含点蚀损伤船体加筋板在纵向压力下的极限强度

针对老龄化船舶结构上的点状腐蚀,利用非线性有限元方法进行计算,分析304个船体加筋板的极限强度,探讨带板柔度、加强筋柔度、腐蚀面积比和腐蚀深度比对纵向压力下含点蚀损伤船体加筋板极限强度的影响,拟合出点状腐蚀下船体加筋板极限强度折减公式并对其适用性进行验证,研究结果具有一定的工程参考意义和价值。     

点蚀板在纵向压力下的极限强度研究

本文着眼于老龄化船舶结构上的局部点状腐蚀和整体点状腐蚀,利用非线性有限元软件分析了超过100个船体板结构的极限强度。研究了蚀坑形状、蚀坑位置、蚀坑大小、蚀坑深度和板的柔度对含局部点状腐蚀船体板的极限强度的影响,蚀坑分布、板的柔度和腐蚀体积对含点状腐蚀船体板的极限强度的影响。拟合出了单面、双面局部点状腐蚀下的船体板极限强度折减公式,单面、双面点状腐蚀下的船体板极限强度折减公式。并得到同时适用于局部和整体点状腐蚀板极限强度的公式。     

Computation of ultimate strength of locally corroded unstiffened plates under uniaxial compression

Over the past decades there have been many losses of the merchant vessels due to either accidents or exposure to large environmentally induced forces. The potential for the structural capability-degrading effects of both corrosion and fatigue induced cracks are of profound importance and must be both fully understood and reflected in vessel's inspection and maintenance programme. The present study is focused on assessing the effects of localized pitting corrosion which concentrates at one or several possibly large area on the ultimate strength of unstiffened plates. Over 256 nonlinear finite element analyses (FEA) of panels with various locations and sizes of pitting corrosion have been carried out. The multi-variable regression method is applied to derive new formulae to predict ultimate strength of unstiffened plates with localized corrosion. The results indicate that the length, breadth and depth of pit corrosion have weakening effects on the ultimate strength of the plates while plate slenderness has only marginal effect on strength reduction. Transverse location of pit corrosion is also an important factor determining the amount of strength reduction. When corrosion spreads transversely on both edges, it has the most deteriorating effect on strength. It was also found out that the proposed formulae can accurately predict the ultimate strength of unstiffened plate with localized corrosion.     

Effect of pitting corrosion on the ultimate strength of steel plates subjected to in-plane compression and bending

Corrosion pits with a circular cone shape are typically observed on coated hold frames of aged bulk carriers which carry exclusively coal and iron ore. In order to ensure the safety of these types of bulk carrier, it is necessary to understand the effect of pitting corrosion on the local strength of hold frames. In order to investigate this effect, a series of nonlinear finite-element (FE) analyses has been performed with pitted plates subjected to in-plane compressive loads and bending moments. It has been shown that the ultimate compression load or bending moment of pitted plates is smaller than that of uniformly corroded plates in terms of average thickness loss, and that predictions of the ultimate strength using the average thickness loss at the minimum cross section would be conservative. In order to establish a method of evaluating strength reduction due to pitting corrosion, it is important to identify the failure mode that would be most detrimentally affected by pitting corrosion. It was found that the reduction of the ultimate compressive load or bending moment due to pitting corrosion is smaller than that of the tensile strength in terms of equivalent thickness.     

A computational investigation of the effects of both-sides general corrosion on the buckling/plastic collapse behaviour and strength of stiffened plates

This paper presents the results of an investigation into the post-buckling behaviour and ultimate strength of imperfect corroded stiffened steel plates used in ships and other marine-related structures. A series of elastic–plastic large deflection finite element analyses is performed on stiffened steel plates suffering general corrosion wastage with random distribution. General corrosion is introduced into the finite element models using a random thickness surface model. The effects of corroded stiffened plate parameters on the post-buckling and ultimate strengths are evaluated in detail. The stiffeners of different symmetrical or unsymmetrical cross-sections are introduced into the models for analysis. Some distinctions are explored and highlighted between the behaviours of steel plates suffering general corrosion in unstiffened and stiffened cases. Finally, a proposal is given in order to simulate the average stress–average strain relationship of stiffened steel plates having both-surface general corrosion wastage.     

在面内压力作用下点腐蚀低碳钢板的非线性有限元分析(英文)

无论是军船还是民船,船体及主要结构构件表面的点腐蚀对于船舶结构强度和安全性都有较大的破坏作用.文中采用系列非线性有限元计算研究了点腐蚀对于低碳钢板极限抗压强度的影响,模型中计及板初始缺陷的影响,详细讨论了板和点腐蚀物理、几何特性的变化对于板极限承载能力的作用.研究发现在众多影响因素中(例如点腐蚀的直径和深度、板的柔度系数等),点腐蚀密集度指标DOP对于板的极限承载能力有主要和直接的影响.此外,在腐蚀环境恶劣的情况下,厚低碳钢板的使用不一定如预期的那样能延长其使用期限.     

含裂纹及腐蚀损伤FPSO结构剩余极限强度评估方法研究

裂纹及腐蚀损伤对于浮式生产储油卸油装置（FPSO）结构来说难以避免，这将削弱结构的极限强度，所以研究含裂纹及腐蚀损伤FPSO结构的剩余极限强度意义重大。目前针对裂纹及腐蚀损伤联合作用下FPSO结构剩余极限强度的研究相对欠缺，本文采用非线性有限元分析方法，研究了不同腐蚀及裂纹损伤组合形式下FPSO结构剩余极限强度的衰减规律。结果表明，腐蚀与裂纹损伤均导致极限强度线性衰减，并且腐蚀损伤对极限强度的影响远大于裂纹损伤。研究结果对FPSO结构的设计、维护与延寿具有一定的参考价值。     

Experimental and numerical study of localized pitting effect on compressive behavior of tubular members

Locally pitted tubular members are usually considered as stub columns to assess the ultimate strength. However, it is not suitable for those with relatively larger slenderness ratios as their failure behavior is more complex and closely related to corrosion features of localized pitting. This paper presents compressive column tests on locally pitted tubular members of a moderate slenderness ratio. Corrosion pits were artificially introduced on local surface of the members, forming corrosion patches with various corrosion features. A numerical modelling method was proposed to reproduce the test specimens. Localized pitting damage was proven to cause substantial declines in the load deformation capacity and ultimate strength, and have a significant effect on the failure mode. The failure of a pitted member is mostly initiated by local buckling after yielding occurs in the corrosion patch, concurrent with pitting closure, and even shear cracking of member wall due to the perforated pits. Moreover, shape change of the corrosion patch most likely results in the failure mode to alter from column buckling to local buckling or interactive buckling. The shape ratio of the corrosion patch is one of the critical factor to influence the ultimate strength of locally pitted members. The proposed modelling method is applicable for extensive stochastic simulations so as to develop an empirical formula and to clarify the probabilistic characteristics of ultimate strength.     

均匀受压含裂纹损伤加筋板的极限承载能力分析

在均匀受压下,针对含损伤裂纹缺陷的加筋板的承载力学特性进行研究,探讨了裂纹参数对其承载能力的影响。通过改变加筋板上裂纹的位置和裂纹尺寸,利用非线性有限元分析软件Abaqus对其进行系列非线性仿真分析,得到含损伤裂纹加筋板的破坏力学特性以及破坏模式。结果表明,损伤裂纹会削弱加筋板架的承载能力,并且当裂纹尺寸超过某临界值时,板架的极限承载力会急剧减小。     

点蚀损耗对船体梁极限强度的影响（英文）

The paper focuses on the assessment of the hull girder ultimate strength,combined with random pitting corrosion wastage,by the incremental-iterative method.After a brief review about the state of art,the local ultimate strength of pitted platings under uniaxial compression is preliminarily outlined and subsequently a closed-form design formula is endorsed in the Rule incremental-iterative method,to account for pitting corrosion wastage in the hull girder ultimate strength check.The ISSC bulk carrier is assumed as reference ship in a benchmark study,devoted to test the effectiveness of the incremental-iterative method,by a comparative analysis with a set of FE simulations,performed by Ansys Mechanical APDL.Four reference cases,with different locations of pitting corrosion wastage,are investigated focusing on nine combinations of pitting and corrosion intensity degrees.Finally,a comparative analysis between the hull girder ultimate strength,combined with pitting corrosion wastage,and the relevant values,complying with the Rule net scantling approach,is performed.Based on current results,the modified incremental-iterative method allows efficiently assessing the hull girder ultimate strength,combined with pitting corrosion wastage,so revealing useful both in the design process of new vessels and in the structural health monitoring of aged ships.     

Ultimate strength assessment of simply supported pitted platings: A new stochastic approach based on Monte Carlo simulation

The ultimate strength assessment of platings affected by random corrosion wastage is a key factor for the reliable design of new ships and the structural health monitoring of aged structures, as pitting corrosion wastage significantly affects the ultimate capacity of platings under compression. In this respect, significant efforts have been undertaken in the last decade to assess the ultimate strength drop-off of pitted platings under compression and several interpolating design formulas, based on a large number of FE simulations, have been developed. Nevertheless, current Rules and guidelines don't provide any explicit strength check criterion for pitted platings. Hence, the main aim of current research is the development of a new framework for the ultimate strength assessment of pitted platings, based on a stochastic approach and the endorsement of Monte Carlo simulation. A new formula, which allows evaluating the statistical properties of the plating ultimate strength in presence of random corrosion wastage, is developed. Subsequently, a benchmark study is carried out, to compare the new formula with the existing ones available in literature and a wide set of FE simulations, carried out by Ansys APDL. Current results are discussed, and the effectiveness of the new formula is verified.     

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。     

腐蚀和裂纹损伤下海洋平台极限强度试验研究

根据墨西哥湾某一典型固定式海洋平台为原型,按照刚度相似性和几何相似性,分别设计并制作了完好模型、腐蚀模型、裂纹模型,并对三个试验模型开展极限强度试验研究,试验结果表明腐蚀、裂纹损伤严重影响试验模型极限承载力,且试验模型失效模式各不相同.同时,采用非线性有限元方法,分别对三个试验模型进行计算,将计算结果与试验结果对比分析,验证了该方法在固定式海洋平台极限强度计算方面的有效性.     

腐蚀对双壳超大型原油运输船船体的影响研究（英文）

This study aims to examine and analyze the effect of corrosion wastage on the ship hull of a double hull very large crude oil carrier. To calculate the ultimate bending moment capacity, along with the neutral axis position at the limit state, section modulus, and moment of inertia, the incremental-iterative method is employed. This paper also considered the residual strength checking criteria of ship hull and the ultimate stress behaviors of the representative structural elements. Then, Paik's probabilistic corrosion, which employs two levels of corrosion rate and three different assumptions of coating life time, is applied to assess the corrosion effects. The calculation results obtained through relevant analyses are also presented.     

Effect of pitting corrosion on local strength of hold frames of bulk carriers (2nd Report)—Lateral-distortional buckling and local face buckling

Pitting corrosion is typical corrosion observed on coated hold frames of bulk carriers which exclusively carry coal and iron ore. In order to secure the safety of these types of bulk carriers, it is important to understand the effect of pitting corrosion on local strength of hold frames.

In order to investigate this effect, a series of 4- and 3-point bend tests on structural models which consist of web, shell and face plates has been carried out. Artificial pitting was created on the web plate to simulate pitting. In the 4-point bend tests, two equal concentrated loads have been applied vertically at the one-third points of simply supported models so that compression load due to bending would act on the face plate. In this testing condition, lateral-distortional buckling occurred before reaching the ultimate strength and local buckling of the face plate was observed after reaching the ultimate strength. The effect of web plate pitting on the lateral-distortional buckling strength was found to be small but the ultimate strength decreases with increase in the degree of pitting intensity. In the 3-point bend tests, concentrated load has been applied vertically at the center of simply supported models so that compression load due to bending would act on the face plate. In this testing condition, local face buckling occurred just after reaching the ultimate strength. The ultimate strength is found to be decreasing with increase in the degree of pitting intensity.

A series of non-linear FE analyses has been performed to simulate the deformation behavior observed in the tests. It has been revealed that even in the case of randomly distributed pitting corrosion the ultimate strength of the structural models was almost the same as that of the structural models with uniform corrosion corresponding to the average thickness loss.     

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。     

含凹陷损伤FPSB典型加筋板剩余极限强度研究

本文选取一型FPSB典型加筋板结构,在考虑初始缺陷的情况下采用非线性元法,通过对比研究,选定了(1/2 1 1/2)的加筋板模型以及合适的边界条件、网格尺寸。分别研究了三种不同凹陷形状对加筋板极限强度的影响,选定了以弧形凹坑为主要研究对象的凹陷形式。分别研究了凹陷损伤加筋板随凹痕深度、凹痕长度、凹痕宽度、凹痕位置变化时结构在单轴受压情况下的极限强度变化情况。本文的计算结果可对此型FPSB加筋板结构在凹陷损伤后的极限强度评估提供一定的参考。     

船体梁极限强度计算中的曲板“硬角”属性

为了解决极限强度计算时曲板能否作为硬角单元的问题,从曲板屈曲的规范公式出发,讨论曲板屈曲与几何参数的关系。采用非线性有限元程序对具有不同初始缺陷的多组曲板进行极限强度计算,研究初始缺陷对曲板极限屈曲强度的影响。依据是否发生屈曲,给出判定曲板归属硬角单元的判据。