Hydrodynamics and Energetics of Undulatory Propulsion

The mechanics of fluid structure interaction is complex. It is the dynamics of this complex interaction that governs aquatic locomotion. Hydrodynamics plays a fundamental role in the shaping the evolution of the morphology and motor function of swimming organisms. Understanding the hydrodynamics of aquatic locomotion is essential to understand the vast diversity of morphology and motor control of swimming organisms seen in nature. It is also essential in understanding the energetics of swimming, and the interplay between morphology, motor control and energetics. From an engineering perspective, an understanding of the mechanics of aquatic locomotion can be useful in the design of efficient biomimetic underwater vehicles. The work in this thesis focuses on developing a fundamental understanding of key aspects of the hydrodynamics and energetics of undulatory propulsion, and on understanding the relationship between energetics morphology and motor control of elongated fins.;Drag and thrust in undulatory swimming are intertwined. A successful separation of drag and thrust in undulatory propulsion has not been demonstrated so far. The only success achieved in this regard was by Lighthill citep{Ligh75a,Ligh71a,Ligh90a} who proposed a mechanism of thrust but none for drag. We demonstrate a mechanism for drag as well as thrust, and we show that it is applicable to real swimming organisms.;Energetics of swimming is a is not a well understood concept. It is believed that swimming animals spend power to overcome drag on their body. This is merely an assertion and lacks evidence. We show that swimming animals do not spend power to overcome drag, the power is spent to achieve the swimming kinematics; swimming motion (and hence drag/thrust) is consequence of swimming kinematics and fluid-structure interaction. This understanding of energetics of aquatic locomotion is useful in two ways. First, based on the understanding of energetics of swimming, we develop a new efficiency parameter called energy consumption coefficient, and in the process we derive the allometric scalings of swimming parameters like frequency, speed, and cost of transport. Second, we investigate how the energy costs of swimming play a role in shaping ribbon fin morphology.;Lastly, we investigate how hydrodynamic forces play a role in the evolution of the elongated fin motor control. There is great diversity in the nature of elongated fin motor control. In fact, some swimming animals with elongated fin are classified based on the nature of the fin motor control. We investigate whether there is an underlying hydrodynamic basis for the observed diversity of elongated fin movements.