Study of resonant frequencies of flexural vibrationof beams immersed in various fluids

• Main Authors: Yuan-Chin Tai, 戴源志
• Other Authors: 張正憲
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/01695894102066443092

碩士 === 國立臺灣大學 === 應用力學研究所 === 104 === This thesis studies the natural frequencies and mode shapes of flexural vibraion of beams immersed in fluids using different beam theories. Next, this work is devoted to investigating the effects of aspect ratio and material coefficient ratio(G/E) on the differences of resonant frequencies obtained from different models based on Euler-Bernoulli, Timoshenko, and Reddy beam theory. In addition, there is a discussion on the resonant frequency differences between shear beam theory and classical beam, which are immersed in air, water, and glycerin. Finally, the simulated results obtained by FEM software have been compared with the results of previous studies. The results of this thesis conclude that aspect ratio, material coefficient ratio ,and mode numder are the essential factors of the differences between shear beam theory and classical beam theory. Specially, the ratio G/E ratio has the great effect on the influence of by fluids. The viscosity of fluids plays an important role on the influence of natural frequencies predicted by different beam theories when the G/E ratio of beams is small, whereas the difference of natural frequencies obtained by different beam theories is influenced by the density of fluids mainly as the G/E ratio becomes large. Besides, the result points out that the natural frequency of Timoshenko beam theory would be same as one of Reddy beam theory even if the fluids are different while the G/E ratio of beams is equal to 0.1. Finally, the fact that the hydrodynamic loading due to viscosity acting on sides of thick beam affects the natural frequencies of beams has been observed from the FEM simulations.