【作者】 王琮；

【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】 浮桥,作为大型浮式结构物应用的一种形式,在军事和国防建设中发挥着至关重要的作用。与传统的船舶与海洋结构物相比,浮桥具有的独特之处在于:(1)水平尺度与高度之比较大,其弹性变形与刚体位移量级相当,结构的弹性变形不可忽略;(2)通常是由各个舟体拼装而成,各舟体间连接构件的动力响应与疲劳强度问题是影响自身安全性的重要因素。本文作为“十五”和“十一五”国防预研重点项目“高流速下通载浮桥的水弹性动力响应研究”的后续研究,主要研究工作有如下几方面:(1)课题相关研究领域的综述——针对水弹性力学理论、浮桥水弹性响应研究、连接器发展状况以及疲劳分析理论四个方面的国内外研究进展进行综述,介绍目前解决这些问题的已有方法、发展过程及应用情况。(2)浮式结构三维水弹性分析理论研究——在有限元理论基础上对浮式结构运动方程进行详细推导;通过对弹性结构所受外载荷特性与流固耦合界面Price-Wu边界条件的分析,得到弹性浮体的三维水弹性响应控制方程,为后续研究波浪作用下及移动载荷作用下浮桥水弹性响应问题奠定理论基础。(3)移动载荷作用下浮桥水弹性分析理论研究——基于非线性有限单元法建立考虑桥节间非线性连接及载荷惯性影响的浮桥水弹性响应运动方程;并采用超单元方法对系统运动方程进行自由度的缩减,以真正实现水弹性分析。(4)波浪及移动载荷作用下浮桥水弹性响应分析——结合(2)与(3)两方面的工作,在对一自由浮体进行水弹性响应分析以验证三维水弹性理论正确性的基础上,首次应用三维水弹性理论对波浪作用下带式舟桥进行水弹性响应分析,并通过与试验结果的比较,表明该理论在浮桥水弹性响应预报中的准确性。此外,研究了移动载荷作用下带式舟桥与桥脚分置式舟桥的水弹性响应特性,对课题组前期进行的“非线性连接浮桥水弹性响应研究”工作(付世晓, 2005)进行拓展,并重点研究接头的连接力响应,为后续接头的疲劳寿命预测提供重要的载荷信息。(5)疲劳分析基础理论研究——对舟桥接头疲劳寿命分析中所涉及的低周疲劳问题以及各种疲劳分析方法进行对比研究;在此基础上,着重讨论局部应力—应变法的原理及其各个疲劳特性参数的确定。(6)浮桥桥垮接头低周疲劳分析——基于上述舟桥水弹性响应分析而求得的桥垮接头的承载历程,并采用局部应力—应变法对所建立的复杂连接接头的实体模型进行疲劳寿命分析,从而建立移动载荷通行速度与接头疲劳寿命之间的关系,指出在舟桥设计过程中,载荷通行速度的重要性。(7)总结与展望——总结全文工作,同时展望未来该领域研究工作的发展方向。本文创新性的研究工作主要表现在:波浪作用下带式舟桥的水弹性响应分析、基于水弹性理论的移动载荷作用下舟桥接头的动响应分析、以及桥垮接头的疲劳寿命分析。通过分析研究得出的主要结论如下:(1)对于波浪作用下的带式舟桥而言,随着入射角角度的不断增大,浮桥中心线处的水弹性响应幅值明显增大;同样,对于同一入射角、入射波波长逐渐增大的情况也是如此,但预报精度略有下降。(2)对于移动载荷作用下的浮桥而言,不论是带式或桥脚分置式,随着通行速度的逐渐增大,桥节间最大连接力响应幅值增加显著,连接接头所承受的交变载荷变化频率加大,致使连接接头所承受的应力幅陡然增大。然而,由于自身重量及所承载重量较大,桥脚分置式舟桥的垂向位移响应及影响范围并不像带式舟桥那样随通行速度增大而显著加大,基本上保持不变。(3)在进行舟桥设计时,必须要充分考虑接头承受动载的顺序、疲劳性能参数的大小、以及材料的极限拉伸强度等问题,尤其要对移动载荷的通行速度进行严格控制,以减少对连接接头造成疲劳破坏。与此同时,还应大力改进连接接头的焊接工艺,以避免由于焊缝处疲劳强度比母材低而造成在结构发生疲劳破坏之前,焊接位置附近先发生疲劳损伤而缩短构件的使用寿命。更多还原

【Abstract】 The floating bridge, as one important application form of the floating structures, is of great significance in the construction of military work and national defense. However, it differs from the traditional ships and offshore structures in: (1) the large ratio of length to height and the equivalent magnitudes between flexible deformation and rigid body displacement, i.e. the flexible deformation of the structure cannot to be neglected; (2) the connected slender configuration by several bridge rafts, which will make the connection force and fatigue behavior of the connectors to be critical factors that influence the safety performance of the integrated bridge.The present study is a post-research of“Hydroelastic Response of the Floating Bridge Subjected to Moving Loads in High Speed Flow”, which is a national defense pre-research project in the 10th and 11th five-year plan, and mainly consists of the following aspects:(1) A literature review of the related research works, including the theory of hydroelasticity, the hydroelastic response analysis of the floating bridges, the development of the connectors, and the theory of fatigue analysis, is presented, in which a description of the existing approaches, development procedure and applied conditions is introduced.(2) Three dimensional hydroelasticity theory of the floating structures. Based on the finite element method, the equation of motion for the floating structures is given. Consequently, three dimensional hydroelastic governing equation is obtained via the analyses of the external loads and the Price-Wu boundary condition at the fluid- structure interface, which can be regarded as the theoretical foundation of the hydroelastic analyses for the floating bridge subjected to waves or a moving load.(3) Hydroelastic response analysis theory of the floating bridge subjected to a moving load. On the basis of nonlinear finite element method, a hydroelastic equation of motion for the floating bridges considering the nonlinearities between rafts, and the inertial effects of the loads is established. To ensure the implementation of the hydroelastic analysis, the super element method is applied to condense the degrees of freedom (DOFs) of the motion equation. (4) Hydroelastic analyses of the floating bridges under wave or a moving load action. Based on the above-mentioned two aspects and accuracy of the approach validated by the hydroelastic analysis of a free floating body, the hydroelastic analysis of a ribbon bridge in waves is first presented and compared with the corresponding experimental results, which indicates that the hydroelasticity theory can be properly applied in the prediction of the floating bridge. In addition, as an extension of the previous work“Hydroelastic Analysis of a Nonlinearly Connected Floating Bridge”(Fu, 2005), an investigation on a ribbon bridge and a pontoon-separated floating bridge subjected to a moving load is performed, with the focus on the connection forces of the bottom connector, which provides the related loading information for the following fatigue analysis of the connector.(5) Fatigue analysis theory. Considering the fatigue analysis of the connectors, the basic concept of low cycle fatigue and different fatigue analyses approaches are discussed and compared, with the concentration on the local stress-strain method and the definition of the corresponding fatigue properties parameters.(6) Low cycle fatigue analysis of the connectors for the floating bridges. Based on the load history of the connectors obtained from the hydroelastic analyses of the floating bridges, the fatigue life prediction is conducted on the complicated connector model constructed by the solid elements via employing the local stress-strain method. Thus, the relation between the passing speed and fatigue life of the connector can be set up, which implies that the passing speed plays a crucial role in the design of the floating bridge.(7) Summary and forecast. Summarizes all the work mentioned in the dissertation and proposes the future development trends of the related fields.The innovative research works in the dissertation are primarily represented as the hydroelastic analysis of the ribbon bridge subjected to wave loadings, the dynamic analysis of the connectors for the floating bridge subjected to a moving load based on the theory of hydroelasticity, and the fatigue life prediction of the connectors, with the associated conclusions being drawn as follows:(1) As for the ribbon bridge in waves, the hydroelastic response amplitude along the centerline of the floating bridge increases with the increase of the incident wave angle. Similarly, for the same incident wave angle, the response amplitude still goes up with the increasing wavelength, however, the accuracy of the prediction method decreases.(2) For the floating bridges, either the ribbon bridge or the pontoon-separated one, subjected to a moving load, the peak connection force rises remarkably with the increasing passing speed, and also the stress amplitude increases sharply due to the increase of the varied frequencies of the alternating loads on the connector. However, considering the heavy self-weight and large loading capacity of the pontoon-separated bridge, the vertical displacement and influential scope keep constantly and do not increase conspicuously as the ribbon bridge does.(3) In the design process of the floating bridge, the sequence of the dynamic loads acting on the connectors, the magnitude of various fatigue properties parameters and the ultimate tensile strength should be sufficiently considered, especially the passing speed of a moving load, so that it can inevitably diminish the fatigue damage of the connectors. Moreover, the welding technology should be further improved to avoid the occurrence that the fatigue damage in the vicinity of the welding position happens prior to that of the connectors due to the higher fatigue strength that the parent metal has, otherwise it will shorten the service life of the connectors.更多还原