Plate tearing and bottom damage in ship grounding

A theoretical method for plate tearing by a rigid wedge is developed in this paper. The studied model is an idealization of ship-grounding and collision damage. The analysis model postulates that the plate curls up into two curved surfaces behind the wedge tip and that the plate material ahead of the wedge is tensioned and ruptured due to the direct pushing. Based on a parametric study, a semi-empirical formula is proposed for determining grounding force in the event of a ship running onto rocks in a high-energy grounding. The bottom strengths of single hull structures and double hull structures in ship-grounding incidents are compared. Finally, simple formulae for determining damage resistance and the extent of damage in ship grounding, expressed in terms of the ship principal particulars, are developed.     

Fatigue life prediction of welded stiffened 350WT steel plates

The propagation of fatigue cracks under constant amplitude cyclic loading was studied in welded stiffened steel plates. The residual stresses in the stiffened plates were measured using the neutron diffraction strain-scanning technique. A finite element model of the stiffened plate was constructed to simulate the residual stresses by an uncoupled thermal and thermo-mechanical analysis. Both the finite element model and the neutron diffraction measurements indicated that in general the residual stresses were tensile near the welded stiffeners and compressive between the stiffeners and ahead of the starter notch tip. Fatigue testing indicated that the fatigue crack growth rates of the stiffened plates were in general lower than that of a corresponding unstiffened plate, especially near the notch tip where compressive residual stresses existed. Both the finite element method and Green's function predicted the fatigue crack growth rates with reasonable accuracy.     

船舶构件共线多裂纹应力强度因子研究

船舶构件中除了单个形式存在的裂纹外,还有多个裂纹同时存在的情况。多裂纹之间的相互干扰作用使得问题远比单裂纹复杂。本文采用比较简单直观的组合法对平板表面多裂纹的应力强度进行了求解并与FRANC 3D求解的结果比较,两者结果较接近,由此可见组合法可以适应工程要求。因此,在平板表面多裂纹问题求解的基础上,推出了T型构件焊趾处表面多裂纹应力强度因子求解的表达式,从而使T型构件多裂纹复杂问题转化为较简单的平板多裂纹问题,可以为工程计算方法提供参考。     

含裂纹有限加筋板应力强度因子的求解

基于裂纹问题的复应力函数方法,对含裂纹有限加筋板中裂纹表面作用分布力时的应力强度因子进行了分析求解.对有限加筋板离散化,不考虑弯曲的影响,将筋条对裂纹板的作用力转化为作用在板边界的切向力,通过对受边界切向力作用的含裂纹有限板问题的求解,从而求解了含裂纹有限加筋板的问题.     

On the fluid-structure response of elastic-plastic ship sides subjected to impact loads

This paper presents a simplified numerical model capable of analysing the interaction between the structural dynamic response of elastic-plastic struck plate wall of a fluid tank subjected to wedge impact and the resulting fluid motion. The Variational Finite Difference Method (VFDM) is applied to analyse the structural dynamics of the struck plate and 2-D linear potential flow theory is used to study the resulting fluid motion and its effects on the structural dynamics of the struck plate. Experiments of a wedge indenter impacting with both empty and 90% filled tanks are carried out to study the structural deformation of the struck plate. The accuracy of the developed numerical model is validated with published results and experimental results, and good agreement is achieved. Through the comparison of the impact behaviour of empty and partially filled water tank, it is found that the resulting water motion helps to reduce the structural deformation of the struck plate since part of the impact energy is dissipated by the resulting water motion. Parametric studies are performed to investigate the effect of impact velocity and water level on the structural dynamics of the struck plate of a partially filled water tank. A case study is also conducted to demonstrate the potential application of the proposed method in analysing ship-ice impact problems.     

考虑塑性损伤的船体裂纹板低周疲劳裂纹扩展行为研究

船舶结构的扩展断裂失效往往是低周疲劳破坏和累积递增塑性破坏耦合作用的结果,疲劳裂纹的扩展就是裂纹尖端前缘材料刚度不断降低延展性不断耗失而逐渐分离的结果.基于弹塑性断裂力学理论,文章提出了考虑累积塑性损伤的低周疲劳裂纹扩展速率预测模型.通过低周疲劳裂纹扩展试验拟合出模型相关材料参数并验证预测模型的合理性.通过系列有限元计算对平均应力及应力幅值的影响因素进行了数值分析.该模型的计算结果与已有实验结果基本吻合;对合理预估船体裂纹板的常幅低周疲劳裂纹扩展寿命有重要意义.     

离散小波方法应用于梁和平板的破损侦测之研究

文章旨在利用小波转换方法来侦测一个铝合金的梁与板的裂缝.研究中将以一维离散小波转换和二维离散小波转换为基础来检测含双重缺陷之梁与板,并经由数值模拟分析以及实验共同进行并比较其结果.测试结果显示,离散小波分析方法可以有效地找出结构中多个缺陷位置,并可应用在其他的复杂结构上.     

Ship scheduling and container shipment planning for liners in short-term operations

Good short-term ship scheduling and container shipment planning are very important for liner operations; however, in Taiwan, most such carriers currently utilize a trial-and-error process. In this study, we employ network flow techniques to construct a model for such activities. A solution algorithm, based on Lagrangian relaxation, a subgradient method, and a heuristic for the upper-bound solution, is developed to solve the model. To demonstrate and to test how well the model and the solution algorithm apply in the real world, we performed a case study using operating data from a major Taiwanese marine shipping company. The test results show that the model and the solution algorithm could be useful references for ship scheduling and container shipment planning.     

低周疲劳下船体缺口板的裂纹尖端张口位移理论及试验研究

文章旨在研究大范围屈服下船体缺口板的裂纹尖端张口位移.基于弹塑性断裂力学理论,建立了循环载荷下船体缺口板CTOD理论模型.进而,对于船用高强度钢AH36进行低周疲劳试验研究,对于影响裂纹尖端张口位移的参数,如应力比、应力幅和平均应力进行了深入探讨.     

柴油机曲轴断裂原因新析

针对柴油机曲轴断裂的原因,提出了一种新见解--"油楔力"的作用是加速曲轴断裂的一个主要原因.指出"初始裂纹"是曲轴断裂的危险信号;交替变形产生的交变负荷是"油楔力"能量的来源;"油楔力"的作用使裂纹加速扩展,从而导致曲轴载荷截面尺寸不足而发生突然折断,使曲轴断裂发生在材料疲劳破坏之前.消除初始裂纹是曲轴安全运转的保证.     

船舶三维数控弯板机成形回弹控制的逐步逼近弯曲法研究

文章依据板材成形理论与实验规律,提出了船板冷压成形的逐步逼近弯曲法,较好地解决了多压头船舶三维数控弯板机板材成形的回弹问题。船板塑性成形加工过程中,采用在线实时测取回弹量来调整可重构模具曲面,实现了船板弯曲回弹问题的实时在线解决。一般逼近2～3次,即可满足加工精度要求,简单而有效地解决了三维曲面船板塑性成形的复杂回弹难题。     

Multi-scale modeling of fatigue crack propagation applied to random sequence of clustered loading

Fatigue crack propagation in marine structures is obviously governed by mechanics of the considerably different four levels of multi-scale problems. Problems of structural response to environmental loads have length scale of several hundred meters, whereas possible detectable size of cracks from initial defects in a weld is of the order of millimeters. Once a fatigue crack initiates, crack tip plasticity is of the order of several grain sizes, while the resulting fatigue crack growth in each load cycle is of the order of nanometers. In our previous work, the first author and their associates have developed the so-called CP-System, which can treat the first two multi-level problems as an integrated system. Furthermore, we have incorporated the third level of mechanics by using the stress intensity range corresponding to the repeated tensile plastic deformation ahead of the crack tip. In the present paper, we shall discuss a more rational integral equation-based formulation in order to integrate the third and fourth levels of micro-mechanics to the first two levels of continuum mechanics.The method is then applied to fatigue crack propagation under the effects of random sequence of clustered loading. As an example of the random sequence of clustered load, we shall use the so-called “storm model”. In the crack propagation simulation, we have to take into account of the plastic wake on the crack surfaces, whose thicknesses are influenced by the material parameters involved in the crack growth model. These parameters are first identified by the fatigue tests under combined constant and random loading using a CT specimen. Then, fatigue crack growth is investigated by numerical simulation and fatigue tests for various random sequences of clustered loading. The experimental and numerical results agree quite well with each other, and fatigue crack propagation is found to be considerably retarded under random sequence loading, so that the conventional equivalent stress approach may provide rather conservative results to the real seaway loading.     

二维离散小波转换应用于加筋板格的损伤检测

文章主要是探讨利用小波转换来探测铝合金加筋板格的多重裂缝,在实验中利用小波包节点范数(Wavelet Packet Node Norm)来建立带有铝合金加筋板格的第一模态振型值,并且利用二维离散小波分析来探测裂缝之所在位置.在数值分析方面,利用有限元法分析软件(ANSYS),进行平板之模态振型分析,并以二维离散小波分析探测裂缝位置,证明此方法之可行性.从数值分析与实验两者之结果均证实所提出之方法对于探测铝合金加筋板格的单一或多个破坏程度之缺陷位置,均有较好的检测能力.     

弯曲载荷作用下含切口T型节点表面裂纹应力强度因子计算

含裂纹修理切口T型节点的切口底部易于产生疲劳损伤,因而需要对该处新萌生的表面裂纹的疲劳寿命进行估算,以评判下次检修的时间.本文采用基于线弹性断裂力学的有限元方法,对弯曲载荷作用下于修理切口底部产生的表面裂纹最深处的应力强度因子进行了计算.计算结果表明,对于同一类型节点,在相同裂纹深度下,裂纹底部的应力强度因子随着a/c的减小而增大.进而,根据修理切口的不同形状,给出了一组具有一定工程适用范围的回归公式.根据基于线弹性有限元计算结果得出的经验公式,对含修理切口T型节点切口底部萌生的表面裂纹扩展规律进行分析,得出了不同裂纹深长比下,裂纹深长增量比随裂纹深度的变化曲线.在数值计算的基础上,采用船用普通钢制备的试件,对切口底部萌生的表面裂纹进行试验研究,描述了在交变弯曲载荷作用下裂纹形貌的变化规律.试验结果表明,试验数据点与计算曲线相比,具有较高的一致性,验证了根据有限元计算结果提出的拟合公式的精度.     

弹塑性裂纹前端部分加强板的止裂效果分析

通过建立Dugdale模型,对裂纹前端部分加强的含裂纹板弹塑性情况下的韧性断裂问题进行了研究.实例计算并分析了加强板条的位置、相对刚度等参数对结构断裂参数的影响,亦对加强板条的止裂作用进行了分析.计算结果表明,裂纹前端布置加强板条能有效地降低裂纹尖端的开口位移,阻止裂纹的扩展,其止裂作用受加强板条的位置、结构参数及加强板条与含裂纹板的材料参数等诸多因素的影响.     

船用厚板高强度钢焊接性及其焊接裂纹的形成和预防

随着各类大型化、超大型化船舶的诞生,使得厚板高强度钢的使用日益广泛,但随之而来的是此类高强度钢易产生焊接裂纹的问题。文章列举了国内外船用厚板高强度钢焊接的工艺特点,分析了焊接裂纹的起因,并就预防措施进行了初步探讨。对从事船体结构的研究人员有一定的帮助。     

舰船RCS整形设计中的电磁分析

减小舰船雷达散射截面（RCS）需要对舰船进行整形设计。本文从分析舰船典型结构——金属板的RCS与雷达波的入射角、频率及几何尺寸的关系出发,采用物理光学法导出了金属平板RCS与倾斜角的理论公式,确定了在单频点或多频点对平板进行雷达隐身设计的最佳倾斜角,通过具体实例说明了在舰船整形设计时,采用本文给出的计算公式可以对舰船的RCS和舱室容积进行折衷设计。结论对舰船雷达隐身设计具有指导意义。     

A study of fatigue crack propagation at a web stiffener on a longitudinal stiffener

Predicting fatigue crack growth after its detection during in-service inspection is necessary to prevent a loss of serviceability, such as the oil and/or water tightness of critical compartments. This paper focuses on the most typical fatigue cracks that start at the weld joint between a flat bar stiffener on a transverse web frame and the flange of a longitudinal stiffener on a bottom plate or inner bottom plate. An experiment is carried out to observe the fatigue crack propagation for two kinds of flat bars at the abovementioned connection. The experimental results, especially the surface crack growth on the flange (which dominates during the total fatigue life of the longitudinal stiffener), are compared with crack growth curves predicted using a few existing formulas. Based on the comparative study, a formula that shows the best agreement with the experiment results is selected. Weld toe magnification factors for the web stiffener are computed from the crack propagation rates measured in the experiment, and two equations for the magnification factors versus crack depth are developed for two types of web stiffeners. The selected existing formula and the proposed equations are applied to two connections at the inner bottom and side longitudinal bulkhead of an LNG carrier. The equivalent stress approach based on a long-term distribution is employed to avoid the complexity involved in dealing with the actual stress history. Using this prediction, the remaining service life until an oil or water leakage occurs at a tank boundary can be estimated when a fatigue crack at the connection is detected.     

基于改进的Logvinovich法对带横摇运动非对称楔形体入水砰击力的计算(英文)

The water entry problem of an asymmetric wedge with roll motion was analyzed by the method of a modified Logvinovich model (MLM). The MLM is a kind of analytical model based on the Wagner method, which linearizes the free surface condition and body boundary condition. The difference is that the MLM applies a nonlinear Bernoulli equation to obtain pressure distribution, which has been proven to be helpful to enhance the accuracy of hydrodynamic loads. The Wagner condition in this paper was generalized to solve the problem of the water entry of a wedge body with rotational velocity. The comparison of wet width between the MLM and a fully nonlinear numerical approach was given, and they agree well with each other. The effect of angular velocity on the hydrodynamic loads of a wedge body was investigated.     

一种螺旋桨模型噪声的试验研究

螺旋桨模型试验中,有时噪声谱中出现窄带噪声峰,有人认为这个峰是梢涡空泡噪声,是“看不见的梢涡空泡”引起的,但这种解释未经实验证明。本文用实验证实这种窄带噪声峰与桨叶梢部流动有关,无论梢涡空泡可见与否,都可能出现。