雙自由度圓柱體的渦激振動(dòng)研究
[Abstract]:In the field of marine engineering, many key components are similar to the cylindrical shape. According to the theory of fluid dynamics, these marine structures are easily subjected to structural vibration and dynamic loads caused by viscous vortex. Especially when the natural vibration frequency is the same as the vortex shedding frequency, the vortex-induced vibration (Vortex-induced Vibration,VIV) of the whole structure will become more intense, resulting in the fatigue failure of the structure. In this paper, based on a detailed review and summary of the research methods and latest dynamics of vortex-induced vibration in risers at home and abroad, the Navier-Stokes equation in incompressible viscous fluid is solved by using FLUENT module in CFD. At the same time, the self-made UDF (User Defined Function) interface program and the dynamic grid technique are used to analyze the forced and self-excited vibration of a cylinder with two degrees of freedom. Based on Van der Bohr equation, a double wake oscillator model is proposed, and a coupled oscillator model is obtained by combining the structural oscillator equation. The main contents of this paper are summarized as follows: 1. A numerical model of the flow field around a fixed cylinder is constructed. The comparison of numerical results verifies the reliability of the numerical methods and models used in this paper, which lays a foundation for the subsequent numerical calculation of forced and self-excited cylindrical oscillations. 2. In order to study the vortex-induced vibration under the combined action of uniform flow and oscillatory flow, the transverse and two-degree-of-freedom forced oscillations of a cylinder in a uniform flow with low Reynolds number are studied. The effects of vibration frequency and amplitude on forced oscillation are studied respectively. The time history curves of lift coefficient and drag coefficient, the vortex shedding frequency of wake field and the variation of wake vortex structure are analyzed in detail. The characteristics of forced motion response of cylinder under the combined action of uniform flow and oscillating flow are analyzed. It is found that the oscillatory flow changes the locking interval, hydrodynamic coefficient and wake vortex shedding mode of forced oscillation. 3. The vortex-induced vibration of a two-degree-of-freedom elastic supported cylinder is numerically simulated, and the vortex shedding frequency and vibration displacement time history curve of wake flow field are obtained. The motion response characteristics and wake shedding of cylindrical system such as motion trajectory and time-history curve of hydrodynamic coefficient; In this paper, the effects of mass ratio and damping ratio on the vortex-induced vibration of a two-degree-of-freedom elastic braced cylinder are studied. The self-excited vibration characteristics of a cylinder under the combined action of uniform flow and oscillating flow are numerically simulated. The results show that the oscillatory flow expands the locking range of the self-excited vibration and increases the amplitude of the vibration along the flow direction. Even more than the most significant value can be excited by the transverse; 4. Based on the Van der Pol equation, the concept of double wake oscillator is proposed, and an example is given to accurately predict the vortex-induced vibration of a cylinder with two degrees of freedom in the experiment by using the coupled oscillator model, and the optimal coupling parameter combination is determined by discussing the parameters of the model. A new type of cylindrical motion trajectory superimposed by two "8" shapes has been observed under the example of high frequency ratio of natural vibration to that of transverse structure.
【學(xué)位授予單位】:哈爾濱工程大學(xué)
【學(xué)位級(jí)別】:碩士
【學(xué)位授予年份】:2016
【分類號(hào)】:U661.44;P75
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