New simplified approach to collapse analysis of stiffened plates

A new simplified model for collapse analysis of stiffened plates is developed in the framework of the idealized structural unit method (ISUM). By idealizing material and geometrical nonlinearities, larger structural units are defined as an element in ISUM than in conventional finite element analysis (FEA). The proposed stiffened plate model consists of ISUM plate elements and beam-column elements. The formulation of the plate element is performed by introducing accurate shape functions to simulate the buckling/plastic collapse behaviour of plate panels. Combining plate and beam-column elements allows for both local buckling of the plate panel and overall buckling of the stiffener.Fundamental collapse modes of plate panels and stiffened plates are investigated by conventional FEA. According to the observed characteristics, the new simplified model is formulated. Comparisons with FEA demonstrate the accuracy of the simplified model and its high applicability to typical stiffened plates in marine structures.     

推力和横向压力作用下加筋板破坏分析的理想化结构单元法

理想化结构单元法(ISUM)已经成为评估结构系统中承受载荷能力的一个有效工具.本文给出了最新的ISUM板元公式,并考虑了双轴向推力和横向载荷对板元的加载.为了精确地模拟加筋板的性能,分别用梁-柱元和板元制作了肋材和板材的模型.与有限元分析(FEA)的比较表明该方法对解决加筋板在横向压力和推力载荷下的问题是适用的.对箱形桁材的四点弯曲试验的分析表明与试验数据吻合良好.     

基于有限元分析的潜艇耐压液舱结构系统可靠性计算

潜艇耐压液舱结构复杂，往往需进行有限元分析以获得结构在极限载荷作用下的应力。此时，由于失效函数缺乏显式表达，故应用一般的可靠性计算方法将遇到困难。作者采用人工神经网络代替传统的多项式函数拟合失效面，并结合方向抽样技术，提出了基于有限元的结构系统可靠性计算的新算法。由于该方法引入了结构有限元分析，且无需进行失效模式间相关性的近似分析，因而计算精度好，适用范围广泛。潜艇耐压液舱结构系统可靠性分析的算例表明，该法有效地解决了复杂工程结构的系统可靠度计算问题。     

船用中压配电装置设计技术研究

船用中压配电装置为船舶中压电力系统的重要组成部分,主汇流排作为中压配电装置的核心部分,其设计正确与否关系到中压电力系统的安全可靠运行。本文阐述了船用中压配电装置主汇流排的设计及分析方法,主要包括船用中压配电装置主汇流排横截面积的计算分析,以及结合实船中压电力系统短路电流计算对主汇流排进行的动稳定性和热稳定性计算分析,并给出相应的计算分析公式,最后结合实际工程项目通过MATLAB的GUI代码编制相应软件对其进行分析计算。     

基于谱分析的FPSB疲劳寿命评估和优化

FPSB是一种新型深远海大型浮式结构物,长期承受交变波浪载荷作用,易发生疲劳而使得结构失效。本文以一艘FPSB为研究对象,使用谱分析法对其疲劳寿命进行了评估。首先建立水动力模型计算波浪载荷响应算子RAO,建立整船结构模型计算船体结构响应,随后选取典型节点建立子模型以得到精确的热点应力传递函数,采用北大西洋海况和P-M海浪谱,基于S-N曲线和线性累积损伤准则对典型节点的疲劳寿命进行计算分析。根据疲劳评估结果,对易损节点进行基于疲劳性能的结构优化,以提高节点形式的合理性及结构安全可靠性。     

破损船体非对称弯曲极限强度分析及可靠性评估

在船体发生破损后,其剩余有效剖面是非对称的,船体还可能倾斜。本文首先对破损船体非对称弯曲进行了弹性和塑性分析,在此基础上假设了破损船体发生整体破坏时的剖面应力分布,给出了破损船体非对称弯曲极限强度分析方法,并采用了比较精细的方法计算加筋板格的屈曲极限强度。以箱型梁模型和超大型油船为例,将本文的计算结果与试验、ＩＳＵＭ法及解析公式的结果进行了比较。基于破损船体极限强度,结合重要性样本法,对６５,００     

结构系统疲劳可靠性分析的一阶和二阶混合方法

本文提出了复杂结构系统疲劳可靠性分析的一阶和二阶混合方法。引进Ｈｏｈｅｎｂｉｃｈｌｅｒ等提出的并联系统可靠性分析的二阶渐近式计算失效途径的疲劳失效概率;利用并联系统等效线性安全余量的概念,形成由失效途径的等效失效单元组成的串联系统;并最终计算整个系统的疲劳失效概率。计算结果表明,这一方法能有效地提高结构系统疲劳失效概率的计算精度。     

基于λ-等效原则的并联系统备件配置方法

针对不同寿命分布类型部件组成的并联系统存在备件配置计算公式较为复杂,较难得到解析解的问题,根据累积失效相等原则,将非指数型部件等效为指数型部件,在此基础上,建立了并联系统的备件配置模型。利用该模型,并结合边际效益方法对并联系统中不同寿命分布类型的部件备件配置数量进行了优化计算。通过相关分析,该计算方法具有计算便利,结果较为准确的优点。最后通过具体案例的应用,对该计算方法进行进一步的说明和检验,为解决并联系统备件配置问题提供一种新思路。     

基于剪流分布规律的节点力加载方式在船体结构有限元分析中的应用

船体结构强度评估是船舶建造与设计过程中的重要环节.本文在总结研究现有的船体结构有限元分析加载方式的基础上,提出基于剪流分布规律的节点力加载方式.对于为模拟船体梁载荷而在各剖面处施加的集中力以及为进行强度计算需在各剖面处施加的调整载荷,使用本文方法将其离散至单元网格节点处并于与加载,得到的结果符合船体梁弯曲时的应力分布规律,这对于正确进行船体结构强度评估具有重要意义.给出适用于计算机实施的规格化加载过程,以实现船体结构有限元分析的自动加载过程.     

Collapase analysis of ship hulls

This paper presents an efficient finite element procedure for the collapse analysis of ship hulls under complicated loads. A set of finite elements, such as beam-column elements, stiffened plate elements, and shear panel elements are developed, directly accounting for the geometrical and material non-linearities and initial imperfections.

Elastic-plastic stiffness matrices for elements have been derived by combining elastic large displacement analysis theories with a plastic hinge model. The buckling and post-buckling behaviour of plates is included using an effective width concept. The procedure is effective, since few mode-points are necessary and numerical integration for evaluating stiffness matrices is avoided. Fracture mechanics criteria are introduced in order to account for tension tearing rupture and brittle failure of the material.

Practical applications to ultimate longitudinal strength analysis of ship hulls and tanker collision analysis are presented. The procedure can also be used for collapse analysis of offshore and onshore structures.     

基于复合建模方法的轴系扭转振动特性及仿真

为了提高主机轴系计算准确度,本文提出了一种新型的主机轴系建模方法,该方法将主机轴系分为连续子系统和离散子系统。推进轴段如螺旋桨轴、中间轴、螺旋桨及法兰划分为连续子系统,柴油机曲轴端划分为离散子系统。分别应用波分析法和多自由度动力特性分析,得到连续子系统和离散子系统的控制方程,同时通过边界条件将两个子系统动态刚度矩阵连接,推导出全局控制方程。对某型主机轴系扭转振动计算进行了仿真分析,并与传统建模方法比较。从计算结果可知,在高阶模态上,新型建模方法计算更精确,更接近真实振动状态,同时在保证相同计算精度的情况下,新型建模计算方法计算时间和计算资源占用较少,相对更为简便。同时,新型建模方法克服了当模态节点集中于轴段时,传统建模方法由于将轴系等效为一至两个质量单元而引起的节点偏移所带来的误差,这在实际主机轴系计算特别是长推进轴和刚度较低的轴系中具有重要意义。     

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).     

Effects of structural flexibility on the dynamic responses of low-height lifting mechanism for offshore wind turbine installation

Installation complexities are one of the major challenges in the floating offshore wind turbine (OWT) industry. The modern concept introduced by the SFI-MOVE project is an effort to overcome the complexities by utilizing a low-height lifting mechanism. It is common to idealize a crane in the lifting mechanism as a rigid body since the structural deflections are smaller than the responses introduced by the other system components. However, structural flexibility can play an essential role in demanding offshore operations with smaller acceptable tolerances. In this study, lifting cranes are modeled using the finite element method and simplified by implementing equivalent 3D beam elements. Dynamic analysis is performed for various environmental conditions, and the responses of the crane structure and the OWT are calculated for each load case. This research reveals that crane structure flexibility influences the relative motion between a floating spar buoy and an OWT during mating operations. Crane structural flexibility contributes significantly to the OWT rotations. In addition, the response deviation between using rigid and flexible cranes increases as the excitation force increases. Therefore, it is recommended to consider the crane structural flexibility in the calculation when strict installation tolerances are needed.     

内河双壳船极限强度分析

对内河双壳船达到极限状态时剖面上的应力分布情况进行假设,采用直接法对极限强度计算的公式进行推导,并对一条内河双壳实船在完整和破损状态的结构极限承载力进行计算与比较.结果表明,所假设的应力分布对这一类型船舶的极限强度的计算结果具有较高的精度,可以用来估算此系列船舶在完整和破损状态下的极限强度.     

考虑部件已工作时间的备件计算模型

借助冷储备系统可靠性模型，导出了考虑部件已工作时间的备件计算模型，并提供了部件寿命服从正态分布时的备件数量计算模型。该模型能较为准确地计算储备多个备件时系统可达到的可靠性。本文的研究成果对科学确定备件储备量具有重要的指导意义。     

Ultimate strength of container ships subjected to combined hogging moment and bottom local loads,Part 2: An extension of Smith's method

This paper is the second of two companion papers concerning the ultimate hull girder strength of container ships subjected to combined hogging moment and bottom local loads. The nonlinear finite element analysis in Part 1 has shown that local bending deformation of a double bottom due to bottom lateral loads significantly decreases the ultimate hogging strength of container ships. In this Part 2, extending Smith's method for pure bending collapse analysis of a ship's hull girder, a simplified method of progressive collapse analysis of ultimate hogging strength of container ships considering bottom local loads is developed. The double bottom is idealized as a plane grillage and the rest part of the cross section as a prismatic beam. An average stress-average strain relationship of plate/stiffened plate elements employed in Smith's method is transformed into an average stress-average plastic strain relationship, and implemented in the conventional beam finite element as a pseudo strain hardening/softening behaviors. The extended Smith's method is validated through a comparison with nonlinear finite element analysis.     

浮筏系统结构参数的功率流灵敏度分析

浮筏系统已经大量地应用在舰船动力装置的减振降噪中，本文介绍了一种浮筏系统功率流灵敏度的分析方法，利用有限元法，将浮筏系统离散为一个个有限单元的集合，在动态分析的基础上，求得系统在所要求的激励点和基础响应点之间的功率流对给定参数的灵敏度。为浮筏系统的设计提供了有用的信息。     

应用奇点法计算流体对结构振动的影响以及关于附连水质量的相似关系

本文把流体力学奇点法与结构有限元法相结合,计算流体对结构振动的影响。这种方法用结构浸水面上的边界元代替流体所占空间内的流体元,可以大大节省计算机容量和减少计算机时。本文还分析了附连水质量计算中的相似关系。文中得出的这些关系使得有可能应用奇点法和有限元法的计算结果为一些较复杂形状的结构得出简便而实用的附连水质量计算公式。文中给出了应用作者所编计算机程序计算附连水质量和水中结构固有振动频率的实际例子——不同浸水情况下的平板、带弹性防挠材的板、实船底部板格以及船舶艉部立体舱段。计算结果与试验结果进行了比较,二者基本符合。     

导管螺旋桨水动力与结构强度计算方法研究

随着导管螺旋桨应用的普及,计算与分析其水动力与结构强度的方法也越来越准确、快速、简便。以荷兰船模试验水池No.19A+Ka4—70螺旋桨为实例,详述了导管螺旋桨计算与分析的整体流程。通过MATLAB计算得到螺旋桨翼面与导管的空间坐标,在Pro/E中建立三维实体模型,在HyperMesh中建立CAE模型。以流体部分网格为分析对象,分别在Fluent与CFX中进行导管螺旋桨水动力分析,并比较了不同计算软件得到的导管螺旋桨水动力分析结果,为导管螺旋桨水动力计算提供了基本思路。以流体-固体网格为研究对象,在CFX平台上中进行流固耦合计算,得到螺旋桨的结构强度分析结果,拓展了螺旋桨结构强度分析方法。该水动力与结构强度分析与研究为导管螺旋桨总体设计提供了有效可行的方法。     

大型组块拖航运输强度分析研究

采用基于频域分析的设计波法,对某大型组块运输进行三维全耦合数值模拟和计算分析,把驳船和组块作为一个整体结构,计入驳船的柔度对组块的结构强度的影响,建立总体结构模型和水动力模型,采用SESAM软件包的多个软件程序进行数值模拟,确保运动分析和结构计算的准确性。