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Modeling, design, and implementation of a bio-inspired propulsion mechanism for underwater vehicles

Omari, Mohamad
A Master of Science thesis in Mechatronics Engineering by Mohamad Omari entitled, “Modeling, design, and implementation of a bio-inspired propulsion mechanism for underwater vehicles”, submitted in April 2021. Thesis advisor is Dr. Mehdi Ghommem and thesis co-advisor is Dr. Lotfi Romdhane. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).
Recent advances in bio-robotics research and smart materials have boosted the development of bio-inspired autonomous underwater vehicles (AUVs) to replace their conventional counterparts driven by rotary propellers. These vehicles can serve in several applications including marine environment exploration, search and rescue, military surveillance, and border patrol. In this Thesis, we investigate the hydrodynamic performance of robotic fish tail inspired from three different fish species, namely the big-eye trevally, the butterfish, and the boxfish. A detailed CAD model of the robotic fish is developed and simulated using the MATLAB tool Simscape Multibody. The bio-inspired propulsion mechanism consists of three articulated segments actuated by servomotors and a caudal fin to produce the desired fish wavy motion. A testing platform, equipped with load cell and distance laser sensor, is developed to measure the produced thrust and associated forward speed over a range of undulation frequencies and lateral amplitude of tail oscillations. The experimental results showed good agreement with Lighthill’s theory of elongated-body propulsion. Then, a comparative study is conducted to examine the swimming capabilities of the aforementioned fish species. The boxfish was found the slowest of the three species, with a mean thrust of 6.46 mN and a forward speed of 10.2 cm/s. This reflects the characteristics of the boxfish being a reef fish, which is best suited for tight maneuvering and bursts of speed rather than a long sustained cruising speed. The trevally is observed to produce the fastest swimming with an estimated forward speed of 25.2 cm/s. The experimental results are also compared to previous studies on robotic fish reported in the literature.
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