Graduation Year

2021

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Brad J. Gemmell, Ph.D.

Committee Member

Ryan M. Carney, Ph.D.

Committee Member

John O. Dabiri, Ph.D.

Committee Member

Stephen M. Deban, Ph.D.

Keywords

anguilliform, energy recapture, suction thrust

Abstract

Moving through a dense fluid such as water presents some unique challenges to minimizing energy use and maximizing performance (i.e., speed). Due to animal-fluid interactions during swimming (drag and thrust production) fish have evolved a variety of morphological structures and locomotor mechanisms. For instance, fish rely on body bending and/or fins to interact with the surrounding water such that energy can be transferred to generate thrust. Typically, this synergy promotes morphologies and behaviors aimed at enhancing propulsive efficiency and/or minimizing metabolic activity to lessen the cost of transport (COT). This work focuses on quantifying the energetic and hydromechanical benefits of distinct swimming modes and morphologies. Eel-like fish exhibit efficient swimming with comparatively low metabolic cost by utilizing sub-ambient pressure gradients to generate thrust, effectively pulling themselves through the surrounding water. This study found that across most swimming speeds, thrust was generated through sub-ambient pressure pulling forces that corresponded to a low net COT. In contrast, at the lowest swimming speed tested, a shift in the recruitment of push and pull propulsive forces, whereby positive pressure gradients dominated thrust production, corresponded to a sharp increase in the overall COT. Though push forces lead to inefficiencies in anguilliform swimmers, carangiform swimmers, such as Silver Mojarras, efficiently harness them to enhance thrust. The results demonstrate the existence of a novel swimming gait, termed pectoral-caudal fins (PCF) coordination, that is characterized by the synchronization of pectoral fin wake vortices with caudal fin motions such that upstream wake energy is transferred to the latter. PCF coordination is proposed as a mechanism for recapturing wake energy to enhance performance. The functional attributes of propulsors such as the fins are also determinant in the type of interactions with water. For example, tail shapes are often correlated with particular swimming modes and ecological roles whereby forked caudal fins generally promote economical, fast cruising, and flat, truncate tails characterize burst swimming and fast accelerations. By comparing the wake patterns and the pressure fields on the surface of both fin morphologies experimentally, I showed that the ‘notch’ in the forked tails incurs an energetic cost during cruising. The results show that forked tails do not always confer a cruising advantage. By investigating the mechanisms driving efficient locomotion in aquatic species, this work provides new insights into the behavioral and physical principles that underlie fish swimming with the aim of nurturing the growing interest in nature as a source of inspiration for the development bio-inspired technologies.

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