Computational study of vortex induced vibration performance with coupled bluff splitter body and elastic plate model / Chin Wei Ken

Chin, Wei Ken (2018) Computational study of vortex induced vibration performance with coupled bluff splitter body and elastic plate model / Chin Wei Ken. Masters thesis, University of Malaya.

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Abstract

Vortex-induced vibration (VIV) had been known as an engineering problem that causes damages and destructions to structures, such as buildings, bridges, stacks and pipelines in the past few decades. With the rapid development of piezoelectric harvester in recent years, vortex induced vibration had been the staple of research as a new form of energy harvesting. This research investigates and enhances the performance of a vortex induced vibration harvester in three aspects, i.e. change in wind speed, difference in structural aspect ratio and difference in bluff splitter body design, in order to. All of the studies were conducted with a T-shaped coupled bluff splitter body and elastic plate model through Fluid Structure Interaction (FSI) Method. In the first part of the first objective, a coupled thin rectangular bluff splitter body and PVEH plate undergoes different wind speeds at 7 m/s, 18 m/s, 19 m/s, 20 m/s, 22 m/s and 25 m/s. Results showed that at 19 m/s flow produced highest vibrational amplitude of 2 mm because the vortex frequency of 75.758 Hz resonates with the model’s natural frequency of 76.955Hz. In the second part, a coupled 1 cm cube bluff splitter body and 4 cm long elastic plate is tested with wind speed range from 0.3 m/s, 0.4 m/s, 0.513 m/s, 0.6 m/s, 0.7 m/s, 1.0 m/s dan 1.5 m/s. Results showed that 0.7 m/s with closeness of vortex frequency 3.94 Hz to the structural natural frequency of 3.087 Hz together with decent fluctuating lift force value is able to generate largest displacement value of 0.0149 m. Second objective is aimed at finding out the effects of bluff splitter body width to elastic plate length ratio or known as aspect ratio of the model on VIV performance. The first part of this section involves a 0.04 m elastic plate coupled with bluff splitter body of 0.01 m length and different width including 0.005 m, 0.01 m, 0.02 m, 0.03 m, 0.04 m, 0.06 m and 0.08 m. The second part involves coupled 0.03 m wide bluff splitter body and different elastic plate length 0.02 m, 0.03 m, 0.04 m, 0.05 m, and 0.06 m. Under 0.513 m/s wind speed, the results from both sections showed that vibration is amplified to the amplitude of 0.0153 m with a coupled 0.03m wide bluff splitter body and 0.04 m elastic plate through closeness of vortex frequency of 3.182 Hz to the structures natural frequency of 3.087 Hz. The last objective investigates the enhancement of VIV through bluff splitter body design. In the first part, different shapes of bluff splitter body including circular, rectangular, triangle, trapezoidal, curve, diffuser and semicircle with concave or convex arrangement were tested. It is proven concave shape is able to generate higher lift force and vortex frequency compared to convex shape. However, rectangular together with convex shaped trapezoidal and semicircle shape which generate closer vortex frequency to the structures’ natural frequency produced higher tip displacement compared to other shapes. The second part involves the change of edge angles between 34.22°, 45°, 60°, 75°, 90°, 120°, and 146.31°. It is shown that trapezoidal shape of 60° edge angle with the closest vortex frequency of 3.03 Hz compared to structure’s natural frequency is the best performing shape, inducing 0.0159 m displacement value 4.605% higher that the rectangular bluff splitter body above. In conclusion, these overall results displayed the importance of matching vortex frequency to the natural frequency of the structure undergoing VIV in the effort of enhancing the performance. This thesis will significantly improve the knowledge in enhancing VIV performance and further encourage VIV harvester development.

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