“How does a fish swim?’ is essentially a fascinating question.  For hundreds of millions of years, adaptation and evolution have enabled fish to achieve excellent propulsion performance with their fast speed and high efficiency. During this long history of evolution, swimming animals have mastered an exquisite capacity to control their bodies and the flow around themselves to efficiently cruise in water. The distinctive swimming abilities of fish have inspired scientists and engineers to analyze locomotive mechanisms and to design fish-like robots. There is no doubt that researchers admire the swimming skills of aquatic animals and hope to have a similar capacity, conscientiously considering swimming performance to be scientific and explained in light of fluid dynamics. Generally, natural swimmers share two major propulsive strategies, including caudal-fin pitching propulsion (e.g. salmon, tuna, dolphins, and sharks) and travelling wave propulsion (e.g. eels and lampreys). A question arises, is the motion of the caudal fin symmetric about the propulsion axis when a fish swims. We therefore first conducted experiments on fish to understand the motion of the caudal fin. The motion is then numerically examined for a hydrofoil. We home in on the insight into the fluid-structure interaction involved and the relationship between the kinematics and thrust or efficiency. This lecture encompasses (i) experiments on fish, (ii) enhancement of both thrust and efficiency using the experimentally obtained motion, (iii) understanding of fluid-structure interaction, and (iv) the hydrodynamic performance of a traveling wavy foil with varying foil kinematics (Strouhal number), fluid properties (Reynolds number), and foil deforming characteristics (wavelength). The results show that the caudal fin motion is asymmetric with the retract stroke being faster than the forward stroke. The pitching motion with the faster retract strokes enhances both thrust and efficiency, and the propulsive force increases with increasing Strouhal number, Reynolds number, and wavelength. A decreasing wavelength leads to a smaller thrust. A slender tail or a slender swimming body cannot have a large traveling wavelength as a large added mass makes the tail or body heavier. A shorter wavelength makes thrust steadier while a longer wavelength enhances maximum instantaneous thrust. The latter is beneficial for prey to escape from a predator.

Alam Md. Mahbub has been a professor at Harbin Institute of Technology (China) since 2012. Prior to this, he served as a senior lecturer at the University of Pretoria (South Africa), research and postdoctoral fellows at the Hong Kong Polytechnic University, and lecturer at the Rajshahi University of Engineering and Technology (Bangladesh). He received MEng and PhD in Mechanical Engineering from Kitami Institute of Technology (Japan) in 2001 and 2004, respectively. He has supervised 9 postdocs, 9 PhD students and 61 master’s students. His extensive publication record includes over 400 technical articles, with more than 230 appearing in high-impact SCI journals such as the Journal of Fluid Mechanics, Journal of Fluids & Structures, Ocean Engineering, Physics of Fluids, and Journal of Sustainable Energy Reviews. His work has garnered significant recognition, amassing over 12,000+ citations in Google Scholar, with an h-index of 56. He has been recognized as a highly cited researcher by Web of Science from 2018 to 2024, placing him in the top 2% of scholars, and he is considered one of China's highly cited scholars. His research focuses on flow-induced vibrations, bluff-body wakes, fluid-structure interactions, hydrodynamics of swimming animals, and energy harvesting from wind and ocean currents. He has chaired and co-chaired eight international conferences and five symposiums, and has delivered 43 keynote speeches at various international conferences.

Prof Alam has received a number of prestigious awards: Japan Government Scholarship (monbusho) for Masters and PhD studies; JSPS (Japan Society for Promotion of Science) Postdoctoral fellowship; South Africa National Research Foundation (NRF) rating ‘Promising Young Researcher, Y1’; China 1000-young-talent scholar; Shenzhen High-Level Overseas Talent; and 2015 Shenzhen Outstanding Teacher. In addition to his accolades, he serves an editorial board member of ‘Wind and Structures, an International Journal’ and Fluid Dynamics and Material processing.