【作者】 陈正寿；

【导师】 于定勇；

【作者基本信息】 中国海洋大学 ， 港口、海岸及近海工程， 2009， 博士

【摘要】 泻涡脱落诱发的涡激振动是海洋立管和众多弹性结构疲劳破坏的主要诱因,越来越受到海洋工程界的关注。目前在涡激振动模态瞬时突变分析,物理实验和数值模拟实施等多方面仍面临很多难题。本文以CFD数值模拟在涡激振动计算仿真的实用化应用为宗旨,在改进振动信号分析方法的基础上,通过物理模型实验和数值模拟相结合对单、多弹性管系统在复杂动荷载作用下的泻涡脱落和与之对应的涡激振动形态等进行了综合研究。本文同时涉及振动信号分解分析方法改进、柔性管涡激振动物理模型实验和基于商业软件的数值模拟仿真三方面工作,各研究工作相互补充,有益结合,自成体系。首先,引入作者研究生论文提出的一种应用于处理平稳并具有各态历经性随机过程的信号分解技术。本文通过追加非模态项分解准则以及改进固有模态函数的“窄带”限定两项措施,将这种基于快速带通滤波原理原本仅适用于平稳过程的信号分解技术,成功应用到非平稳涡激振动信号分解分析中去,建立了一种全新的3D瞬时频率—能量谱振动信号分析方法。这种新的分解方法,既可以非常有效的将非模态项分离出来,又不会对第一振动模态所携带的能量构成任何消减;同时新的“窄带”限制条件保证了固有模态函数分量真正意义上两两正交。其次,本文采用物理实验验证和数值模拟结合的方法深入研究了弹性管的涡激振动机理。物理模型实验和数值模拟工作相互补充,前者为后者提供模型建立的方向性指导并作为判断计算结果可靠性的依据;经过优化设计的后验型数值模拟则为物理模型实验提供对应的弹性管尾流区泻涡发放形态及结构位移和变形的瞬时综合信息,从漩涡发放形态随时间和沿弹性管轴向变化的角度进一步阐述动荷载诱导因素对弹性管振动的影响。同时,本文对数值模拟的结果和物理模型实验观测的结果之间存在的差异给予合理的说明,并提出改进方案。最后,本文进行了一系列采用数值模拟替代模型实验的仿真尝试,旨在解决物理模型实验无法进行,而在实际海洋工程中又经常遇到的复杂动荷载和复杂柔性管结构的涡激振动相关问题。先验的数值模拟尝试对与实际工程应用密切相关的管内附加流动的大跨度弹性管剪切流场中的自激振动,小跨度弹性管波-流联合作用下的受迫振动和多弹性管系统在内外流共同作用下的涡激振动进行了相关的模拟。这些模拟过程不仅得到了一些与对应工况研究结果相符的结论,也得到了一些新的发现。这些先验的模拟工作对指导今后的物理模型实验以至相关的实际海洋工程实践都具有重要的参考价值。本文创新性的工作体现在:本文改进的振动信号分解、分析方法为实验、模拟结果提供了强有力的数据分析工具,物理模型实验与数值模拟相关的很多重要结论完全受益于此。同时,通过物理模型实验与数值模拟的结合,很多弹性管涡激振动相关的振动模态、振幅间相互作用、泻涡发放变化规律、弹性管振动模态瞬时突变、弹性管群的复合耦合振动及尾流区复杂的泻涡发放形态等方面都从流固耦合的角度给予了合理的解释。更多还原

【Abstract】 As a complicated synchronization phenomenon of Fluid-Structure Interaction (FSI), Vortex-Induced Vibration (VIV) which is related mainly to flexible cylindrical structures acts as the dominant fatigue damage to risers systems widely used in offshore engineering. Although there are many research works have been done concerning model tests and numerical simulation, the aspects related to the efficient method to combine them together and an instantaneous frequency-energy analysis method for oscillation mode identification are still left unsolved. For the sake of actualizing the numerical application of CFD method to VIV study, a sysmatic research related to VIV have been carried out, including the innovation of data analysis method, the interpretation between vortex sheding pattern and pipe oscillation. The model tests and numerical simulations related to single pipe and multi-assembled pipe systems subject to VIV and other hydrodynamic loads has been carried out, in order to provide meaningful reference to optimal design of offshore riser systems and accurate assessment for fatigue damage. This paper is a systematic report about vortex-induced vibration, including the innovation for data analysis method, the combination of model tes and numerical simulation.Firstly, a signal decomposition method based on FFT band-pass filtering technology has been introduced to analyze nonstationary vortex-induced vibration data. In this newly developed signal decomposition method, some critical innovations, that is, a“modeless component”decomposition criteria and a“narrow band”redefinition have been adapt to make this method out for more complicated nonstationary VIV signals. By the way, it has obtained great success when appling it to stationary random wave theory in my previous master degree thesis. By means of those two applicable improvements, the energy dissipation resulting from nonstationary and the disability of instantaneous frequency-energy spectrum has been well conquerd. And then 3D instantaneous frequency-energy Hilbert spectrum based on the improved decomposition method has been developed and applied to instantaneous oscillation modal analysis.Secondly, the model tests and numerical simulation tasks works as supplementary to each other. The former provided the orientation and instrument for the setup of the latter, and acted as reliable criteria for numerical simulation result estimation; in turn, the well-designed post-test numerical simulation offered the former supplementary vortex shedding visualization behind the pipe’s wake and the corresponding instantaneous displacement information; taking advantage of the combination between pipe oscillatiom from model tests and vortex shedding pattern from numerical simulation, some coupled phenomena about fluid-structure interaction has been well comprehended.Finally, a series of pre-test numerical simulation tasks aiming at solving more complicated problems have been accomplished. The tentative pre-test simulation tasks mentioned above which have a tight relation with practical engineering application have been carried out, including the self-excited vibration simulation task related to a large-scale pipe system exposed to external shear current and internal flow simultaneously, the forced vibration simulation task related to a short pipe system subject to the coupled dynamic load resulting from wave and current and the dual-assembled pipe systems undergoing. Based on the well-performed simulation tasks, not only some conclusions consistent with the published research works, but also some new discoveries have been observed. The tentative pre-test numerical tasks accomplished in this paper will be an available orientation and reference to the further model tests and even to the practical engineering application.The innovations in this thesis can be concluded as follows: the improvement in data analysis method has provided a powerful tool to extract efficient information in both model tests and numerical simulation tasks; many important conclusions obtained from model tests and numerical simulation tasks are based on them; taking advantage of the combination between model tests and numerical simulation tasks, some problems related to the correlation between vibration mode and amplitude, the vortex shedding modes related to reduced velocity and instantaneous amplitude have been well solved. In addition, the intrinsic principle related to the instantaneous mode jump observed in model test has been concluded, as well as the rules about the coupled oscillation in the multi-assembled pipe systems and the vortex shedding pattern corresponding to different VIV styles.更多还原