Publications
197 results found
Murua J, Palacios R, Graham JMR, 2012, Assessment of Wake-Tail Interference Effects on the Dynamics of Flexible Aircraft, AIAA Journal, Vol: 50, Pages: 1575-1585
Ng BF, Palacios R, Graham JMR, et al., 2012, Robust control synthesis for gust load alleviation from large aeroelastic models with relaxation of spatial discretisation, European Wind Energy Association Annual Event, Copenhagen, Denmark
Murua J, Palacios R, Graham JMR, 2012, Open-Loop Stability and Closed-Loop Gust Alleviation on Flexible Aircraft Including Wake Modeling, 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference,Honolulu, Hawaii, USA
Palacios R, Wang Y, Karpel M, 2012, Intrinsic models for nonlinear flexible-aircraft dynamics using industrial finite-element and loads packages, 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Honolulu, Hawaii, USA
Murua J, Palacios R, Graham JMR, 2012, Open-loop stability and closed-loop gust alleviation on flexible aircraft including wake modeling
This paper numerically investigates the dynamics of a flexible, lightweight, unmanned aircraft, evaluating its stability boundaries and focusing on the response of the aircraft under atmospheric disturbances. This is achieved by integrating a time-domain 3-D unsteady vortex-lattice aerodynamics method with a geometrically-exact composite beam model encompassing elastic and rigid-body degrees of freedom. The resulting framework is a medium-fidelity tool for the analysis of vehicles that exhibit substantial couplings between their aeroelastic and flight dynamics responses. In its general nonlinear form, the unified model captures the instantaneous shape of the lifting surfaces and the free wake, including large geometrically-nonlinear displacements, in-plane motions, and aerodynamic interference effects. The linearization of the equations leads to a monolithic state-space assembly, ideally suited for stability analysis and control synthesis. The numerical studies illustrate these capabilities, designing linear PID controllers in order to alleviate gust-induced loads and trajectory deviations. © 2012 by Joseba Murua. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.
Hesse H, Murua J, Palacios R, 2012, Consistent structural linearization in flexible aircraft dynamics with large rigid-body motion, ISSN: 0273-4508
This paper investigates the linearization, using perturbation methods, of the struc- tural deformations in the nonlinear flight dynamic response of aircraft with slender, flex- ible wings. This has been achieved by first coupling a displacement-based, geometrically- nonlinear flexible-body dynamics formulation with the 3D Unsteady Vortex-Lattice Method, followed by a consistent linearization of the structural degrees of freedom, which are as- sumed to be small in a body-fixed reference frame. The translations and rotations of that reference frame can be arbitrarily large, however. The resulting system preserves all cou- plings between rigid and elastic motions and can be projected onto a few vibration modes of the unconstrained aircraft with arbitrarily-large, geometrically-nonlinear deformation at a trim condition. The dynamics of the system are then written in tensor form, with up to cubic terms due to the nonlinear rigid-body terms, and with a limited number of coefficients that can be pre-computed prior to the time-marching simulation. Numerical studies on a representative HALE UAV are presented to illustrate the approach and results are compared to the mean-axes solution. © 2012 AIAA.
Palacios R, Wang Y, Karpel M, 2012, Intrinsic models for nonlinear flexible-aircraft dynamics using industrial finite-element and loads packages
A procedure is introduced to construct 1-D geometrically-nonlinear structural dynam- ics models from built-up 3-D finite-element solutions. The nonlinear 1-D model is based on an intrinsic form of the equations of motion, that uses beam velocities and internal forces as primary degrees of freedom. It is further written in modal form, which yields a description of the beam dynamics through ordinary differential equations with quadratic non-linearities. We show that the evaluation of the coeficients in these nonlinear equa- tions of motion does not require the generation of a beam finite-element model. Instead, they are directly identified in the 3-D model through a process of static condensation of the dynamics on nodes defined along along spanwise stations, as it is done in aircraft dy- namic load analysis. In fact, the method exploits the multi-point constraints of linear load models, that are normally used to obtain sectional loads, and we show how it can be inte- grated in full-vehicle aeroelastic analysis. Finally we illustrate this approach on an isotropic cantilever box beam modelled using shell elements. © 2012 by Rafael Palacios, Yinan Wang and Moti Karpel.
Dizy J, Palacios R, Pinho ST, 2012, Homogenization of slender periodic composite structures
A homogenization technique is developed to obtain the equivalent 1-D stiffness properties of complex slender periodic composite structures with varying cross-sections. All this is done while removing the limitation of a constant cross-section often imposed in literature. The problem is posed using a unit cell approach and applying periodic boundary conditions such that: 1) the microscopic strain state averages to the macroscopic conditions, and 2) the deformation energy is conserved between scales. The methodology also allow for stress recovery and local buckling analysis. Numerical examples are shown to illustrate the diverse capabilities of the method: An isotropic ribbed prismatic beam is used to introduce the method, show the reinforcements and local buckling capabilities; a composite laminated cylinder is shown to demonstrate span-wise varying properties and parametric analysis and, finally, a composite blade section exemplifies it for complex geometries. © 2012 by Julian Dizy, Rafael Palacios and Silvestre T. Pinho.
Ronch AD, Badcock K, Wang Y, et al., 2012, Nonlinear Model Reduction for Flexible Aircraft Control Design, AIAA Atmospheric Flight Mechanics Conference
Da Ronch A, Badcock KJ, Wang Y, et al., 2012, Nonlinear Model Reduction for Flexible Aircraft Control Design, AIAA Atmospheric Flight Mechanics Conference, Minneapolis
Palacios R, 2011, Greener, Lighter Airframes, Publisher: Airlines International
Cook R, Palacios R, Goulart P, et al., 2011, Robust Manoeuvring and Gust Alleviation of Very Flexible Aircraft using Novel Control Effectors, 15th International Forum of Aeroelasticity and Structural Dynamics, Paris, France
Hesse H, Palacios R, 2011, Consistent structural linearisation in flexible-body dynamics with large rigid-body motion, 15th International Forum of Aeroelasticity and Structural Dynamics, Paris, France
Murua J, Palacios R, Graham JMR, 2011, A discrete-time state-space model with wake interference for stability analysis of flexible aircraft, 15th International Forum of Aeroelasticity and Structural Dynamics, Paris, France
Murua J, Hesse H, Palacios R, et al., 2011, Stability and Open-Loop Dynamics of Very FlexibleAircraft Including Free-Wake Effects, 52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Denver, Colorado
Arbos-Torrent S, Pang ZY, Ganapathisubramani B, et al., 2011, Leading and trailing edge effects on the aerodynamic performance of compliant aerofoils, 49th AIAA Aerospace Sciences Meeting, Orlando, Florida, USA
Arbos-Torrent S, Pang ZY, Ganapathisubramani B, et al., 2011, Leading and trailing edge effects on the aerodynamic performance of compliant aerofoils, 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Orlando, Florida, USA
Palacios R, Epureanu BI, 2011, An Intrinsic Description of the NonlinearAeroelasticity of Very Flexible Wings, 52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Denver, Colorado
Palacios R, 2011, Nonlinear Normal Modes in an Intrinsic Theory of Anisotropic Beams, Journal of Sound and Vibration, Vol: 330, Pages: 1772-1792
Arbos-Torrent S, Pang ZY, Ganapathisubramani B, et al., 2011, Leading and trailing edge effects on the aerodynamic performance of compliant aerofoils, 49th AIAA Aerospace Sciences Meeting, Orlando, Florida, USA
Palacios R, Murua J, Cook R, 2010, Structural and Aerodynamic Models in the Nonlinear Flight Dynamics of Very Flexible Aircraft, AIAA Journal, Vol: 48, Pages: 2648-2659
Murua J, Palacios R, Graham JMR, 2010, Modeling of Nonlinear Flexible Aircraft Dynamics Including Free-Wake Effects, AIAA Guidance, Navigation, and Control Conference, Toronto, Canada
This paper addresses the unified aeroelastic and flight dynamics characterization of lowspeedslender-wing aircraft, including free-wake effects and aerodynamic interference. An analysis framework is presented that targets the prediction of stability and handling qualities of high-altitude long-endurance vehicles, which are prone to experience large wing excursions, leading to an inherently nonlinear and coupled problem between aerodynamics, elasticity and flight dynamics. In this work, the structural dynamics are based on a geometrically-exact composite beam model, discretized using displacement-based finite elements, and cast into an extended flexible-body dynamics model. The aerodynamic model is defined by a general unsteady vortex lattice method. The governing equations of motion of the integrated system are formulated in a tightly-coupled state-space form, which allows for the equations to be solved simultaneously. Verification of the model has been carried out for static and dynamic problems, including both rigid and flexible wings. Numerical studies are presented for the particular case of prescribed rigid-body motions, paying special attention to the likely interference between wake and tail. Results show that the current approach represents a suitable alternative for configuration analysis of flexible atmospheric vehicles, offering a good balance between degree of fidelity and computational cost.
Cook RG, Palacios R, Roberts I, 2010, Manoeuvre Efficiency of Unconventional Control Effectors on Very Flexible Aircraft, RAeS Applied Aerodynamics Conference, Bristol, England
This paper presents a numerical framework to evaluate the efficiency of roll control e ectors on very flexible aircraft. Trailing edge control surfaces may be impractical on this class of aircraft, which drives the need to research novel and unconventional control devices. Here, we introduce a coupled aeroelastic and flightdynamics model using a strain-based structural model with indicial response potential flow aerodynamics. This model is used on a representative twin-boom, solar-powered, high-altitude long-endurance unmanned air vehicle (HALE UAV) to compare the roll response obtained from ailerons deployed on the main wings, with that obtained from using spoilers on various wing sti nesses. Results show that for this aircraft, at the designed cruise velocity, the ailerons exhibit full control reversal, while spoilers perform very well, and only show major ine ciencies on the most flexible wing covered. This conclusion suggests that spoilers may bemore suitable control devices than alierons for HALE UAVs. Potential for improvements are suggested which would increase the e ciency of the spoiler, but also a simple control method is presented which exploits the adverse control reversal that was shown by the aileron quite e ectively.
Murua J, Palacios R, Peiro J, 2010, Camber effects in the dynamic aeroelasticity of compliant airfoils, International Forum of Aeroelasticity and Structural Dynamics, Seattle, Washington, USA, Publisher: ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, Pages: 527-543
This paper numerically investigates the effect of chordwise flexibility on the dynamic stability of compliant airfoils. A classical two-dimensional aeroelastic model is expanded with an additional degree of freedom to capture time-varying camber deformations, defined by a parabolic bending profile of the mean aerodynamic chord. Aerodynamic forces are obtained from unsteady thin airfoil theory and the corresponding compliant-airfoil inertia and stiffness from finite-element analysis. V g and state-space stability methods have been implemented in order to compute flutter speeds. The study looks at physical realizations with an increasing number of degrees of freedom, starting with a camber-alone system. It is shown that single camber leads to flutter, which occurs at a constant reduced frequency and is due to the lock in between the shed wake and the camber motion. The different combinations of camber deformations with pitch and plunge motions are also studied, including parametric analyses of their aeroelastic stability characteristics. A number of situations are identified in which the flutter boundary of the compliant airfoil exhibits a significant dip with respect to the rigid airfoil models. These results can be used as a first estimation of the aeroelastic stability boundaries of membrane-wing micro air vehicles. (C) 2010 Elsevier Ltd. All rights reserved.
Chimakurthi SK, Tang J, Palacios R, et al., 2009, Computational Aeroelasticity Framework for Analyzing Flapping Wing Micro Air Vehicles, AIAA Journal, Vol: 47, Pages: 1865-1878
Palacios R, Cesnik CES, 2009, Structural Models for Flight Dynamic Analysis of Very Flexible Aircraft, 50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Palm Springs, California, USA
Friedmann P, Glaz B, Palacios R, 2009, Incorporation of VABS Composite Beam Sectional Analysis Into a Comprehensive Rotorcraft Analysis Code with Application to Aeroelastic Tailoring, American Helicopter Society 65th Annual Forum and Technology Display, Grapevine, Texas, USA
Friedmann PP, Glaz B, Palacios R, 2009, A moderate deflection composite helicopter rotor blade model with an improved cross-sectional analysis, International Journal of Solids and Structures, Vol: 46, Pages: 2186-2200
The compatibility between a composite beam cross-sectional analysis based on the variational asymptotic approach, and a helicopter rotor blade model which is part of a comprehensive rotorcraft analysis code is examined. It was found that the finite element cross-sectional analysis code VABS can be combined with a moderate deflection rotor blade model in spite of the differences between the formulations. The new YF/VABS rotor blade model accounts for arbitrary cross-sectional warping, in-plane stresses, and moderate deflections. The YF/VABS composite rotor blade model was validated against experimental data and various rotor blade analyses by examining displacements and stresses under static loads, as well as aeroelastic stability of a composite rotor blade in hover, and forward flight vibratory hubloads of a four bladed composite rotor.
Thepvongs S, Cesnik CES, Palacios R, et al., 2008, Finite-State Aeroelastic Modeling of Rotating Wings with Deformable Airfoils, American Helicopter Society 64th Annual Forum and Technology Display, Montreal, Canada. 29 April - 1 May 2008
Tang J, Chimakurthi S, Palacios R, et al., 2008, Computational Fluid-Structure Interaction of a Deformable Flapping Wing for Micro Air Vehicle Applications (AIAA Paper 2008-0615), 46th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, USA, January 2007
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