3
chapter one
Hydrodynamics
Jeremy A. Goldbogen, Frank E. Fish, and Jean Potvin
1.1 Introduction
High-performance locomotion at a low energetic cost is critical for many life functions including capturing food, avoiding predators, and long-distance migration. For marine mammals,
aquatic transport is a necessity and thus demands efficient locomotor capacity. Because marine
mammals evolved from terrestrial ancestors, these animals exhibit secondary adaptations to
the physical challenges associated with life in water. The most fundamental of these challenges are resistive forces, generally known as drag, that limit the body’s movement through
water. Drag arises because water has mass and viscosity, so the motions of animals through
the water are not free from the perspective of energy economics. These resistive forces are
complex and are largely dependent on shape, scale, and speed. Marine mammals exhibit a
wide range of morphologies that reflect different locomotor demands and ecological functions. However, across taxa, most marine mammals are unified by a convergent, fusiform
body profile that decreases resistive forces and increases the efficiency of locomotion.
Contents
1.1 Introduction ............................................................................................................................3
1.2 Hydrodynamic forces at play during locomotion: Drag, lift, and thrust ......................4
1.2.1 Flow structures around a body moving underwater ...........................................4
1.2.2 Resistive forces ...........................................................................................................6
1.2.3 How to limit drag: Forward and backward taper .................................................8
1.2.4 Lift and propulsion ....................................................................................................9
1.3 Evolutionary biomechanics of marine mammal locomotion: How different
marine mammals achieve different levels of locomotor performance ........................ 11
1.3.1 Mechanics of drag-based paddling ....................................................................... 11
1.3.2 Mechanics of lift-based oscillation ........................................................................ 11
1.3.3 Undulatory swimming ........................................................................................... 13
1.3.4 Transition from drag-based to lift-based locomotion ......................................... 13
1.3.5 Surface versus submerged and buoyancy control .............................................. 15
1.3.6 Maneuverability ....................................................................................................... 16
1.3.7 Maneuverability in cetaceans ................................................................................ 17
1.3.8 Maneuverability in pinnipeds ............................................................................... 18
1.3.9 Energy capture from the external environment ................................................. 19
1.4 Tools and methods for hydrodynamics research ............................................................ 20
1.5 Lingering mysteries and future challenges ..................................................................... 21
Acknowledgment ..........................................................................................................................22
References .......................................................................................................................................22
chapter one
Hydrodynamics
Jeremy A. Goldbogen, Frank E. Fish, and Jean Potvin
1.1 Introduction
High-performance locomotion at a low energetic cost is critical for many life functions including capturing food, avoiding predators, and long-distance migration. For marine mammals,
aquatic transport is a necessity and thus demands efficient locomotor capacity. Because marine
mammals evolved from terrestrial ancestors, these animals exhibit secondary adaptations to
the physical challenges associated with life in water. The most fundamental of these challenges are resistive forces, generally known as drag, that limit the body’s movement through
water. Drag arises because water has mass and viscosity, so the motions of animals through
the water are not free from the perspective of energy economics. These resistive forces are
complex and are largely dependent on shape, scale, and speed. Marine mammals exhibit a
wide range of morphologies that reflect different locomotor demands and ecological functions. However, across taxa, most marine mammals are unified by a convergent, fusiform
body profile that decreases resistive forces and increases the efficiency of locomotion.
Contents
1.1 Introduction ............................................................................................................................3
1.2 Hydrodynamic forces at play during locomotion: Drag, lift, and thrust ......................4
1.2.1 Flow structures around a body moving underwater ...........................................4
1.2.2 Resistive forces ...........................................................................................................6
1.2.3 How to limit drag: Forward and backward taper .................................................8
1.2.4 Lift and propulsion ....................................................................................................9
1.3 Evolutionary biomechanics of marine mammal locomotion: How different
marine mammals achieve different levels of locomotor performance ........................ 11
1.3.1 Mechanics of drag-based paddling ....................................................................... 11
1.3.2 Mechanics of lift-based oscillation ........................................................................ 11
1.3.3 Undulatory swimming ........................................................................................... 13
1.3.4 Transition from drag-based to lift-based locomotion ......................................... 13
1.3.5 Surface versus submerged and buoyancy control .............................................. 15
1.3.6 Maneuverability ....................................................................................................... 16
1.3.7 Maneuverability in cetaceans ................................................................................ 17
1.3.8 Maneuverability in pinnipeds ............................................................................... 18
1.3.9 Energy capture from the external environment ................................................. 19
1.4 Tools and methods for hydrodynamics research ............................................................ 20
1.5 Lingering mysteries and future challenges ..................................................................... 21
Acknowledgment ..........................................................................................................................22
References .......................................................................................................................................22