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.     

Experimental and numerical investigation of lashing bridge and container stack dynamics using a scaled model test

Previously reported container losses were generally attributed to extremely violent motions of containerships due to adverse weather conditions. However, most existing specifications or standards adopted for containers and lashing equipment meet the requirement of static conditions. Hence, further researches on safer container shipping under heavy sea states are required. Consequently, an experimental study method is proposed to measure the dynamic response of 1/10 scaled lashing bridge and container stack. The scaled model of the lashing bridge is constructed based on the similarity theory. Based on two dimensionless numbers, Froude's number and Cauchy's number, eleven container scaled models are employed. A series of experiments with controlled parameters are performed using a three-degrees shaking table (roll, pitch, heave) to present sufficient data to verify the effectiveness of the numerical model. The results of experiments, numerical simulations and calculations of the VERISTAR procedure (developed according to the BV rule) are compared. This study aimed to explore the mechanical behavior of the lashing bridge and container stack under predetermined driving excitations (roll and pitch) which simulated heavy sea states. According to the results, the model can predict conditions similar to real situations of the lashing bridge and container stacks while storages on the weather deck.     

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.     

A general scaled model design method of stiffened plate subjected to combined longitudinal compression and lateral pressure considering the ultimate strength and collapse modes

A general and efficient scaled method for stiffened plates subjected to combined longitudinal compression and lateral pressure is proposed based on slenderness, simply by adjusting the number of stiffeners. The design method makes it easier to determine the dimensions of the scaled model for a given scale ratio compared with the previously proposed method. The emphasis is on the influence of the plate slenderness, the column slenderness, and the non-dimensional parameter of the lateral pressure on the ultimate strength. By maintaining the consistency of the plate slenderness and column slenderness, the proposed method is applicable for designing scaled models with materials of different yield stresses and Young's moduli. A similar effect of the lateral pressure on the ultimate strength of the prototype and scaled models is achieved by maintaining the non-dimensional parameter. In addition, the applicability of the scaled method to the initial deflection is considered, which provides a reference for similar models. The similitude of the scaled method is verified for several typical buckling modes, including the beam–column, tripping, web and overall collapse modes. Given the numerical results, the proposed general and fast scaled method can provide reasonable dimensions of scaled stiffened plates subjected to combined loads.     

Ice impact response and energy dissipation characteristics of PVC foam core sandwich plates: Experimental and numerical study

In this paper, the dynamic responses and energy dissipation characteristics of polyvinyl chloride (PVC) foam core sandwich plates under ice impact are investigated. The ice impact tests of PVC foam core sandwich plates were conducted by employing the horizontal impact experimental apparatus. The finite element simulations were conducted to analyze the dynamic response of PVC foam core sandwich plates based on soil and concrete material model for ice impactor. It was demonstrated that numerical results were in good agreement with experimental results. The deformation modes of the top facesheets were coupling of local indentation with global bending deformation, while the deformation modes of bottom facesheets were overall bending deformation. The permanent deformation of face sheets show that the impact resistance of sandwich plate is better than that of equivalent weight hull plate (EWHP). In addition, based on the actual navigation environment of ship, the effect of impact angle and ice floe shape on dynamic response and energy dissipation are analyzed.     

On the importance of mooring system parametrisation for accurate floating structure designs

This paper analyses the importance of mooring design parametrisation on the dynamic behaviour of mooring loads. An exhaustive sensitivity analysis is performed to evaluate the variability of mooring loads because of inaccuracies in the definition of model inputs, including physical and numerical parameters. Results show a relevant dependence on the length and significance in other parameters, such as the weight together with the hydrodynamic equivalent diameter and the drag forces. An inaccuracy below 1% in the mooring reference length can generate loads of up to twice the design, and an incorrect definition of the weight or the drag coefficient in the mooring design can lead to a design load variability of up to 30%. Stiffness plays a crucial role in snap events, reaching load differences of 19% depending on the stiffness selected.This research is based on a set of numerical models capable of predicting the mooring system response. A dynamic numerical model with two schemes of resolution is implemented and calibrated according to an experimental test campaign. Other sources of results provided by a quasi-static model and commercial software, Sesam (DNV-GL), are incorporated. In general, the dynamic numerical models show a good accuracy with an experimental database composed by a set of 2D prescribed movement tests at the fairlead of the mooring system.     

相似理论在水下爆炸冲击波载荷中的应用

以相似理论为基础,采用数值仿真试验的方法,探讨舰船结构遭受水下爆炸冲击波载荷作用时的动响应相似性问题。以某型舰原型作为基准模型,根据实际工程需要对舰船进行缩比仿真试验。原型有限元模型与缩比试验有限元模型数值结果表明:通过试验模型可以准确预测原型结构遭受水下爆炸冲击波时的动响应特性,将几何相似律应用到水下爆炸冲击波载荷相似性研究中是可行的。     

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.     

Dynamic response and performance of submarine tunnel subjected to surface explosions

Recently, external terrorist activities have become one of the most influential events on structural safety because of the absence of proper mechanisms to detect these events. In this study, the effects of surface explosions on the dynamic response and blast resistance of a submarine tunnel are investigated by using a coupled Lagrange and Euler (CLE) method. The feasibility and accuracy of the numerical method and material models are verified against the experimental data. After that, the numerical model is utilized to investigate the dynamic behavior and damage evolution of the submarine tunnel subjected to surface explosions. The dynamic behavior of the tunnel under various detonation scenarios in terms of the explosive weight and water depth is explored. Both the localized damage mechanism and the global structural response of the tunnel are examined. Empirical formulas are proposed to predict the failure modes of tunnel. Besides, studies of tunnel protection against potential attacks by using carbon fibre reinforced polymer (CFRP) and ultra-high performance concrete (UHPC) are also discussed. Numerical results in this study provide tunnel owners and engineers with thorough and important information on the structural performance of submarine tunnels subjected to blast loads, helping them in choosing effective protection strategies for potential explosion events.     

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.     

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.     

A probabilistic damage tolerance concept for welded joints. Part 1: data base and stochastic modelling

The present paper presents the necessary crack growth statistics and suggests stochastic models for a reliability analysis of the fatigue fracture of welded steel plate joints. The reliability levels are derived from extensive testing with fillet-welded joints for which the entire crack growth history has been measured, not only the final fatigue life. The statistics for the time to reach given crack depths are determined. Fracture-mechanics-derived crack growth curves are fitted to the measured experimental curves and the best fit defines the growth parameters involved for each test specimen. The derived statistics and distribution function for these parameters are used as variables in a Monte Carlo simulation (MCS). In addition a Markov model is developed as an alternative stochastic model. It is a Markov chain for which the discrete damage states are related to chosen crack depths in the material. This model works directly with the experimental time statistics. It is a “stochastic bulk approach” not involving any random variables or fracture mechanics modeling. Both models are fitted to the data base and scaled to in-service conditions. Both methods are compared and discussed. The aim is to provide data for the variables used in a MCS and to develop a Markov chain for fast reliability calculation, especially when predicting the most likely influence of numerous future inspections.     

穿甲弹侵彻靶板数值模拟研究

基于Johnson-cook材料屈服模型描述材料本构关系,引入材料失效参数与单元删除技术,运用ABAQUS建立穿甲弹侵彻目标靶板的三维数值模型,研究探讨穿甲弹对靶板结构的毁伤机理及弹体碰撞冲击作用下靶板结构的损伤模式和动响应特性。分析结果表明：单元失效删除技术适用于处理侵彻冲击等大变形问题,穿甲弹侵彻靶板是典型的冲塞破坏,数值模拟的弹体剩余速度与参考文献结果吻合较好,充分验证了文中所建立的数值模型在预测侵彻过程中的动力响应及损伤的合理准确性。该研究方法与结论可为进一步研究物体碰撞时的侵彻和材料失效问题提供依据,也为穿甲弹结构优化设计及舰船结构装甲防护设计提供参考。     

船舶典型管路冲击动力响应和变形特性数值模拟方法及试验研究

根据船舶典型管路段按1∶10比例设计管路试验模型,冲击试验台上分别进行了不同管夹及支吊架的布置方式下的冲击试验,并对试验结果进行分析,给出典型管路系统冲击响应及变形特点,在此基础上采用时域法结合接触有限元建模技术,对试验模型管路在试验工况下的冲击响应、动态变形进行了数值模拟并与试验结果进行对比分析,结果表明:数值模拟结果的仿真精度较高同时可以很好的模拟管路系统的破坏形式和变形特点.     

船用917钢抗冲击性能试验

无论金属材料或是非金属材料,其力学性能都是与应变率相关的.由于应变率历史效应以及在高速变形条件下产生绝热剪切带等不稳定性因素,使得材料对于高应变率响应的问题变得十分复杂,而一些实验方法则起到了重要作用.材料的本构关系是与水下爆炸等现象仿真研究的精度直接相关的,材料在高应变率下本构关系的确定,对水下爆炸等产生高应变率现象进行仿真研究具有重要意义.本文通过Hopkinson杆装置对船用917低磁钢进行了抗冲击性能研究,并由试验给出了仿真研究中适用的本构关系.     

Nonlinear dynamic response of blast-loaded stiffened plates considering the strain rate sensitivity

The aim of the present paper is to develop a simple theoretical method which can quickly calculate the nonlinear dynamic response of stiffened plates under a blast loading. The large deformation behavior of the stiffened plate is analyzed by using a singly symmetric beam model as representative of the stiffened plate. The material is assumed to be rigid-perfectly plastic, and the strain rate sensitivity is considered by using the Cowper–Symonds constitutive model (CS model). By Lee's extremum principle, the instantaneous modes of nonlinear structural response are determined. A series of calculations are performed to investigate the influence of pulse intensity, pulse duration, plate thickness, stiffener spacing and material property on the displacement response. The obtained results are in good agreement with those of numerical simulations performed by software package ABAQUS, and then a definition for the cases when the simplified method proposed here can be used is provided.     

Towards a unified methodology for the simulation of rupture in collision and grounding of ships

The aim of the work is the definition of a procedure for the numerical simulation of the response of ship structures under accidental loading conditions, which suffer various different modes of failure, such as tension, bending, tearing and crushing and in particular to investigate the effect of material modeling, i.e. material curve and rupture criterion as well as mesh size and strain rate effect on the results. To this end, different material models and simulation techniques were used for the simulation of eighteen indentation tests conducted by different research groups. The simulations were performed using the explicit finite element code ABAQUS 6.10-2. The tests refer to the quasi-static and dynamic transverse and in-plane loading of various thin walled structures which represent parts of a ship structure. Three rupture criteria are incorporated into VUMAT subroutine, which interacts with the explicit finite element code and refers to an isotropic hardening material that follows the J₂ flow theory assuming plane stress conditions, in order to investigate the prediction and propagation of rupture. The focus is on investigating whether it is possible to define a unified methodology, which is appropriate for the simulation of all different tests. Consistency in the numerical results is observed with the use of an equivalent plastic strain criterion, in which formulation a cutoff value for triaxialities below −1/3 is included.     

海洋平台相似模型设计及模态实验分析

通过理论分析，研究了材料阻尼对相似模型设计及实验数据分析的影响，在此基础上，设计并建造了海洋平台相似模型，并通过多输入单输出的方法对相似模型进行模态实验，得到其固有频率、空间振型、阻尼比等动力学参数。结果表明，材料阻尼对相似模型的几何尺寸没有影响，对模型的固有频率影响不大，可以忽略；但对模型的动力响应影响很大，在实验数据分析中必须加以考虑；为了方便应用，还给出已知阻尼比和阻尼系数时的转换关系。将模态实验数据与仿真分析结果进行对比，二者符合较好，从而验证了相似模型设计与建造的一致性及实验数据的可靠性。     

升船机提升系统动力特性试验研究

本文根据流体和结构动力相似理论导出了升船机提升系统试验模型和实物之间几何和物理量之间的相互对应关系.依照这些关系,就整个提升系统进行了1:30缩比模型的探索性试验,并通过对试验结果的分析,得到了一些有益的结论.     

粘弹性阻尼夹层板动力特性分析及其试验研究

本文在数值计算和试验的基础上研究了阻尼夹层板的动态特性和振动响应计算方法.在小变形线弹性理论的基础上,构造了阻尼夹层板单元.将三层板都看成Mindlin板单元,以各层的中面为坐标平面建立局部坐标系来建立有限元模型,考虑了偏心阵的作用,大大简化了计算程序.粘弹性采用常复数模型,用求解复特征值的方法求得了其固有频率和损耗因子.在此基础上编制了相应的有限元计算程序,进行了较详细的数值计算与分析,并讨论了粘弹性阻尼层的厚度、模量、损耗因子对结构动力特性的影响,得到了有工程应用价值的一些结论.同时分别对单层铝板、自由阻尼层板和约束阻尼层板进行了模态试验和响应试验,识别了结构的阻尼,验证了理论计算的正确性.本文还给出了阻尼夹层板结构动力响应的一种近似计算方法:将粘弹性材料看成完全弹性的材料,将粘弹性材料的阻尼以比例阻尼的形式给出,利用试验得出或估算公式给出结构模态阻尼,采用直接积分法求解.计算了简谐激励下的响应,并与实测的结果进行了比较分析.结果表明了该计算方法的合理性,为工程近似计算提供了一种简便的计算方法.