管束结构流固耦合振动及失稳机理研究

The research intends to study the instability mechanism and post-critical dynamical behaviour of tube bundles in cross flow with fluid-structure interaction (FSI), both theoretically and numerically. . The main contributions of this research can be summarized as follows: Firstly, nonlinear partial differential equations of motion of the tubes based on Hamilton’s principle will be derived. The partial differential equations of motion of the tubes will be discretized involving the use of the Galerkin method. The fluidelastic instablity and post-critical dynamical behaviour of this fluid-structure interaction system will be studied, the fluidelastic instability boundaries of tube bundles will be discussed, the influence of pitch-to-diameter ratio, void fraction, mass damping and reduced flow velocity on fluidelastic instability will be analyzed, and the bifurcation and chaotic motions of the tubes will also be investigated. Secondly, the relationship between the structural parameters, flow velocity and the structural mobility will be studied based on mobility analysis method, and the laws of vibrational energy distribution and transmission of tubes will be investigated, which can provide the theoretical basis for the passive and active vibration isolation. Thirdly, the investigation of the dynamics of tube bundles with loose supports in cross flow will be conducted, each support will be mathematically characterized by a contact-equivalent stiffness element and a damper element, a mathematical model of the impact force between tubes and supports will be established, and a new FSI model for tube bundles with loose-supports will be presented, which can be used to analyze precisely the vibration responses of tube bundles in engineering, provide the theoretical foundation for improve bundled-tube structural design, and ensure the safe and stable operation of bundled-tube systems.

本课题拟通过理论研究、数值模拟和实验分析，进行管束流固耦合失稳机理及其复杂动力特性研究。旨在通过基于Hamilton变分原理，建立管束流固耦合振动非线性模型，采用Galerkin法求解非线性方程，分析其流体弹性不稳定性和复杂动态响应，探求管束的流体弹性失稳边界，分析节径比、体积含气率、质量阻尼参数和对比流速与管束流体弹性失稳的关系，研究其分叉与混沌行为；基于导纳理论分析管结构物理参数和流体流速对管结构流固耦合导纳的影响，研究管束结构振动能量分布与振动响应传递规律，为采取主被动控制策略达到减振的目的提供理论依据；同时开展非有效支承管束流固耦合研究，以刚度单元和阻尼单元来表征支承结构，探求管束与支承间碰撞力数学模型，建立非有效支承时管束流固耦合模型，从而准确地分析工程实际中管束结构的流固耦合振动，为管束结构的合理设计提供理。

输流管道在横向外流的作用下会发生颤振现象，其中流体弹性不稳定性是管束振动中最重要的激振机理，由于流体弹性不稳定性而导致管道的的长期的振动极易使其产生疲劳损坏。. 通过理论分析，数值模拟以及实验研究的途径完成输流管道简化模型在横向水流冲击作用下的流固耦合振动运动机理的研究，并总结出管束产生弹性失稳的临界流速随不同管束排布方式以及节径比的分布规律。. 建立管结构流固耦合振动非线性方程，采用Galerkin法求解方程，研究管结构流固耦合非线性动力特性。研究无量纲流速、管质量、阻尼、直径、固有频率、流体密度等参数对管束失稳特性的影响，给出流体弹性失稳曲线，探求各参数与管束失稳机理的关系，并提炼归一化参数表征管束的失稳特性；开展横向流作用下输流管道的流固耦合分析的数值模拟研究，总结临界流速的变化规律；将数值模拟与实验结果做对比，以确保模型的可靠性。. 本研究为为换热器管束受到横向流体冲刷而产生振动的防护措施提供理论基础，为输流管道长期高效运行提供保障，具有较大的社会及经济效益。