Objectives:Through the use of advanced visualization techniques, the parametric dependence on transverse and longitudinal flapping foil propulsor spacing and individual propulsor kinematics will be optimized to advance the design of effective multiple foil propulsion technology. This proposal is a modified version of the original proposal and is focused on investigating the signature and efficiency of the original flapping foils. Ongoing work with low aspect ratio foils has offered a clearer understanding of the three-dimensional vortical structures in the wake and can be used to guide a critical path research effort. This study will help develop an optimized model of efficient multi foil propulsor configurations. A small multiple foil mechanism will be constructed to fit inside the MIT Hydrodynamics Tunnel.Methodology:Experimental force measurements and quantitative flow visulaization will be used to systematically quantify the three dimensional hydrodynamic characteristics of multiple flapping foil wakes. Tests using multiple foils will be performed to gain further insight into the manipulation of three dimensional vortical structures by tandem and staggered flapping foils and the resulting forces experienced by each foil. Flapping foil studies will be guided by existing knowledge of fish schooling behavior. Three component velocity measurements will be made using scanning stereo PIV techniques to determine the vortex ring interactions generated from arrays of multiple swimmers. Optically clear foils will be used to avoid casting shadows while using the laser for PIV. A multi foil apparatus will be constructed to facilitate this endeavor. Rationale:Fish schooling energetics are very important in biology. An understanding of these behaviors can give insight into the migration of fish schools searching for food and response of schools to incoming flow disturbances or predators. While biologists have suggested classic schooling models, a true understanding of the three dimensional hydrodynamics is not fully realized. Technologically the configuration of multiple flapping foils as propulsive mechanisms in underwater vehicles has often been based on physical constrains of the vehicle design, versus optimal hydrodynamic configurations. Vehicles designed for use in highly energetic environments, such as the surf zone, will greatly benefit from an optimized foil configuration that reduces energy expenditure and enhances vehicle performance in forward swimming and maneuvering.