A Study on Efficient Methods for Estimating Strength and Reliability and Their Application to Preliminary Structural Design of Large Floating Structures

1)通过分析，从初步设计的角度，探讨了长波峰作用下浮筒式VLFS强度和可靠性评估的有效方法。首先，提出了不规则海况条件下VLFS概率载荷效应的简化估计方法。其次，提出了VLFS甲板、舱壁和底部加筋板在压缩、剪切和侧压联合作用下屈曲和极限倒塌强度的极限状态和可靠性分析方法。然后，通过非线性有限元分析，验证了简化估计方法的有效性。通过东京湾恶劣海况条件下5000米级VLFS试验设计的数值算例，研究了上述方法的适用性。采用灵敏度分析方法，数值计算了板厚、加劲筋和舱壁间距等设计参数对可靠性水平特性的影响。2)提出了一种更有效的斜波浅水中矩形板模拟VLFS水弹性特性的估计方法。研究了入射波数、入射角、展弦比和结构抗弯刚度对响应特性的影响。3)多次重复荷载作用下结构钢的疲劳行为，作为海洋结构疲劳寿命估计基础研究的一部分。研究了试样在完全反拉和反压条件下的滞回线能量变化和温升速率等疲劳行为。将线性累积疲劳损伤规则（Miner规则）与上述试验结果相结合，提出了一种估算剩余疲劳寿命的方法。4)采用非线性有限元法研究了含腐蚀加筋板的抗压极限强度。结果表明，加筋板的极限强度取决于腐蚀最严重截面的参数。在此基础上，提出了计算极限强度的简单设计公式。5)提出了腐蚀圆管弯曲压缩残余强度的简化计算方法。结果表明，上述腐蚀厚度减小对极限强度劣化影响的估计结果与基于壳单元弹塑性有限元法的分析结果有较好的对应关系。少

1)Efficient methods are investigated for estimating strength and reliability of pontoon type VLFS under long crested waves from view point of preliminary design by analysis. Firstly, a simplified estimation method is presented for the probabilistic load effect of VLFS under irregular sea-state conditions. Next, a limit state and reliability analysis method is presented for the buckling and ultimate collapse strength of stiffened panels under combined compression, shear and lateral pressure in deck, bulkhead and bottom parts of VLFS. Then, the validity of the simplified estimation method is shown by using non-linear finite element analysis. The applicability of the methods is investigated through numerical examples for 5,000m-class VLFS under trial design for the severe sea state-condition in Tokyo Bay. Effects of design parameters such as plate thickness, stiffener and bulkhead space on characteristics of the reliability level are numerically shown by using sensitivity analysis.2)An ef … More ficient method is presented for estimating hydro-elastic behavior of VLFS modeled by a rectangular plate on the shallow water in oblique waves. Effects of incident wave-number, incident angle, aspect ratio and bending rigidity of the structure on the response behavior are investigated.3)Fatigue behavior of structural steels under multiple repeated loads as a part of basic studies on fatigue life estimation of marine structures. The fatigue behaviors such as the change of hysteresis loop energy and temperature rise rate of specimens under completely reversed tension and compression are investigated with much circumstance. A method for estimating the remaining fatigue life is presented by using a method combined the linear cumulative fatigue damage rule (Miner's rule) with above experimental results.4)The compressive ultimate strength of stiffened plates with corrosion is investigated by the non-linear finite element method. It is found that the ultimate strength is determined by the parameters of the most corroded cross section of stiffened plates. Simple design equation to estimate the ultimate strength is proposed by considering above results.5)Simplified method is presented for estimating the residual strength of corroded circular tubes under bending and compression. It is found that the above estimation results for effects of the reduced thickness due to corrosion on the ultimate strength deterioration are in comparatively good correspondence to analytical results based on elasto-plastic finite element method using shell elements. Less