Derivation of ODEs and Bifurcation Analysis of a Two-DOF Airfoil Subjected to Unsteady Incompressible Flow

An airfoil subjected to two-dimensional incompressible inviscid flow is considered. The airfoil is supported via a translational and a torsional springs. The aeroelastic integro-differential equations of motion for the airfoil are reformulated into a system of six first-order autonomous ordinary differential equations. These are the simplest and least number of ODEs that can present this aeroelastic system. The differential equations are then used for the bifurcation analysis of an airfoil with a structural nonlinearity in the pitch direction. Sample bifurcation diagrams showing both stable and unstable limit cycle oscillation are presented. The types of bifurcations are assessed by evaluating the Floquet multipliers. For a specific case, a period doubling route to chaos was detected, and mildly chaotic behavior in a narrow range of velocity was confirmed via the calculation of the Lyapunov exponents

A FLUID DYNAMICS STUDY OF A MODIFIED LOW-REYNOLDS-NUMBER FLAPPING MOTION

ABSTRACT The objective of the present study is to investigate the low Reynolds number (LRN) fluid dynamics of an elliptic airfoil performing a novel figure-eight-like motion. To this mean, the influence of phase angle between the pitching and translational (heaving and lagging) motions and the amplitude of translational motions on the fluid flow is simulated. NavierStokes (NS) equations with Finite Volume Method (FVM) are used and the instantaneous force coefficients and the fluid dynamics performance, as well as the corresponding vortical structures are analyzed. Both the phase angle and the amplitudes of horizontal and vertical motions are of great importance to the fluid dynamic characteristics of the model as they are shown to change the peaks of the fluid forces, fluid dynamic performance, and the vortical patterns around the model. INTRODUCTION Forced and flow-induced oscillations are highly prevalent in a wide range of fluid engineering applications. These unsteady conditions could be useful when assisting in the generation of the fluid forces such as wing flapping, or be destructive when becoming the undesired oscillations such as wing flutter. Flapping motions are the most common means of force generation in micro aerial vehicles and swimming robots. The physical characteristics and the fluid phenomena of such motions strongly depend on the governing flow and system parameters. LRN flapping flows are mostly accompanied with non-linear vortex dynamics, such as dynamic stal

Cytochrome Oxidase Content and Respiratory Rates of Etiolated Wheat and Barley Seedlings.

Conference agenda: http://www.aiaa.org/agenda.cfm?lumeetingid=1998This paper analyzes task assignment for heterogeneous air vehicles using a guaranteed conflict-free assignment algorithm, the Consensus Based Bundle Algorithm (CBBA). We extend this recently proposed algorithm to handle two realistic multi- UAV operational complications. Our rst extension accounts for obstacle regions in order to generate collision free paths for UAVs. Our second extension reduces task planner sensitivity to sensor measurement noise, and thereby minimizes churning behavior in flight paths. After integrating our enhanced CBBA module with a 3D visualization and interaction software tool, we simulate multiple aircraft servicing stationary and moving ground targets. Preliminary simulation results establish that consistent, conflict-free multi-UAV path assignments can be calculated on the order of a few seconds. The enhanced CBBA consequently demonstrates signfi cant potential for real-time performance in stressing environments