Progressive Collapse Behavior of Ship Hull and Efficient Method of Its Analysis

本文从理想结构单元法(ISUM)的推广和动力显式方法在准静态有限元分析(FEA)中的应用两个方面，探索了一种有效的船舶结构构件和系统连续倒塌分析方法。在ISUM中，将结构离散成可能的最大单元，并通过适当的形函数和屈服准则来理想化这些单元由于屈服和大挠度而产生的非线性行为。因此，与有限元分析相比，求解的自由度大大减少，从而减少了计算工作量和时间。本文的主要研究成果如下：(1)对ISUM矩形板单元进行了扩展，使其既能考虑侧压力，又能考虑推力载荷。还可以考虑板材和加筋板中焊接残余应力的影响。进步的co…对一个纯弯曲的船舶横截面进行了较详细的分析，证明了ISUM的高精度和高效性。计算时间约为有限元分析的1/70。(2)建立了双壳结构连续倒塌分析的ISUM梁单元。在计算刚度矩阵时，通过适当选择积分点，可以考虑楼板或大梁中剪切的影响。双层底板结构在均布侧向压力作用下的连续倒塌分析表明了该模型的有效性和准确性。ISUM所需的CPU时间约为有限元的1/70-1/100。(3)讨论了采用动态显式方法进行准静态有限元分析所需的加载条件。结果表明，该条件是与屈曲模式相似的固有振型所对应的固有周期的函数。(4)进行了箱梁试件的循环弯曲试验，研究了试件的循环倒塌行为，包括板件屈曲后引发低周疲劳裂纹。测试结果与ISUM分析结果的比较表明，ISUM分析的准确性令人满意。较少

An efficient method of progressive collapse analysis of ship structural members and systems was pursued in this study from two different aspects, one is the extension of Idealized Structural Unit Method (ISUM) and the other is the application of dynamic explicit method to quasi-static Finite Element Analysis (FEA). In ISUM, the structure is discretized into possible largest elements and the nonlinear behavior of such elements due to yielding and large deflection is idealized by appropriate shape functions and yielding criteria. The degree of freedom to solve for is therefore significantly reduced compared to FEA, resulting inthe reduction of computational efforts and time. The major achievements in this study can be summarized as follows:(1) ISUM rectangular plate element was extended so that the lateral pressure can be considered as well as the thrust loads. It was also made possible to consider the effect of welding residual stresses both in plate and in stiffener. The progressive co … More llapse analysis of a ship cross section under pure bending was performed, and a good accuracy and an efficiency of ISUM were demonstrated. CPU time required for ISUM was about 1/70 of that for FEA.(2) ISUM girder element for the progressive collapse analysis of double hull structure was developed. The effect of cutouts in the floor or girder can be considered by appropriately selecting integration points for the calculation of stiffness matrices. The progressive collapse analysis of a double bottom structure subjected to uniform lateral pressure showed the efficient and accurate applicability of the proposed ISUM model. CPU time required for ISUM was about 1/70-1/100 of that for FEA.(3) The loading condition necessary for the quasi-static FEA using dynamic explicit approach was discussed. It was shown that the condition is given as a function of natural period corresponding to the natural vibration mode resembling the buckling mode.(4) Cyclic bending test of a box-girder specimen was performed to investigate the cyclic collapse behavior including the initiation of a low cycle fatigue cracking after panel buckling. A comparison between test and ISUM analysis exhibited the satisfactory accuracy of ISUM analysis. Less