【作者】 张运良；

【导师】 林皋；

【作者基本信息】 大连理工大学 ， 水工结构工程， 2002， 博士

【摘要】 海冰-结构的动力相互作用、冰激振动及冰载荷的识别问题，仍是目前工程海冰界的核心和热点问题。但由于问题的复杂性，公认的能够描述冰-结构动力相互作用力学机制的数学物理模型还远未找到，对冰激振动机理的认识远未统一，现有各类冰载荷的识别方法还存在着许多不尽人意之处，因此，本文利用室内模型实验、数值分析和模拟等手段开展了以下三个方面的初步研究：(1)海冰-柔性结构动力相互作用时冰载荷的识别方法；(2)冰激柔性锥体振动的室内实验模拟；(3)基于DDA方法的冰-结构动力相互作用的数值模拟。相应地，主要研究内容和研究成果分为三部分： 工程实际中冰载荷的获取有直接测量法和识别反演法两大类，各具优势和特点，都有一定的效果。本文第2章着重开展了动态载荷(包括冰载荷)的识别方法研究，它为本文后续工作的开展打下了必要的基础。首先，介绍、比较和总结了现有文献中关于冰载荷识别的各类主要的频域和时域方法，然后，针对现有时域识别方法的计算繁复、工作量大、稳定性和抗噪能力都较弱的缺点，对具有工程应用前景的一类载荷时域识别方法作了进一步的改进：放弃了目前现有文献中关于未知外载荷在离散时间间隔内为阶跃常荷载的假定，采取在微小的时段内外载荷是按线性规律变化的更为合理的假设；重新推导并建立了对于比例阻尼系统的一套新的载荷识别公式和程序。同时，通过对离散时间间隔的控制，可以保证该识别计算具有很强的数值稳定性和抗噪能力。依据本文的识别模式和程序，能够实现由结构的任一种类型的响应(位移或速度或加速度或应变)或各类响应的组合来确定未知作用力的时程。经算例详细地论证，作者提出的载荷识别公式相对于文献中所给出的公式而言，形式简洁、明了，应用方便，计算量小且效率高，并且具有较强的稳定性和抗噪能力，适用于稳态和非稳态等各类载荷的识别。该方法成功地应用于如下冰激锥体振动实验中动态冰载荷的识别。 模型实验是探讨冰激锥体振动机理和特点的一个有效途径，因而第3章就介绍了作者利用DUT-1非冻结可破碎模型冰和自行设计的柔性加锥模型结构，所设计的冰速变化而其它参数固定时模拟冰激锥体振动的室内实验方案。测量了模型冰排和小冰样的弹性模量和弯曲强度，以及相互作用过程中结构上特定点处的位移、加速度和动应变时程，拍摄了冰排-结构动力相互作用的整个过程。利用作者在第2章中提出的动态载荷时域识别方法，依据结构的振动响应，识别了作用于模型结构上的动态冰载荷时程，进而得到了相应的载荷Fourier频谱，并对反演计算的效果进行了说明和验证。从实验和计算结果得出的结论是：冰激锥体振动是一种间歇性的随机受迫振动+自由阻尼振动，且以低频振动为主；DUT-1模型冰排在与锥体模型结构动力相互作用时，主要以弯曲折断的方式破坏，兼有压缩、剪切型破坏，与原型观测较为符合；依据结构的动态响应所识别的动 大连理工大学博士学位论文一冰力，在量级上比较符合实际，而冰力随冰速和时间的双重变化关系不ggffi简单的函数定量地描述，但冰力最大幅值有随冰速的提高而增大的趋势：动冰力具有较为丰富的频率成分，主要集中在0～3他的频带范围内：在某一特定条件下，冰激锥体振动sic产生动力放大的共振现象，但需要进一步的实验验证。 数值模拟是研究冰—结构相互作用及冰激振动的另一个有效途径。第4章所涉及的是非连续变形分析（DDA）方法在模拟海协结构相互作用领域的初步应用。首先简单介绍了二维DDA方法的基本理论，然后将高速运动的冰排理想化为弹脆性材料，并应用＊）f＼H维程序将冰排和结构都离散成块体系统，结合两个算例探讨了DDA方法的适用性。结果中不仅直观地给出了小结构相互作用时冰排的破坏就，而且给出了柔性结构上代表观测点的位移及速度响应时程，接触面上结构的局部水平应力曲线，以及结合作者提出的动载时域识别技术利用响应反演得到了作用于结构上的等效总动冰载荷。根据模拟结果，认为DDA方法为研舶冰与结构的动力相互作用和冰激振动问题跳了一条可行的新思路。更多还原

【Abstract】 Dynamic interactions of sea ice with offshore structures, ice-induced vibrations and ice loads identification, are still the hot and key problems in ice engineering. However, due to the complexity of sea ice mechanics, a widely accepted physical model describing the mechanism of dynamic ice-structure interactions and ice-induced vibrations has not yet been well developed, especially the methods for identifying dynamic ice loads are not so satisfactory. Therefore the main work of this thesis is to deal with the following topics: (1) methods for identifying dynamic ice loads during the process of ice-flexible structures interactions; (2) Simulation of ice-induced vibrations of flexible conical structures by laboratory tests; (3) Numerical simulation of ice-structure interactions by DDA method. Accordingly the contents of this thesis include three parts as follows.There are two ways to get the dynamic ice loads in ice engineering, i.e., direct measurement and indirect identification. Both of them have advantages and disadvantages. Chapter 2 mainly treats with different methods for dynamic ice load identification. First, several kinds of methods in frequency and time domain for identifying dynamic ice loads are introduced, summarized and compared. Then the emphasis is concentrated on improving of the present methods in time domain. These methods have the advantage that they can provide time history of the unknown dynamic force directly, with no need performing Fast Fourier Transformation (FFT), and therefore are welcomer by engineers compared with those methods in frequency domain. However, the methods in the time domain also have disadvantages that the processes of calculations are much too heavy and complicated, as well as with no strong anti-noise ability. So based on more reasonable assumption that the unknown external forces vary linearly within the discrete time interval, an improved method for dynamic load identification for proportional damping system is presented by authors. A set of concise recursive formulae for determining the values of these forces is derived, only any kind of structural response: displacement, velocity, acceleration or strain needed for the input. Practical examples show in detail that compared with other formulae given in recent literature, the approach given by the authors is simple, effective, with strong anti-noise ability and can be applied to identify all kinds of dynamic loads in the engineering.Performing laboratory tests is an effective way to explore the mechanism of ice-induced vibrations of conical structures. So Chapter 3 introduced a laboratory test program designed by the authors for the simulation of ice-induced vibrations of a flexible conical structure, in which DUT-1 model ice sheet are driven by the multi-function trailer at different velocity. The elastic modulus and flexural strength of both ice sheet and ice samples are measured. The responses of the model structure, including accelerations, displacements and strains are measured and some typical photos recording the ice failure process are presented. According to the method of dynamic load identification developed by the authors in Chapter 2, time histories and Fourier spectrums of the global ice loads exerted on the conical structure model are given. From the measured and calculated results, some conclusions are drawn, i.e., The ice-induced vibration of aflexible conical structure is a kind of intermittent free-damped vibration after a forced vibration, dominated by modes of low frequencies; The predominant failure mode of DUT-1 ice sheet before the conical structure is bending failure, mixed with other modes such as crushing and shearing failure, which are illustrated by typical photos taken on the spot; the magnitude of the identified ice loads coincides with that of the measured ice force in Bohai Sea, However, variation of ice loads with time and velocity, while other parameters are set, cannot be expressed by a simple function; The trend of maximum ice load increasing with the ice velocity is obta更多还原