111 results found
Glaz B, Palacios R, Friedmann PP, 2009, Incorporation of VABS composite beam sectional analysis into a comprehensive rotorcraft analysis code with application to aeroelastic tailoring, Pages: 689-706, ISSN: 1552-2938
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 comprehensive analysis code can be upgraded with the finite element cross-sectional analysis code VABS (Variational Asymptotic Beam Sectional Analysis) without modifying the existing computer code structure. The new rotor blade model accounts for arbitrary cross-sectional warping, in-plane stresses, and moderate deflections. The 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. Furthermore, the upgraded analysis code was used to examine the effectiveness of aeroelastic tailoring for vibration reduction when using aerodynamic models of varying sophistication, and to study the effects of aeroelastic tailoring on vibration and strain levels when employing active vibration reduction. Copyright © 2009 by the American Helicopter Society International, Inc.
Palacios R, Cesnik CES, 2009, Structural models for flight dynamic analysis of very flexible aircraft, ISSN: 0273-4508
Dissimilar analysis models are considered for the large structural deformations of aircraft with high-aspect-ratio composite wings. The different approaches include displacement-based, strain-based, and intrinsic geometrically-nonlinear beam models. Comparisons are made in terms of numerical efficiency and simplicity for integration of full aircraft flexibility in flight dynamics models. An analysis procedure is proposed based on model substructuring with a (linear) modal representation of both fuselage and tail and (nonlinear) intrinsic beam elements for the flexible wings. Copyright © 2009 by Rafael Palacios and Carlos E. S. Cesnik.
Chimakurthi SK, Tang J, Palacios R, et al., 2008, Computational Aeroelasticity Framework for Analyzing Flapping Wing Micro Air Vehicles, 49th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Schaumburg, Illinois, USA, April 2008.
Palacios R, Cesnik CES, 2008, Geometrically nonlinear theory of composite beams with deformable cross sections, AIAA JOURNAL, Vol: 46, Pages: 439-450, ISSN: 0001-1452
Palacios R, Cesnik CES, 2008, On the one-dimensional modeling of camber bending deformations in active anisotropic slender structures, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, Vol: 45, Pages: 2097-2116, ISSN: 0020-7683
Palacios R, Cesnik CES, 2008, Low-Speed Aeroelastic Modeling of Very Flexible Slender Wings with Deformable Airfoils, 49th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Schaumburg, Illinois, USA, April 2008
Tang J, Chimakurthi S, Palacios R, et al., 2008, Computational fluid-structure interaction of a deformable flapping wing for micro air vehicle applications
Motivated by micro air vehicle applications, a fluid-structure coupling procedure between a Navier- Stokes solver and a three-dimensional FEM beam solver is presented along with selected results highlighting some of the aerodynamics implications. The fluid model includes laminar, the k -ε turbulence closure, and a filter-based k -ε closure. The structural model is based on an asymptotic approximation to the equations of elasticity. Using the slenderness as the small parameter, the equations are decomposed into two independent variational problems, corresponding to (i) crosssectional, small-deformation and (ii) longitudinal, large deformation analyses. A model example problem corresponding to a NACA0012 wing of aspect ratio 3 in pure heave motion is presented and the results compared against available experiment data. Quantitative comparisons with experiment are done for the rigid wing and the implications of wing flexibility on aerodynamics are presented in a qualitative sense. It was observed that phase lag of the wing tip displacement relative to the flapping motion becomes more pronounced as the fluid density increases. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc.
Thepvongs S, Cesnik CES, Palacios R, et al., 2008, Finite-state aeroelastic modeling of rotating wings with deformable airfoils, Pages: 2352-2369, ISSN: 1552-2938
This paper presents a new low-order aeroelastic model for rotating wings with deformable airfoils. The structural formulation captures plate-like deformation in a geometrically-nonlinear beam-like framework, allowing the use of conventional aeromechanical approaches. The aerodynamics model consists of finite-state formulations of both a two-dimensional deformable airfoil theory and dynamic inflow theory. Preliminary numerical studies are conducted to examine basic performance and vibration-related characteristics of camber-actuated rotor blades.
Palacios R, Cesnik CES, 2007, A Ritz approximation to the deformation of anisotropic slender structures with finite-size cross sections, Pages: 6932-6957, ISSN: 0273-4508
A one-dimensional theory of slender structures with heterogeneous anisotropic materials is presented. It expands Cosserat's description of beam kinematics by allowing deformation of the beam cross sections. For that purpose, a Ritz approximation is introduced on the cross-sectional warping field, which defines additional elastic degrees of freedom (finitesection modes) in the 1-D model. This results in an extended set of beam dynamic equations that includes direct measures of both the large global displacement and rotations of a certain reference line, and the small local deformations of the cross sections. Two situations of interest are then studied in which this approach provides a simpler alternative to nonlinear shell models: First, we look at the detailed structural response of thin-walled composite beams with distributed loads. In particular, the case of a composite construction with embedded piezoelectric actuators is considered. Second, this methodology is applied to study the low-frequency response characterization of a thin-walled composite beam. Numerical results are presented in both cases, in which a reduced set of finite-section modes allows a full characterization of the actual 3-D structure within a strictly 1-D framework solution.
Palacios R, Chimakurthi SK, Cesnik CES, 2007, Local deformation effects in transonic aeroelasticity of very flexible slender wings, ECCOMAS Coupled Problems, Ibiza, Spain, May 2007
Cesnik CES, Palacios R, 2005, On the application of asymptotic reduction methods of slender structures to fluid-structure interaction problems, Pages: 612-616
A methodology for the aeroelastic analysis of highly flexible slender structures is presented. The structural model is based on an asymptotic approximation to the displacement field, which separates the problem into a long-scale problem involving geometrically-nonlinear deformations of the reference line and a small-scale problem that captures deformation in the cross section. The combination of them provides a three-dimensional solution to the structural dynamics of flexible vehicles suitable for aeroelastic simulations. © 2005 Elsevier Ltd.
Palacios R, Cesnik CES, 2005, Cross-sectional analysis of nonhomogeneous anisotropic active slender structures, AIAA JOURNAL, Vol: 43, Pages: 2624-2638, ISSN: 0001-1452
Palacios R, Cesnik CES, 2005, Static nonlinear aeroelasticity of flexible slender wings in compressible flow, Pages: 1789-1798, ISSN: 0273-4508
A high-fidelity numerical formulation is presented for the high-speed aeroelastic behavior of slender composite wings. The compressible flow is modeled using the 3-D Euler equations on a deform able mesh, and an asymptotic approximation of the 3-D kinematically-nonlinear equations of elasticity models the anisotropic slender structure. The transfer of the distributed loads and displacements at the fluid-structure interface is based on detailed 3-D representations of the deformed aerodynamic and structural domains. Finally, a time-domain solution is implemented for the closely-coupled fluid-structure interaction problem. This procedure handles the large deflections appearing in very slender wings under aerodynamic loads using a description of the deformation that includes all geometrically-nonlinear effects in the aeroelastic analysis. Using this approach, the static nonlinear aeroelastic response of a 16:1 half-aspect ratio wing is investigated for steady flight conditions. The impact of the detailed 3-D representation of the fluid-structure interface on the aeroelastic response is investigated. For that purpose, numerical results are compared to the representation of the structure using a geometrically- nonlinear 1-D beam model.
Palacios R, Cesnik CES, 2004, Cross-Sectional Analysis of Piezoelectric Composite Slender Structures, 15th International Conference of Adaptive Structures and Technologies
Palacios R, Cesnik CES, 2004, Reduced structural modeling of integrally-strained slender wings, Pages: 5475-5485, ISSN: 0273-4508
This paper introduces a procedure to model the dynamics of active slender structures with embedded actuators and sensors. The objective is to construct a low-order high-accuracy formulation for easy parameterization of the design space in nonlinear aeroelastic analysis. Main assumptions are small local strains and local rotations, large deflections and global rotations, quasielectrostatic behavior, linear electroelastic constitutive relations, and slenderness of the structure. The model also includes anisotropic material properties, electroelastic coupling, hygrothermal effects, and is integrated with the vehicle flight dynamics. The condition of slenderness is used to define a three-step analysis scheme based on asymptotic approximations to the electroelastic field, which can adequately represent the passive or active structural dynamics of a quite general class of air vehicles, including future morphing vehicle concepts. Two main configurations are investigated in this work: a rotor blade with embedded piezoceramics (Active Twist Rotor), and a joined-wing configuration for unmanned SensorCraft. On the Active Twist Rotor, a deformation mode for the camber bending is added to classical beam strain measures. Then, the response of this typical plate mode to the embedded actuation is studied and quantified within a 1-D model. On the SensorCraft, the structural characterization of the aircraft with joined-wing and flexible fuselage are investigated and compared to detailed 3-D build-up finite-element models. Copyright © 2004 by Rafael Palacios and Carlos E. S. Ccsnik. Published by the American Institute of Aeronautics and Astronautics, Inc.
Cesnik CES, Palacios R, 2003, Modeling Piezoelectric Actuators Embedded in Slender Structures, 11th AIAA/ASME/AHS Adaptive Structures Conference
Cesnik CES, Park RS, Palacios R, 2003, Effective cross-section distribution of anisotropic piezocomposite actuators for wing twist, Smart Structures and Materials 2003 Conference, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, Pages: 21-32, ISSN: 0277-786X
Palacios R, Cesnik CES, 2003, Structural Dynamics of Integrally Strained Slender Wings, 2003 International Forum of Aeroelasticity and Structural Dynamics, Amsterdam, The Netherlands
Palacios R, Climent H, Karlsson A, et al., 2003, Assessment of Strategies for Correcting Linear Unsteady Aerodynamics Using CFD or Experimental Results, Progress in computational flow-structure interaction, Editors: Haase, Selmin, Winzell, Publisher: Springer Verlag, Pages: 209-224, ISBN: 9783540439028
Palacios R, Climent H, Karlsson A, et al., 2001, Assessment of Strategies for Correcting Linear Unsteady Aerodynamics Using CFD or Experimental Results, International Forum of Aeroelasticity and Structural Dynamics
Wang Y, Wynn A, Palacios R, Nonlinear Aeroelastic Control of Very Flexible Aircraft Using ModelUpdating, Journal of Aircraft, ISSN: 0021-8669
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