Prof.  Alam Md.  Mahbub
Center for Turbulence Control, Mechanical and Automation Engineering Department, Harbin Institute of Technology (Shenzhen),  China

Title: Kinematics and hydrodynamics of fish swimming

Abstract:

"How do fish swim?" is indeed a captivating question. Throughout hundreds of millions of years, fish have adapted and evolved to achieve remarkable propulsion performance characterized by their speed and efficiency. Over the course of evolution, aquatic animals have honed fine control over their bodies and the flow surrounding them, allowing them to efficiently navigate through water. The exceptional swimming abilities of fish have not only intrigued scientists and engineers, but have also served as inspiration for the analysis of locomotive mechanisms and the development of fish-inspired robots. Undoubtedly, researchers hold a deep admiration for the swimming prowess of marine creatures and aspire to replicate such capabilities, thereby viewing swimming performance through a scientific lens grounded in fluid dynamics.

Broadly speaking, natural swimmers utilize two primary propulsive strategies: caudal-fin pitching propulsion (e.g., salmon, tuna, dolphins, and sharks) and travelling wave propulsion (e.g., eels and lampreys). This leads to the question: is the motion of the caudal fin symmetrical about the propulsion axis during fish swimming? To explore this, we initially conducted experiments on fish to observe the caudal fin motion, which was further analyzed numerically using a hydrofoil. Our focus lies in understanding the fluid-structure interaction involved and establishing the correlation between kinematics and thrust or efficiency.

This discussion encompasses several key aspects: (i) experiments on fish, (ii) optimization of thrust and efficiency utilizing experimentally derived motion data, (iii) comprehension of fluid-structure interaction, and (iv) assessment of the hydrodynamic performance of a traveling wavy foil with varying foil kinematics (Strouhal number), fluid properties (Reynolds number), and foil deformability (wavelength). Results indicate an asymmetric caudal fin motion, with the retract stroke being quicker than the forward stroke. The pitching motion with accelerated retract strokes enhances both thrust and efficiency, with propulsive force increasing in tandem with the Strouhal number, Reynolds number, and wavelength. A reduction in wavelength results in decreased thrust, as a slender tail or body cannot sustain a large traveling wavelength due to added mass making it heavier. Shorter wavelengths contribute to steadier thrust, whereas longer wavelengths enhance maximum instantaneous thrust, beneficial for prey evading predators.

Biography:

Alam Md. Mahbub has held the position of professor at the Harbin Institute of Technology (China) since 2012. Prior to this, he served as a senior lecturer at the University of Pretoria (South Africa), a postdoctoral fellow at the Hong Kong Polytechnic University, a research fellow at the same university, and a lecturer at the Rajshahi University of Engineering and Technology (Bangladesh). His extensive academic contributions include authoring and co-authoring over 400 technical articles, with more than 205 published in SCI journals. Notably, his papers have been featured in esteemed publications such as the Journal of Fluid Mechanics, Journal of Fluids & Structures, Ocean Engineering, Physics of Fluids, and Journal of Sustainable and Energy Reviews.His work has garnered significant attention, with over 10,500 citations (h-index 54) in the Google Scholar database, and he has been recognized as a highly cited researcher for 2018 - 2023 (single year) by Web of Science, ranking in the top 2%. Prof. Alam’s research primarily focuses onflow-induced vibrations, bluff-body wake, fluid-structure interactions, hydrodynamics of swimming animals, and energy harvesting from wind and ocean currents.In addition to his research accomplishments, he has played a pivotal role in the academic community, having chaired and co-chaired many international conferences, symposiums, and sessions. He has delivered over 35 keynote speeches at international conferences.