A statistical investigation of time-variant hull girder strength of aging ships and coating life

Risk- and reliability-based approaches are increasingly being applied in assisting inspection and maintenance planning. One of the keys to such approaches is properly predicting the hull girder strength (HG) of gradually degradated hull structures. The development has been limited by the lack of data on aging ships—validation of the developed methods has not been possible. To fill the gap of knowledge on hull strength of ships in service, this paper presents a database of as-gauged hull structures and a statistical study of the time-variant HG of tankers. The expanded data set was collected from 2195 as-gauged girth belts (transverse sections) of 211 single-hull tankers that were 12–32 years old. It was intended to (1) provide actual data on hull girder section modulus (HGSM) of tankers, (2) investigate the general trends of the change in the HG over ships’ service life, and (3) propose formulations for presenting time-variant HGSM and coating life.

The data set demonstrated a high variation of HGSM that changed over time. The mean value and standard deviation of HGSM loss were derived as functions of time. The probability density function (pdf) of coating life was also derived. Comparisons were made between previous studies on HG and the current data set. It was found that almost all previous studies showed much greater HG loss than what this database revealed. The refinement of existing calculations appears to be needed. The data set and statistical study were expected to form the basis for validating formulations of HG that are key components in risk- and reliability-based approaches.     

The argument for twin screw tankers

According to the CTX tanker casualty database, machinery failures are an important cause of tanker oil spillage. This paper argues that the current large (over 10,000 deadweight) tanker fleet is experiencing at least two full losses of power or steering per day, and probably more than ten. If this fleet were twin screw, properly implemented, this number would be cut by a factor of one thousand. At the same time, tanker low speed maneuverability would be improved dramatically. All this could be done for a net cost of less than that of the double hull.     

Bottom damage scenarios for the hull girder structural assessment

This article covers the reliability assessment of the hull girder of a crude oil tanker, referring to a scenario in which the ship is exposed to sea loads after a damage to the bottom of the hull has occurred. A number of possible flooding configurations are examined, each one caused by a group of damage cases, characterized by different location and extent. Static loads, wave loads and residual structural resistance are determined for each damage case, with the objective of obtaining a prediction for the probability of the hull girder's failure. The various damage cases are compared to each other and unconditioned to derive the probability of failure extended to the ship's life due to a generic bottom damage.A probabilistic Bayesian Network model has been created to deal with these variables and with the dependency relationships existing between them. The results provided by the model are analyzed with the aim of identifying the parameters most influencing the problem. The work is intended to contribute to the development of a more rational treatment of accidental conditions in design structural requirements for ships.     

满足油船共同结构规范的船体梁剪切强度分析

通过对共同结构规范（CSR）条款的分析,归纳总结了CSR对船体梁剪切强度的具体要隶。采用微分法对剪流以及船体梁承剪能力进行了灵敏度分析,并以某阿芙拉型油船为例,通过直接计算剖面剪流的方法对微分法的计算结果进行了验证,其结果表明微分法的计算令人满意。最后,还就如何对中间／中心纵舱壁承剪构件进行优化设计作了阐述。     

破损船体的剩余极限强度分析

基于ABS和DNv规范关于剩余强度规范要求,对船舶碰撞与搁浅的破损部位和范围的假定,考虑了发生碰撞与搁浅破损后,其船体梁剩余有效剖面的非对称性和可能发生不同程度倾斜的情况,采用结构共同规范(CSR)中的逐步破坏分析方法和船体梁非对称剖面计算模型,分别计算了散货船和油船破损船体在两种破损模式和不同倾斜情况下的剩余极限强度,并对不同破损范围的影响进行了分析和比较。研究结果为协调结构共同规范(HCSR)的制定提供了有价值的参考。     

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.     

船舶上层建筑振动的最优控制分析

本文讨论了最优控制理论在船舶上层建筑振动控制中的应用。文中将船体和上层建筑简化为相应的船体梁和上层建筑梁模型，并将上层建筑梁的振动响应处理为支承激励下的响应。用模态分析法得到船体梁和上层建筑梁的动力特性（固有频率和固有振型），再用模态（振型）叠加法得到受控前上层建筑顶端的稳态动力响应，接着根据最优控制理论，设定目标函数，求解Riccati方程，得到主动控制力，将其作用在上层建筑梁的顶部，用模态（振型）叠加法得到受控后上层建筑梁顶部的稳态动力响应。以一条50000吨的油船为算例进行数值仿真，受控后上层建筑顶部的稳态振动位移减小了30％，可见最优控制在船舶上层建筑的振动控制中是可行的和有效的。     

波激振动和砰击颤振对大型油船疲劳强度影响研究

文章给出线性波激振动和砰击颤振引起的大型油船结构疲劳贡献度的计算方法。基于三维线性水弹性理论可计算得到包括刚体和2节点的振动模态下的垂向弯矩的传递函数,采用谱分析法对某30万吨油船进行结构疲劳强度计算,分析波激振动对船体结构疲劳损伤影响;基于二维非线性波浪载荷程序（含砰击颤振的波浪载荷）,采用时域方法对该油船进行船体梁弯矩计算,分析砰击颤振对船体梁弯矩及疲劳载荷的影响;结果表明对于该类大型油船波激振动和砰击颤振对船体的结构疲劳损伤的影响不可忽略。     

船体结构最优风险评估维护计划（英文）

Various structures such as marine structures age over time. In order to always maintain safety conditions, maintenance processes including inspection and repair should be implemented on them. Corrosion and fatigue cracks are two main factors that reduce the ultimate strength of the ship's hull girder over time and thus increase the probability and risk of failure. At the time of inspection,the structural conditions must be checked so that, if necessary, the required repairs can be done on it. The main objective of this paper is to provide optimized maintenance plans of the ship structure based on probabilistic concepts with regard to corrosion and fatigue cracks. Maintenance activities increase the operational costs of ships; therefore, it is advisable to inspect and repair in the optimal times. Optimal maintenance planning of the ship structure can be conducted by formulating and solving a multi-objective optimization problem. The use of risk as a structural performance indicator has become more common in recent years. The objective functions of the optimization problem include minimizing the structure's lifecycle maintenance costs, including inspection and repair costs, and also minimizing the maximum risk of structural failure during the ship's life. In the following,to achieve better responses, reliability index has been added to the problem as the third objective function. The multi-objective optimization problem is solved using genetic algorithms. The proposed risk-based approach is applied to the hull structure of a tanker ship.     

CFRP修复的FPSO点蚀船体梁极限强度分析

采用非线性有限元法对中拱和中垂工况条件下碳纤维增强聚合物(Carbon Fiber Reinforced Polymer, CFRP)修复的浮式生产储卸油装置(Floating Production Storage and Offloading, FPSO)点蚀船体梁极限强度进行仿真分析。对比FPSO的完整船体梁、点蚀船体梁和CFRP修复的点蚀船体梁的中拱极限弯矩和中垂极限弯矩，分析CFRP对FPSO点蚀船体梁的修复效果，并分析胶层失效规律。结果表明，CFRP可为船舶的高效修复提供一种新的方式。     

基于Matlab油船意外泄油性能的程序设计

基于概率方法的意外泄油性能参数计算是2010年1月1日及以后新造船破舱稳性需要评估的性能之一,满足一定的衡准要求方可。根据油船的分舱分别进行船底破损概率和船侧破损概率的插值,然后按照一定的公式求出船底破损后与船侧破损后的泄油量的加权之和,即意外泄油性能参数。由于手工计算费时费力,文章基于Matlab平台,开发了意外泄油性能参数的自动计算程序模块。计算结果与文献结果相比较,证明了本程序的计算精度,具有较好的工程实用价值。     

典型补给油船抗冲击性能研究

基于通用仿真软件,对某油船进行了远场水下爆炸的动响应分析。研究了药包沿船长方向分布、沿水深分布和不同攻角对船体结构的影响。可以看出,中远场水下爆炸对油船的冲击响应,主要表现为总体响应,局部效应并不明显;爆距对冲击响应有很大的影响,而在远场爆炸时攻角对其影响不明显,随着爆距的增加,船体结构响应逐渐减小;武器的毁伤效应对船体外板影响最为显著,随着能量在船体内的传播,到主甲板时迅速衰减。通过进行计算分析得出了一些结论,为油船的设计及建造提供参考。     

油船市场现状与策略

分析了油船市场的现状,明确指出国有油船运输缺口很大。认为目前我国已具备了发展油船船队的实力,提出了应采取的竞争策略,以适应国家经济建设和参与国际化市场竞争的需要。     

水下爆炸气泡载荷作用下船体梁的动态水弹性响应

文章基于势流理论,针对水下爆炸气泡脉动载荷作用下船体梁的动态水弹性鞭状响应及其共振效应进行了研究。阐述了水下爆炸气泡与船体梁之间的流固耦合理论分析,并分别建立了一个考虑气泡迁移,自由面效应和气泡阻力的气泡模型和一个船体梁的弹性响应的计算模型。文中以两条实船作为算例,研究了刚体运动对船体梁弹性振动响应的影响,分析了船体梁在气泡脉动载荷作用下产生的共振破坏的机理。     

15万吨级穿梭油船结构减重设计与EEDI影响评估

以15万吨级穿梭油船为例,提出一种可有效减少船体空船重量的设计方案,并评估船体减重对能效设计指数(EEDI)的影响。结果表明：与母型船相比,设计船的空船重量减少1 464 t;设计船将减重用于增加货物载重量,其EEDI可降低约1.0%。该穿梭油船的结构减重方案与可靠性评估方法可为同类型船舶的设计与开发提供参考。     

Analysis of the accident of the MVNakhodka. Part 2. Estimation of structural strength

In the early morning of January 2, 1997, a Russian tanker, the MVNakhodka, broke in two in the Sea of Japan. The fore part of the vessel drifted and was stranded on the coast of Japan, and the aft part sank. The coast of Japan was seriously polluted by spilled heavy oil. Following this disaster, the Japanese Government established a Committee for the Investigation of the Causes of the Casualty of theNakhodka. This paper deals with the structural strength of MVNakhodka at the time of the accident. First the structural characteristics of theNakhodka are described, and the reduction in thickness of the structural members are estimated based on the data measured on the fore part of the vessel which drifted ashose. Then the ultimate longitudinal strength of the hull girder at the time of the accident is evaluated by applying Smith's method, and the possibility of break-up collapse due to excess loads is discussed. The mechanism of fracture at the bottom plate is also discussed based on the observed fracture surfuce of the cross section. Finally an FEM (finite element method) simulation of the break-up of the hull girder is performed. It is shown that buckling/plastic collapse took place at the deck plate near Fr.153, which was followed by the successive buckling collapse of the side shell plate of the hull girder. Right after the collapse of the deck structure, the bottom plate fractured just in front of the transverse bulkhead at Fr.153. This article is based on an article that appeared in Japanese in the Journal of the Society of Naval Architects of Japan, vol. 183 (1998).     

船体在疲劳和腐蚀损伤下的可靠性

在疲劳和腐蚀作用下，船体梁舯剖面模数折减，导致极限承载能力下降，在此基础上进行可靠性分析。文中腐蚀率是一个有常数平均值的随机变量，疲劳裂纹根据Paris公式计算，当静水弯矩和波浪弯矩的组合值超过船体梁极限承载能力时，发生船体梁失效。以一艘散货船为例，计算其可靠性随时间的变化。计算结果可为船东和船级社评估船舶营运期间疲劳和腐蚀对船舶可靠性的影响提供参考。     

基于船体梁的船体弹性变形预报方法

将船体简化成一根两端完全自由、质量和刚度沿船长方向分布不均匀的变截面梁,采用迁移矩阵法算出船体梁的固有频率和振形;将三维势流理论和结构动力学方程相结合,求出船体振动的主坐标,再利用模态叠加原理得到计算点的幅频位移响应;利用谱分析方法计算不同工况时的船体变形,并根据雷利分布得到其统计值。以某船为例,利用该方法计算船体相对变形,并对结果进行分析,得到了船体变形随着航速大小和浪向角改变的规律。     

油船结构形式的变化及发展

介绍油船的发展历史,总结油船结构形式的变化及相关法规的主要内容。分析油船共同规范的制定实施对油船设计的影响和油船结构的发展趋势。展望中国油船建造的发展前景。通过全面系统地阐述油船结构特点,可使相关设计、建造和使用人员能较全面了解油船结构形式的发展历程,从而更清楚油船设计和建造中的有关标准和规范。     

An approach to estimating the hull girder response of a ship due to springing

This article describes an estimation method for the hull girder response of a ship due to springing. The linear and nonlinear springing effects on the hull girder are evaluated. Previous studies on the springing response focused mainly on the symmetric response, or vertical response. In this article, however, the springing analysis is extended to asymmetric responses, or horizontal and torsional responses. The Timoshenko beam model was used to calculate the hull girder response and the quadratic strip method was employed to calculate hydrodynamic forces and moments on the hull. To remove irregular frequencies, a rigid lid was adopted on the hull free surface level and hydrodynamic coefficients were interpolated for asymptotic values. Applications to two ships for the symmetric and asymmetric responses were carried out and the effect of springing responses is also discussed.