Marine accident analysis for collision and grounding in oil tanker using FTA method

In this study, collision and grounding data registered in GISIS (Global Integrated Shipping Information System) were investigated for oil tankers. The database includes the information of the collision and grounding accidents during the period between 1998 and 2010 in oil tankers. The risk assessments were carried out using fault tree analysis (FTA) programme for the incidents as collision and grounding occurred in oil tankers. In this study, we were able to investigate first the potential problems which cause the collision and grounding accidents have been determined, second, the occurrence of accidents has been shown with causal factors by the FTA method, and, finally, the significance degree of the initial events causing occurrence of accidents have been put forth. Collision in oil tanker resulted in economical loss (81%), pollution (6%) and death or injury (13%). Grounding in oil tanker resulted in economical loss (91%) and pollution (9%). According to the FTA results, the main reason for the accidents originating from human error is as follows: for collision accidents, Convention on the International Regulations for Preventing Collisions at Sea (COLREG) violation and the lack of communication between vessels; and for grounding accidents, the interpretation failure of the officer on watch and lack of communication in the bridge resource management.     

Elements of risk analysis for collision and grounding of a RoRo passenger ferry

Newly developed software was applied to study the effects of damages due to collision and grounding. The annual risk of collision and grounding was computed for an example RoRo passenger ferry. Collision frequency was evaluated for a specified route taking into account traffic data. Grounding frequency was calculated for an artificial obstacle located close to the traffic route. The consequences of collision and grounding scenarios were estimated by introducing damage criteria that link the calculated distribution of damage size and damage location to monetary units. Loss of human life and reputation was not considered. It was shown that the main part of the calculated annual risk is caused by capsize of the vessel after severe damage.     

The influence of fluid structure interaction modelling on the dynamic response of ships subject to collision and grounding

Analysis of the dynamic response of ships in accident scenarios requires a realistic idealisation of environmental and operational conditions by multi-physics models. This paper presents a procedure that simulates the influence of strongly coupled FSI effects on the dynamic response of ships involved in typical collision and grounding events. Our method couples an explicit 6-DoF structural dynamic finite element scheme with a hydrodynamic method accounting for (a) 6-DoF potential flow hydrodynamic actions; (b) the influence of evasive ship speed in the way of contact and (c) the effects of hydrodynamic resistance based on a RANS CFD model. Multi-physics simulations for typical accident scenarios involving passenger ships confirm that suitable FSI modelling may be critical for either collision or grounding events primarily because of the influence of hydrodynamic restoring forces.     

船舶碰撞机理与耐撞性结构设计研究综述

研究船舶碰撞和触底事故的机理,以及如何提高船舶结构耐撞性是船舶碰撞研究领域的热点.文章介绍了解析法、数值仿真技术和风险分析法的发展与应用特点,阐述了近些年来船舶碰撞、船舶触底、缓冲船首设计、船桥碰撞和船舶与海洋平台碰撞等领域的研究成果,列举了一些降低船舶碰撞和触底事故风险的新型结构设计,并对今后的研究方向提出了若干建议.     

Analysis of structural crashworthiness of double-hull ships in collision and grounding

A conceptual design framework for collision and grounding analysis is proposed to evaluate the crashworthiness of double-hull structures. This work attempts to simplify the input parameters needed for the analysis, which can be considered as a step towards a design-oriented procedure against collision and grounding. Four typical collision and grounding scenarios are considered: (1) side structure struck by a bulbous bow, (2) side structure struck by a straight bow, (3) bottom raking, (4) bottom stranding. The analyses of these scenarios are based on statistical data of striking ship dimensions, velocities, collision angles and locations, as well as seabed shapes and sizes, grounding depth and location. The evaluation of the damage extent considers the 50- and 90-percentile values from the statistics of collision and grounding accidents. The external dynamics and internal mechanics are combined to analyse systematically the ship structural damage and energy absorption under accidental loadings.     

GRACAT: software for grounding and collision risk analysis

From 1998 to 2000 an integrated software package for grounding and collision analysis was developed at the Technical University of Denmark within the project: Information technology for increased safety and efficiency in ship design and operation. The cost of the software development was 6 man-years. The software provides a toolbox for a multitude of analyses related to collision and grounding accidents. The software consists of three basic analysis modules and one risk mitigation module: (1) frequency, (2) damage, and (3) consequence. These modules can be used individually or in series and the analyses can be performed in deterministic or probabilistic mode. Finally, in the mitigation module risk profiles for the calculated consequences can be calculated and compared to alternative solutions by assignment of a cost function to the consequences. Thus, the possible analyses range from a deterministic crash analysis to a comparative risk analysis of two vessels operating on a specified route where the result is the probability density functions for the cost of oil outflow in a given area per year for the two vessels. In this paper, we describe the basic modelling principles and the capabilities of the software package. The software package can be downloaded for research purposes from www.ish.dtu.dk/GRACAT.     

基于蜂窝单元的海上交通风险分析

传统的船舶交通风险分析是将研究水域作为一个整体来评估其风险状况的。基于蜂窝单元的船舶交通风险分析,把研究水域按一定标准划分为若干地理单元,将历史数据、数学模型以及专家学者的经验和判断有机地结合起来,用以评估每一地理单元船舶碰撞和搁浅事故的概率,其输出结果以地理分布的形式突出了高风险区域。相对于传统的风险分析,该理论更能够全面、准确地描述水域的风险状况,为采纳和实施正确的安全措施提供了强有力的支持。     

试样极限塑性和船舶触礁模型试验校准计算

船舶碰撞与搁浅时的结构损伤是一个复杂的动态非线性过程。国际船舶与离岸结构会议碰撞与搁浅委员会（ISSC－V.3)组织其成员进行了两项专题研究：（1）材料极限塑性极限应变试验数据用于有限元模型计算时的尺度修正系数；（2）各种计算方法用于船舶搁浅（触礁）计算的准确性。介绍了作者承担上述两项研究的成果，给出了极限塑性极限应变的尺度修正系数的计算方法和结果，论证了非线性有限元显式积分方法及MSC／Dytran软件用于搁浅计算的准确性。     

Understanding ship-grounding events

The paper presents a simple procedure to estimate the damage to a ship bottom and the associated seabed topology that results from a dynamic grounding event. The seabed is modeled as a rigid body and parameterized by a quadratic surface, i.e., a paraboloid, which can in principle model a wide range of seabed topologies. A nonlinear finite element program (LS-DYNA) is used to simulate the contact force versus the lateral penetration, from which the horizontal force component of powered grounding is estimated. The simplified procedure for analyzing dynamic and static grounding events is outlined. Simulations are performed for different ship speeds and for different initial levels of obstruction over the keel. It is shown that a static approach may replace the dynamic grounding simulation, thereby considerably reducing the computational work. The static approach allows for the quick estimation of the energy absorption during powered grounding, which is imperative for decision making during critical situations. The ultimate goal of the study is to provide a near real-time prediction of the risk of rupture of the cargo tanks and hull girder failure. Moreover, the residual strength of damaged ships is an important issue that is related to operations involved in the salvage of wrecked vessels, such as re-floatation and towing.     

A simplified grounding damage prediction method and its application in modern damage stability requirements

This paper presents the analyses and results aimed at developing damage stability requirements which take into account the structural vulnerability to grounding damage, i.e. the kinetic energy available to generate damage and the structural resistance. The paper presents analysis of new damage statistics in order to determine impact scenarios, in particular in terms of impact speed, impact location, and width and height of damage. Furthermore a new empirical damage prediction formula is developed based on a combination of full-scale testing and extensive non-linear finite element analyses. This deterministic prediction method is validated against grounding experiments and then used in a probabilistic (Monte Carlo) simulation framework. First the simulation method is calibrated and validated against the real statistical damage data for conventional ships and then it is used to generate damage statistics for high-speed craft. It turns out that the grounding damage statistics for all ships can be characterized by a single parameter; the Grounding Damage Index, GDI, which includes the ship kinetic energy and its structural resistance to grounding damage. Simple, closed-form expressions are developed for the GDI and it is shown how the probability of exceeding a box-shaped damage is a simple function of the GDI and the size of the box. The paper therefore gives the background and the results for a new generation of damage stability rules where the structural crashworthiness is taken into account and where the passive safety level is explicitly expressed. It furthermore gives simplified prediction tools and data for actual ships, i.e. a toolbox that is readily available for risk analysis regarding grounding damage.     

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.     

Assessment of a ship's performance in accidents

This paper reviews the state-of-the-art research on collision and grounding. It focuses on the three issues that a standard for design against accidents needs to address: definition of accident scenarios, evaluation approaches, and acceptance criteria. Accident scenarios may be created through surveys of historical data, consulting experts’ opinions, or performing risk analysis. Structural crashworthiness of ships, oil outflow performance, and residual strength of damaged ships can be estimated using simple formulae, simplified analytical methods, or non-linear FEM techniques of different complexity. Performance of a ship in an accident can be measured by energy dissipation, penetration depth, quantity of oil outflow or residual hull girder strength. Acceptance criteria should be established on extensive comparative studies, and provide a means for balancing numerous variables in order to achieve an optimal solution.     

Full six degrees of freedom coupled dynamic simulation of ship collision and grounding accidents

By taking advantage of the user-defined load subroutine (loadud) and the user common subroutine (usercomm) in LS-DYNA, the authors proposed a new coupled approach for simultaneously calculating structural damage and the planar 3DOF ship motions in ship collisions. The coupled procedure aimed at predicting the detailed structural damage together with reasonable global ship motions. This paper extends the method to consider the full 6DOF ship motions; thus, ship collision as well as grounding accidents can be properly handled. This method is particularly useful for design purposes because the detailed ship hull profile is not needed.A traditional ship maneuvering model is used for the in-plane surge, sway and yaw degrees of freedom with a series of nondimensional coefficients determined from experiments. It is assumed that the out-of-plane degrees of freedom are not coupled with the in-plane ship motions, and there is no coupling among roll, pitch and heave motions. The implementation is verified through free decay tests, and the obtained natural periods show good agreement with theoretical results.Several collision and grounding cases are simulated in which a supply vessel crashes into rigid plates with different orientations. The effects of the roll motion, the heave and pitch motions and the full 6DOF motions are studied. The results are compared with those from a 6DOF decoupled method. Ship motions through the proposed method compare reasonably well with SIMO results. It is found that several consecutive impacts may occur in the simulation of one collision case due to the periodic motions. This is not taken into account in the decoupled method, which makes this method unconservative.     

模拟器中船舶搁浅危险性评价方法的研究

在航海模拟器中,如何对模拟训练的过程实时、连续地进行航行安全评价一直是急待解决的重要课题。通过建立狭水道航行船舶搁浅危险性定量分析的数学方法,提出了基于大型船舶操纵模拟系统的狭水道航行船舶搁浅危险性评价模型。该模型能实时、连续地评价航行于狭水道等受限水域船的搁浅危险性,是一种对航海模拟训练评价的较客观、科学的方法。     

Experimental and numerical modelling of ductile crack propagation in large-scale shell structures

This paper presents a combined experimental–numerical procedure for development and calibration of macroscopic crack propagation criteria in large-scale shell structures. A novel experimental set-up is described in which a mode-I crack can be driven 400 mm through a 20(+) mm thick plate under fully plastic and controlled conditions. The test specimen can be deformed either in combined in-plane bending and extension or in pure extension. Experimental results are described for 5 and 10 mm thick aluminium and steel plates. By performing an inverse finite-element analysis of the experimental results where the simulated crack growth is forced to correspond to the experimental observations, empirical criteria for ductile crack propagation emerge very clearly. Using the experiments with edge crack specimens (ECS) in combined in-plane bending and extension, crack propagation criteria are developed for steel and aluminium plates, mainly as curves showing the critical element deformation versus the shell element size. These derived crack propagation criteria are then validated against a separate set of experiments considering centre crack specimens (CCS) which have a different crack-tip constraint. The applicability of the often-used equivalent strain criterion is discussed versus a more rationally based criterion which takes into account the stress tri-axiality. A large-scale grounding experiment is also simulated showing very good agreement with measurements. The performance of the proposed model is in general good and it is believed that the presented results and experimental–numerical calibration procedure can be of use in practical finite-element simulations of collision and grounding events with the use of shell elements. As discussed, the paper provides a clean framework for further development of macroscopic crack propagation criteria in large-scale plate structures.     

受损船体极限强度分析与可靠性评估

对预报船舶极限强度的解析公式作局部改进，使其更有效地用于评估或预报现代船舶剩余极限强度。将该方法同MVFOSM相结合，对一艘油船进行了完整船体（新建／老龄）与受损结构（搁浅／碰撞）极限总纵强度分析和可靠性评估及预报；某些结论可作为深入研究剩余强度理论或指导实船结构设计的参考。     

破损散货船剩余极限强度的评估与分析

船体发生破损后.其剩余有效剖面是非对称的,船体还可能倾斜.根据IACS共同规范(CSR),采用逐步破坏分析法计算船体梁在不同破损情况下的剩余极限强度,同时编制了计算程序.对1艘散货船在完整和不同破损状态下的船体结构安全性进行了系统评估,并得到了一些有意义的结论.     

逐步破坏法破损油船剩余强度研究

基于IACS共同规范研制了逐步破坏法计算完整油船极限强度和破损剩余强度的程序.考虑了船体发生搁浅碰撞后,其剩余有效剖面是非对称的,船体还可能发生不同程度倾斜的实际情况,计算了双壳油船在不同破损情况下破损船体的剩余强度,并给出了实例及结果分析.     

波浪引起破损船的垂向运动和弯矩（英文）

The wave-induced vertical ship motions and bending moments of a double hull-oil tanker in realistic flooding conditions are studied. The scenarios investigated are represented by water ingress into the starboard ballast tanks for collision damage cases and both starboard and portside ballast tanks for grounding situations. Seakeeping computations are performed for eight damage scenarios and for the intact condition, each corresponding to different changes in displacement, trim, and heel. For each of the damage conditions, transfer functions of vertical motions and loads are calculated using a potential linear 3 D panel hydrodynamic code in the frequency domain that includes effect of the motion of the water in flooded tanks. A MATLAB code is developed to facilitate automated hydrodynamic simulation of many damage scenarios. Verification of seakeeping results is performed by comparing transfer functions with results of the previous study. Wave-induced vertical responses of damaged ship are then compared to those of intact ship using two spectral-based methods originating from uncertainty analysis of wave loads, which are convenient tools to assess consequences of damage on short-term ship responses. Generally, observed trend is that vertical wave-induced responses of damaged ship converge toward those of intact ship with increasing wave period. Fairly small differences between responses of asymmetrically damaged ship with respect to the symmetrical incoming wave directions are found. The results of the study are an efficient method for seakeeping assessment of damaged oil tankers and the framework for evaluating consequences of damage scenarios, heading angles, and sea conditions on seakeeping responses of damaged ships.The results can be used to decide if the intact ship model can be used instead of the damaged one for the emergency response procedure or for the risk assessment studies when modeling and computational time represent important limitations.     

舰船自动智能避碰数学模型及其仿真研究

为了提高舰船航行的安全和效率,达到最佳操船效果,需要建立舰船自动智能避碰数字模型.当前模型在分析舰船避碰风险度的基础上,通过人工智能、进化计算和软计算等方法实现舰船自动智能避碰,存在避碰识别准确率较低的问题.本文提出一种新的舰船自动智能避碰数学模型,首先对舰船会遇态势进行判断;然后建立预测舰船碰撞风险判断模型,预测本舰船实施自动智能避碰方案后的复航时机是否已到,以及本舰船立即复航是否能够让清目标舰船或其他所有目标舰船;最后依据舰船碰撞风险判断结果,以当前舰船潜在碰撞风险为例,建立舰船自动智能避碰数学模型.仿真结果证明,所提模型能够实现舰船自动智能避碰.