The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Earl H Dowell - One of the best experts on this subject based on the ideXlab platform.
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stability of rectangular plates in Subsonic Flow with various boundary conditions
Journal of Aircraft, 2015Co-Authors: Chad S Gibbs, Ivan Wang, Earl H DowellAbstract:The aeroelastic stability of rectangular plates in Subsonic Flow is well documented in literature. For example, the stability of a cantilever plate with a clamped edge parallel to the Flow is well understood due to the similarity of this system to an aircraft wing. However, an ongoing push for lighter aerospace structures and novel designs requires advancing the understanding of the aeroelastic stability of plates with nonconventional boundary condition combinations. This paper summarizes the aeroelastic theory and experimental results on the flutter and/or divergence mechanisms of a rectangular plate with different sets of structural boundary conditions. The theory combines a linear plate structural model with a three-dimensional vortex lattice aerodynamic mode to create a high-fidelity frequency domain aeroelastic model. The paper also discusses the development of a modular experimental test bed to test the different boundary conditions. A pair of well-understood boundary condition configurations acts a...
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aeroelastic stability of a cantilevered plate in yawed Subsonic Flow
Journal of Fluids and Structures, 2014Co-Authors: Chad S Gibbs, Deman Tang, Ivan Wang, Anosh Sethna, Earl H DowellAbstract:Abstract The aeroelastic stability of cantilevered plates with their clamped edge oriented both parallel and normal to Subsonic Flow is a classical fluid–structure interaction problem. When the clamped edge is parallel to the Flow the system loses stability in a coupled bending and torsion motion known as wing flutter. When the clamped edge is normal to the Flow the instability is exclusively bending and is referred to as flapping flag flutter. This paper explores the stability of plates during the transition between these classic aeroelastic configurations. The aeroelastic model couples a classical beam structural model to a three-dimensional vortex lattice aerodynamic model. The aeroelastic stability is evaluated in the frequency domain and the flutter boundary is presented as the plate is rotated from the flapping flag to the wing configuration. The transition between the flag-like and wing-like instability is often abrupt and the yaw angle of the Flow for the transition is dependent on the relative spacing of the first torsion and second bending natural frequencies. This paper also includes ground vibration and aeroelastic experiments carried out in the Duke University Wind Tunnel that confirm the theoretical predictions.
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a theoretical and experimental investigation of the effects of a steady angle of attack on the nonlinear flutter of a delta wing plate model
Journal of Fluids and Structures, 2003Co-Authors: Peter J Attar, Earl H Dowell, Deman TangAbstract:Limit cycle oscillations (LCO) of wings on certain modern high performance aircraft have been observed in flight and in wind tunnel experiments. Whether the physical mechanism that gives rise to this behavior is a fluid or structural nonlinearity or both is still uncertain. It has been shown that an aeroelastic theoretical model with only a structural nonlinearity can predict accurately the limit cycle behavior at low Subsonic Flow for a plate-like wing at zero angle of attack. Changes in the limit cycle and flutter behavior as the angle of attack is varied have also been observed in flight. It has been suggested that this sensitivity to angle of attack is due to a fluid nonlinearity. In this investigation, we study the flutter and limit cycle behavior of a wing in low Subsonic Flow at small steady angles of attack. Experimental results are compared to those predicted using an aeroelastic theoretical model with only a structural nonlinearity. Results from both experiment and theory show a change in flutter speed as the steady angle of attack is varied. Also the LCO magnitude increased at a given velocity as the angle of attack was increased for both the experiment and theory. While not proving that the observed sensitivity to angle of attack of LCO in aircraft is due to a structural nonlinearity, the results do show that a change in the aeroelastic behavior at angles of attack can be caused by a structural nonlinearity as well as a fluid nonlinearity. In this paper, only structural nonlinearities are considered, but an extension to include aerodynamic nonlinearities would be very worthwhile.
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Limit cycle oscillations of two-dimensional panels in low Subsonic Flow
International Journal of Non-Linear Mechanics, 2002Co-Authors: Deman Tang, Earl H DowellAbstract:Limit cycle oscillations of a two-dimensional panel in low Subsonic Flow have been studied theoretically and experimentally. The panel is clamped at its leading edge and free at its trailing edge. A structural non-linearity arises in both the bending stiffness and the mass inertia. Two-dimensional incompressible (linear) vortex lattice aerodynamic theory and a corresponding reduced order aerodynamic model were used to calculate the linear flutter boundary and also the limit cycle oscillations (that occur beyond the linear flutter boundary).
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limit cycle oscillations of a cantilevered wing in low Subsonic Flow
AIAA Journal, 1999Co-Authors: Deman Tang, Earl H Dowell, Kenneth C HallAbstract:A nonlinear, aeroelastic analysis of a low-aspect, rectangular wing modeled as a plate of constant thickness demonstratesthatlimitcycleoscillationsoftheorderoftheplatethicknessarepossible.Thestructuralnonlinearity arisesfrom doublebendinginboth thechordwiseand spanwisedirections.Thepresentresultsusing a vortex lattice aerodynamic model for low-Mach-numbere owscomplementearlierstudiesforhigh supersonicspeed thatshowed similar qualitative results. Also, the theoretical results are consistent with experimental data reported by other investigators for low-aspect-ratio delta wings.
Deman Tang - One of the best experts on this subject based on the ideXlab platform.
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aeroelastic stability of a cantilevered plate in yawed Subsonic Flow
Journal of Fluids and Structures, 2014Co-Authors: Chad S Gibbs, Deman Tang, Ivan Wang, Anosh Sethna, Earl H DowellAbstract:Abstract The aeroelastic stability of cantilevered plates with their clamped edge oriented both parallel and normal to Subsonic Flow is a classical fluid–structure interaction problem. When the clamped edge is parallel to the Flow the system loses stability in a coupled bending and torsion motion known as wing flutter. When the clamped edge is normal to the Flow the instability is exclusively bending and is referred to as flapping flag flutter. This paper explores the stability of plates during the transition between these classic aeroelastic configurations. The aeroelastic model couples a classical beam structural model to a three-dimensional vortex lattice aerodynamic model. The aeroelastic stability is evaluated in the frequency domain and the flutter boundary is presented as the plate is rotated from the flapping flag to the wing configuration. The transition between the flag-like and wing-like instability is often abrupt and the yaw angle of the Flow for the transition is dependent on the relative spacing of the first torsion and second bending natural frequencies. This paper also includes ground vibration and aeroelastic experiments carried out in the Duke University Wind Tunnel that confirm the theoretical predictions.
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a theoretical and experimental investigation of the effects of a steady angle of attack on the nonlinear flutter of a delta wing plate model
Journal of Fluids and Structures, 2003Co-Authors: Peter J Attar, Earl H Dowell, Deman TangAbstract:Limit cycle oscillations (LCO) of wings on certain modern high performance aircraft have been observed in flight and in wind tunnel experiments. Whether the physical mechanism that gives rise to this behavior is a fluid or structural nonlinearity or both is still uncertain. It has been shown that an aeroelastic theoretical model with only a structural nonlinearity can predict accurately the limit cycle behavior at low Subsonic Flow for a plate-like wing at zero angle of attack. Changes in the limit cycle and flutter behavior as the angle of attack is varied have also been observed in flight. It has been suggested that this sensitivity to angle of attack is due to a fluid nonlinearity. In this investigation, we study the flutter and limit cycle behavior of a wing in low Subsonic Flow at small steady angles of attack. Experimental results are compared to those predicted using an aeroelastic theoretical model with only a structural nonlinearity. Results from both experiment and theory show a change in flutter speed as the steady angle of attack is varied. Also the LCO magnitude increased at a given velocity as the angle of attack was increased for both the experiment and theory. While not proving that the observed sensitivity to angle of attack of LCO in aircraft is due to a structural nonlinearity, the results do show that a change in the aeroelastic behavior at angles of attack can be caused by a structural nonlinearity as well as a fluid nonlinearity. In this paper, only structural nonlinearities are considered, but an extension to include aerodynamic nonlinearities would be very worthwhile.
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Limit cycle oscillations of two-dimensional panels in low Subsonic Flow
International Journal of Non-Linear Mechanics, 2002Co-Authors: Deman Tang, Earl H DowellAbstract:Limit cycle oscillations of a two-dimensional panel in low Subsonic Flow have been studied theoretically and experimentally. The panel is clamped at its leading edge and free at its trailing edge. A structural non-linearity arises in both the bending stiffness and the mass inertia. Two-dimensional incompressible (linear) vortex lattice aerodynamic theory and a corresponding reduced order aerodynamic model were used to calculate the linear flutter boundary and also the limit cycle oscillations (that occur beyond the linear flutter boundary).
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limit cycle oscillations of a cantilevered wing in low Subsonic Flow
AIAA Journal, 1999Co-Authors: Deman Tang, Earl H Dowell, Kenneth C HallAbstract:A nonlinear, aeroelastic analysis of a low-aspect, rectangular wing modeled as a plate of constant thickness demonstratesthatlimitcycleoscillationsoftheorderoftheplatethicknessarepossible.Thestructuralnonlinearity arisesfrom doublebendinginboth thechordwiseand spanwisedirections.Thepresentresultsusing a vortex lattice aerodynamic model for low-Mach-numbere owscomplementearlierstudiesforhigh supersonicspeed thatshowed similar qualitative results. Also, the theoretical results are consistent with experimental data reported by other investigators for low-aspect-ratio delta wings.
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limit cycle oscillations of delta wing models in low Subsonic Flow
AIAA Journal, 1999Co-Authors: Deman Tang, James K Henry, Earl H DowellAbstract: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 similar qualitative results. The theoretical results for the flutter boundary (beyond which LCO occurs) have been validated by comparison to the experimental data reported by other investigators for low aspect ratio delta wings. Also the limit cycle oscillations found experimentally by previous investigators (but not previously quantified prior to the present work) are consistent with the theoretical results reported here. Reduced order aerodynamic and structural models are used to substantially decrease computational cost with no loss in accuracy. Without the use of reduced order models, calculations of the LCO would be impractical. A wind tunnel model is tested to provide a quantitative experimental correlation with the theoretical results for the LCO response itself.
Yi Ren Yang - One of the best experts on this subject based on the ideXlab platform.
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on the stability and chaos of a plate with motion constraints subjected to Subsonic Flow
International Journal of Non-linear Mechanics, 2014Co-Authors: Yi Ren YangAbstract:Abstract The non-linear dynamical behavior of a cantilevered plate with motion constraints in Subsonic Flow is investigated in this paper. The governing partial differential equation is transformed to a series of ordinary differential equations by using the Galerkin method. The fixed points and their stabilities of the system are presented in a parameter space based on qualitative analysis and numerical studies. The complex non-linear behavior in the region of dynamical instability is investigated by using numerical simulations. The region of dynamical instability is divided into four sub-regions according to different types of plate motion. Results show that symmetric and asymmetric limit cycle motions would occur after dynamical instability; the route from periodic motions to chaos is via doubling-period bifurcation; symmetric and asymmetric period-3 and period-6 motions appear along with chaotic motions; chaotic divergence and divergent motions occur with the increases of dynamic pressure.
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nonlinear dynamics analysis of a two dimensional thin panel with an external forcing in incompressible Subsonic Flow
Nonlinear Dynamics, 2012Co-Authors: Yi Ren YangAbstract:Based on the potential theory of incompressible Flow and the energy method, a two-dimensional simply supported thin panel subjected to external forcing and uniform incompressible Subsonic Flow is theoretically modeled. The nonlinear cubic stiffness and viscous damper in the middle of the panel is considered. Transformation of the governing partial differential equation to a set of ordinary differential equations is performed through the Galerkin method. The stability of the fixed points of the panel system is analyzed. The regions of different motion types of the panel system are investigated in different parameter spaces. The rich dynamic behaviors are presented as bifurcation diagrams, phase-plane portraits, Poincare maps and maximum Lyapunov exponents based on carefully numerical simulations.
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melnikov s method for chaos of a two dimensional thin panel in Subsonic Flow with external excitation
Mechanics Research Communications, 2011Co-Authors: Yi Ren Yang, Minglu ZhangAbstract:Abstract In this brief communication, Melnikov's method is adopted to study the chaotic behaviors of a two-dimensional thin panel subjected to Subsonic Flow and external excitation. The nonlinear governing equations of the Subsonic panel system are reduced to a series of ordinary differential equations by using Galerkin method. The critical parameters for chaos are obtained. It is found that the critical parameters obtained by the theoretical analysis are in agreement with the numerical simulations. The method suggested in this paper can also be extended for other fluid-structure dynamic systems, such as the fluid-conveying system.
Dehua Wang - One of the best experts on this subject based on the ideXlab platform.
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on two dimensional sonic Subsonic Flow
Communications in Mathematical Physics, 2007Co-Authors: Guiqiang Chen, Constantine M Dafermos, Marshall Slemrod, Dehua WangAbstract:A compensated compactness framework is established for sonic-Subsonic approximate solutions to the two-dimensional Euler equations for steady irrotational Flows that may contain stagnation points. Only crude estimates are required for establishing compactness. It follows that the set of Subsonic irrotational solutions to the Euler equations is compact; thus Flows with sonic points over an obstacle, such as an airfoil, may be realized as limits of sequences of strictly Subsonic Flows. Furthermore, sonic-Subsonic Flows may be constructed from approximate solutions. The compactness framework is then extended to self-similar solutions of the Euler equations for unsteady irrotational Flows.
Guiqiang Chen - One of the best experts on this subject based on the ideXlab platform.
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Existence and stability of multi-dimensional transonic Flows through an infinite nozzle of arbitrary cross-sections
2015Co-Authors: Guiqiang Chen, Mikhail FeldmanAbstract:Abstract. We establish the existence and stability of multidimensional steady transonic Flows with transonic shocks through an infinite nozzle of arbitrary cross-sections, including a slowly varying de Laval nozzle. The transonic Flow is governed by the inviscid potential Flow equation with supersonic upstream Flow at the entrance, uniform Subsonic downstream Flow at the exit at infinity, and the slip boundary condition on the nozzle boundary. Our results indicate that, if the supersonic upstream Flow at the entrance is sufficiently close to a uniform Flow, there exists a solution that consists of a C1,α Subsonic Flow in the unbounded downstream region, converging to a uniform velocity state at infinity, and a C1,α multidimensional transonic shock dividing the Subsonic Flow from the supersonic upstream Flow; the uniform velocity state at the exit at infinity in the downstream direction is uniquely determined by the supersonic upstream Flow; and the shock is orthogonal to the nozzle boundary at every point of their intersection. In order to construct such a transonic Flow, we reformulate the multidimensional transonic nozzle problem into a free boundary problem for the Subsonic phase, in which the equation is elliptic and the free boundary is a transonic shock. The free boundary conditions are determined by the Rankine-Hugoniot conditions along the shock. We further develop a nonlinear iteration approach and employ its advantages to deal with such a free boundary problem in the unbounded domain. We also prove that the transonic Flow with a transonic shock is unique and stable with respect to the nozzle boundary and the smooth supersonic upstream Flow at the entrance. 1
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on two dimensional sonic Subsonic Flow
Communications in Mathematical Physics, 2007Co-Authors: Guiqiang Chen, Constantine M Dafermos, Marshall Slemrod, Dehua WangAbstract:A compensated compactness framework is established for sonic-Subsonic approximate solutions to the two-dimensional Euler equations for steady irrotational Flows that may contain stagnation points. Only crude estimates are required for establishing compactness. It follows that the set of Subsonic irrotational solutions to the Euler equations is compact; thus Flows with sonic points over an obstacle, such as an airfoil, may be realized as limits of sequences of strictly Subsonic Flows. Furthermore, sonic-Subsonic Flows may be constructed from approximate solutions. The compactness framework is then extended to self-similar solutions of the Euler equations for unsteady irrotational Flows.
