| Summary: | 博士 === 國立清華大學 === 動力機械工程學系 === 97 === 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.
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