群游策略對於魚類游動性能及節能之影響

An Investigation of the Energy-Saving Mechanism in Fish School

陳思詠(Szu-Yung Chen)

指導教授 ： 楊鏡堂

國立臺灣大學/工學院/機械工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.01906

摘要

本文以群游現象鮮明之泰國鯽為分析對象，利用模擬分析與實驗觀測同步研究群魚隊形排列對於游動性能與節能機制之影響，並探討跟隨魚隻之流場結構與游動策略。前人之文獻著重於魚隻擺尾頻率與生理參數變化分析，鮮少深入討論節能機制與魚隻間流場結構，且未見群魚生物流場之量測。因此本研究以活體實驗為基底，並建構出合理的物理模型，藉由實驗及模擬解析群魚游動隊形策略以及節能機制。
為了分析單因子變數之效應，本文以二維與三維群魚游動生成渦漩之交互作用，藉由調整上下游魚隻側向與游動方向之間距以瞭解群體魚隻最佳省能、推進及游動效率之空間分佈。流場可視化實驗顯示下游魚隻頭部擺動方向會受到上游魚隻產生之逆卡門渦漩所吸引，同時魚類會隨環境渦漩和彼此邊界條件交互影響而改變其跟隨距離。下游魚隻藉由調整跟隨位置避開射流使其有效回收渦漩能量以達成節能的效果。
本文對於魚類群游結構進行最佳化模擬，二維游動功率分析結果揭示群游之節能機制為：(1)下游魚隻受到槽道效應之影響輔助身軀擺動，分別於不同之時間步態達成頭部身軀和尾部擺動之節能效應；(2)調整排距接收上游魚隻生成渦漩的強度輔助尾部擺動。本文發現當上下游魚隻呈現游動向0.5倍身長、側向0.15倍身長時，平均單隻魚隻可減少達20%功率損耗。接著本文進行三維群游之數值模擬，並導入自身推進的技術模擬魚隻跟隨的互動行為。定點擺動之模擬結果顯示出相似於二維的推力表現，三維模型因前後壓差弱化，使得群游魚隻推力係數差異減小，而兩隻魚隻的跟隨互動下，無論有無擺尾調變策略，其魚隻平均游速皆大於單一魚隻之游速，證實跟隨游動有助於節能。本研究對於未來群體水下載具之發展深具意義，特別是在群體控制與空間安排上可提供一良好的機動策略。

關鍵字

逆卡門渦漩 ； 節能機制 ； 空間排列 ； 群魚

並列摘要

In this study, the swimming patterns and energy-saving mechanism in fish school is numerically and experimentally investigated. The fish school phenomenon is first observed and qualitatively studied in experiment. To further investigate the energy-saving mechanism of fish school with mono-factor variable, we quantitatively characterized the wake flow structures, forces, and power consumption using numerical simulation with respect to various swimming patterns.
The results show that the spatial arrangement of school and the shed vortices are highly correlated and significantly affect the performances of the thrusts and power consumption of the fish group. The low pressure suction force produced by the reverse Karman vortices shed by the upstream fish decreases form drag of the downstream fish and facilitates the undulating movement periodically. The head and tail of the downstream fish reveal negative work output at specific time step because of the low pressure region between the downstream fish assisting the body undulation This mechanism reduces the power consumption of each fish in school by 20% averagely compared with that in solo.
In three dimensional simulation self-propelled cases, the results show that the average swimming velocity of the fish following case is greater than that of fish swimming in solo with the same body undulating motion. The energy-saving mechanism reveals in this work offer a physical insight into bio-inspired arrays for the underwater vehicles.

並列關鍵字

fish school ； energy-saving mechanism ； spatial optimization ； vortex structure ； low-pressure kernel

參考文獻

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Becco, C., Vandewalle, N., Delcourt, J., and Poncin, P., "Experimental Evidences of a Structural and Dynamical Transition in Fish School," Physica A- Statistical Mechanics and Its Applications, 2006, 367, pp. 487-493.

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