應用船艏振動翼於波浪推進之初步探討

Preliminary Study on a Concept of Wave Propulsion by an Oscillating Bow Fin

李文富(Ｗen-Fu Li)

指導教授 ： 邱逢琛

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.02781

摘要

隨著石化燃料日漸枯竭，使得能源成本逐漸提高，以及環境保護與永續發展的意識日益抬頭，因而除了積極尋求替代性能源之外，如何提升能源的使用效率或發展節能方法也益加受到重視。
一直以來，科學家不斷研究海洋生物如何以低耗能、高效率的方式進行推進，期望透過仿生的運動模式提高能源的使用效率；也將仿生的成果應用於波浪推進中，汲取波浪能量，但大多為被動式的。
本研究以實船比例之主動式振動翼(NACA0012)於波浪推進的效率探討為前提，根據文獻預估其可能之效率，再以計算流力套裝軟體FLUENT進行模擬探討，觀察雷諾數(Reynolds number)與自由液面(free surface)對振動翼推進效率的影響。
本研究利用FLUENT，模擬二維振動翼流場，並解析流體動力係數，使用RANS(Reynolds – Average Navier – Stokes equations)描述流場狀態，紊流模型使用Realizable κ-ε搭配壁面函數(Wall function)，求解方法採用PISO (Pressure –Implicit with Splitting of Operators)。
透過FLUENT分析，確認當雷諾數越大時，其推力雖增加，但推進效率會隨著遞減；且振動翼推進性能受自由液面的負面效應，其效率隨著沒水深度越淺而遞減。然而縱使如此，本研究顯示只需利用投影面積與水線面積比約1/285的振動翼即能對一艘全長321公尺的VLCC，在本研究計算的12~16.5節船速範圍，輔助推進並節能約達3.1%~9.5%，確認了只做強制旋轉的船艏振動翼作為輔助波浪中推進之節能裝置是可行的。

關鍵字

船艏振動翼 ； 波浪推進 ； 自由液面 ； 計算流力

並列摘要

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.

並列關鍵字

oscillating bow fin ； wave propulsion ； free surface ； CFD ； FLUENT

參考文獻

1. Lighthill, M.J., Note on the swimming of slender fish. Journal of Fluid Mechanics, 1960. 9(2): p. 305-317.

2. Wu, T.Y., Swimming of a waving plate. Journal of Fluid Mechanics, 1961. 10(3): p. 321-344.

3. Wu, T.Y., Hydromechanics of swimming propulsion. Part 1. Swimming of a two-dimensional flexible plate at variable forward speeds in an inviscid fluid. Journal of Fluid Mechanics, 1971. 46(3): p. 337-355.

4. Wu, T.Y., Hydromechanics of swimming propulsion. Part 2.Some optimum shape problems. Journal of Fluid Mechanics, 1971. 46(2): p. 337-355.

5. Wu, T.Y., Hydromechanics of swimming propulsion. Part 3. Swimming and optimum movement of slender fish with side fins. Journal of Fluid Mechanics, 1971. 46(3): p. 545-568.