Numerical prediction and mitigation of out-of-plane welding distortion in ship panel structure by elastic FE analysis

As an application to predict and mitigate the out-of-plane welding distortion by elastic FE analysis based on the inherent deformation theory, a panel structure of a pure car carrier ship is considered. The inherent deformations of different types of welded joints included in this ship panel structure are evaluated beforehand using thermal elastic plastic FE analysis. Applying idealized boundary condition to focus on the local deformation, elastic FE analysis shows that the considered ship panel structure will buckle near the edge and only bending distortion is dominant in the internal region. In order to mitigate out-of-plane welding distortion such as buckling and bending, straightening using line heating is employed. In the internal region, only inherent bending with the same magnitude as welding induced inherent bending is applied on the opposite side of welded joints (fast moving torch). On the other hand, only in-plane inherent strain produced by line heating is introduced to the edge region to correct buckling distortion (slow moving torch). The magnitude of out-of-plane welding distortion in this ship panel structure can be minimized to an accepted level.     

Analysis of the accident of the MVNakhodka. Part 2. Estimation of structural strength

In the early morning of January 2, 1997, a Russian tanker, the MVNakhodka, broke in two in the Sea of Japan. The fore part of the vessel drifted and was stranded on the coast of Japan, and the aft part sank. The coast of Japan was seriously polluted by spilled heavy oil. Following this disaster, the Japanese Government established a Committee for the Investigation of the Causes of the Casualty of theNakhodka. This paper deals with the structural strength of MVNakhodka at the time of the accident. First the structural characteristics of theNakhodka are described, and the reduction in thickness of the structural members are estimated based on the data measured on the fore part of the vessel which drifted ashose. Then the ultimate longitudinal strength of the hull girder at the time of the accident is evaluated by applying Smith's method, and the possibility of break-up collapse due to excess loads is discussed. The mechanism of fracture at the bottom plate is also discussed based on the observed fracture surfuce of the cross section. Finally an FEM (finite element method) simulation of the break-up of the hull girder is performed. It is shown that buckling/plastic collapse took place at the deck plate near Fr.153, which was followed by the successive buckling collapse of the side shell plate of the hull girder. Right after the collapse of the deck structure, the bottom plate fractured just in front of the transverse bulkhead at Fr.153. This article is based on an article that appeared in Japanese in the Journal of the Society of Naval Architects of Japan, vol. 183 (1998).     

基于过载法的船舶板架冗余度研究

针对两种损伤模式,建立基于过载法的船舶板架结构冗余度计算模型,推导板架结构连续垮塌的最大屈曲利用因子计算公式。计算了6艘CSR船舶船底、内底板、舷侧板和甲板等板架损伤态的屈曲利用因子,验证船舶板架的冗余度。     

薄壁圆柱在轴向冲击力作用下的动力学响应

利用有限元软件ABAQUS分析了钢和铝合金薄壁圆柱在轴向冲击力作用下的动力学响应。在相同的参数条件和初边值条件下,通过与相关文献的数值结果对比验证了所取参数的正确性和可靠性。讨论了不同碰撞速度,不同质量比,不同边界条件对平均作用力,塑性铰的形状和个数的影响。数值实验表明,随着碰撞速度的提高,平均作用力会相应增大,撞击薄壁结构的刚性质量块和薄壁结构的质量比对平均作用力没有影响。薄壁结构吸收的能量和薄壁结构本身的几何特性和材料特性将决定变形后塑性铰的个数。     

船舶砰击动力屈曲

本文移植两维水弹性砰击与波激力短程序，应用B－R准则，以对应的静态屈曲阈值为基点搜索动态屈曲。本文分析了波高、失稳临界值和屈曲发生时间的关系，得出了一些供远洋船舶设计参考的结论。     

圆筒形生活平台总体强度分析

参考挪威船级社海工规范要求,分析平台极限载荷状态下的总体结构强度.应用海工规范公式对主船体结构中的板和筋进行规范校核,对主船体双层壳内的环形梁进行屈服和局部屈曲的强度校核,对大的板架结构开展针对各种屈曲类型的校核,结果表明,该生活平台在目标海况下的结构承载能力满足船级社的规范要求.     

变截面开口薄壁钢箱稳定性分析

从薄板基本理论出发,利用单块板的平衡状态,将基本方程建立在变形后的结构上,用假想荷载法推导出了薄壁构件弯扭平衡微分方程;以变截面开口薄壁钢箱为研究对象,用有限元软件ANSYS对大量不同尺寸的结构进行了屈曲分析。研究发现:受竖向均布荷载作用下变截面悬臂开口薄壁钢箱有3种基本屈曲形态,即板件的局部屈曲、截面的畸变屈曲和构件的整体屈曲;随着结构尺寸的变化,一阶屈曲形式也在发生变化,并且呈一定的规律。     

海底埋设管线屈曲剧变理论研究综述

海上生产的烃类必须在高温高压下运输以使流体舒缓而避免蜡组分的凝固。由于内外压差和温差引起强制膨胀导致轴向压缩力,此时便产生了海底管线的屈曲。此压缩力既能引起管线在海床平面内的侧向屈曲,也能造成垂向屈曲。通常将管线埋于沟槽内从而确保与其它海洋活动的干扰最小化。在此情况下,侧向土约束超过了由管线浮重造成的垂向隆起约束。因此,要特别注意挖沟埋设管线的垂向屈曲。最近对中国高温管线和渤海湾几起事故的关注引发中国海洋工程师对此现象的强烈兴趣。文章综述了海底埋设管线垂向屈曲的理论研究历史,以及作者对此问题的一些经验。希望海洋工程师能从本领域的文献综述和总结中受益。文中同时研究了管线的防护层设计,最后明确了未来发展的方向。     

基于Abaqus的环肋圆柱壳长舱段稳定性分析与结构优化

采用大型非线性有限元软件Abaqus分析了环肋圆柱壳长舱段的稳定性规律,对于环肋圆柱壳长舱段,随着舱段长度的增加,其稳定性的数值仿真解与解析解差别逐渐增大,有限元计算结果能够更加合理准确地反映其稳定性状况.现行规范对于环肋圆柱壳长舱段稳定性的求解适用性有所下降,应该考虑对理论公式进行修正.针对某种典型的环肋圆柱壳长舱段,分别采用一根和两根框架肋骨的方案进行结构优化以提高其总体稳定性,结果表明,一根框架肋骨的优化方案重量较轻,稳定性指标更加接近规范的容许值,两根框架肋骨则比较节省舱内空间.综合考虑,一根框架肋骨的方案更加合理.     

改进弧长法求解屈曲问题

为了解决结构非线性有限元分析求解过程中结构失稳或材料出现软化时传统Newton-Raphson法无法通过极值点的问题,在传统弧长法的基础上,提出了求解过极值点问题的改进弧长法.该方法将非线性方程求解过程中出现的不平衡力向量分解为两个相互正交的向量,并建立其弧长的约束方程,求解得到非线性计算中的荷载因子.在求解过程中,给出了改进的确定弧长方法,通过弧长调整避免了求解荷载系数中出现复根的问题.通过两个拱型结构的屈曲分析算例,分别考虑几何非线性和几何材料双重非线性效应,对两个拱形结构进行了非线性屈曲分析,结果表明:结构在出现屈曲时发生急跳现象,验证了改进的弧长法在结构出现材料软化和失稳时能通过极值点.