Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Mechanical Engineering | en_US |
| dc.contributor.advisor | Tang, Hui (ME) | en_US |
| dc.creator | Yuen, Tsz Wai | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/13801 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Fish swimming behind multiple cylinders | en_US |
| dcterms.abstract | Fish migration is a practice performed by many species of fish on a regular basis. It has been long observed that fish swim behind natural or man-made structures to exploit generated vortices to minimize locomotory costs. This phenomenon has attracted attentions from researchers and enlightened many studies. Although experiments qualitatively demonstrated the ability of fish to extract energy from environmental vortices, it is challenging to obtain quantitative results. With the fast development of computational hardware and algorithms in the last two decades, numerical simulations were widely employed to investigate fish swimming. However, in most cases, the fish models were either oversimplified, represented only by a filament or lack of self-propulsion ability. Moreover, few research has considered different structure arrangements. | en_US |
| dcterms.abstract | To bridge these research gaps, we conduct a series of simulations to improve our physical understanding in fish swimming behind various structures. A fish-like model is developed based on an airfoil, being able to swim with a more realistic kinematics. This fish model can do self-propulsion with free swimming in both streamwise and crossflow directions. The underlying fluid-structure interactions are studied with an in-house numerical framework based on the immersed boundary lattice Boltzmann method (IB-LBM). With this framework, a fish model swimming with different motion modes behind single or multiple cylinders are examined. Four motion modes are applied, i.e. swimming without translation and rotation, swimming with only rotation, swimming with only translation and free swimming. For each motion mode, a parametric study is conducted. | en_US |
| dcterms.abstract | For the study on the fish model undulating without translational and rotational motions behind a single cylinder, it is revealed that increasing free-stream velocity or cylinder diameter could reduce drag imposed on the fish body, depending on the cylinder-fish distance. Shortening streamwise and crossflow distances between the fish and the cylinder is found to be beneficial in drag reduction of the fish. Detailed flow structures and frequency spectra are analysed to reveal the underlying physics. This study is followed by the investigation on the fish model undulating with only rotations. It is found that rotation angle is a key contributing factor to the drag experienced by the fish model. Moreover, the fish model is overturned as the result of excessive rotation about its centroid when placed in the shed shear layer. | en_US |
| dcterms.abstract | A parametric study is then carried out for the fish model translating only in the streamwise direction. It reveals that the fish only swims towards the cylinder with oscillatory rotations for any initial streamwise distance equal to or shorter than 3.4 times of the fish model’s length. For longer distances, the fish is drifted away as the strong shed vortices cause the fish to overturn. It is also observed that the fish only swims towards the cylinder when it is near the cylinder’s centreline such that it is not affected by the shear layers shed from the cylinder. For the study on free swimming, a unique scenario is observed. That is, apart from simply swimming towards or away from the cylinder, the fish initially swims towards the cylinder but is then driven away by the cylinder’s wake. | en_US |
| dcterms.abstract | Fish swimming behind two cylinders in two different arrangements is also investigated. The drifting-down and drifting-up modes are observed. A distribution of these two modes with two transition regions is presented. On the contrary, the drifting-up-then-down mode is revealed in free swimming behind two side-by-side cylinders. However, no obvious distribution motion-mode patterns are observed for different combinations of streamwise cylinder-fish distance and cylinder-cylinder crossflow distance. | en_US |
| dcterms.abstract | The findings from this research have improved our understanding of fish swimming behind stationary objects. They contribute to bridging the research gaps of oversimplified fish model, lacking of self-propulsion ability. The results provide some useful insights into biomimetic applications such that more energy efficient underwater vehicles and robots for navigation and exploration of aquatic environment could be developed. | en_US |
| dcterms.extent | xvi, 124 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2025 | en_US |
| dcterms.educationalLevel | M.Phil. | en_US |
| dcterms.educationalLevel | All Master | en_US |
| dcterms.LCSH | Fishes -- Migration | en_US |
| dcterms.LCSH | Fishes -- Locomotion | en_US |
| dcterms.LCSH | Hydrodynamics | en_US |
| dcterms.LCSH | Hong Kong Polytechnic University -- Dissertations | en_US |
| dcterms.accessRights | open access | en_US |
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