本文是以實驗的方法來探討細小圓柱線在二維噴射流內剪切層中的流體引致振動現象，並且透過各種不同的圓柱直徑和圓柱與流體之間的質量比去觀察出圓柱的振動情形以及實際的動態反應，由於在剪切層內流體-彈性不穩定的影響，圓柱振動的振幅將隨著噴流速度的變化而改變。本實驗是以磁場感應的方法，來量測細小圓柱的振動，並且結合熱線測速儀量測流場速度的變化，以探討不同直徑、質量和阻尼系數的圓柱在剪切層中產生振動的臨界速度。此外，當噴流速度上升時，圓柱受流體-彈性不穩定所激發的振動軌跡與噴流速度下降至停止時，圓柱停止振動時所對應的振動下降軌跡，有明顯的相異，證實磁滯現象的存在。透過圓柱在剪切流場中振動的測試，本文探討不同圓柱與流體之間的質量比，圓柱的直徑，以及不同的阻尼系數，圓柱產生的臨界速度與剪切參數(無因次的速度梯度)的關係，及對磁滯現象的影響。

Flow-induced vibration of small elastic cylinders mounted in the shear flow of a two-dimensional jet is investigated experimentally. There has been a great deal of work concerned with different vibrating conditions and practical dynamic responses by way of mass ratios and diameters of various different cylinders. In such cases, the amplitude of the cylinder oscillation changed along with the variation of the jet velocity is due to the influence of fluid elastic instability. The experiment is based on the method of the magnetic field induction to measure the motion of the small cylinder, and it involves measurements of the varying velocity in a jet through the hot- wire anemometer. The critical velocity of the cylinder vibration in the shear flow with different diameters, mass ratios and damping factors are examined. Moreover, the oscillation traces of the cylinder by fluid elastic instability were observed when the jet velocity was increased, and then decreased for examination of hysteresis phenomena. The results show that the bifurcation of the cylinder vibration traces is remarkable especially for cylinders with high mass ratios. By the amplitude diagrams of the cylinder vibration, the critical velocity for onset of fluid elastic vibration was determined. The dependence of the critical velocity and hysteresis phenomena on the mass ratio and damping factor are discussed.

TABLE OF CONTENTS ………………………………………………… i
FIGURE CAPTIONS ……………………………………………………iii
摘要 ……………………………………………………………………vi
ABSTRACT ……………………………………………………………vii
NOMENCLATURE ………………………………………………………viii

1. INTRODUCTION …………………………………………………… 1
1.1 Background …………………………………………… 1
1.2 Literature Review ………………………………… 2
1.3 Motivations and Objectives ……………………… 4 2. EXPERIMENTAL APPARATUS ……………………………………… 6
2.1 Facility ………………………………………………… 6
2.1.1 Two-dimensional air jet facility 6
2.1.2 Installation of small cylinders 7
2.2 Experimental instrumentation ……………………… 7
2.2.1 Vibration measurement…………… 7
2.2.2 Measurement of jet velocity profile 9
3. RESULTS AND DISCUSSION ……………………………………… 11
3.1 Velocity profile with and without cylinder ……11
3.2 Cylinder vibration in the shear layer ………… 11
3.3 Observation of hysteresis phenomena …………… 13
3.4 Correlation between reduced velocity and mass ratio …………………………………………………………………15
3.5 Effect of the damping factor on the critical velocity ………………………………………………… …………16
3.6 Frequency response for vibrating cylinder …… 17
3.7 Orbit evolution of cylinder vibration ………… 17
4. CONCLUSIONS …………………………………………………… 18
REFERENCES ………………………………………………………… 20
TABLE 1……………………………………………………………… 23
TABLE 2……………………………………………………………… 24
APPENDIX A ………………………………………………………… 45
APPENDIX B ………………………………………………………… 46
APPENDIX C ………………………………………………………… 47
APPENDIX D……………………………………………………………48

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