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.     

船舶搁浅于刚性斜坡数值仿真的模型化技术

显式非线性有限元分析已逐渐成为研究船舶搁浅问题的重要方法,但其模型化技术是实现数值仿真的关键。本文将搁浅船处理为可变形结构,用弹塑性材料模拟并进行整船建模,斜坡处理为刚体,用刚性材料模拟,船舶与斜坡之间定义为主从接触,船艏定义为自接触。通过仿真计算,获得并讨论了搁浅过程中的船体运动情况、搁浅接触力曲线、能量转化及船舶损伤变形情况。算例表明本文的模型化技术可以用于船舶搁浅的仿真计算。     

Bow door slamming of Ro/Ro ferries

This paper addresses the structural response of clam-type bow doors of Ro/Ro vessels under slamming loading conditions. The structural analysis is performed with the finite element code MSC/NASTRAN. The loading conditions were determined on the basis of towing tank tests, numerical calculation and regulations of classification societies. Slamming loads are applied statically and the FE code accounts for both material and geometrical nonlinearities. Apart from stress distributions, which are determined for different loading patterns, the results are used to calculate the forces and moments induced on the locking and securing elements, which secure the doors among themselves and the doors to the bow structure. The modelling methods reported may be used for the finite element analysis of similar structures. Such analyses of bow doors response under slamming loading could be submitted to classification societies for approval.     

船底座礁实验数值模拟中选择参数影响研究

非线性有限元方法是分析船舶碰撞和搁浅问题的一个强有力工具,但是数值模拟结果的可靠性很大程度上依赖于对工程问题的恰当处理和有限元软件中主要参数的准确控制.本文以某单壳船底结构准静态座礁实验结果为例,用非线性有限元软件LS-DYNA进行数值模拟,研究了下列选择参数对单壳船底结构抗撞性的影响:边界条件;船底结构的材料模型;壳单元类型;船底结构与礁石模型之间的摩擦系数;船底结构的残余应力.通过比较计算结果的碰撞力曲线,能量吸收曲线来评价这些参数对数值模拟的影响并给出了一些建议.     

基于显式有限元方法的二维楔形刚体入水砰击载荷并行计算预报

局部砰击载荷是在船舶首部结构设计时重点关注的问题。文章基于显式有限元方法,选用任意拉格朗日—欧拉算法(ALE),针对某30°二维楔形刚体入水砰击问题,开展了数值预报工作。针对模型网格密度开展了收敛性分析。数值预报的加速度、砰击压力等时域结果与已公开发表的模型实验的结果进行了比较,吻合非常好。鉴于在微机上数值计算时间比较长的问题,文中探讨了并行计算技术在模拟中的应用。     

Plastic deformation of ship plate subjected to repeated patch loads at different locations - Elastoplastic numerical analysis and design equation

Ship structures may be subjected to repeated random patch loads at different locations. Under these circumstances, ship plates will have large accumulated permanent deformations, which will result in some serious negative effects on their work and safety performance. Therefore, the elasto-plastic response of ship structure under repeated patch loads at different locations are studied by using finite element method. The permanent deformations of plate in the whole loading and unloading process are investigated. In addition, the residual stress and plastic strain states of the panel and stiffeners are studied based on a typical wheel-on-deck interaction scenario. Moreover, according to Hughes's hypothesis, the equivalent method between repeated patch loads at different locations and full uniform pressure load is studied. Considered the influence of plate slenderness, the improved formula for equivalent load coefficient is proposed, showing a good correlation with experimental data and numerical results. The proposed equivalent method can be used for estimating the permanent deformations of ship structures under repeated patch loads at different locations in ship life.     

船闸闸首非线性有限元计算分析

在船闸下闸首工程的结构计算分析中,考虑地基土体材料的非线性特性,采用非线性有限单元法,对嘉陵江新政船闸下闸首进行了计算分析研究。运用ANSYS10.0通用计算软件,建立了三维非线性弹塑性有限元模型,采用D-P准则对闸首的回填土和地基土体进行计算,经对嘉陵江新政船闸闸首在不同工况下的应力和应变分布特征进行分析比较,验证了模型的正确性和实用性。     

复合材料层合板螺栓连接接头极限强度分析

对基于不同渐进失效准则计算复合材料层合板螺栓连接接头极限承载力的高精度预报方法展开研究。基于Abaqus有限元软件,采用USDFLD子程序对接头进行渐进失效分析。分别采用最大应力准则、蔡-希尔失效判据、霍夫曼失效准则、蔡-吴失效准则、哈辛失效准则等5种失效准则进行数值计算。建立不同的场变量描述纤维、基体、界面的损伤状态,研究复合材料层合板螺栓连接接头在拉伸载荷作用下的损伤发展过程。研究表明,基于这5种失效准则计算的有限元仿真结果均与试验值较为接近,其中采用纤维失效和基体失效分开考虑的哈辛失效准则计算的复合材料层合板螺栓连接接头的极限强度与试验结果的准确度吻合最好,较适用于复合材料螺栓连接结构的有限元仿真。     

Collapase analysis of ship hulls

This paper presents an efficient finite element procedure for the collapse analysis of ship hulls under complicated loads. A set of finite elements, such as beam-column elements, stiffened plate elements, and shear panel elements are developed, directly accounting for the geometrical and material non-linearities and initial imperfections.

Elastic-plastic stiffness matrices for elements have been derived by combining elastic large displacement analysis theories with a plastic hinge model. The buckling and post-buckling behaviour of plates is included using an effective width concept. The procedure is effective, since few mode-points are necessary and numerical integration for evaluating stiffness matrices is avoided. Fracture mechanics criteria are introduced in order to account for tension tearing rupture and brittle failure of the material.

Practical applications to ultimate longitudinal strength analysis of ship hulls and tanker collision analysis are presented. The procedure can also be used for collapse analysis of offshore and onshore structures.     

船体表面应力腐蚀问题的一种无网格计算方法研究

文章采用无网格方法(MLPG)中最简单的MLPG5技术,对船舶表面微裂缝在腐蚀工作环境中向内扩展情形进行了数值计算模拟,计算中假设了船体材料为各向同性,并引入了线弹性假设。对比以往的有限元计算方法,发现处理裂缝扩展的数值计算问题时,无网格计算方法显示了其独特的优越性。同时,根据材料特性、外荷载以及温度等参数的变化,文中分别描述了三种可能的裂缝扩展方式:裂缝钝化、稳态以及非稳态的快速破环等。     

Experimental and numerical analysis of a tanker side panel laterally punched by a knife edge indenter

The paper presents finite element simulations of a small-scale stiffened plate specimen quasi-statically punched at the mid-span by a rigid indenter, in order to examine its energy absorbing mechanisms and fracture. The specimen, scaled from a tanker side panel, is limited by one span between the web frames and the stringers. The paper provides practical information to estimate the extent of structural damage within ship side panels during collision accidents. Moreover, the results of this investigation should have relevance to evaluate grounding scenarios in which the bottom sustains local penetration. This is possible since the structural arrangement of the double hull and the double bottom of tanker vessels is very similar. The experimentally obtained force–displacement response and shape of the deformation show good agreement with the simulations performed by the explicit LS-DYNA finite element solver. The numerical analysis includes aspects of particular relevance to the behaviour of ship structures subjected to accidental loads which could give rise to difficulties in interpreting finite element calculations. In particular, the paper comments on the material nonlinearities, the importance of specifying the precise boundary conditions and the joining details of the structure. The considerable practical importance of these aspects has been the focus of attention in previous publications of the authors which evaluate the experimental-numerical impact response of simple ship structural components, such as beams and plates. Therefore, this paper uses the definitions proposed in those references to evaluate its applicability in the scaled tanker side panel, as an example of a more complex ship structure.     

Comparison of the crashworthiness of various bottom and side structures

The purpose of this work is to compare the resistance with damage of various types of double bottom structures in a stranding event. The comparative analyses are made by use of a commercial, explicit finite element program. The ship bottom is loaded with a conical indenter with a rounded tip, which is forced laterally into the structures in different positions. The aim is to compare resistance forces, energy absorption and penetration with fracture for four different structures. Those four structures are: a conventional double bottom, a structure (presently protected through a patent) with hat-profiles stiffened bottom plating, a structure where all-steel sandwich panel is used as outer shell and a bottom structure stiffened exclusively with hat-profiles. The paper shows that it is indeed possible to elevate the crashworthiness of side and bottom structures with regards to the loading considered here without increasing the structural weight.     

小型快艇结构耐撞性研究

船舶碰撞是一种复杂非线性瞬态响应过程,在碰撞区内的构件一般迅速进入塑性流动状态,出现撕裂、屈曲等形式的破坏和失效,因此对小型快艇结构碰撞特性进行分析非常必要。分析了艇艏撞击作用下快艇舷侧加筋结构的渐进破坏过程,给出了撞深曲线。为表征小型快艇船体结构的耐撞性能,建立了基于综合考虑塑性应变衡准和撞深衡准的小型艇结构耐撞性评价模型。最后,运用有限元法进行数值分析,开展快艇改进舷侧的结构耐撞性优化研究。数值分析表明,对于中小型快艇,碰撞损伤主要是艇体的总体弯曲变形,损伤变形区域占全船的比例较大,采用塑性应变衡准和撞深衡准能有效地刻画中小型快艇结构耐撞性。     

底板厚度对双铰底板式闸室结构工作特性的影响

以工程实例为依托,基于大型有限元软件ANSYS,考虑闸室的三维结构体系和复杂荷载工况,对双铰底板式闸室结构进行数值模拟,并对底板厚度对双铰式闸室结构工作特性的影响进行分析,力图找到影响双铰式闸室结构的关键因子,为船闸结构选型和设计优化提供科学依据。     

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.     

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.     

The influence of the material relation on the accuracy of collision simulations

The non-linear finite element method is widely used to simulate marine structures subjected to collisions. Furthermore, common to all non-linear finite element simulations is the need to implement the non-linear material behaviour including failure. However, the influence of the material relation on the accuracy of numerical results is not presented in detail in the present literature even though different material relations are used. Additionally, the material relation needs to include an appropriate criterion for treating the occurrence of fracture within the marine structure. Thereby, the crash resistance until inner hull failure should be predicted reliable and realistic. Therefore, this article seeks to describe the common choice of a material relation and compares this with a recent finite element-length dependent material relation based on optical measurements. As a result, this comparison gives an insight into the influence of the material relation on the accuracy of non-linear finite element simulations. Hence, this comparison can support the future use of an appropriate material relation for collision simulations.     

舰船结构空中爆炸载荷的高精度数值计算程序

给出了一种舰船结构空中爆炸载荷的高精度数值计算程序.该程序采用基于通量修正算法的有限差分格式编写.它在冲击波阵面处达到四阶精度且耗用计算资源较少,是一种简单高效的计算程序.因此该程序特别适用于大尺度船舶结构受空中爆炸载荷的计算.程序的可靠性和准确性通过击波管试验和空中爆炸试验数据进行了检验.最后给出了一个典型船舶结构受空中爆炸载荷的算例.     

基于固有应变理论的船体焊接变形仿真研究

大型船舶构件尺寸大、焊缝分布广,传统的有限元焊接仿真方法难以满足其大尺寸结构计算的要求。基于热弹塑性有限元法对T型局部接头进行焊接变形计算,获取焊缝处平均固有应变值,然后将其作为初始载荷施加在全尺寸壳单元分段模型上进行弹性计算,最终得到大型分段的整体焊接变形。仿真结果表明,结合小模型的热弹塑性法和大结构固有应变法,能准确高效的预测大型结构的焊接变形。     

Numerical simulation of fatigue crack propagation under biaxial tensile loadings with phase differences

Fatigue crack propagation under the biaxial tensile loading, which loading directions are normal and parallel to the initial crack position, is highlighted in this study. Most of in-service structures and vessels are subjected to many types of loading. Generally, these loadings have different axial components with different phases. However, the structural integrities of structures and vessels are evaluated according to design codes based on theoretical and experimental investigations under a uniaxial loading condition. Most of these codes are based on the S–N curves approach. An approach that does not use S–N curves has been favored by researchers, with the fracture mechanics approach preferred for evaluating the fatigue life of structures. An advanced fracture mechanics approach was developed based on the Re-tensile Plastic zone Generating (RPG) stress criterion for fatigue crack propagation. In this study, fatigue crack propagation tests under biaxial loading with six different phase and loading conditions are performed and the effect of the phase difference under biaxial loading is evaluated. A numerical simulation method of fatigue crack propagation based on the RPG stress criterion under different biaxial loading phase conditions is presented and compared to measured data.