SYNOPSIS.The understanding of fish maneuvering and its application to underwater rigid bodies are considered. The goal is to gain insight into stealth. The recent progress made in NUWC is reviewed. Fish morphology suggests that control fins for maneuverability have unique scalar relationships irrespective of their speed type. Maneuvering experiments are carried out with fish that are fast yet maneuverable. The gap in maneuverability between fish and small underwater vehicles is quantified. The hydrodynamics of a dorsal fin based brisk maneuvering device and a dual flapping foil device, as applied to rigid cylindrical bodies, are described. The role of pectoral wings in maneuvering and station keeping near surface waves is discussed. A pendulum model of dolphin swimming is presented to show that body length and tail flapping frequency are related. For nearly neutrally buoyant bodies, Froude number and maneuverability are related. Analysis of measurements indicates that the Strouhal number of dolphins is a constant. The mechanism of discrete and deterministic vortex shedding from oscillating control surfaces has the property of large amplitude unsteady forcing and an exquisite phase dependence, which makes it inherently amenable to active control for precision maneuvering. Theoretical control studies are carried out to demonstrate the feasibility of maneuverability of biologically inspired bodies under surface waves. The application of fish hydrodynamics to the silencing of propulsors is considered. Two strategies for the reduction of radiated noise are developed. The effects of a reduction of rotational rate are modeled. The active cambering of blades made of digitally programmable artificial muscles, and their thrust enhancement, are demonstrated. Next, wake momentum filling is carried out by artificial muscles at the trailing edge of a stator blade of an upstream stator propulsor, and articulating them like a fish tail. A reduction of radiated noise, called blade tonals, is demonstrated theoretically. FIG. 1. Definition of length scales of a fish. FIG. 2. Morphology of dorsal fins of fish families.

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The bubble flow and transom wave associated with the naval research vessel Athena I was characterized during a field experiment conducted in June 2005 by several research groups. The bubbly flow around the passing ship was documented by stationary divers using underwater cameras. The free surface behind the ship was characterized in the near field using Quantitative Visualization, a laser-imaging technique developed and used by the Naval Surface Warfare Center, Carderock Division. The far-field transom wave was quantified using LIDAR instrumentation operated by the Scripps Institution of Oceanography. Results from the near and far-field measurements in the stern, along with images of from underwater video, are given in the report. The overall objective of the current experiment was to obtain fullscale qualitative and quantitative breaking wave field data of the naval combatant surface ship for use in CFD code development and validation. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON OF ABSTRACT OF PAGES Thomas Fu a. REPORT b. ABSTRACT c. THIS PAGE 19b. TELEPHONE NUMBER (include area UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED unlimited 21 code) 301-227-7058 Standard Form 298 (Rev. 8-98)