| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 97 === Nowadays, there are many researches on the motion mechanism of fishes, birds and other animals, but few on tiny creatures has been investigated. The objective of this study is to understand the influence of cilia for a rotifer (Philodina) on its process of turning and swimming. We utilized micro-particle-image velocimetry (μ-PIV) to measure the velocity fields in vortecies which are induced by the cilia of Philodina and to evaluate the corresponding hydrodynamic force to know how can Philodina perform highly efficient and maneuverable swimming locomotion in the water. In addition, the experiments are carried out using nothing to limit the locomotion of Philodina because Philodina is a tiny creature (200~400μm in length) and is sensitive to environment. Therefore, the two factors to affect body-turning of Philodina are difference between strength of two vortices induced by cilia and body-turing. Both of them can not be eliminated. The qualitative flow visualization of vortices produced by Philodina show that there are three locomotion types. (1) position holding with cilia beating, (2) body-bending with cilia beating , (3) pure forward swimming. The flow field measurement by using μ-PIV shows that vortex pairs were generated by cilia of Philodina and the central jet force was produced as a result of cilia beating. When Philodina is at the same position with no body-bending, there is no significant difference between two front vortices generated from the corona cilia. While turning clockwise, size and strength of the left vortex produced by cilia of Philodina is larger than the right one, and vice versa. While swimming forward, the two lateral vortices are larger than front ones in size and strength. Moreover, the two front vortices help Philodina push fluid toward tail-like part and give reacting force to Philodina to become the main source of thrust and the two lateral vortices help Philodina swim forward because they decrease friction drag while Philodina is swimming. The maximum velocity of Philodina is 5.17mm/s and the maximum thrust is 0.197nN. Therefore the maximum thrust per unit weight is 5.25μN/g. Consequence, we can conclude that Philodina has to spend this kind level of force at to hold on the same place.
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