Date of Award
12-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Electrical and Computer Engineering (Holcomb Dept. of)
Committee Chair/Advisor
Richard Groff
Committee Member
Phanindra Tallapragada
Committee Member
Fatemeh Afghah
Committee Member
Yongqiang Wang
Abstract
Underwater vehicles play a critical role in a variety of applications, including exploration, surveillance, and environmental monitoring. Traditionally, these vehicles have relied on propellers for propulsion. However, the efficiency with which animals move through fluids, both air and water, evolved over many millions of years, has long been a source of inspiration for engineers seeking better ways to design propulsion systems. Fish have been a particularly rich source of inspiration due to their highly evolved swimming efficiency, agility, and maneuverability. This has led to the development of bioinspired underwater vehicles that aim to replicate fish-like motion for enhanced performance. Most traditional bioinspired designs use mechanical linkages or cable-driven systems, often involving multiple actuators. While such designs have demonstrated impressive speed and control, they are mechanically complex, expensive to manufacture, and prone to failure. This work takes a completely different approach by using a single internal rotor actuator coupled with a passive flexible tail. While similar concepts have been explored in the past, those robots have typically been limited in their maneuverability, confined to two-dimensional motion, and lacking in both efficiency and speed.
The first part of this dissertation focuses on enhancing the maneuverability of the robot through the use of a passive flexible tail. While this approach has been explored in previous work, a key distinction here is the investigation of elastic instability and multistability as mechanisms to improve performance. A bioinspired robot with a passive bistable flexible tail is developed that incorporates this concept. A new turning gait, referred to as the powered turning gait, is introduced to enable distinct and controlled changes in direction. In addition, a second new gait, known as the snap-turn gait, allows the robot to perform rapid, agile turns. Importantly, this is achieved while retaining all of the original capabilities of internally rotor-driven robots. A mathematical model of the tail is developed to analyze the characteristics of these gaits, including their frequency-dependent behavior. The robot is also capable of fluidly transitioning between gaits, enabling a versatile and efficient mode of locomotion suited for a range of underwater tasks.
The second part of this dissertation focuses on developing a novel propulsion method for fish-like locomotion, specifically by exploring the mechanisms behind undulatory motion, which is fundamental to the swimming behavior of fish. This approach leverages the principles of resonance and fluid–structure interaction (FSI) to generate efficient thrust. A robot is developed using an unbalanced rotor as the core actuation mechanism, demonstrating that parametric excitation is a powerful strategy for aquatic propulsion. This design results in one of the most efficient fish-like robots to date, achieving a cost of transport (CoT) as low as 0.3, and a CoT of 1.02 at a high speed of 2.4 body lengths per second (BL/s). In addition to its efficiency, the robot also exhibits excellent turning capabilities, with a small turning radius of 0.3 body lengths and a sustained average turning rate of 180 degrees/s.
The third part of this dissertation extends the unbalanced rotor-driven robot into three-dimensional (3D) motion, resulting in the development of a fully capable 3D swimmer. This robot is able to perform complex 3D maneuvers and supports a wide range of diverse locomotion strategies, including a unique “dolphin mode” resulting in agile rolling maneuvers while swimming. In addition to its versatility, the system serves as a foundation for building a library of motion primitives, enabling more advanced and adaptive underwater behaviors.
Recommended Citation
Chivkula, Prashanth, "Motion Primitives in an Underactuated Fish-Like Robot" (2025). All Dissertations. 4184.
https://open.clemson.edu/all_dissertations/4184
Included in
Acoustics, Dynamics, and Controls Commons, Aerodynamics and Fluid Mechanics Commons, Applied Mechanics Commons, Controls and Control Theory Commons, Dynamics and Dynamical Systems Commons, Electro-Mechanical Systems Commons, Engineering Mechanics Commons, Non-linear Dynamics Commons, Numerical Analysis and Computation Commons, Ocean Engineering Commons, Ordinary Differential Equations and Applied Dynamics Commons, Other Mechanical Engineering Commons, Robotics Commons, Systems and Integrative Engineering Commons