基于浮框式三节段模型的矩形断面涡激力参数识别研究

发布时间：2018-02-25 19:11

本文关键词： 浮框式三节段模型矩形断面风洞试验涡振参数识别 CFD　出处：《湖南大学》2014年硕士论文　论文类型：学位论文

【摘要】：气流流经某些断面结构时会发生流动分离并产生周期性漩涡脱落现象,漩涡脱落的频率与风速的关系可以用斯托洛哈数来表示,当涡脱频率和结构的某阶频率相等或相近时,结构将发生涡激振动。涡激振动是一种带有自激和强迫性质的振动,限幅、发生风速低是涡激振动的特点。虽然涡激振动不是毁灭性风致振动,但其周期性的振动不仅会影响行车行人舒适性,还会导致结构疲劳损伤。大跨度桥梁具有质量轻、结构柔、阻尼比低的特点,在低风速下很容易发生涡激振动。然而,目前涡激振动的发生机理尚未被完全认识,至今仍未建立起完美描述涡激振动的方程。涡激力作为涡激振动发生时的重要研究数据,现有研究很少直接测试涡激力,大多通过位移响应和参数识别间接得到。鉴于此,本文以自主开发的三节段测力测振模型为研究对象,测试得到涡振发生时作用在模型上的涡激力,并对所测涡激力进行分析,探索涡激响应机理。主要内容如下： (1)基于ANSYS有限元软件对浮框式三节段模型进行设计,确定支撑框、悬浮框、消扰构件的几何尺寸,得到最优设计参数。同时,对模型进行模态分析,得到模型的各阶模态频率,确保在后续风洞试验研究中不出现局部振动的现象。 (2)在均匀流场中对节段模型进行自由悬挂试验,测试得到悬浮段在涡激振动发生时的位移、加速度响应时程和动态合力时程。对模型受力分析后提取出涡激力。为评价所测涡激力的测试精度,将基于平均加速度法算得的位移响应时程与实测位移响应时程进行对比,结果表明,计算和实测位移时程曲线吻合良好。与此同时,对各风速下的涡激振幅进行统计,得到宽高比为6的矩形断面的涡振锁定区间。 (3)在均匀流场中对节段模型进行强迫振动试验。分别测试得到强迫振动时有风和无风条件下作用在模型上的动态合力,两动态合力相减即得到作用在模型上的气动力。比较强迫振动和自由悬挂状态下气动力的大小,发现前者要大一些。 (4)分别根据振动响应时程和涡激力时程对Scanlan经验线性模型、Scanlan经验非线性模型进行参数识别,比较两种方法识别参数的精度后发现基于涡激力时程方法的识别精度更高。 (5)对宽高比为6的矩形断面进行CFD数值模拟分析,计算得到静止绕流条件下模型的升力系数和涡激振动条件下的响应时程、涡激力时程,并将模拟结果与实测结果对比。发现锁定区间和涡激力幅值与实测结果相近。
[Abstract]:The flow separation and periodic vortex shedding will occur when the flow flows through some cross-section structures. The relationship between the frequency of vortex shedding and the wind speed can be expressed by Stolohart number. When the vortex stripping frequency is equal to or close to a certain order frequency of the structure, Vortex-induced vibration will occur in the structure. Vortex-induced vibration is a kind of vibration with self-excited and forced properties. Limiting amplitude and low wind speed are the characteristics of vortex-induced vibration. Although vortex-induced vibration is not destructive wind-induced vibration, However, the periodic vibration will not only affect the comfort of pedestrians, but also lead to fatigue damage. The long-span bridge has the characteristics of light weight, flexible structure and low damping ratio, and it is easy to occur vortex-induced vibration at low wind speed. At present, the mechanism of vortex-induced vibration has not been fully understood, and a perfect equation describing vortex-induced vibration has not been established. The vortex-induced force, as an important research data of vortex-induced vibration, is rarely measured directly. Most of them are obtained indirectly by displacement response and parameter identification. In view of this, the self-developed three-segment force measurement model is taken as the object of study. The vortex-induced forces acting on the model when the vortex vibration occurs are measured and the measured vortex-induced forces are analyzed. The mechanism of vortex-induced response is explored. The main contents are as follows:. 1) based on the ANSYS finite element software, the floating frame three-segment model is designed, and the geometric dimensions of the supporting frame, suspension frame and disturbance elimination member are determined, and the optimum design parameters are obtained. At the same time, the modal analysis of the model is carried out, and the modal frequencies of each order of the model are obtained. Ensure that no local vibration occurs in the subsequent wind tunnel test. 2) the free suspension test of the segmental model is carried out in the uniform flow field, and the displacement of the suspension section is obtained when the vortex-induced vibration occurs. In order to evaluate the accuracy of the measured vortex-induced forces, the displacement response time history calculated by the average acceleration method is compared with the measured displacement response time history. The results show that the calculated displacement time history curve is in good agreement with the measured displacement time history curve. At the same time, the vortex-induced amplitudes of each wind speed are statistically analyzed, and the vortex locking interval of rectangular section with a ratio of width to height of 6 is obtained. 3) the forced vibration test of the segmental model is carried out in a uniform flow field, and the dynamic forces acting on the model under the condition of wind and no wind are obtained, respectively. The aerodynamic force acting on the model is obtained by subtracting the two dynamic forces, and the magnitude of the aerodynamic force under forced vibration and free suspension is found to be larger. (4) according to the vibration response time history and vortex-induced force time history, the parameters of the Scanlan empirical linear model and the Scanlan empirical nonlinear model are identified. Comparing the accuracy of the two methods, it is found that the vortex-induced force time-history method has higher recognition accuracy. (5) the CFD numerical simulation of rectangular section with ratio of width to height of 6 is carried out, and the lift coefficient of the model and the response time history and vortex-induced force time history under the condition of vortex-induced vibration are calculated under static flow conditions. The simulation results are compared with the measured results. It is found that the locking interval and the amplitude of vortex-induced force are close to the measured results.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U441.3

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