Direct-forcing immersed boundary modeling of vortex-induced vibration of sphere at moderate Reynolds number
| Autor: | Yun-Hui Zhou, 周贇輝 |
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| Rok vydání: | 2019 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 107 A numerical study of the vortex-induced vibration (VIV) of an elastically mounted sphere using the direct-forcing immersed boundary (DFIB) method incorporating the virtual force term is undertaken. The fluctuating hydrodynamic forces may cause damage when a solid structure interacts with fluid flow. Especially in the so-called lock-in situation, the vibration phenomenon results in the failure of the structure. The present study shows that a dynamically mounted sphere is allowed to vibrate transversely only or both in the in-line and the transverse directions in a uniform flow at a moderate Reynolds number of 300. The effect of reduced velocity on VIV is discussed in this study. Aerodynamic coefficients of a freely vibrating sphere are analyzed in time and spectral domains. The maximums of the lift coefficient and the drag coefficient show hysteresis jump at the low end of the lock-in region. The ratio between the vortex shedding frequency and the natural frequency of the structure reveals the so-called soft lock-in. Moreover, two shedding mode hairpin and spiral mode are found in different vibration response regimes. This study proves the capability of the proposed DFIB model can be useful for the investigation of VIV of the structure. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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