【作者】 刘峰；

【导师】 崔维成；

【作者基本信息】 上海交通大学 ， 船舶与海洋结构物设计制造， 2007， 博士

【摘要】 船舶碰撞是指船舶在海上或者与海相通的可航水域发生接触造成损害的事故,它往往会引起灾难性的后果,例如人员伤亡,船只沉没,甚至环境污染等。引起船舶碰撞事故的原因有很多种,许多国家的研究者都试图寻找可以避免船舶发生碰撞事故的方法。目前,由于人为因素的影响,船舶碰撞事故还不可能完全杜绝。从船舶结构的角度而言,基于船舶碰撞安全性的考虑,大量单壳船舶正逐步淘汰或改建成双壳船舶。众多事故报告说明,目前的常规排水型船舶的结构并不具有很好的防撞能力,船舶结构存在着改进和革新的余地。船舶碰撞问题的研究涉及到多学科、多领域。船舶结构的碰撞分析需要综合结构动力学、断裂力学、塑性力学、材料力学和水动力学等众多门类的知识,还需要掌握一定的有限元使用技术和理论分析水平。船舶碰撞过程具有各种非线性特征,如几何非线性、运动非线性、接触非线性和材料非线性等,整个过程持续的时间比较短,通常在0.1-10秒之间。发生碰撞的船体区域可能位于流场之中,因此,严格来说,船舶碰撞问题也是一个流固耦合或水弹性的问题,其相关理论对问题的研究也是很有帮助的。船舶结构的碰撞分析主要有三类方法:试验法、简化解析法和数值仿真法。试验法包括实际事故调查和实船或船模碰撞试验,它所得到的结果具有很好的直观性,对于理论方法的指导意义不言而喻,然而它耗费的资金代价往往非常大。简化解析法的精度比较低,它将碰撞中的船舶作了大量的简化处理,运用解析的方法和一些经验数据,建立半解析/半经验的船体或局部船舶结构件的力学方程,评估船体的碰撞特性。数值仿真法的优势是可以对真实船舶碰撞场景进行虚拟再现,它借助于一些有限元分析软件,船舶碰撞过程中的各种物理量都可以作为结果输出。船舶碰撞的数值仿真大都采用非线性有限元方法,一些大型的商业有限元软件已经很好地证明,它们是可以比较精确地模拟船舶碰撞过程的。然而,由于仿真模型的建立需要一定的知识、经验和处理技巧的积累,模型的计算精度并非总能令人满意,数值仿真法的结果仍然需要试验或其它研究者的计算结果来相互检验。本文将船舶之间、船舶与海洋结构物之间或船舶与其它障碍物之间的以瞬态脉冲载荷为特点的动态接触过程称为广义上的船舶碰撞,具体地说,它包括船-船碰撞,船-桥碰撞,船-海洋平台碰撞,船舶搁浅等等。本论文在对船舶碰撞过程的仿真再现中,试图从船舶结构耐撞性的角度探寻降低船舶碰撞事故损伤的方法,主要包括:在一定的碰撞分析基础上,对现有船舶结构进行耐撞性优化;对现有船舶结构进行改进,提高其耐撞性指标,即碰撞事故中单位质量的结构材料所吸收的能量。通过对本论文的研究,可以对船舶结构在各种碰撞载荷作用下的响应和能量吸收机制有比较明确的认识,为制定新的引入结构耐撞性的船舶设计和制造规范提供一定的依据。同时,一些新船舶结构设计理念的提出,可以为船舶结构的改进和革新提供借鉴。本文的主要研究工作包括如下几个方面:⑴总结、分析了船舶碰撞领域的研究现状,主要包括船-船碰撞、船舶搁浅、船-桥/海洋平台碰撞、新型耐撞结构、船体剩余强度/极限强度、数值仿真技术、耐撞结构优化和船舶碰撞风险分析等方面。⑵回顾、总结了非线性有限元方法的发展历程和基本理论,并重点讨论了船舶碰撞数值仿真中所涉及的关键技术和处理技巧。⑶利用数值仿真法分析了舷侧结构碰撞危险点问题。舷侧结构的碰撞危险点主要有三类:纵桁与横框架的交叉点,纵桁或横框架的跨距中点,舷侧板格中心点。研究表明,对于船首-双层舷侧结构垂直碰撞场景,舷侧内壳板的破裂与否和结构吸能多少并无本质关联,而主要取决于内壳板以及由纵桁、横框架组成的十字形结构的受力和变形;对于常规尺寸和厚度的船舶舷侧结构,纵桁和横框架组成的十字框架总是有利于减缓碰撞损伤的。对于由纵桁和横框架组成的十字形结构,当厚度超过某个临界板厚时,其传递的碰撞力会使舷侧内壳板先于撞头到达时破裂。本论文给出了确定双层舷侧结构中的十字框架临界板厚的方法。⑷在双层舷侧结构碰撞数值仿真的基础上,分析总结了估算舷侧结构碰撞吸能的简化方法。对于船首-舷侧垂直碰撞场景,本文考虑了多种计算条件的变化,包括撞击位置,舷侧结构尺寸,网格密度和计算模型范围的选取等。Minorsky公式和Paik的修正公式可以估算船体碰撞吸能,然而,他们未考虑到船首瘦削程度以及船侧纵桁、强横框架等强构件对碰撞损伤的影响,本文对其进行了修正。⑸通过数值仿真法的比较研究,分析了船底纵桁对于船底结构搁浅吸能的影响,从而对Zhang的经验公式进行了修正。在新的船底搁浅吸能估算公式的基础上,利用混合离散变量优化方法对双层底结构进行了抗搁浅优化设计,优化计算的变量是船底结构的尺寸,约束函数是船底结构的重量。⑹利用数值仿真法,对典型双层舷侧结构的碰撞性能进行了分析,并提出三种旨在提高抗撞击能力的改进型双层舷侧结构:箱形梁双壳结构、槽形筋双壳结构和斜纵骨夹层板双壳结构。新型舷侧结构是在常规舷侧结构的基础上作了一些简单的改动,其共同的设计理念是在可能的碰撞区域增加吸能结构件。通过比较研究发现,新结构的耐撞性指标明显优于常规结构。⑺对典型双层底结构进行了搁浅数值仿真分析,并从横向、纵向和板架三个方面考虑结构的改进,提出三种新型抗搁浅船底结构:双槽形肋板双底结构、槽形纵骨双底结构和波纹纵骨夹层板双底结构。研究表明,这些改进型结构可以有效地提高船舶的抗搁浅能力。此外,对于船舶搁浅吸能,船底结构的横向构件和板架结构的改进效果要比纵向结构的改进明显。⑻对球鼻型船首与双层舷侧结构的碰撞进行了同步损伤分析。由于船舶碰撞事故中,船首结构的损伤可能不如舷侧结构的损伤引起的事故后果严重,本文提出多层横舱壁船首的结构设计,其宗旨是降低船首结构的纵向刚度。通过比较研究发现,新的结构设计使双层舷侧结构的碰撞损伤程度大幅度降低,货舱区域舷侧结构的损伤一定程度地转移到了船首结构上,这有利于防止船舱中货物的泄漏。⑼提出一种新式的防撞结构设计理念——附加甲板结构,它是船首区域主甲板以上的箱式结构。通过弹射或滑离等操作机制,使其落下,阻隔碰撞双方的直接接触,并且吸收一部分碰撞能量,从而达到保护主要船体结构的目的。本论文的主要创新点为:⑴舷侧结构碰撞危险点概念的提出及分析;⑵利用混合离散变量优化方法对船底结构进行抗搁浅优化设计;⑶一些新型耐撞结构和防撞结构设计理念的提出。综上所述,本论文主要研究的是船舶碰撞事故可能造成的主要船体结构损伤,以此为基础,提出一些结构改进措施或新型耐撞结构设计理念。通过本文的研究,可以对船舶碰撞机理,尤其是损伤区域的结构响应和变形模式有一定的了解。为了增强船舶的安全性,类似于爆炸、砰击等偶然性载荷,船舶碰撞事故中的结构行为有必要体现在新的船舶设计规范中,本论文对几种典型碰撞场景下的数值仿真研究可以为其提供一定的依据。新型耐撞船舶结构形式和防撞结构设计理念的可以为试图对船舶结构进行创新设计的研究者提供一定的借鉴。更多还原

【Abstract】 Ship collision is a kind of marine damage accidents of ships contacting with other objects. Catastrophic aftermaths will be brought by ship collision, such as personnel loss, vessel sinking, environment pollution and so on. There are many reasons that will cause a ship collision accident. Researchers of many countries are trying to find the method avoiding ship collision accidents.Nowadays, due to factitious effect, ship collision accidents cannot be avoided entirely. From the point of ship structure, a lot of single-skinned ships fall into disuse or are refitted to double-skinned ships. From the statistics of accidents, large numbers of accident reports do not show that the structures of conventional vessels have good crashworthiness. In order to enhance security, the conventional ship structure needs to be improved or reformed.The ship collision problem is involved in a lot of subjects and domains. The collision analysis of ship structure needs many kinds of knowledge, such as structural dynamics, fracture mechanics, plastic mechanics, hydrodynamics, etc. The FEM technology and theoretical analysis are also useful for the research. The process of ship collision has various non-linear conditions, such as geometric, kinetic, contact, material, etc. The duration of the whole process is very short, which is normally between 0.1 and 10s. The collision region of ship hull is probably under the water, therefore, ship collision is a problem of fluid-structure coupling or hydroelasticity, and whose theory is helpful for the research.The methods of ship structure collision research are mainly categorized into three kinds, which are experiment, simplified analysis and numerical simulation. The experiment method includes accident investigation of real ships and collision model tests. Its results are clear and simple, which play an important act for theoretical methods. However, the experiment method is very expensive and costs a lot. Simplified analysis method has relatively low precision, which deals with the ship in collision by a lot of simplification, and semi-analysis and semi-empirical mechanics equations of ship structure are established. The numerical simulation method has the advantage that the real ship collision scenario can reappear. With the help of some FEM analysis software, all kinds of physical variables in the ship collision process can be outputted. The simulation of ship collision mainly uses non-linear FEM, and some commercial FEM software has well shown that they can simulate this process with good precision. Establishing a simulation model needs certain knowledge, experience and skills, and sometimes computation precision is not satisfaction, so verification by experiment or other researcher’s calculation is necessary.In this paper, the universal concept of ship collision is defined as dynamic contact under instantaneous impulse loads between ships, between a ship and other marine structures, or between a ship and other obstacles, which mainly includes ship-ship collision, ship-bridge collision, ship-platform collision, ship grounding, etc. According to structural crashworthiness, this paper tries to find the method that can reduce the loss of ship collision accident by simulation of the collision process. There are mainly two approaches. One is crashworthiness optimization based on certain collision analysis, and the other is to improve the conventional ship structure and present novel concepts of structural design. Research of this paper makes it clear that mechanism of structural response and energy absorption in ship collision, and provides design and manufacture criteria with new crashworthiness data.The major research work and conclusions of this paper are summarized as follows:⑴The research status of ship collision is summarized and analyzed, which includes several aspects, such as ship-ship collision, ship grounding, ship-platform collision, novel anti-collision structure, residual strength and ultimate strength of ship hull, technology of numerical simulation, structural optimization of anti-collision, risk assessment of ship collision, etc.⑵The development process and basic theory of FEM is reviewed and summarized. The key technology and modeling skills of ship collision simulation are discussed.⑶The problem of dangerous points of side structure collision is analyzed by numerical simulation. There are three kinds of dangerous points, which is the intersection point of girder and transverse frame, the mid-span point of girder or transverse frame and the center of plate lattice. The research shows that the ultimate status of collision is not essentially related to energy absorption of structure for bow-double side scenario, but to resistance and deformation of cross frames and inner side shell plating. For ship side structure of conventional size and thickness, the cross frame formed by girder and transverse frame is always advantageous to reduce collision damage. When the thickness of the cross frame exceeds certain critical value, the collision force will make the inner shell fracture before the bow of the striking ship touches the inner shell. This paper gives the method to evaluate the critical thickness of the cross frame.⑷Based on numerical simulation of double side structure, the simplified method of assessing energy absorption of collision is analyzed and summarized. For the scenario of bow-side vertical collision, several calculation conditions are considered, such as impacting location, side structure size, mesh density, region of computational model, etc. The Minorsky’s and Paik’s equations can evaluate energy absorption in ship collision. However, they do not consider the effect of bow curvature, side girder and transverse frame on collision damage, and the paper revises them.⑸According to comparison of numerical simulation, the effect of bottom girder on energy absorption of grounding is analyzed, and Zhang’s empirical equation is revised. Based on the new grounding equation of assessing energy absorption, double bottom structure is optimized by the method that can deal with both discrete and continuous variables. The variables of optimization are the size of ship bottom, and restriction function is the weight of bottom structure.⑹The collision capability of the typical double-skinned side structure is analyzed by the numerical simulation method. Three novel side structures aimed at anti-collision are presented, which are box girder structure, trough stiffener structure and sandwich panel structure with inclined stiffeners. These novel structures are derived from simply changing conventional double side structure, and their common design concept is to increase components of energy absorption in the area of possible contact. According to comparative studies, crashworthiness of the novel structures is evidently better than the conventional structure.⑺The grounding of typical double bottom structure is analyzed by numerical simulation method. The conventional double bottom structure is improved from three aspects: transverse, longitudinal and plate. Three new anti-grounding bottoms are presented, which are double bottom with double-trough floor, double bottom with trough stiffeners and double bottom with ripple stiffeners and sandwich panel. The research shows that these novel structures can enhance the capability of ship anti-grounding. Moreover, according to energy absorption of ship grounding, improvement of transverse components and panel structure have better effects than improvement of longitudinal structure.⑻Collision damage of bulbous bow and double-skinned side structure is analyzed simultaneously. As bow has less damage than side structure in most ship collision accidents, the paper presents the new design of multi-bulkhead bow, whose function is to decrease longitudinal stiffness of bow. According to the comparative studies, the novel structure design can transfer some damage from side structure of the struck ship to bow structure of the striking ship, which is good for preventing oil spill.⑼A novel structural design concept of anti-collision, additional deck structure, is presented, which is a box structure above the main deck of bow. Mechanism of ejecting or sliding is used to make the additional deck structure fall and prevent direct contact of both sides of collision. The new structure can absorbs a part of whole collision energy and protect main ship structures.The main innovations of this thesis include three aspects:⑴The problem of dangerous points of side structure collision is presented and analyzed;⑵Against grounding, double bottom structure is optimized by the method that can deal with both discrete and continuous variables;⑶Some novel structures and new structural design concepts of anti-collision are presented.Altogether, this paper researches the damage of ship hull during collision accidents, and some new types of structure design are presented. The mechanism of ship collision, especially structural response and deformation mode in the damage area, are understood to a certain extent. In order to protecting ship, structural behavior under some accidental loads, such as collision, explosion, slamming and so on, should be embodied in the new structure design rules. In this thesis, the numerical simulation research of different collision scenarios is helpful for the rule revision, and the new structures of anti-collision or structure design concepts will provide reference for other researchers to innovating in ship structure design.更多还原