基于形函数插值理论预测轴力作用下T型管节点热点应力的分布规律

海洋平台中管节点的疲劳寿命由焊缝周围热点应力的分布情况决定.该文采用有限元方法分析了承受轴向力作用下T节点焊缝周围的应力分布规律.通过对140个具有不同几何形状的T节点模型的有限元分析结果.提出了一种基于形函数插值理论的方法预测T节点焊缝周围的应力分布,并且通过比较插值法得到的结果和有限元结果进行比较,验证了这种方法的准确性.     

基于应力集中系数的SWATH船疲劳节点筛选方法研究

小水线面双体船的疲劳强度问题十分突出,疲劳强度校核节点众多且目前还没有一个明确的疲劳节点筛选原则。针对这些问题,研究基于典型节点的热点应力集中系数有限元计算和名义应力分析,对小水线面双体船全船结构中可能发生疲劳强度失效的节点进行疲劳寿命估算,并根据估算结果对需要进行热点应力分析的疲劳节点进行筛选。计算结果表明,该方法在处理大量结构节点的疲劳寿命估算问题中,计算效率较高,能够反映全船的节点疲劳强度特性,且估算结果较为可靠。该方法不仅适用于小水线面双体船,对于其他类型的船舶,该方法同样具有适用性。     

LNG船疲劳强度评估及低温影响的讨论

以某LNG船为研究对象,建立三舱段有限元模型,并根据美国船级社薄膜型LNG船体结构疲劳强度指南,基于SN曲线法的疲劳积累损伤原理,分别采用名义应力和热点应力法,对船体典型节点进行疲劳强度评估,同时对计算结果进行分析;讨论低温下材料性能改变对节点疲劳寿命评估的影响。研究表明,采用常温下SN曲线进行LNG船疲劳强度评估是合适的。     

双轴加载下船底纵骨疲劳寿命试验与数值模拟研究

以实尺度制作了疲劳试验的试件,对45000DWT江海直达散货船船底纵骨与水密及非水密实肋板连接处进行了双轴恒幅循环载荷下的疲劳试验,记录了热点处的疲劳裂纹扩展长度和对应循环次数,获得船底纵骨疲劳特性;根据不同节点处裂纹萌生和扩展情况,得出非水密节点处是疲劳危险处;用动态应变仪记录热点处的应变,根据新版《船体结构疲劳强度指南》中的热点应力法计算热点应力,用试验数据拟合了一条S-N曲线,与指南提供的D曲线进行了对比分析,验证了D曲线的合理性。同时用MSC.Patran软件建立有限元模型,选取2007版《船体结构疲劳强度指南》中名义应力法对应结构形式的F曲线,用MSC.fatigue模块计算了相应节点的总疲劳寿命,将有限元结果和试验结果进行对比,验证了热点应力法的准确性。     

三体船型疲劳强度评估和分析

参照相关规范,对三体船结构的典型节点进行疲劳强度分析。通过波浪载荷计算和试验结果分析了三体船的载荷特征。通过粗网格下的全船有限元应力计算确定了疲劳热点部位。对这些部位采用精细网格进行了基于谱分析的热点应力计算,从而给出了热点部位的累积损伤。最后总结了三体船的疲劳特性。     

船舶舱口角隅疲劳强度及热点应力研究

舱口角隅部分的疲劳问题是疲劳分析的重要内容.本文建立了某船的全船有限元模型并分别采用嵌入式模型和外部模型对舱口角隅进行细化.比较不同的单元类型、热点应力选取方式对疲劳损伤的影响.同时采用直接计算的谱分析方法计算了舱口角隅的疲劳损伤.发现当选用最大主应力作为热点应力时实体单元计算结果较壳单元偏小.同一类型单元节点数目的不同对损伤结果影响不大.热点应力选取方式对疲劳损伤的计算影响较大,在对舱口角隅疲劳强度进行分析时建议选用最大主应力插值的方式计算热点应力.     

流固耦合网格插值方法研究

网格插值方法是流固耦合领域的重点和热点。文中针对固液交界面上网格尺寸不一,网格节点不重合的情况,利用PCL和VC开发耦合边界的网格处理程序,通过适当的插值方法将流场计算结果插值到固体节点上,形成相应的边界条件。结合算例对比了流场计算结果与六面体Lagrange插值法、四面体体积插值法的计算结果,分析结果表明通过插值得到的结果云图与原始结果吻合,表明了本插值法的有效性及应用前景。     

BINGO9000半潜式钻井平台疲劳强度分析

本文对BIGO9000半潜式钻井平台进行了疲劳强度分析。首先，建立了该平台整体三维有限元模型，结合北海波浪长期分布资料，计算了72种波浪载荷工况下的整体结构应力，为管节点结构局部应力分析提供边界条件。其次，建立管节点避部有限元模型进行疲劳强度分析。在计算管节点结构应力范围时，本文应用热点应力法，并根据DNV规范提供的S－N曲线，以及Miner线性劳累积损伤准则计算管节点结构的疲劳寿命。本文提出给出一些有意义的结论，为国内外后同类半潜式钻井平台的设计和建造提供了宝贵的技术依据。     

船舶舱口角隅疲劳强度及热点应力研究

舱口角隅部分的疲劳问题是疲劳分析的重要内容。本文建立了某船的全船有限元模型并分别采用嵌入式模型和外部模型对舱口角隅进行细化。比较不同的单元类型、热点应力选取方式对疲劳损伤的影响。同时采用直接计算的谱分析方法计算了舱口角隅的疲劳损伤。发现当选用最大主应力作为热点应力时实体单元计算结果较壳单元偏小。同一类型单元节点数目的不同对损伤结果影响不大。热点应力选取方式对疲劳损伤的计算影响较大,在对舱口角隅疲劳强度进行分析时建议选用最大主应力插值的方式计算热点应力。     

某5000t风电安装船主吊车筒体底座疲劳强度优化

根据5 000 t风电安装船主吊车筒体底座的结构特点,对易产生疲劳问题的关键部位进行优化设计。利用有限元软件对主吊车筒体结构的力学性能进行分析,通过热点应力法对疲劳损伤进行评定。分析结果表明,通过优化结构连接节点,改善局部的构造细节以降低热点应力水平,从而提高疲劳强度是一种有效的方法。     

轴力作用下X型焊接管节点热点应力的分布规律

海洋平台中的焊接管节点的疲劳寿命是由热点应力的大小和分布决定。热点应力的大小决定了管节点在疲劳失效前所能承受的循环荷载的次数,而热点应力的位置则决定了疲劳裂纹的萌生位置和扩展方式。文中采用有限元方法分析了承受轴向拉力作用的X型焊接管节点在焊缝周围的热点应力的分布情况,通过对112个X节点进行的模型分析,研究了节点几何参数对热点应力大小和分布规律的影响。     

等效热点应力法结合临界面法评估焊接接头多轴疲劳强度研究

基于焊缝本身引起的非线性分布应力自平衡的性质,在板厚方向应力峰值零点位置定义等效热点应力,结合基于临界面法的MWCM法建立评估复杂焊接接头多轴疲劳强度的方法。采用数值计算分析零点位置的变化规律,建立零点位置拟合方程。利用公开发表的试验数据以及现有的热点应力法有限元计算结果对等效热点应力法进行精度验证。结果表明,等效热点应力法和现有的热点应力法具有很好的一致性,能在一定程度上考虑厚度效应对疲劳强度的影响,可以评估多轴疲劳强度。     

Novel hot spot stress calculations for welded joints using 3D solid finite elements

This paper presents a novel numerical method through which less mesh-sensitive local stress calculations can be achieved based on the 3D solid finite element, adhering strictly to the original definition of hot spot stress. The traction stress, which is defined at 0.5t and 1.5t away from the weld toe, was calculated using either a force equivalent or work equivalent approach, both of which are based on the internal nodal forces on the imaginary cut planes. To confirm the validity of the proposed method, 5 typical welded joints widely used in ships and offshore structures were analyzed using 5 different solid element types and 4 different mesh sizes. Finally, the methodology was applied to the more complicated pontoon-column connection part of a semi-submersible RIG under a realistic wave load, and the performance of the proposed method was compared with the traditionally used surface stress extrapolation method.     

On stress concentration factors for tubular Y- and T-Joints in frame structures

This paper is written as a result of some years experience with fatigue analysis of offshore jacket structures where the connections are made as tubular joints. The hot spot stresses at the tubular joints in such analysis are normally derived based on parametric equations for stress concentration factors. These stress concentration factors are normally related to the axial force in the brace. It is observed that the hot spot stresses at the crown positions of the tubular joint in some cases are significantly affected by the local loading on the chord and the bending moment in the chord. In order to use the existing formulae in these cases some engineering effort is required to derive correct hot spot stress. This work can be avoided by using the nominal stress in the chord as the basis for calculating the hot spot stress at the crown position instead of using the axial force in the brace as basis for the analysis. This also extends the validity of the equations for stress concentration factors for T- and Y- joints in design standards. The proposed modification makes it also simpler to include the effect of joint flexibility in a proper way. The basis for a proposed revision of the equations for stress concentration factors for these joints is presented in this paper. It is considered that this modification leads to minor changes of the computer code, but that it will save analysis work for engineers and reduce the possibility of calculating incorrect fatigue lives in tubular frame structures.     

船舶折角型节点的疲劳裂纹扩展计算

文章以船舶折角型节点为研究对象,运用有限元软件WALCS和PATRAN分别预报某船的水动力响应和结构热点应力响应.为避免计算表面裂纹应力强度因子时需要在PATRAN有限元模型中疲劳热点区域采用体单元建模,文中提出了一种计算波浪载荷下船海结构物三维表面裂纹应力强度因子而无需在PATRAN中建立体模型的方法,并通过与广泛认可的经验公式对比验证其精度.将此方法应用于该船船舯底边舱折角处表面裂纹应力强度因子计算,计算并总结出波浪载荷下该类节点处表面裂纹应力强度因子的无量纲计算经验公式.应用一种基于谱分析构建结构疲劳载荷谱的方法,结合单一曲线模型对该节点进行裂纹扩展计算.计算结果表明:该船船舯底边舱折角疲劳寿命不满足设计要求,建议对节点进行改进.     

船舶舷侧细节结构的热点应力计算中的不确定性因素研究

疲劳是船舶结构一种重要的失效模式。在过去的十多年间，涌现出了一些不同的疲劳强度的评估方法，其中S－N曲线法在船级社中得到了广泛的应用。但是，仅就S－N曲线法中的热点应力法而言，不同的组织和个人所预报的疲劳寿命通常也存在很大差异，而计算所得的热点应力集中系数的不同是产生这些差异的一个重要影响因素。本文运用有限元比较研究的方法，对某船舶舷侧细节结构的热点应力计算中可能存在的不确定因素进行了综合分析。通过采用不同的单元类型，不同的建模方法以及不同的有限元软件ABAQUS和ANSYS，得出了相关结论，为正确计算此类船舶结构细节的热点应力提供了指导。     

FPSO船典型节点疲劳强度分析

本文对浮式生产储油轮(FPSO)肋骨框架局部结构的节点进行了疲劳强度分析和计算。使用通用的有限元分析软件——ANSYS，对一个典型的局部结构节点建立了计算模型并进行参数分析。该局部结构为舷侧纵桁与腹板的连接节点。大量的调查实践证明，此处是疲劳损伤的高发区。文中选取了挪威科技大学建立的一个试验模型作为参考依据，采用美国船级社的计算规范对局部结构的两个热点应力区的疲劳强度进行了估算，并将计算结果与试验模型的结果进行了比较。结果表明：合理的补板以及腹板开口的尺寸可以提高该局部结构的疲劳寿命；疲劳损伤的定义需要根据疲劳失效后果加以确定从而给出基于风险的最佳检测和维修计划。     

Adaptive approximation in multi-objective optimization for full stochastic fatigue design problem

As the size of ship has grown rapidly, the importance of exact fatigue strength assessment has been recognized more and more. High concern about fatigue crack often raises target fatigue life to two or three times of ship lifetime. This leads to the use of very thick plates to reduce dynamic stress range or the application of weld toe grinding to reduce stress concentration or removing weld defects. However, such measures can cause some troubles in fabrication process. As a fatigue strength assessment procedure, full stochastic fatigue analysis based on wave loads analysis has been recommended due to its high accuracy and straightforward approach. However, its huge computing time hinders a ship designer from making iterative explorations for a better design to minimize the use of aforementioned measures.This paper proposes an efficient approach to optimize plate thicknesses around hot spots and the applications of weld toe grinding with meeting the required target fatigue life based on the full stochastic fatigue assessment. Two conflicting objectives are taken into consideration; to minimize steel weight and to minimize total weld toe grinding length. Whether to employ weld toe grinding or not for a hot spot can be seen as a selection variable. In order to treat such selection variables along with continuous variables in the multi-objective optimization, Multi-objective Genetic Algorithm (MOGA) is introduced. This paper also employs adaptive approximation framework to resolve the computational burden of the full stochastic fatigue analysis in the optimization. The strategy to refit approximations iteratively can minimize the required number of analysis. A convergence criterion of the adaptive approximation framework is newly proposed considering the feature of discrete objective function attributed to the introduction of selection variables. One of the objective functions, toe grinding length, is purely depending on how many hot spots toe grindings are applied to. The proposed approach is applied to a liquid dome opening problem of LNG carrier, which is known as one of the most difficult parts to satisfy required fatigue strength due to the stress concentration caused by its large opening and weld attachments on upper deck.