Evaluation of ultimate strength of stiffened panels under longitudinal thrust

A series of collapse analyses is performed applying nonlinear FEM on stiffened panels subjected to longitudinal thrust. MSC.Marc is used. Numbers, types and sizes of stiffeners are varied and so slenderness ratio as well as aspect ratio of local panels partitioned by stiffeners keeping the spacing between adjacent longitudinal stiffeners the same. Initial deflection of a thin-horse mode is imposed on local panels and that of flexural buckling and tripping modes on stiffeners to represent actual initial deflection in stiffened panels in ship structures. On the basis of the calculated results, buckling/plastic collapse behaviour of stiffened panels under longitudinal thrust is investigated. The calculated ultimate strength are compared with those obtained by applying several existing methods such as CSR for bulk carriers and PULS. Simple formulas for stiffened panels, of which collapse is dominated fundamentally by the collapse of local panels between longitudinal stiffeners, are also examined if they accurately estimate the ultimate strength. Through comparison of the estimated results with the FEM results, it has been concluded that PULS and modified FYH formulas fundamentally give good estimation of the ultimate strength of stiffened panels under longitudinal thrust.     

Assessment of IACS-CSR implicit safety levels for buckling strength of stiffened panels for double hull tankers

The present study aims at applying structural reliability methods to assess the implicit safety levels of the buckling strength requirements for longitudinal stiffened panels implemented in the IACS Common Structural Rules (CSR) for double hull oil tankers. The buckling strength requirements considered are used in the initial stage of the hull girder scantlings’ design to control the buckling capacity of longitudinal stiffened panels subjected to the compressive loads induced by the hull girder vertical bending. The following buckling collapse failure modes are explicitly considered in the design formulation: uniaxial buckling of the plating between stiffeners, column buckling of stiffeners with attached plating and lateral-torsional buckling or tripping of stiffeners.The paper presents the procedure used to assess the implicit safety levels of the strength requirements for the three buckling collapse failure modes above mentioned, which includes the optimization of the scantlings of the plate panels and longitudinal stiffeners in order to reflect the minimum strength required by the formulation. A first order reliability formulation is adopted, and stochastic models proposed in the literature are used to quantify the uncertainty in the relevant design variables. A sample of five oil tankers representative of the range of application of the IACS-CSR design rules is considered. The effect of corrosion in the implicit safety levels is quantified based on the three corrosion levels of the Net Thickness Approach (NTA) adopted in the design rules. Sensitivity analyses are also performed to quantify the relative contribution or importance of each design random variable to the implicit safety levels.     

初始缺陷对加筋板结构极限强度的影响研究

采用非线性有限元软件Ansys研究包含3种初始缺陷加筋板结构在单轴压缩载荷作用下极限强度的变化趋势,即初始变形、残余应力和凹陷。以单筋单跨加筋板模型为研究对象,考虑初始变形,不同半径及不同速度的撞击球所形成的凹陷及残余应力对加筋板极限强度的影响。结果表明,初始缺陷的存在降低了结构的极限承载力,而且缺陷的叠加作用比单独缺陷存在时对结构极限强度的影响大;加筋板的极限强度随着凹陷深度的加深而减小;3种初始缺陷中,残余应力相对于初始变形和凹陷对结构极限强度的削弱影响更大。     

初始缺陷对加筋板结构极限强度的影响研究

采用非线性有限元软件Ansys研究包含3种初始缺陷加筋板结构在单轴压缩载荷作用下极限强度的变化趋势,即初始变形、残余应力和凹陷.以单筋单跨加筋板模型为研究对象,考虑初始变形,不同半径及不同速度的撞击球所形成的凹陷及残余应力对加筋板极限强度的影响.结果表明,初始缺陷的存在降低了结构的极限承载力,而且缺陷的叠加作用比单独缺陷存在时对结构极限强度的影响大;加筋板的极限强度随着凹陷深度的加深而减小;3种初始缺陷中,残余应力相对于初始变形和凹陷对结构极限强度的削弱影响更大.     

Transverse strength analysis of catamarans

Stresses and deformations relevant for transverse strength analysis are calculated for a 60 m catamaran by a compartment model and are compared with corresponding results from a global model. It is found that the flexibility of the partial bulkheads typical for a twin-hull Ro/Ro-vessel is so large that the interaction with the surrounding structure has to be accounted for. If springs are applied, the results are sensitive to the spring stiffness. A web frame model that does not include any bulkheads, gives large errors and is not recommended.     

含初始变形船体加筋板有效宽度及剩余极限强度研究

为了评估舰船结构损伤后的剩余强度,对船体加筋板出现初始几何变形后,参与总纵强度的有效宽度和加筋板剩余极限强度进行研究。将加筋板受到垂直于平面压力后的变形,作为其初始几何变形,改变变形的方向和大小,利用有限元软件Ansys对加筋板结构进行线性和非线性分析。定义了板有效宽度计算方法,对不同变形方向和变形幅值时板的有效宽度和加筋板的极限强度进行对比分析,并拟合得到了计算板有效宽度和加筋板极限强度的经验公式。结果表明,初始几何变形会削弱加筋板结构的强度。在对损伤后船体结构强度进行分析和校核时,提出的经验公式可以直接用来计算板的有效宽度和加筋板的极限强度。     

船舶结构极限强度可靠性分析方法研究

针对船舶总纵极限强度极限状态方程不能以显式表达的实际情况，提出采用响应面与映射变换相结合的方法展开船舶总纵强度可靠性分析，指出相关随机变量在正态化前后相关系数的差异应予以考虑，并应用于实际船舶的计算，验证了理论的合理性。     

复合材料船体层合板的极限强度分析

基于更新拉格朗日格式,应用非线性层合三维退化壳元,结合有效的复合材料失效准则、刚度退化模型以及文中提出的刚度矩阵奇异判断准则,对复合材料层合板在轴向载荷作用下的轴向压缩极限强度问题进行深入研究.讨论了铺层方式、板厚等对极限强度的影响.通过与试验结果进行比较,表明基于文中提出的刚度矩阵奇异判断准则,结合增量更新拉格朗日格式下非线性层合三维退化有限元的计算方法能有效计算复合材料层合板的轴向压缩极限强度,并具有很高的精度.     

Buckling strength assessment of corrugated panels in offshore structures

There is an increasing trend of living quarters in offshore structures being constructed using corrugated panels in order to save construction time and cost. Different from corrugated bulkheads in ship structures, the corrugated panels used in the living quarters are designed in triangular or trapezoidal profile with unequal flanges and with a corrugation angle between 45° and 90°. Industry needs have prompted the American Bureau of Shipping to develop design recommendations for the buckling strength assessment of these corrugated panels. This paper describes the main features and the principles of the recommendations based on ABS experience, along with the technical background. The modeling uncertainty associated with the recommended criteria has been established by comparing the predictions with laboratory tests and finite element analysis results. Two design examples are provided to demonstrate the application of the recommendations.     

半潜平台结构强度及全寿命强度可靠性研究

利用ANSYS及AQWA有限元方法进行某半潜平台下水前的自存工况整体强度校核,根据目前的技术状况报告评估其腐蚀度与裂缝情况,并由腐蚀度折算钢板厚度,进行现行自存工况下的整体强度校核。文中选取了JONWASP谱描述的7种海况,分别进行整体强度计算和构件强度可靠性分析,最终获得该半潜平台目前在整个使用寿命过程中的整体强度及可靠性变化的规律。     

基于广义切线模量理论的铝合金加筋板结构轴压极限强度分析

研究铝合金加筋板结构的极限强度,有利于充分发挥铝合金材料的强度潜力和结构的后屈曲承载能力。本文将广义切线模量理论应用于铝合金加筋板结构的轴压极限强度计算,并推导了适用于加筋板的协调参数、极限弯矩系数及结构系数等相关参数的解析算式,建立了铝合金加筋板结构的强度利用率函数,从而得到结构的极限强度,进一步完善了广义切线模量理论在加筋板结构极限强度研究领域的应用。通过将广义切线模量法计算结果与经验公式、有限元计算结果进行比较,验证了其适用性与可靠性,可用于工程分析计算。     

Numerical investigation on the ultimate strength behaviour and assessment of continuous hull plate under combined biaxial cyclic loads and lateral pressure

The ultimate strength of continuous hull plate under combined biaxial cyclic loads and lateral pressure is investigated in the present paper by using nonlinear finite element method. Geometric nonlinearity due to large deflection and material nonlinearity induced by kinematic hardening and isotropic hardening are both accounted for. A parametric study is designed and completed to examine the longitudinal ultimate compressive strength behaviours in the cycles on the basis of a large number of load-shortening curves. Effects of series of parameters especially the plate slenderness ratio, transverse cyclic compression, lateral pressure and cycle number are analyzed with details. It is found that the strength characteristic and collapse mode are highly affected by the coupling influence of the mentioned factors as well material behaviours. A dimensionless unified formulation as a function of the decisive factors is empirically proposed to accurately assess the ultimate strength of continuous hull plate in various cycles.     

复合材料帆船桅杆强度可靠性分析

针对帆船桅杆失效事件,基于船舶领域可靠度理论,对复合材料帆船桅杆的可靠度进行计算。建立复合材料帆船桅杆的有限元模型,对某一铺层方案进行强度校核。基于可靠性理论,采用JC法和Matlab软件对复合材料帆船桅杆的强度可靠性进行分析,最终得到复合材料桅杆的可靠性指标。该研究能避免传统强度校核采用的确定性方法不能保证结构每个位置在一定概率下都是安全的缺点,对复合材料桅杆的结构可靠性研究具有一定的参考价值。     

铝合金夹心板结构极限承载能力有限元分析

随着新材料及新型结构的不断出现,以往的线性理论已不能满足现代工程设计的需要.本文利用MSC.NASTRAN的弧长法对一种新型铝合金夹心板结构进行了极限承载能力有限元分析,跟踪出了其屈曲平衡路径以及破坏模式.为验证有限元模拟的准确性,对结构进行了静载强度模型试验.研究结果表明,计算结果与试验符合较好.     

船体梁极限强度非线性有限元计算方法研究

文章针对Dow 1/3比例护卫舰模型,进行多种方案的船体梁极限强度非线性有限元计算,通过与Smith方法和模型试验结果的对比分析,研究船体梁极限强度非线性有限元建模技术,给出一种较为准确高效的船体梁极限强度非线性有限元计算方法。对于完善《船体梁极限强度的非线性有限元方法计算指南》具有一定的参考价值。     

船体板格极限强度数值计算影响因素及敏感分析

船体板格极限强度的有限元计算方法应用广泛,但其计算方法具有一定的不稳定性,计算结果受多种因素的影响.本文针对船体板格有限元计算方法的不稳定性进行研究,通过将有限元计算结果与其他学者的研究成果进行对比,验证本文所采用的有限元方法的可靠性,然后针对板格材料、初始缺陷、网格密度、边界条件等几种因素的敏感性进行具体研究,发现理想应力应变关系会使得结果偏于危险.网格形状和网格密度对于结果均有影响,边界条件对于有限元结果有影响,最大误差在7.2%,并且模型3会使得结果偏于危险.初始缺陷是一敏感因素,最大误差在20%,因此需要根据实际缺陷选取合适的屈曲模态和比例因子.     

The ultimate strength of doubler plate reinforced Y-joints under compression loading

It is common practice in the offshore industry to solve the punching shear problem due to compression by using doubler plate. The finite-element method is a useful tool for studying this problem. The aim of this paper is to study the static strength of doubler plate reinforced Y-joints subjected to compression loading. The finite-element method is adopted in numerical parametric studies. The individual influences of the geometric parameters βand τd （ doubler plate to chord wall thickness ratio） and ld/d1 （ dubler plate length to brace diameter ratio） on the ultimate strength are made clear. The results show the size of plate may have important effects on the strength of reinforced joints. It is found that the ultimate strength of Y-joints reinforced with appropriately proportioned doubler plates can be greatly improved nearly up tothree times to un-reinforced Y-joints.     

加筋压筋夹层板的固有频率分析

这是ISSC的BENCHMARK研究内容.首先对没有敷设层时的计算结果与实验结果进行了比较,以验证计算模型的有效性.对两种加筋压筋夹层板结构的固有频率进行了分析.对夹心层和厚表层分别采用偏心壳单元和固体单元进行了计算,并与实验结果进行了比较.结果表明,对于夹心层无论厚薄,均为采用固体单元较适宜.最后对有无夹层处理的结构固有频率也进行了比较.     

某船设备系固卡板结构及连接焊缝强度直接计算

根据某船装载设备基座的卡板设计和载荷,采用有限元方法对其结构和连接焊缝的强度进行计算和分析,并依据应力计算结果对原设计进行修改直到卡板结构及其连接焊缝在设计载荷作用下满足强度要求。     

K型、双K型圆管相贯节点极限承载力的非线性有限元分析

利用非线性分析的有限元方法对K型和双K型圆管相贯节点进行了数值计算，揭示了节点极限承载力随各几何参数的变化规律及主管作用荷载对节点极限承载力的影响，分别绘制出各影响参数的载荷一位移曲线，并将分析结果和钢结构标准GB50017—2003进行了比较，所得结论供工程设计参考应用。