构撑杆接头在主要船级社方法、国际焊接学会推荐方法和多轴疲劳谱分析几种方法下的疲劳损伤结果。研究认为,除少数浪向外,单方向来波下主应力方向变化不大,多轴效应对结构的疲劳寿命影响较小;但考虑到结构在寿命周期内会持续遭遇到不同方向的来波,此时主应力方向变化较大,多轴效应会降低结构的疲劳寿命。因此建议考虑超大型浮式结构物在全方向来波下的主应力变化对疲劳寿命的影响。
[Abstract]:The super-large floating structure is a kind of large-scale offshore engineering platform, which can be arranged in the predetermined sea area for aircraft take-off and landing and personnel stationed. It plays an important role in the protection of marine safety and the exploitation of marine resources. The super-large floating structure is usually connected by several modules, the scale of which is more than kilometer, and it will bear complex marine environmental load. The critical joints will bear combined loads, such as bending, torsion and shear, which may lead to serious fatigue problems. At present, the S-N curve method has been widely used in fatigue assessment of ship and ocean engineering structures, but there is no uniform standard in the field of ship and ocean engineering for fatigue damage assessment under complex stress condition. Therefore, in this paper, the multi-axis fatigue estimation of the single-module bracing joint in the form of longitudinal brace of the super-large floating structure is carried out, which provides the basis for the design and construction of the super-large floating structure. It can also be used as a reference for the study of multi-axial fatigue life assessment method for ship and marine engineering structures. The load of the single module in the wave is closely related to the structure form of the super-large floating structure. In this paper, the moment transfer function in the regular wave is calculated, and the influence of the center distance of the lower floating box on the vertical bending moment is analyzed. Then the stress response of brace joint is calculated by commercial finite element software and its amplitude and phase distribution are given to further analyze the multi-axial degree of stress at the joint. The change degree of principal stress direction is determined by the amplitude and phase of stress. Based on the analysis of stress response in regular wave and short-term sea condition, the change degree of principal stress direction is given in this paper. It provides a basis for multiaxial fatigue evaluation. Then, according to the results of multi-axial fatigue test, this paper analyzes and compares the common methods of selecting facing interface under simple multi-axis fatigue criterion, and discusses the effect of proportional and non-proportional stress state on multi-axial fatigue life, according to which the influence of proportional and non-proportional stress state on multiaxial fatigue life is discussed. It provides a basis for selecting multi-axial fatigue criterion for spectral fatigue analysis. Finally, a concrete method of fatigue spectrum analysis using multi-axis fatigue criterion under complex stress condition is established, and the spectrum analysis forms of stress spectrum transformation and common multi-axis fatigue criterion are given. Based on the short-term and long-term prediction, the fatigue damage results of structural brace joints under the main classification society method, the method recommended by the International Welding Society and the multi-axis fatigue spectrum analysis are compared. It is found that, except for a few waves, the direction of principal stress changes little under the unidirectional wave, and the effect of multi-axial effect on the fatigue life of the structure is small. However, considering that the structure will continue to encounter waves in different directions during the life cycle, the direction of principal stress changes greatly, and the multi-axis effect will reduce the fatigue life of the structure. Therefore, it is suggested to take into account the effect of the principal stress change on fatigue life of super-large floating structures under all-direction incoming waves.
【学位授予单位】：中国舰船研究院
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U661.4

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