【作者】 杨磊；

【导师】 王德禹；

【作者基本信息】 上海交通大学 ， 船舶与海洋工程， 2020， 博士

【摘要】 船舶在航行过程中受多变的海洋环境,人为因素等的影响,难免出现碰撞事故。对于运输石油、LPG(液化石油气)、LNG(液化天然气)、化学物品等船舶,一旦发生碰撞,极易造成严重事故。在巨大的碰撞载荷下,船体结构往往会出现损伤,甚至破裂,进而造成货物泄漏、环境污染、人员伤亡等灾难性后果。人为因素是造成船舶碰撞主要原因,也是难以杜绝的。本文从人员安全、保护环境、减少经济损失等方面出发,深入研究船体结构在碰撞载荷作用下的动态响应、损伤变形和能量吸收规律以及失效机理,考虑双向应力和应变率的影响,结合落锤碰撞试验和数值仿真技术建立了船舶结构碰撞失效准确评估方法。论文的主要研究内容如下:(1)总结整理了国内外关于船舶结构碰撞损伤机理和失效评估准则等方面的研究现状和研究方法,阐述了有待补充和完善的内容,提出本文的研究意义和主要研究内容。(2)针对考虑双向应力的BWH失效准则,基于Swift塑性不稳定性理论,提出了改进的BWH失效准则(m-BWH),该失效准则能提高材料在高应变比应力状态下的失效评估精度。考虑双向应力和应变率的影响,结合Cowper-Symonds模型,提出动态BWH失效准则。基于塑性应力更新算法,使用Fortran语言对Abaqus进行用户材料子程序(VUMAT)二次开发,实现了失效准则在数值仿真中的应用。(3)开展了船用高强钢双向拉伸试验,采用6种不同形状的试件研究不同双向应力状态对材料失效的影响。用VUMAT子程序的方法,将m-BWH失效准则和BWH失效准则嵌入到仿真模型中对双向拉伸试验进行数值仿真研究,并与常应变失效准则仿真结果进行对比分析,试验验证了考虑双向应力影响的失效准则更能准确预测材料的失效。(4)开展了船用高强钢的高速拉伸试验、分离式霍普金森压杆(SHPB)试验,板架落锤碰撞试验。用VUMAT子程序的方法将动态BWH失效准则嵌入到数值仿真模型中对板架落锤碰撞试验进行数值仿真研究,并与常应变失效准仿真结果进行对比分析,试验验证了所提出动态失效准则的准确性。并讨论了摩擦系数、应变率、网格尺寸对板架碰撞破口形状的影响。(5)在前面几章的研究基础上,对某集装箱船在不同初始撞击速度下舷侧结构的动态响应、损伤变形和能量吸收规律、结构失效模式和破坏特性进行了研究。结果表明用动态BWH失效准则所预测的舷侧结构整体抗碰撞性能强于常应变失效准则所预测的结果。不同撞击位置对结构失效的影响表明,撞击点处的舷侧纵桁与横框架十字交叉结构比仅有舷侧纵桁或横框架结构更容易引起外板破裂。不同摩擦系数对结构失效的影响表明,在撞击初始速度较小时,摩擦系数增大会影响舷侧内板破口裂纹走向和破口形状,减轻舷侧上部结构的撕裂程度。当摩擦系数增大对摩擦耗散能的影响小于摩擦作用时间和作用行程减小的影响时,摩擦耗散能占比反而减小。更多还原

【Abstract】 Due to the influence of changeable marine environment and human factors,collision accidents are inevitable.In case of collision between ships that transporting petroleum,LPG(liquefied petroleum gas),LNG(liquefied natural gas)and chemicals,serious accidents are easy to occur.Under the huge impact load,the hull structure will often be damaged or even broken,resulting in cargo leakage,environmental pollution,casualties and other catastrophic consequences.Human factors are the main causes of ship collision,which are also difficult to eliminate.In this paper,for the aim of personnel safety,environmental protection and economic loss reduction,the dynamic response,damage deformation,energy absorption and failure mechanism of the hull structure under the impact load are studied in depth.Considering the influence of biaxial stress and strain rate,combined with the falling weight collision experiments and numerical simulation technology,the accurate collision failure evaluation method of the ship structure is established.The main research contents of this paper are as follows:(1)This paper summarizes the research status and research methods of collision damage mechanism and failure evaluation criteria of ship structures at home and abroad,expounds the contents that need to be supplemented and improved,and puts forward the research significance and main research contents of this paper.(2)Based on Swift?s plastic instability theory,a modified BWH failure criterion(m-BWH)is proposed to improve the failure evaluation accuracy of materials under high strain ratio stress.Considering the influence of biaxial stress and strain rate,combined with the Cowper-Symonds model,a dynamic BWH failure criterion is proposed.Based on the plastic stress updating algorithm,the secondary development of user material subroutine(VUMAT)for Abaqus is carried out by Fortran language,and the application of failure criterion in numerical simulation is realized.(3)The biaxial tension experiments of high strength hull steel were carried out.Six specimens with different shapes were used to study the effect of different biaxial stress states on material failure.By using the method of VUMAT subroutine,the m-BWH failure criterion and BWH failure criterion are embedded into the simulation model to carry out numerical simulation research on the biaxial tension experiments and compared with the simulation results of the constant strain failure criterion.The experiments verify that the failure criterion considering the influence of biaxial stress is more accurate in predicting the failure of materials.(4)The high-speed tensile experiments,SHPB compression bar experiments of high strength hull steel and falling weight collision experiments of stiffened panels were carried out.The dynamic BWH failure criterion is embedded in the numerical simulation model by using the method of VUMAT subroutine.The numerical simulation of falling weight collision experiments of stiffened panels is carried out,and the results are compared with the simulation results of the constant strain failure criterion.The experiments verify the accuracy of the proposed dynamic failure criterion.The effects of friction coefficient,strain rate and grid size on the fracture shape of the stiffened panels are discussed.(5)Based on the research in the previous chapters,the dynamic response,damage deformation,energy absorption,structural failure mode and failure characteristics of the side structure of a container under different initial impact speeds are studied.The results show that the overall anti-collision performance of the ship structure predicted by the dynamic BWH failure criterion is better than that predicted by the constant strain failure criterion.The influence of different impact positions on the structural failure shows that the cross structure of the side longitudinal truss and the web frame at the impact point is more likely to cause the fracture of the outer plate than where there is only side longitudinal truss or web frame structure.The influence of different friction coefficient on structural failure shows that when the initial velocity of impact is small,the increase of friction coefficient will affect the crack direction and fracture shape of the side inner plate,and reduce the tearing degree of the side upper structure.When the increase of friction coefficient has less effect on friction dissipation energy than the decrease of the friction action time and the friction work,the friction dissipation energy may decrease.更多还原