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.     

碰撞/搁浅事故中船体强桁材结构损伤机理解析预报方法研究

随着航运业的快速发展,海上航行的船舶越来越多.尽管人们做了许多努力避免海上意外事故的发生,但海难事故依然不可避免.为了降低上述事故造成的损失,需要在设计阶段快速并准确地预报船舶的结构耐撞性.本文以强桁材结构为研究对象,通过开展准静态冲压试验及相应的数值仿真,分析强桁材结构在面内冲压载荷作用下的变形机理,并基于试验与仿真所得到的结构变形特点,提出强桁材面内受压时的变形模式.以此为基础,运用塑性力学理论,推导出结构变形能、瞬时结构变形抗力及平均结构变形抗力的解析预报公式,并将计算结果与试验结果进行比较验证.研究得到的结构面内受压变形能和抗力解析计算公式,可以快速评估事故载荷下结构的响应情况,包括结构变形阻力及能量耗散,具有使用方便,计算速度快,计算结果相对可靠的优点,对船体耐撞结构设计及抗撞性能评估具有一定的指导意义.     

Simplified method for quasi-static collision assessment of a damaged tanker side panel

The paper presents a simplified analytical method to examine the energy absorbing mechanisms of intact and damaged small-scale stiffened plate specimens, quasi-statically punched at the mid-span by a rigid wedge indenter. The specimens scaled from a tanker side panel are limited by one span between web frames and stringers. The influence of the initial damage on the impact response is based on the plastic behaviour of an intact specimen. The initial damage is provoked at one-quarter from the support by the same indenter that, afterwards, punches the specimen at the mid-span. In practice, initial imperfections of this type could be due to minor incidents during ship service operation, such as collision of ships with floating objects. To validate the proposed simplified method, experiments and numerical simulations are conducted. The experimentally obtained force-displacement responses and shapes of the deformation show good agreement with the simulations performed by the explicit LS-DYNA finite element solver. The analytical method derives expressions to estimate the energy dissipated by the intact and the damaged specimens based on the plastic deformation mechanisms, assuming that both the plate and stiffener structural components absorb the incident energy through the rotation of the plastic hinges at the point of contact and at the supports and the membrane tension over the plastically deforming region between the loading and the supports.     

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.     

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.     

自升式平台管结构碰撞损伤机理研究

文章以自升式海洋平台桩腿直管结构为研究对象,采用简化解析法和有限元数值仿真法对其在侧向冲击载荷作用下的变形机理进行了研究。文中首先基于前期试验,对管结构的变形模式进行了简化,并利用塑性力学理论求解出管结构的碰撞力与撞深解析表达式。然后利用有限元软件ABAQUS,对管结构的动态响应进行了数值模拟,将得到的碰撞力与撞深曲线与解析结果对比,以此验证文中解析方法的准确性。该文的研究成果可以为大型平台结构碰撞性能研究提供技术支撑。     

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.     

Estimation of the response of a deeply immersed cylinder to the shock wave generated by an underwater explosion

The work presented in this paper is focused on the development of a simplified method to study the structural response of a deeply immersed cylinder subjected to the primary shock wave generated by an underwater explosion. The proposed analytical model is based on the string-on-foundation method initially developed by Hoo Fatt and Wierzbicki, who converted the two dimensional boundary value problem of a cylindrical shell to an equivalent one-dimensional problem of a plastic string on a plastic foundation. This method has already been extended by the authors to study the shock wave response of an unstiffened cylinder immersed in shallow water. The present work focuses on deep-immersed cylinders subjected to both high hydrostatic pressure and explosion shock wave. The elastic deformation energy of the cylinder under hydrostatic pressure is first calculated and used to determine the initial conditions of the dynamic problem. Cylinder deflection and plastic deformation energy are then calculated for various immersion depths. When confronted to numerical results, the proposed model appears to underestimate the increase of deflection and absorbed energy with the immersion depth. A thorough analysis of the results post-processed from Ls-Dyna/USA finite element simulations highlights a new mechanism which is due to the action of hydrostatic pressure that continues to push inward the immersed cylinder. In order to improve the analytical model, a correction factor on the hydrostatic pressure is introduced but it is finally concluded that a new mechanism dedicated to the late action of the hydrostatic pressure still needs to be developed.     

Analysis of ship–ship collision damage accounting for bow and side deformation interaction

This paper presents a procedure to analyse ship collisions using a simplified analytical method by taking into account the interaction between the deformation on the striking and the struck ships. Numerical simulations using the finite element software LS-DYNA are conducted to produce virtual experimental data for several ship collision scenarios. The numerical results are used to validate the method. The contributions to the total resistance from all structural components of the collided ships are analysed in the numerical simulation and the simplified method. Three types of collisions were identified based on the relative resistance of one ship to the other. They are denoted Collision Types 1 and 2, in which a relatively rigid ship collides with a deformable ship, and Collision Type 3, in which two deformable ships are involved. For Collision Types 1 and 2, estimates of the energy absorbed by the damaged ships differ by less than 8% compared to the numerical results. For Collision Type 3, the results differ by approximately 13%. The simplified method is applicable for right angle ship collision scenario, and it can be used as an alternative tool because it quickly generates acceptable results.     

考虑细长杆件不同坠落角度的海洋平台甲板损伤预报方法

[目的]在海洋平台吊装作业中,因吊机设备老化以及违规操作等而造成的坠物事故在海洋平台作业中时有发生,其中在杆件结构,如套管、钻铤等设备方面的问题最为常见,因杆件坠落时接触面积小,常会导致板架结构的损伤破坏。[方法]选取细长杆件坠物撞击甲板结构的场景开展结构损伤研究。在此基础上,考虑坠落角度对结构损伤的影响,确定结构损伤变形模型,并运用塑性力学理论,建立考虑杆件坠落角度影响的结构损伤解析预报方法。[结果]结果显示,小角度坠落场景下的结构损伤变形大,结构吸能高,根据结构响应可将坠落角度分为4个角度区间;解析计算结果与仿真计算得到的吸能曲线在数值以及变化趋势上相近。[结论]在杆状结构以一定角度撞击甲板结构时,甲板产生的塑性变形区域形状会随着撞深而产生变化,针对各阶段甲板变形特点的解析计算对海洋平台甲板板架结构抗撞设计评估具有一定的指导意义。     

Numerical weight function method for the structural analysis of ships: a speedy direct calculation with condensed structural information

The weight function method was originally derived for crack problems to calculate stress intensity factors for arbitrary loading conditions. In this article, a numerical weight function method has been extended to formulate the structural response analyses of two-dimensional elasticity, plate-bending, and three-dimensional plate-structures by using the finite-element method. The solution procedure is based on the well-known Maxwell–Betti reciprocal theorem, which is applied to the original and properly defined auxiliary problems. The present numerical weight function may be considered as a finite-element version of a Green’s function in an integral equation solution scheme. Although ship structures are certainly analysed by the finite-element method in a practical design procedure, the weight function approach has not yet been realized. The method is very useful for the analysis of structures subjected to a vast range of loading conditions, because structural responses can simply be calculated by the inner product of the universal weight function and load vectors. The validity and convergence characteristics of the present method are investigated by two-dimensional elastic and plate-bending problems, respectively. Finally, the method is applied to the calculation of the response amplitude operator of a stress component at a critical structural detail of a double-hull tanker, and the speed and efficiency of the method are quantitatively discussed based on the practical results.     

架空直立式码头结构三维数值塑性破坏分析

利用有限元法对性质复杂的混凝土结构——架空直立式码头进行塑性破坏分析，其中包括根据室内模型试验得到的混凝土参数，利用有限元软件进行数值模拟分析；结合重庆市寸滩码头模型试验资料，对数值模拟结果进行对比分析。结果表明：码头结构在受到顶层撞击力后最先破坏的是结构底层的联系梁；随着撞击荷载的增大，结构上部的纵撑、横撑两端均出现不同程度的开裂区，但整个结构未出现较大位移，表明此种结构具有较强的塑性变形能力，符合框架结构的设计原则，与试验数据比较吻合。     

Parametric dependencies of the post-ultimate strength behavior of a ship’s hull girder in waves

To rationally assess the consequence of a ship’s hull girder collapse, it is necessary to know the post-ultimate strength behavior of the hull girder including the global deformation and motions under extreme wave-induced loads. In the foregoing research, the authors proposed a numerical analysis system to predict the collapse behavior in waves including the post-ultimate strength behavior. The primary objective of the present paper is to clarify the parametric dependencies of the severity of the collapse in a rational manner. The parameters may include those related to load-carrying capacity and the extreme loads. To this end, an analytical solution to describe the post-ultimate strength behavior is derived. Assuming that a plastic hinge is formed at the midship during the collapse procedure, the whole ship is modeled as a two-rigid-bodies system connected to each other amidship via a nonlinear rotational spring, which represents the nonlinear relationship between the bending moment and the rotational angle. The relationship may be modeled as piece-wise linear curves. It is further assumed that large motions and elastic/plastic deformations of the hull girder may not affect the load evaluations, and that the hull girder is subjected to a large single wave. Some important parameters to predict the severity of the collapse are specified based on the analytical solution.     

A simplified analytical method to estimate the resistance of plane lock gates impacted by river barges

This paper presents a simplified analytical method to evaluate the resistance of a single plating lock gate impacted by a river barge. The approach is based on the assumption that the gate behavior may be divided into two successive phases. At the beginning of the collision, local crushing of some structural elements occurs concomitantly with small overall elastic motion of the entire gate. Then, when the penetration of the barge into the gate becomes important, a global plastic mechanism develops over the entire structure. In addition to the membrane and bending deformations occurring classically in such collisions, the particular flat shape of the striking barge bow leads to shear deformations near the gate edges. For all these deformation modes, closed-form expressions of the gate resistance are derived for both local and global deformation phases by applying the upper-bound method. These analytical developments are then validated through comparisons with numerical solutions obtained from non-linear finite-element simulations.     

预测船体分段焊接变形方法概述

船体分段在焊接过程中产生的焊接变形会使船体结构强度降低,精确预测和控制焊接变形是现代造船工艺的要求.焊接变形分析方法包括实验法、解析法、数值分析法、等效载荷法等,常用的是后两种方法.数值分析法采用热弹-塑性有限元模型精确模拟焊接现象,但计算工作量大;等效载荷法计算焊接区域的固有应变,并将其转化为等效载荷,进而应用弹性有限元分析求得整个结构的焊接变形.     

Hydroelasto-plasticity approach to predicting the post-ultimate strength behavior of a ship’s hull girder in waves

Dynamic collapse behavior of a ship’s hull girder in waves is investigated; post-ultimate strength behavior is the focus. Firstly, a simulation method is proposed. Assuming that a plastic hinge is formed during the collapse of the hull girder, the whole ship is modeled as two rigid bodies connected amidship via a nonlinear rotational spring. The post-ultimate strength behavior, such as the reduction of load carrying capacity due to buckling and yielding, is reflected in the model. Hydrodynamic loads are evaluated by using nonlinear strip theory to account for the effect of large plastic deformations on the loads. A scaled model for validation of the simulation is designed and fabricated. Then a series of tank tests is conducted using the scaled model to validate the simulation results. Post-ultimate strength behavior characteristics in waves are clarified by using the numerical and tank test results. It is shown that the hull girder collapses rapidly after reaching ultimate strength, and then the plastic deformation grows until unloading starts at the collapsed section. Finally, several parametric dependencies of the extent of the collapse behavior are discussed based on a series of the simulations.     

裂纹尖端区的应变和三轴应力

鉴于全塑性解存在的问题,Tian and Gao(2004y1]导出能反映弹性应变的弹塑性裂纹尖端场.本文给出了其三轴应力和应变分布,并给出了相应的有限元数值解.分析表明,高三轴应力引起的高弹性体变形和弹性能是诱发裂纹扩展的主要因素.     

船体长期监测系统的应用现状及发展趋势

船体长期监测系统(SHLTMS)用于对船体重要结构、关键构件及敏感部位进行结构应力实时监测和船体强度在线评估,时刻了解船体在各级海况下船体各部分的应力状态及运动状态。它对保障船体结构和人员安全、指导船舶的操纵以及船体寿命评估具有十分重要的意义。本文首先对船体长期监测系统进行概述,简要介绍船体长期监测系统的工程价值,接着对船舶长期监测系统的发展与应用现状进行分析,详细阐述国内外一些具有代表性的工程应用成果。最后对船舶长期监测系统存在的问题和未来发展趋势进行论述,为后续研究提供借鉴。     

大型浮式结构物结构碰撞性能分析

碰撞事故是基于事故极限状态设计重点考虑的对象,在设计中越来越受到重视。文章以某大型浮式结构物为研究对象,总结分析ISO、API、HSE、DNV、ABS、BV、LR等标准及规范对碰撞场景的相关规定,提出碰撞分析场景及设计衡准;基于简化分析技术建立碰撞力学模型,利用动态非线性结构分析软件ABAQUS进行仿真分析,通过分析塑性应变、塑性变形、吸能、碰撞力及运动等,校核评估舷侧结构的耐撞性能;分析不同碰撞位置、撞击船型式等对碰撞性能的影响。研究表明:目标大型浮式结构物舷侧结构碰撞事故极限强度满足规范要求,首柱撞击相对比较危险,可作为计算分析控制工况。     

基于累积塑性破坏的船体板低周疲劳裂纹扩展寿命研究

船体板的总体断裂破坏往往是低周疲劳破坏与累积塑性破坏两种破坏模式耦合作用的结果,故在船体板低周疲劳裂纹扩展寿命评估中,其基于累积塑性应变的船体板低周疲劳裂纹扩展寿命分析能够更为符合实际地评估船体板的总体断裂承载能力。船体板低周疲劳裂纹扩展寿命由宏观可检测裂纹扩展到临界裂纹而发生破坏这段区间的寿命。船体在实际航行中受到多次波浪外载作用而使其进入塑性变形不断累积或不断反复的破坏过程,并最终导致低周疲劳裂纹的萌生及扩展而使结构破坏,其破坏形式分别对应于增量塑性变形破坏（或棘轮效应）或交变塑性变形破坏（或低周疲劳）。局部塑性变形的累积会加剧低周疲劳裂纹不断扩展,因而基于累积塑性破坏研究船体板低周疲劳扩展寿命更为合理。文中以船体板单次循环载荷后塑性应变大小为基础,依据累积递增塑性破坏过程及弹塑性理论,计算经过N次变幅循环载荷后船体板累积塑性应变值,结合循环应力—应变曲线获得相应的稳定的迟滞回线,确定裂纹尖端应力应变曲线及确定相关塑性参量并依据选取的断裂判据判定裂纹扩展。建立循环载荷下基于累积递增塑性破坏的船体板低周疲劳裂纹扩展寿命的计算模型考虑应力比对此裂纹扩展寿命计算模型的影响。由该方法计算出的疲劳裂纹扩展寿命将对正确预估船舶结构的低周疲劳强度从而提高船舶安全性有重要意义。