| Summary: | 碩士 === 國立臺灣大學 === 工程科學及海洋工程學研究所 === 101 === It has been a long time since scientists found that marine animals can swim in high efficiency. Therefore, it’s considered a good way to promote propulsion efficiency through biomimetics. Most of the developments of wave devouring propulsion system using oscillating fin in waves are passive.
In the present study, the propulsion efficiency of an active oscillating bow fin with NACA 0012 section in full scale is investigated. Firstly, the published data base on a two dimensional oscillating fin is used for preliminary estimation. Then the CFD software FLUENT is applied for simulation, and the effects of Reynolds number and free surface to the efficiency are investigated.
The CFD software FLUENT is applied to simulate the two-dimensional flow field of an oscillating foil, and then the hydrodynamic coefficients are analyzed. The governing equations are RANS (Reynolds – Average Navier – Stokes equations), while realizable κ-ε model with wall function is adopted as a turbulent model. The solver used is PISO (Pressure –Implicit with Splitting of Operators).
Through the simulation and analysis using FLUENT, it has been confirmed that the thrust increases but the efficiency decreases with larger Reynolds number. It has also been confirmed that the free surface has negative effects to the propulsion performance of an oscillating foil. Namely, the efficiency decreases with shallower submerged depth. However, even on these facts, the validity of a partially active oscillating bow fin to produce significant amount of thrust to assist to propel a ship in waves has been confirmed. As an example, for a VLCC of 321 meter in length, a bow fin with projected area to water line area ratio of 1/285 can save energy about 3.1%~9.5%, in the ship speed range of 12~16.5 knots calculated in the present study.
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