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.     

Model test on the collapse strength of the buffer bow structures

The adoption of double hull system in the side hull of oil tanker has been recognized as an effective countermeasure to prevent a disastrous damage induced by collision accident which might cause cargo oil spill from a struck oil tanker. However, when considering that ocean-going vessels are increasing not only in size but also in speed, a threat of disastrous collision accident should be further mitigated even on the responsibility of striking ships.A series of crush tests using scale models of the buffer bow has been carried out. The test results were compared with those obtained by FEA simulation and a simple analysis. The performance of the buffer bow is discussed focusing on the collapse mechanism and the P–δ characteristics. Then the guidelines for the practical design of buffer bow structure are presented.     

船艏横向加强框架对船艏耐撞性能的影响

在撞击过程中船艏结构的典型损伤是外壳板和内加筋的褶皱，撕裂和弯曲。在以前的船舶结构的碰撞分析的简化方法或数值模拟中往往略去横向肋骨框架对船艏碰撞性能的影响。本文利用有限元数值仿真方法研究了横向肋骨框架在碰撞损坏过程中的作用，发现其对船艏结构的损伤形态、碰撞力及能量耗散有重要影响。因而是碰撞计算中不可忽略的因素。     

船舶碰撞缓冲型球鼻艏概念探讨--球鼻曲率对碰撞的影响

船舶碰撞事故中，被撞油船船侧的破裂会引起严重的海洋污染，故油船双层船壳设计成为防止被撞油船破损的有效措施。但随着海上运输船舶的数目及尺度的日益增大，双层船壳已不能满足防止船侧破损的要求。本文提出了缓冲型球算般的构思。在船舶相撞的过程中，球鼻艏曲率的尖锐程度影响被撞船船侧的损伤程度，故提出并讨论了表征球鼻艏碰撞特性的标志性参数。通过对不同曲率的球鼻艏一系列的碴撞数值仿真计算，详细描述了外形曲率对球鼻艏的变形形态、碰撞力、碰撞力密度及能量吸收的影响，指出船舶采用钝形的球鼻艏能有效减小碰撞时的穿透损伤。     

Design of offshore structures against accidental ship collisions

In this paper, we investigate the damage to offshore platforms subjected to ship collisions. The considered scenarios are bow and stern impacts against the column of a floating platform and against the jacket legs and braces. The effect of the ship–platform interaction on the distribution of damage is studied by modeling both structures using nonlinear shell finite elements. A supply vessel of 7500-ton displacement with bulbous bow is modeled. A comprehensive numerical analysis program is conducted, and the primary findings are described herein. The collision forces from the vessel are compared with the suggested force–deformation curves in the NORSOK code. For collisions with floating platforms we particularly focus on the crushing behavior and potential penetration of the bulbous bow and stern sections into the cargo tanks or void spaces of semi-submersible platforms. For fixed jacket platforms we investigate whether jacket braces can penetrate into the ship without being subjected to significant plastic bending or local denting.Adequate treatment of the relative strength between the interacting bodies is especially relevant for impacts with high levels of available kinetic energy, for which shared energy or strength design is aimed at. Simplifying one body as rigid quickly leads to overly conservative and/or costly solutions, and is in some cases non-conservative.The numerical analysis is used to develop a novel pressure–area relation for the deformation of the bulbous bow and stern corners of the supply vessel. Procedures for strength design of the stiffened panels are discussed. Refined methods and criteria are proposed for strength design of platforms, including both floating and jacket structures. The adequacy of the NORSOK design guidance for collisions against jacket legs is evaluated. The characteristic strength of a cylindrical column is used to develop a novel criterion for the resistance to local denting from stern corners and bulbous bows.     

船-桥碰撞力学问题研究现状及非线性有限元仿真

归纳研究了船舶与桥梁碰撞力学的几种典型计算方法，并对各自的特点进行了分析。文中借助DYTRAN非线性有限元程序，以一艘4万吨级的油船与长江上某一斜拉索桥发生正向碰撞为例，演示了有限元法仿真计算船-桥碰撞问题的一般过程。反映了船-桥碰撞过程中船艏、桥梁承合、桥面和拉索的力与变形的时间历程，得到了具有指导意义的结论。     

油轮艏部结构碰撞特性研究

在船舶碰撞中,船艏是主要作用方.船艏结构的碰撞特性是影响船-船碰撞过程中被撞船舷侧结构损伤程度的决定因素.为减少碰撞事故损失,应从碰撞的观点对船艏结构的特性进行研究,提出一种研究船艏的碰撞特性的方法及表征船艏碰撞特性的特征量,据以改进船艏设计.根据船艏结构本身的碰撞破损过程,对船艏结构碰撞力与破损深度的关系、艏部构件在碰撞过程中的损伤形态和能量耗散进行了研究,指出碰撞力曲线是船艏结构的一种固有特性.提出了碰撞力面积密度曲线的概念,它可以用于定量表达船艏结构对其它结构的破坏能力.利用有限元数值模拟方法计算了一艘4万吨船艏的碰撞损坏实例,显示了上述碰撞特征并讨论了提高碰撞数值模拟计算精度的方法.     

考虑流场影响下破冰船艏部结构响应研究

通常考虑船-冰碰撞附连水的水动力效应有附加质量法和流固耦合法。本文建立了破冰船破冰场景,基于流固耦合法进行了数值仿真计算,分析了水域流场对船体的冲击压力变化、流场的速度分布变化以及流场的动能变化。同时与附加质量法的计算结果进行了比较,对比分析了船艏的碰撞力大小、损伤变形以及局部冰载荷等差异,揭示了流场对船-冰碰撞的影响规律,对于破冰船结构设计具有重要的参考价值。     

高强度钢缓冲型船艏研究

在船舶碰撞事故中，一般船侧的破损程度比船艏大，从环境保护的全局意识及降低整体经济损失的角度出发，应该在保证船艏结构在能够承受常规载荷的前提下适当地减小其纵向刚度，使其在撞击船侧时导致船侧破损的可能性降低。笔者从损伤形态，碰撞力，碰撞力密度和能量吸收等方面对采用高强度钢的缓冲船艏进行研究，发现船艏结构采用高强度钢在等强度的条件下，可减少结构的板厚和船艏结构的临界压溃载荷，从而降低对被撞船舶侧结构的破坏。     

基于整船整桥模型的船桥碰撞数值仿真

桥梁在船舶碰撞时受到的动力载荷和响应是复杂的动力非线性问题。近代非线性有限元技术为该问题的求解提供了有效的工具。本文简述了该技术的基本原理，并基于整船整桥模型，对一艘4万吨实船与桥梁的碰撞过程进行了计算。仿真结果显示了船艏结构损坏、碰撞力演变、能量传递和桥墩内部应力变化的详细情景，讨论了船—桥碰撞的力学特征。本文演示的方法比传统的经验公式和简化解析法提供了更为精确的结果。所提供的桥墩应力状态对桥梁的设计与碰撞后的损伤评估有重要参数价值。     

Design of bridges against ship collisions

The paper outlines a rational design procedure for bridge piers and pylons against ship collision impacts. Firstly, a set of risk acceptance criteria are proposed. This is followed by a mathematically based procedure for calculation of the probability of critical ship meeting situations near the bridge, and the probability of ship collision accidents caused by human errors as well as technical errors. This first part of the paper leads to identification of the largest striking ship, “design vessels”, a given bridge pier must withstand without structural failure in order for the bridge connection to fulfil the risk acceptance criteria. The final part of the paper is devoted to an analysis of the needed impact capacity for the bridge pylons and piers exposed to ship bow impact loads from these “design vessels”. For a number of different ship types and different tonnage merchant vessels, load – displacement relations for ship bow collisions against rigid walls are derived. Based on these comprehensive numerical results, a new empirical relation is derived which is suited for design against bow collisions. This expression for maximum bow collision forces is compared with a previously published expression for ice-strengthened ships and with existing standards for assessment of bow crushing forces. It is shown that there is need for an update of these existing standards. For design of piers and pylons against local impact pressure loads, a pressure - area relation for bulbous bow impacts is derived.     

Drift-wood collision load on bow structure of high-speed vessels

Impact load estimation of drift-wood hitting against the bow structure of high-speed vessels has been investigated. It may be difficult for the craft operator to detect in advance a drift-wood floating just below the ocean surface and to avoid the collision with it. It is particularly difficult for operators of the high-speed vessels in night cruising mode. The probability of the accident may be higher than that of the collision with rocks or other ships because of the difficulties of early detection of the floating object. Impact loads are estimated for drift-wood of different sizes and craft speed considering whipping motion and local crushing of the wood at the hitting region. A simplified formula for the load estimation is proposed based on the modal approach and the energy balance. Predicted impact loads can be applied to the initial design of the bow structure and collision bulkhead of the craft to secure the structural safety against a possible accident.     

潜艇水下碰撞特性数值研究

为分析碰撞中潜艇结构的损伤特性,选取2500t级双壳体潜艇作为研究对象,对潜艇结构进行等比例实体建模,并采取潜艇船艏与舷侧部位的撞击形式.利用大型非线性有限元软件Ls-Dyna,从能量、碰撞力和冲击环境3个角度研究碰撞的影响,得出以下结论：潜艇外壳及中间结构是吸能的主要结构,刚度较弱的潜艇艏部会产生大的塑性变形区,而刚度较强的舷侧结构的响应则以动能为主,且伴随着小范围的塑性变形区;撞击力在艏部临界速度附近,产生单峰值及双峰值现象,并确定临界速度值约为15～16kn;船长方向的冲击环境成对数函数分布,按中级损伤程度,对艇员的影响区域为距离船艏撞击区约0.11倍艇长范围.     

船桥碰撞中桥墩防撞装置性能研究

利用ANSYS/LS-DYNA显示非线性有限元软件,对天兴洲大桥某桥墩的防撞装置进行了船-防撞装置碰撞模拟,分析防撞装置在碰撞中结构的损伤情况和各构件的吸能特性,结合计算结果,对防撞装置提出合理的改进意见,以提高防撞装置的防撞性能。     

自卸式散货船强度评估与加强方案研究

本文以68000t非CSR自卸式散货船为研究对象,对其首、尾货舱及C-Loop局部结构的屈服和屈曲强度进行分析评估,在此基础上提出加强方案.本文中的分析流程、加强方案和相关结论对同类船舶有一定的参考意义.     

Experimental and analytical investigations on the response of stiffened plates subjected to lateral collisions

Rational structural design of ships or offshore platforms against collisions requires prediction of the extent of damage to stiffened plates generated by lateral impact. In predicting the extent of collision damage, most researchers employ numerical analysis methods using commercial software packages. Like other structural problems, any nonlinear dynamic analysis methods should be substantiated with relevant test data prior to being employed for design. Unfortunately, full-scale collision tests on marine structures are very rare. Still, results from collision tests on marine structural elements can help to substantiate theoretical methods for collision analyses. Lateral collision test data for unstiffened plates are available, but it is difficult to find results from tests on stiffened plates in the open literature. In this paper, the results of lateral collision tests on 33 stiffened plates are reported. A simplified analytical method is developed for the prediction of the extent of damage to stiffened plates due to lateral collisions and this method is substantiated with the test results. Also proposed is a simple criterion with which the occurrence of crack damage can be judged.     

Determinants of the property damage costs of bulk barge accidents

This study investigates determinants of the vessel, cargo, and other-property damage costs of bulk barge accidents in US inland waterways. Tobit estimation of a three-equation recursive model suggests that, in bulk barge accidents: (1) vessel damage cost is greater for collision, fire/explosion, and material/equipment failure accidents than for groundings; (2) cargo damage cost is greater at night and when the weather is foggy and increases with barge age; and (3) otherproperty damage cost is greater for multi-vessel accidents, but decreases with barge size. A dollar of vessel damage cost increases other-property damage cost by $1.38, while a dollar of cargo damage cost increases this cost by $6.90. An important result for formulating bulk barge accident cost-reduction policies is that a given determinant might have a negative effect on one type of damage cost but a positive effect on another.     

缓冲型球艏的艏柱设计计算分析

依据缓冲球艏设计要求,提出棱柱型艏柱设计方案,运用有限元分析软件LS-DYNA对采用传统艏柱与棱柱型艏柱结构的12 000 t油船进行船艏碰撞的仿真分析,发现棱柱型艏柱结构比传统艏柱结构球艏更易被压溃.     

水介质对船冰碰撞结构响应的影响

以极地运输船舶艏部作为研究对象,建立基于流固耦合算法的船-水-冰耦合技术对三维船艏与冰体碰撞的结构响应问题进行了研究,结合非线性有限元软件LS-DYNA对比分析了考虑流固耦合(即有水介质)的船-水-冰碰撞模型和不考虑流固耦合(即无水介质)的船-冰碰撞模型与同质量不同速度的冰体发生碰撞下的结构响应问题,揭示了不同碰撞工况下船舶在损伤变形、碰撞力、速度等方面的变化特征及差异,同时阐述了水介质在船冰碰撞中的作用,可以为极地运输船舶的抗冲击结构设计提供参考。     

A comparative study on the structural integrity of single and double side skin bulk carriers under collision damage

The primary aim of the present study is to investigate the collision resistance and residual strength of single side skin (SSS) and double side skin (DSS) bulk carriers subject to collision damage. The impact dynamics analyses were conducted using ANSYS LS-DYNA for the evaluation resistance forces, energy absorption and penetration depth for various collision scenarios. The struck vessels of Capsize SSS and DSS designs were assumed to be entirely standstill and the striking vessels of an Aframax-type oil tanker with different bulbous bow shapes were modeled as rigid bodies. The findings were compared, where possible, with existing analytical tools. Residual strength calculations on SSS and DSS vessels were computed corresponding to all considered collision damage scenarios. Traditional Smith's method was applied with the average stress — average strain relationships of elements based on derived semi - analytically. The effect of corrosion was also evaluated by Joint Bulker Project (JBP) Rules on the influence of plate and stiffener thickness. The safety of the vessels was determined as a ratio of the ultimate hull girder strength to bending moment in damaged condition. Finally, results and insights derived from the present work are summarized.