| Limit Cycle Oscillations and Nonlinear Aeroelastic Wing Response: Reduced Order Aerodynamic Models |
31 DEC 2003 |
24 pages |
| Authors:
Earl H. Dowell; Kenneth C. Hall; DUKE UNIV DURHAM NC DEPT OF MECHANICALENGINEERING AND MATERIALS SCIENCE
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 | To develop an eigenmode or proper orthogonal decomposition (POD) modal representation of unsteady aerodynamic forces on oscillating flexible airfoils and wings and thereby reduce the size and cost of mathematical models for such forces by several orders of magnitude. Building on earlier work for two-dimensional inviscid flows, we seek to extend our models to. three- dimensional flows with viscous effects included. Also a novel form of the harmonic balance (HB) ... |
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| Nonlinear Reduced-Order Modeling of Limit Cycle Oscillations of Aircraft Wings and Wing/Store |
DEC 2003 |
148 pages |
| Authors:
P. C. Chen; Danny D. Liu; Xiaowei Geo; Kenneth C. Hall; Earl H. Dowell; ZONA TECHNOLOGY INC SCOTTSDALE AZ
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| Significant progress has been made by the ZONA-Duke team in Phase II of our work. A novel and computationally efficient method for calculating transonic limit cycle oscillations (LCO), flutter and other nonlinear aeroelastic phenomena has been developed. To solve the general 3D Euler and Reynolds Averaging Navier-Stokes( Eulen/RANS) equation, a Harmonic Balance(HB) method formulated in the frequency domain in combination with a proper ormogonal decomposition (POD) technique and reduced order ... |
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| Theoretical Prediction of Limit Cycle Oscillations in Support of Flight Flutter Testing |
31 AUG 2003 |
24 pages |
| Authors:
Earl H. Dowell; Kenneth C. Hall; DUKE UNIV DURHAM NC DEPT OF MECHANICALENGINEERING AND MATERIALS SCIENCE
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| Using a novel harmonic balance method and a state of the art computational fluid dynamics (CFD) model, limit cycle oscillations have been calculated for a conventional and supercritical airfoil as well as the F-16 wing. The latter result is the first of its kind. |
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| Dynamics and Control of Nonlinear Fluid-Structure Interaction |
JUL 2003 |
16 pages |
| Authors:
Earl H. Dowell; Robert L. Clark Jr.; Lawrence N. Virgin; DUKE UNIV DURHAM NC DEPT OF MECHANICALENGINEERING AND MATERIALS SCIENCE
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| Experimental and theoretical studies of the nonlinear dynamics and control of aeroelastic systems including airfoils and wings have been conducted. Nonlinear geometric stiffness and freeplay have been considered specifically and good theoretical / experimental correlation obtained. Active control systems have been designed, built and tested to increase flutter speed and reduce limit cycle oscillations (LCO). Our most recent work includes theoretical studies of aerodynamic nonlinearities in the transonic range and ... |
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| Limit Cycle Oscillations (LCO) and Nonlinear Aeroelastic Response: Reduced Order Models |
01 NOV 2001 |
13 pages |
| Authors:
Earl H. Dowell; DUKE UNIV DURHAM NC DEPT OF MECHANICALENGINEERING AND MATERIALS SCIENCE
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| Unsteady aerodynamic computational models for aeroelastic phenomena such as flutter and limit cycle oscillations are complex and high dimensional. Under this grant, reduced order models are being developed that offer increased physical insight and greatly reduced computational cost. Transonic flows are emphasized because of their practical importance and significant technical challenge. |
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| Nonlinear Dynamics and Control of Wings and Panels |
26 DEC 2000 |
7 pages |
| Authors:
Earl H. Dowell; Robert L. Clark Jr.; Lawrence N. Virgin; DUKE UNIV DURHAM NC DEPT OF MECHANICALENGINEERING AND MATERIALS SCIENCE
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| This is the Final Report of AFOSR Grant F49620-97-1-O414. The objective of this study was to develop a more fundamental understanding of the causes and modifications of limit cycle oscillations and other dynamic and control phenomena arising from nonlinear effects in aeroelastic systems. A combined experimental-theoretical study was pursued to validate and improve our physical understanding and mathematical models for design and analysis to enable flight of aircraft safely and ... |
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| Nonlinear Dynamics and Control of Wings and Panels |
NOV 2000 |
7 pages |
| Authors:
Earl H. Dowell; Robert L. Clark Jr.; Lawrence N. Virgin; DUKE UNIV DURHAM NC DEPT OF MECHANICALENGINEERING AND MATERIALS SCIENCE
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| Experimental and theoretical studies of the nonlinear dynamics and control of aeroelastic systems including airfoils and wings have been conducted. Nonlinear geometric stiffness and freeplay have been considered specifically and good theoretical / experimental correlation obtained. Active control systems have been designed, built and tested to increase flutter speed and reduce limit cycle oscillations (LCO). |
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| Limit Cycle Oscillations (LCO) and Nonlinear Aeroelastic Wing Response: Reduced Order Aerodynamic Models |
APR 1999 |
15 pages |
| Authors:
Earl H. Dowell; DUKE UNIV DURHAM NC SCHOOL OF ENGINEERING
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| A nonlinear, aeroelastic analysis of a low aspect, delta wing modeled as a plate of constant thickness demonstrates that limit cycle oscillations (LCO) of the order of the plate thickness are possible. The structural nonlinearity arises from double bending in both the chordwise and spanwise directions. The present results using a vortex lattice aerodynamic model for a low Mach number flow complement earlier studies for rectangular wing platforms that showed ... |
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| Limit Cycle Oscillations (LCO) and Nonlinear Aeroelastic Wing Response |
04 DEC 96 |
13 pages |
| Authors:
Earl H. Dowell; DUKE UNIV DURHAM NC
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| Limit cycle oscillations (LCO) have been observed for elastic wings at moderate to high angles of attack where separated flow is thought to occur. At transonic flow conditions with shock waves present, flow separation may occur at moderate angles of attack. For higher angles of attack, separation may occur at (low) subsonic conditions. Empirical quasi steady aerodynamic models based on steady state experimental data have shown some success in predicting ... |
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| Nonlinear Dynamics and Control of Wings and Panels |
04 DEC 1996 |
18 pages |
| Authors:
Earl H. Dowell; Lawrence Virgin; Robert Clark; DUKE UNIV DURHAM NC
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| A multidisciplinary team of experts in aeroelasticity, control and nonlinear dynamics will study experimentally and theoretically the control of prototypical aeroelastic systems. Emphasis will be given to those systems with significant nonlinear characteristics, e.g. freeplay structural behavior and aeroelastic stall behavior for airfoils and wings and geometrical structural behavior and aeroelastic stall behavior for airfoils and wings and geometric structural nonlinearities of panels (plates and shells). Research in nonlinear dynamics ... |
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| Nonlinear Dynamics and Aeroelasticity of Rotorcraft in Forward Flight |
FEB 95 |
4 pages |
| Authors:
Earl H. Dowell; DUKE UNIV DURHAM NC DEPT OF MECHANICAL ENGINEERING AND MATERIALS SCIENCE
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| Large amplitude (nonlinear) oscillations of rotor blades due to self- excitation (flutter) or external excitation (mechanical or aerodynamic) frequently occur and are often design critical for rotorcraft. The present work is a combined theoretical-experimental study to develop improved understanding and mathematical models for enhanced design and performance. (AN) |
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| Chaos in Mechanical Systems with Especial Reference to Rotorcraft and Missiles |
FEB 93 |
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| Authors:
Earl H. Dowell; DUKE UNIV DURHAM NC DEPT OF MECHANICAL ENGINEERING AND MATERIALS SCIENCE
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 | Work has focussed on the following topics using the buckled beam as prototypical generic system. The effect of higher modes on the response of the buckled beam initial condition maps and their interpretation Lyapunov exponents (nonlinear eigenvalues) as a predictor of chaos necessary and sufficient conditions for chaos to occur systems with both positive and negative linear stiffness systems with nonlinear damping a (buckled) beam-tube with an internal flowing fluid ... |
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| Workshop on Dynamics and Aeroelastic Stability Modeling of Rotorcraft Systems (3rd), Held in Durham, North Carolina on March 12-14, 1990 |
14 MAR 90 |
239 pages |
| Authors:
Earl H. Dowell; DUKE UNIV DURHAM NC SCHOOL OF ENGINEERING
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| The workshop was held as scheduled. Sessions included rotorcraft dynamics research, physical modeling, rotorcraft centers of excellence, aeroelasticity and stability, response dynamics and control, mathematics of modeling, and experimental-theoretical investigations. Keywords: Rotorcraft systems, Rotorcraft dynamics, Aeroelasticity, Response dynamics, Stability modeling, Workshop. (js) |
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| ASYMPTOTIC MODAL ANALYSIS AND STATISTICAL ENERGY ANALYSIS |
JUL 88 |
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| Authors:
Earl H. Dowell
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| statistical energy analysis (sea) is defined by considering the asymptotic limit of classical modal analysis, an approach called asymptotic modal analysis (ama). the general approach is described for both structural and acoustic systems. the theoretical foundation is presented for structural systems, and experimental verification is presented for a structural plate responding to a random force. work accomplished subsequent to the grant initiation focusses on the acoustic response of an interior ... |
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| THE FLUTTER OF VERY LOW ASPECT RATIO PANELS, |
JUL 1964 |
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| Authors:
Earl H. Dowell; MASSACHUSETTS INST OF TECH CAMBRIDGE AEROELASTIC AND STRUCTURES RESEARCH LAB
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Reports by Author
