魚類操控式游動之流體動力與生物物理學研究

A Study of Hydrodynamics and Biophysics of Swimming Maneuvers on Fishes

丁上杰(Shang-Chieh Ting)

指導教授 ： 楊鏡堂 ； 葉孟考

國立清華大學/工學院/動力機械工程學系/博士(2009年)

摘要

本論文以實驗方法研究魚類操控式游動之流體動力與生物物理學機理，相較於穩態直線游動而言，魚類的操控式游動是一種更為普遍且重要之游動模式。本論文以血鸚鵡魚及朱文錦魚為實驗研究對象，深入剖析探討尾鰭波傳遞(caudal fin-wave propagation)、胸鰭拍撲、游動姿態俯仰穩定控制、快速起動轉彎(fast-start turn)等四種重要的游動操控機制。
尾鰭波傳遞行為常出現於魚類的操控式游動之中，本文研究結果表明：尾鰭波傳遞之主要功能，是使魚類於下潛或上浮游動時獲得俯仰姿態穩定；魚類藉尾鰭波傳遞產生補償式俯仰力矩，用以平衡抵消魚體浮力及胸鰭拍撲所引起之俯仰不穩定力矩。對於下潛游動之血鸚鵡魚而言，胸鰭拍撲會產生不穩定之下傾俯仰力矩，但胸鰭又同時產生大量側向力，提供魚身側向翻滾穩定力矩。
朱文錦魚的快速起動轉彎分成三個連續階段：魚身作瞬間彎曲、尾鰭側向回擺、魚身恢復筆直；第一階段產生推進射流，提供推進力；第二階段產生側向射流及推進射流，分別提供轉彎所需之旋轉力矩以及朝轉彎方向前進之推力；第三階段產生側向射流，提供魚身補償式的平衡穩定力矩。
本文揭示一個重要且有趣的魚類游動渦漩能量回收利用機制，游動時張開的胸鰭會導致‘阻力’式尾流之形成，魚類能夠將胸鰭渦漩的能量回收利用，胸鰭與尾鰭之間的渦漩交互作用，有助於推進力之產生。此外，本文提出一個重要的學理觀念：生物在流體中推進，如果同時使用了數個運動器官，它們所產生的渦漩可能會交互影響，則所產生之尾流結構，將可能無法正確反映出推進力之作用方式與產生機制，因此在對生物流場結構進行分析解釋時，必須要考量上述這個問題點，否則將可能導致對推進機制的錯誤解釋與結論。
在實驗方法方面，本文發展一種創新且重要的仿生力學量測技術，可同步量測分析生物之三維運動參數與三維流體速度場，此技術結合立體粒子影像測速儀(SDPIV)以及本文所提出之三維空間位置重建方法；其應用範圍廣泛，包含生物之游動與飛行研究。
在流體物理分析方面，本文提出魚類流場高能結構之萃取技術；本文採用奇異值分解法(SVD) 對流體速度、渦度、渦漩檢知數、環流量(circulation)等物理量進行分析，依據本文所提出之福祿效率(Froude efficiency)準則，可成功萃取出魚類流場之高能結構；本文進一步提出魚類流場之拓樸分析方法，依據拓樸臨界點理論(topological critical-point theory)，對SVD萃取出來之魚類流場高能結構進行拓樸分析，結果表明此分析方法可大幅提升魚類流場在解釋判讀上的正確性及便利性。
最後，本文依據對魚類游動機制之研究成果，提出具多自由度仿生水下載具(Biomimetic Aquatic Vehicle)之概念設計，可應用於具操控式游動功能之仿生水下載具的設計與研發。
本文的研究核心及原創性貢獻包含以下幾點：研究並揭示魚類操控式游動之流體動力學機理、提出魚類的胸鰭渦漩能量回收利用機制、發展創新實用的仿生力學實驗量測技術、提出魚類流場高能結構的萃取與拓樸分析方法。

關鍵字

魚類操控式游動 ； 流體動力學 ； 生物物理學 ； 尾鰭波傳遞 ； 姿態俯仰穩定控制 ； 快速起動轉彎 ； 立體粒子影像測速儀 ； 仿生力學量測技術 ； 奇異值分解法 ； 拓樸臨界點理論 ； 渦漩能量回收利用

並列摘要

This thesis experimentally investigated the hysrodynamics and biophysics associated with the swimming maneuvers of a fish. Fish in natural environments applies more maneuvering swimming than steady swimming. In this thesis, Parrot Cichlid and Crucian Carp were used as the experimental objects. Maneuvering mechanisms involving caudal fin-wave propagation, pectoral-fin stroke, stabilization and control of posture in pitch, and fast-start turn were thoroughly investigated and dissected.
Caudal fin-wave propagation is a behavior commonly observed in a maneuvering fish. The experimental results indicate that the main function of caudal fin-wave propagation is to facilitate pitching stabilization during sinking or rising locomotion of a fish. Caudal fin-wave propagation assists in the production of a compensating pitching moment that counterbalances the destabilizing pitching moment induced by the buoyancy and pectoral-fin stroke of a fish. As to a sinking Parrot Cichlid, its stroking pectoral fins produce concurrently a destabilizing head-down pitching moment and considerable lateral forces that are stabilizing in roll.
The fast-start turn of a Crucian Carp is divisible into three continuous stages including prompt body bending, contralateral tail beat, and body straightening. A thrusting jet accounting for forward movement is produced within the first stage. Lateral and thrusting jets are separately produced within the second stage, respectively accounting for the angular moment and thrust force required for the fish to perform the turn. A lateral jet is produced within the third stage, inducing a compensating stabilizing moment on the fish.
This thesis also reveals an important and intriguing mechanism associated with the recycling of vortex energy exploited by a fish. The abducted pectoral fins of a swimming fish result in the formation of a ‘drag’ wake. A fish beneficially recycles the energy of the pectoral-fin vortices. Vortex interaction among pectoral fins and tail fin facilitates the generation of thrust. Moreover, a fundamental and significant concept is introduced in this thesis－the wake structure might lead to inaccurate interpretation of propulsive mechanisms of animal locomotion in fluids, given that multiple appendages have been concurrently utilized for propulsion. Interpretation based on wake flow data for hydrodynamic analysis of animal locomotion requires considering carefully vortex interaction among multiple appendages of an animal.
In the present study, an innovative and important experimental technique for biomimetic mechanics has been developed, which is useful for simultaneous measurement of three-dimensional kinematics parameters and flow velocities of a locomoting animal in fluids. This technique is based on combined use of the SDPIV and the method of reconstruction of 3D spatial positions introduced in this thesis. This technique is applicable to research on animal swimming and flight.
A method for extracting energetically dominant flow features in a complicated fish wake is introduced. The singular-value decomposition is employed to analyze the data of fluid velocity, vorticity, and vortex detector within a fish flow field. The energetically dominant flow features in a fish wake can be successfully extracted according to the criterion based on the Froude propulsive efficiency. A method for topological analysis of a fish flow field is introduced as well. SVD-extracted fish flow fields are analyzed based on the topological critical point theory. The accuracy and convenience of interpretation of a fish flow field can be greatly improved through the use of this topological method.
Finally, according to the experimental results associated with fish maneuvering, a concept design of a biomimetic aquatic vehicle is proposed, which can be adopted for the future design of biomimetic aquatic vehicles capable of performing maneuvers.
The originality and main contributions of this study comprise the following points: the revelation of the mechanism of maneuvering swimming in a fish、the revelation of the mechanism of recycling pectoral-fin energy in a fish、the development of an innovative and useful experimental technique for biomimetic mechanics、the introduction of methods for extracting energetically dominant flow features and for conducting topological analyses of fish flow fields.

並列關鍵字

maneuvering swimming of fish ； hydrodynamics ； biophysics ； caudal fin-wave propagation ； pitching stabilization ； fast-start turn ； SDPIV ； experimental technique for biomimetic mechanics ； singular-value decomposition ； topological critical-point theory ； vortex-energy recycling

參考文獻

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