Maneuverability is critical to the performance of autonomous underwater vehicles (AUV) and fast swimming marine mammals which use rapid turns to catch prey. Overhead video records were analyzed for seven cetacean species (29-4536 kg) and sea lions (88-138 kg) turning in the horizontal plane. Powered and unpowered turns were executed by body flexion in conjunction with use of control surfaces, including flukes, flippers, dorsal fin, and caudal peduncle. Banking was used in powered turns and in unpowered turns where major control surfaces were horizontally oriented. Turning radius was dependent on body mass and swimming velocity. Relative minimum radii were 9-17% of body length and were equivalent for pinnipeds and cetaceans. However, Zalophus had smaller turning radii at higher speeds than cetaceans. Rate of turn was inversely related to turn radius. The highest turn rates were observed in Lagenorhynchus at 453 deg/s and Zalophus at 690 deg/s. Centripetal acceleration measured over 3 g for small cetaceans and 5.1 g for Zalophus. While cetaceans are configured for stability, otariid pinnipeds use their relatively large area flippers to produce increased instability with greater turning performance. This work was supported by the Office of Naval Research. INTRODUCTION An important consideration in the performance of autonomous underwater vehicles (AUV) is the ability to maneuver or turn. Rapid turns with small radii while maintaining speed are paramount to quickly locating objects, avoiding obstructions in confined and complex environments, and maintaining stability. Animal performance in terms of maneuverability can be superior to manufactured underwater vehicles [1]. Animals, therefore, can serve as effective model systems in exploring body and control surface designs which can be introduced into the design of AUVs to foster increased maneuverability. Animals rarely move continuously in straight lines. This is especially true in instances where potential prey must out-maneuver a predator or the reverse for a predator to turn fast enough to catch its prey [2, 3]. In addition, the search patterns employed by animals use continuous turning maneuvers. Even the largest of all animals, whales, display considerable proficiency in their maneuverability [4]. Various morphologies within animal lineages have evolved which foster maneuverability. Within the marine mammals there are divergent body designs that suggest differences in turning performance. Of the fastest swimming marine mammals, the pinnipeds (e.g., sea lions, seals) and cetaceans (e.g., whales, dolphins) display considerable variation in both their morphology and propulsive mode [5]. To understand how variation in the morphology of marine mammals can affect maneuverability, consideration should be given to parameters associated with stability. In that maneuverability represents a controlled instability, the possession of morphological characters that deviate from a design which maintains stability is expected to enhance turning performance. Based on analysis of aerodynamics, the following features are associated with stability [6, 7]: 1. Control surfaces located far from the center of gravity 2. Concentration of control surface area posterior of center of gravity 3. Anterior placement of center of gravity 4. Dihedral of control surfaces 5. Sweep of control surfaces 6. Reduced motion of control surfaces 7. Reduced flexibility of body If we compare the placement and design of control surfaces on sea lions and cetaceans (Fig. 1), we see marked differences between the two groups. The control surfaces of sea lions are represented by foreand hindflippers with the larger foreflippers near the center of gravity. Because of the high mobility of the foreflippers, both the sweep and the dihedral of the flippers is variable. For the cetaceans, the flippers, flukes, dorsal fin, and caudal peduncle are the control surfaces with the more mobile surfaces distance from the center of gravity. The flippers, flukes, and dorsal fin, when present, can be highly sweep, particularly in the faster species. Flexibility in the body of cetaceans is generally constrained [8]. In comparison, pinnipeds display significant axial flexibility [9]. Comparison of the morphology between pinnipeds and cetaceans suggests the whales and dolphins have a more stable design than marine mammals such as sea lions. Therefore, it is predicted that pinnipeds will be more highly maneuverable compared to cetaceans. MATERIALS AND METHODS To study variation in maneuverability based on differing body and control surface morphologies and propulsive modes, I examined the turning performance of eight species of marine mammals (seven cetaceans, one pinniped) with different swimming capabilities. All were captive animals which were maintained in pools at various research and zoological facilities including Sea World, Pittsburgh Zoo, and Long Marine Laboratory of the University of California Santa Cruz. For the cetaceans, these included the bottlenose dolphin ( Tursiops truncatus ), killer whale (Orcinus orca), Commerson's dolphin ( Cephalorhynchus commersonii ), Pacific white-sided dolphin (Lagenorhynchus obliquidens ), false killer whale ( Pseudorca crassidens ), beluga ( Delphinapterus leucas), and Amazon river dolphin ( Inia geoffrensis ). Orcinus was the largest cetacean with one individual of 4536 kg; whereas the smallest at 29 kg was Cephalorhynchus . Pseudorca and Lagenorhynchus are regarded generally as fast swimmers; whereas, Delphinapterus and Inia are considered to be slow swimmers. Delphinapterus and Inia are different from the other cetaceans by possessing mobile necks and flippers. Inia is capable of a notable degree of lateral flexion. In addition, the dorsal fin is reduced in Inia or absent in Delphinapterus . The cetaceans all use oscillations of the caudal flukes in the vertical plane for propulsion [4, 5]. Analysis of maneuverability has not been performed previously. 1000
[1]
Robert W. Blake,et al.
The Kinematics and Performance of the Escape Response in the Angelfish (Pterophyllum Eimekei)
,
1991
.
[2]
H. Howland.
Optimal strategies for predator avoidance: the relative importance of speed and manoeuvrability.
,
1974,
Journal of theoretical biology.
[3]
William H. Nedderman,et al.
Low-Speed Maneuvering Hydrodynamics of Fish and Small Underwater Vehicles
,
1997
.
[4]
C. A. Hui,et al.
Maneuverability of the Humboldt penguin (Spheniscus humboldti) during swimming
,
1985
.
[5]
Paul W. Webb,et al.
SPEED, ACCELERATION AND MANOEUVRABILITY OF TWO TELEOST FISHES
,
1983
.
[6]
Frank E. Fish,et al.
Transitions from Drag-based to Lift-based Propulsion in Mammalian Swimming
,
1996
.
[7]
F. Fish,et al.
Hydrodynamic design of the humpback whale flipper
,
1995,
Journal of morphology.
[8]
D. A. Pabst,et al.
Locomotor design of dolphin vertebral columns: bending mechanics and morphology of Delphinus delphis.
,
1997,
The Journal of experimental biology.
[9]
EFFECTS OF SWIMMING PATH CURVATURE ON THE ENERGETICS OF FISH MOTION
,
2004
.
[10]
J. Gál,et al.
Mammalian spinal biomechanics. I. Static and dynamic mechanical properties of intact intervertebral joints.
,
1993,
The Journal of experimental biology.