Efficiency and persistence in models of adaptation

A cut-and-paste model which mimics a trial-and-error process of adaptation is introduced and solved. The model, which can be thought of as a diffusion process with memory, is characterized by two properties, efficiency and persistence. We establish a link between these properties and determine two transitions for each property, a percolation transition and a depinning transition. If the adaptation process is iterated, the antipersistent state becomes an attractor of the dynamics. Extensions to higher dimensions are briefly discussed.Comment: 4 pages, 4 figures, submitted to publicatio

Leading-edge flow criticality as a governing factor in leading-edge-vortex initiation in unsteady airfoil flows

A leading-edge suction parameter (LESP) that is derived from potential flow theory as a measure of suction at the airfoil leading edge is used to study initiation of leading-edge vortex (LEV) formation in this article. The LESP hypothesis is presented, which states that LEV formation in unsteady flows for specified airfoil shape and Reynolds number occurs at a critical constant value of LESP, regardless of motion kinematics. This hypothesis is tested and validated against a large set of data from CFD and experimental studies of flows with LEV formation. The hypothesis is seen to hold except in cases with slow-rate kinematics which evince significant trailing-edge separation (which refers here to separation leading to reversed flow on the aft portion of the upper surface), thereby establishing the envelope of validity. The implication is that the critical LESP value for an airfoil–Reynolds number combination may be calibrated using CFD or experiment for just one motion and then employed to predict LEV initiation for any other (fast-rate) motion. It is also shown that the LESP concept may be used in an inverse mode to generate motion kinematics that would either prevent LEV formation or trigger the same as per aerodynamic requirements

Comparative Study of Pitch-Plunge Airfoil Aerodynamics at Transitional Reynolds Number

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76128/1/AIAA-2008-652-591.pd

Flowfield Evolution vs. Lift Coefficient History for Rapidly-Pitching Low Aspect Ratio Plates

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90678/1/AIAA-2011-3118-471.pd

Unsteady Force Measurements in Pitching-Plunging Airfoils

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77153/1/AIAA-2009-4031-237.pd

Free-to-Pivot Flat Plates in Hover for Reynolds Numbers 14 to 21,200

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140682/1/1.j053169.pd

Effects of Planform Geometry and Pivot Axis Location on the Aerodynamics of Pitching Low Aspect Ratio Wings

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106469/1/AIAA2013-2992.pd

Unsteady Force Generation and Vortex Dynamics of Pitching and Plunging Flat Plates at Low Reynolds Number

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90670/1/AIAA-2011-220-550.pd

Effect of Aspect Ratio on Rigid Lifting Flat Plates in Pitch-Plunge Motion at Low Reynolds Numbers

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83600/1/AIAA-2010-389-744.pd

Small UAV Research and Evolution in Long Endurance Electric Powered Vehicles

This paper describes recent research into the advancement of small, electric powered unmanned aerial vehicle (UAV) capabilities. Specifically, topics include the improvements made in battery technology, design methodologies, avionics architectures and algorithms, materials and structural concepts, propulsion system performance prediction, and others. The results of prototype vehicle designs and flight tests are discussed in the context of their usefulness in defining and validating progress in the various technology areas. Further areas of research need are also identified. These include the need for more robust operating regimes (wind, gust, etc.), and continued improvement in payload fraction vs. endurance