船舶双层底结构与台形礁石碰撞能量及搁浅阻力分析

提出一套基于双层底油轮搁浅于台型礁石场景下的结构损伤变形非线性机理模型和解析计算方法,并通过数值仿真计算验证该机理模型和解析方法的准确性。在整合双层底板材变形解析计算模型和加强筋变形解析计算模型的基础上,提出的结构变形机理模型能够同时考虑船底板材和加强筋的变形模态。以双层底油轮的一个舱段作为研究对象,使用数值仿真软件LS_DYNA在较大的撞深和礁石倾角变化范围内进行仿真计算,并进行比较。研究结果表明该解析计算模型的总变形能和平均水平搁浅阻力与数值结果吻合得较好,从而验证了机理模型和解析计算方法的可靠性。研究成果可以方便地应用到双层底船舶搁浅场景的结构性能快速预报,以及船舶耐撞性能结构设计中。     

船舶搁浅于台型礁石场景极限强度解析预报方法

针对双层底油轮搁浅于台型礁石的事故场景,通过对船底构件结构损伤机理的分析,提出一套结合船底结构损伤程度推算方法和Smith方法,评估损伤后船体剩余极限强度的解析计算预报方法。研究中应用数值仿真技术,模拟了船舶搁浅过程中的结构损伤及搁浅后船体极限承载过程,并与解析预报方法的结果进行了对比。结果表明,文中提出的对搁浅损伤后船舶剩余强度的解析预报方法准确性较好,对船舶双层底耐撞性结构设计和安全性评估都有一定的指导意义。     

固支圆板耐撞性能分析的近似解析方法

提出了一种评估板结构耐撞性能的近似解析方法.从理论上分析了固支圆板在刚性圆球撞头作用下的力学过程,采用对数曲面模拟圆板变形的局部挠曲面,忽略板弯曲效应的影响,导出了能量吸收和板变形之间的近似解析关系式.实例计算结果与有限元计算结果的比较表明,该简化解析方法能够对板结构的耐撞性做出合理的预报.     

帽型加筋板在碰撞冲击载荷作用下的损伤变形机理

以帽型加筋板结构为研究对象,设计开展落锤碰撞冲击试验,分析其损伤变形情况.在此基础上,分析确定帽型加筋板结构在碰撞冲击载荷作用下的变形模式,进而推导得到瞬时结构抗力的解析计算公式,并与试验结果比较验证解析计算方法的合理性.该解析方法对帽型加筋板的碰撞性能设计及评估具有指导意义.     

双壳船体结构在楔形物撞击下的损伤特性试验及数值仿真分析

[目的]船舶碰撞的后果往往是灾难性的,尤其是由双壳油轮碰撞或搁浅事故所造成的海洋生态灾难,多年都难以恢复。为评估双壳结构的耐撞性能,开展双壳船体结构在楔形物撞击下的损伤特性试验与仿真研究。[方法]首先,针对双壳体结构模型开展准静态碰撞实验;然后,利用有限元软件LS-DYNA对双壳体结构试验模型进行数值仿真。[结果]结果显示:试验和数值仿真结果在撞击载荷响应与变形破坏模式上吻合较好;双壳体结构内、外壳板的变形及破坏模式区别较大;内、外壳板之间的横隔板产生的塑性变形会延迟外壳板的断裂。[结论]所做研究可用于船体舷侧结构或船底结构在遭受碰撞或搁浅时的损伤性能评估。     

船舶碰撞仿真分析中的单元尺寸与失效应变关系研究

随着船舶向大型化发展势头迅猛,船舶碰撞所带来的灾难性后果也显著增大.为评估船舶结构的耐撞能力,国内外研究人员分别从试验和数值模拟2个方面开展研究工作.针对船舶碰撞场景的仿真模拟中,经常采用常应变失效准则来定义单元是否失效.然而失效应变取值强烈依赖于单元尺寸大小,因此,开展失效应变与单元网格尺寸关系研究对船舶结构的耐撞性能准确评估意义重大.本文通过对光板及加筋板的耐撞性能的试验研究,并应用非线性有限元软件LS-DYNA对试验结果进行仿真模拟,探讨了光板及加筋板的单元尺寸和失效应变之间的关系.结果表明:光板和加筋板的单元尺寸与失效应变关系曲线明显不同,因此采用常应变失效准则时应区别对待,不能混用.研究结论对船舶结构碰撞有限元仿真具有一定的指导意义.     

船舶抗碰撞性能研究

船舶在海上航行时,存在与其他船舶发生主动或被动碰撞的风险。为准确评估船舶的耐撞性能,以某船为例,考虑多种计算工况,对目标船的耐撞性能进行动态响应计算,获得机舱及艏部区域的结构损伤、应力、能量吸收等动态结构响应,并计算获得被撞船达到临界状态时的极限撞击速度。研究成果可为船舶的防撞结构设计提供参考。     

新型舷侧防护结构耐撞性能研究

采用数值仿真的方法对船舶碰撞动力学过程进行仿真再现。系列仿真计算结果表明,传统的舷侧结构在耐撞性能方面存在很多缺陷,针对大型VLCC船舶设计帽形、菱形、半圆管形三种新型纵桁形式的双层舷侧结构模型,并从碰撞载荷、结构损伤变形、能量的吸收与转换等角度对此三种新型舷侧结构与传统舷侧结构的耐撞性能进行对比分析,结果表明半圆管纵桁形式的双层舷侧结构模型具有最好的耐撞性。     

船舶碰撞仿真分析中的单元尺寸与失效应变关系研究

随着船舶向大型化发展势头迅猛,船舶碰撞所带来的灾难性后果也显著增大。为评估船舶结构的耐撞能力,国内外研究人员分别从试验和数值模拟2个方面开展研究工作。针对船舶碰撞场景的仿真模拟中,经常采用常应变失效准则来定义单元是否失效。然而失效应变取值强烈依赖于单元尺寸大小,因此,开展失效应变与单元网格尺寸关系研究对船舶结构的耐撞性能准确评估意义重大。本文通过对光板及加筋板的耐撞性能的试验研究,并应用非线性有限元软件LS-DYNA对试验结果进行仿真模拟,探讨了光板及加筋板的单元尺寸和失效应变之间的关系。结果表明:光板和加筋板的单元尺寸与失效应变关系曲线明显不同,因此采用常应变失效准则时应区别对待,不能混用。研究结论对船舶结构碰撞有限元仿真具有一定的指导意义。     

船舶加筋板结构耐撞性能分析

提出计及摩擦力影响后船舶舷侧加筋板耐撞性能分析的一种简化分析方法,详细讨论了球鼻艏撞击作用下舷侧加筋板的渐进破坏过程,给出了相应的撞击力-撞深曲线和吸收能量-撞深曲线。通过与已有试验结果的比较表明,该简化分析方法能对船舶舷侧加筋板结构的耐撞性能做出合理预报,从而可用于设计阶段评估船体舷侧结构的耐撞性能。     

Simplified analytical method for evaluating web girder crushing during ship collision and grounding

The paper presents a simplified analytical method to examine the crushing resistance of web girders subjected to local static or dynamic in-plane loads. A new theoretical model, inspired by existing simplified approaches, is developed to describe the progressive plastic deformation behaviour of web girders. It is of considerable practical importance to estimate the extent of structural deformation within ship web girders during collision and grounding accidents. In this paper, new formulae to evaluate this crushing force are proposed on the basis of a new folding deformation mode. The folding deformation of web girders is divided into two parts, plastic deformation and elastic buckling zones, which are not taken into account for in the existing models. Thus, the proposed formulae can well express the crushing deformation behaviour of the first and subsequent folds. They are validated with experimental results of web girder found in literature and actual numerical simulations performed by the explicit LS-DYNA finite element solver. The elastic buckling zone, which absorbs almost zero energy, is captured and confirmed by the numerical results. In addition, the analytical method derives expressions to estimate the average strain rate of the web girders during the impact process and evaluates the material strain rate sensitivity with the Cowper-Symonds constitutive model. These adopted formulae, validated with an existing drop weight impact test, can well capture the dynamic effect of web girders.     

An analytical method for predicting the ship side structure response in raked bow collisions

As an increasing number of ships continue to sail in heavy traffic lanes, the possibility of collision between ships has become progressively higher. Therefore, it is of great importance to rapidly and accurately analyse the response and consequences of a ship's side structure subjected to large impact loads, such as collisions from supply vessels or merchant vessels. As the raked bow is a common design that has a high possibility of impacting a ship side structure, this study proposes an analytical method based on plastic mechanism equations for the rapid prediction of the response of a ship's side structure subjected to raked bow collisions. The new method includes deformation mechanisms of the side shell plating and the stiffeners attached. The deformation mechanisms of deck plating, longitudinal girders and transverse frames are also analysed. The resistance and energy dissipation of the side structure are obtained from individual components and then integrated to assess the complete crashworthiness of the side structure of the struck ship. The analytical prediction method is verified by numerical simulation. Three typical collision scenarios are defined in the numerical simulation using the code LS_DYNA, and the results obtained by the proposed analytical method and those of the numerical simulation are compared. The results correspond well, suggesting that the proposed analytical method can improve ship crashworthiness during the design phase.     

Experimental numerical and analytical analysis of the penetration of a scaled double-hull tanker side structure

The paper presents experimental, numerical and analytical analyses of a small-scale double-hull structure quasi-statically punched at the mid-span by a rigid flat edge indenter, to examine its energy-absorbing mechanism and fracture. The present study aims to further validate the numerical analysis procedure and the analytical method of individual stiffened panels and web girders against the experiment of the double-hull structure. The specimen, scaled from a tanker's double side structure, includes three spans between the web frames and two spans between the stringers. The paper provides practical information to estimate the extent of structural damage within ship sides during collision accidents. The experimentally obtained force-displacement response and deformation shape show a good agreement with the simulations performed by the explicit LS-DYNA finite element solver. The analysis of the double-hull structure demonstrates the accuracy of the procedure for identifying standard inputs used in numerical codes, in particular the definition of material plastic hardening and the calibration of the critical failure strain by tensile test simulation. The experimental and numerical results are used to validate the analytical method proposed in previous investigations at the plastic deformation stage and a revised semi-analytical method is proposed in the present study for the large penetration stage.     

Plastic mechanism analysis of structural performances for stiffeners on bottom longitudinal web girders during a shoal grounding accident

A theoretical model is introduced in this paper for structural performance of stiffeners on double-bottom longitudinal girders in a shoal grounding accident. Major emphasis is placed on establishing the characteristic deformation mechanism of stiffeners and identifying major energy dissipation patterns. Numerical simulations using the LS-DYNA nonlinear finite-element program were carried out to examine thoroughly the progressive deformation process during sliding deformation. Stiffener deformations were observed to fall into two categories: stiffeners fully contacted with the indenter, and stiffeners subjected to indirect deformation due to energy transfer from attached girders. Grounding performance of stiffeners is substantially influenced by that of the attached plating, and therefore a review of the existing deformation models of longitudinal girders (i.e. Simonsen 1997, Midtun 2006 and Hong 2008) was included. Hong's model of bottom girders was found not capable of representing the effects of stiffeners, and a new model of girders was thus developed. Based on observation of the numerical deformation process and the new analytical girder model, a kinematically admissible model of stiffeners on bottom longitudinal girders was built. Using the methods of plastic mechanism analysis, simplified analytical expressions for energy dissipation by girder-attached stiffeners, both fully contacted and noncontacted, were formulated, and equations for grounding resistance were subsequently obtained. The theoretical expressions agree favorably with results from nonlinear finite-element simulations and capture two significant characteristics of the problem: that energy varies little with indentation for stiffeners that fully contacting the indenter, and that energy is independent of slope angle for indirectly deformed stiffeners. The proposed theoretical model helps to predict analytically shoal grounding performance of stiffeners on longitudinal girders with reasonable accuracy.     

Deformation process of web girders in small-scale tanker double hull structures subjected to lateral impact

Experimental drop weight impact tests are performed to examine the dynamic response of web girders in a one-tenth scaled tanker double hull structure struck laterally by a knife edge indenter. The small stiffeners of the full-scale prototype are smeared in the small-scale specimen by increasing the thicknesses of the corresponding plates. The plastic response is evaluated at two impact velocities and the impact location is chosen between two web frames to assure damage to the outer shell plating and the stringers. The laboratory results are compared with numerical simulations performed by the LS-DYNA finite element solver. In the simulations, the strain hardening of the material is defined using experimental data of quasi-static tension tests and the strain rate sensitivity is evaluated using standard coefficients of the Cowper–Symonds constitutive model. The experimental permanent deflection and shape of the deformation show a good agreement with the collision simulations. It is found that the crushing resistance of the specimens is determined by the deformation mechanism of the stringers. Thus, the deformation process is described and compared with theoretical deformation modes for web girders subjected to large in-plane quasi-static loads. Additionally, the influence of the stiffeners on the shape of the deformation of the stringers is illustrated through simulations of stiffened structural elements.     

基于正交设计与 BP -GA 算法的船体结构耐撞性能优化设计

船体结构耐撞性优化设计的主要目的是在船舶碰撞研究的基础上对结构进行优化设计,提高船体结构的耐撞性能。基于正交试验设计、BP神经网络和遗传算法,形成了船体结构耐撞性能优化设计方法。提出了一种耐撞性综合指标,并以此指标作为优化的目标函数,以结构质量为约束条件,利用MSC/Dytran有限元软件对船舶碰撞进行数值仿真,完成对某船舷侧结构进行耐撞性优化设计,结果表明优化过后结构耐撞性能有较大提高,这为结构耐撞性能优化设计提供了一种新的思路和方法。     

内河双壳油船舷侧结构耐撞性分析

提出了内河双壳油船舷侧结构耐撞性能的简化分析方法,详细讨论了球鼻艏撞击作用下内河双壳油船舷侧结构的总体破坏模式及其渐进破坏过程.在考虑舷侧外壳板发生断裂破坏后的剩余抗撞能力的基础上,给出了双壳舷侧结构的撞击力―撞深曲线和吸收能量-撞深曲线,并与有限元仿真分析结果进行了比较.简化分析方法得到的结果与有限元分析基本上是一致的,这表明该方法能对内河双壳油船结构的耐撞性能做出合理预报,可用于这类油船耐撞性能的评估.     

船舶舷侧结构耐撞性分析

为研究船舶舷侧结构的碰撞损伤过程,采用非线性动态响应分析方法,使用ANASYS/LS-DYNA显式动力分析软件,对船艏和船舷垂直碰撞过程进行数值仿真,获得了碰撞力、能量吸收和结构损伤变形的时序结果。为了分析船舶舷侧结构耐撞性能,本文对比了常见油船、新型Y型和X型舷侧结构的仿真过程,结果表明新型舷侧结构在整体的耐撞性能上优于传统的舷侧结构,承载构件的不同也会对结构的耐撞性产生很大的差异。     

Strength of ship plates under combined loading

Strength of ship plates plays a significant role in the ultimate strength analysis of ship structures. In recent years several authors have proposed simplified analytical methods to calculate the ultimate strength of unstiffened plates. The majority of these investigations deal with plates subjected to longitudinal compression only. For real ship structural plating, the most general loading case is a combination of longitudinal stress, transverse stress, shear stress and lateral pressure. In this paper, the simplified analytical method is generalized to deal with such combined load cases. The obtained results indicate that the simplified analytical method is able to determine the ultimate strength of unstiffened plates with imperfections in the form of welding-induced residual stresses and geometric deflections subjected to combined loads. Comparisons with experimental results show that the procedure has sufficient accuracy for practical applications in design.     

Research on the dynamic buckling of a typical deck grillage structure subjected to in-plane impact Load

The dynamic buckling of the main deck grillage would result in the total collapse of the ship hull subjected to a far-filed underwater explosion. This dynamic buckling is mainly due to the dynamic moment of the ship hull when the ship hull experiences a sudden movement under impact load from the explosion. In order to investigate the ultimate strength of a typical deck grillage under quasi-static and dynamic in-plane compressive load, a structure model, in which the real constrained condition of the deck grillage was taken into consideration, was designed and manufactured. The quasi-static ultimate strength and damage mode of the deck grillage under in-plane compressive load was experimentally investigated. The Finite Element Method (FEM) was employed to predict the ultimate strength of the deck grillage subjected to quasi-static in-plane compressive load, and was validated by comparing the results from experimental tests and numerical simulations. In addition, the numerical simulations of dynamic buckling of the same model under in-plane impact load was performed, in which the influences of the load amplitude and the frequency of dynamic impact load, as well as the initial stress and deflection induced by wave load on the ultimate strength and failure mode were investigated. The results show that the dynamic buckling mode is quite different from the failure mode of the structure subjected to quasi-static in-plane compressive load. The displacements of deck edge in the vertical direction and the axial displacements are getting larger with the decrease of impact frequency. Besides, it is found that the dynamic buckling strength roughly linearly decreased with the increase of initial proportion of the static ultimate strength P₀. The conclusions drawn from the researches of this paper would help better designing of the ship structure under impact loads.