STUDIES ON RELIABILITY ANALYSIS SYSTEMS OF LARGE FLOATING STRUCTURES

本文研究了大型浮式结构物的结构完整性和可靠性分析系统。主要研究成果如下：1）采用解析方法，采用简单梁模型，研究了超大型浮式结构物（VLFS）的动力响应和强度特性。通过对同一结构用平面框架代替的分析结果，指出在低频区不仅要考虑竖向弯曲振动，还要考虑水平弯曲振动和纵向振动。2）提出了一种基于流固耦合分析的考虑挠度波传播的结构动力响应特性的估算方法。根据分析结果，考察了入射波的波长和方向对响应和强度的影响。结合以上结果，提出了长峰不规则波作用下结构动力响应和强度的简化估算方法。通过对4700 m级超大型浮体结构的数值算例，验证了该方法的适用性。4）提出了一种估算大型浮体结构在较高频率区域的流体阻尼矩阵和振动水平的方法。5）作为一种结构参数识别方法，为超大型浮体结构的整体分析提供了可能的建模方法。提出了考虑甲板和底板剪切变形的板架梁单元抗扭刚度的合理公式。6）作为海洋板结构可靠性分析研究的一部分，提出了一种用8节点六面体单元模型进行倒塌和可靠性分析的简化方法。

This study is concerned with structural strengty and reliability analysis systems of large floating structures. Results obtained in this study are summarized as follows :1) Characteristics are investigated for the dynamic response and strength of a very large floating structure (VLFS) using the simple beam modeling by analytical methods. From analytical results for the same structure replaced with a plane framework, it is also pointed out that not only vertical bending vibrations but horizontal bending and longitudinal vibrations should be considered at the lower frequency zone.2) An estimation method is also proposed for the dynamic response behavior of such a structure considering deflection wave propagation based on fluid-structure interaction analysis. From analytical results, effects of wave length and direction of incident waves on the response and strength are examined. Moreover, the dispersion relation of the deflection wave is also derived based on the analogy of the linear water wave theory.3) A simplified estimation method for dynamic response and strength under long crested irregular wave conditions is presented by combining above results. The applicability of the method is investigated through numerical examples carried out for 4700m class VLFS.4) An estimation method is presented for the fluid damping matrix and vibration level of large floating structures on comparatively higher frequency zone.5) As a structual parameter identification method ion the possible modeling for overall structural analysis of a VLFS,rational formulation of a torsional stiffness of grillage beam elements considering shear deformation of deck and bottom plating is proposed.6) As a part of the study on the structural reliability analysis of marine plate structure, a simplified method is presented for the collapse and reliability analysis using 8 node hexahedral element models.