Publications
197 results found
Maraniello S, Palacios R, 2017, Geometrically-nonlinear effects in lateral manoeuvres with coupled flight dynamics and aeroelasticity
© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. An investigation on the aeroelastic effects in lateral manoeuvres with very flexible wings is presented. The aim is to identify efficient actuation strategies from fully coupled non- linear aeroelastic/flight dynamics models, which account for potential large wing deections to improve vehicle manoeuvrability. The flexible vehicle dynamics is described using geometrically-exact composite beams on a body-attached frame and an unsteady vortex lattice with arbitrary kinematics of the lifting surfaces, while rolling manoeuvres are identified through optimal control. A flight-dynamics model based on elastified stability derivatives is used as a reference, and it is observed to capture the relevant dynamics either under slow actuation or for stiff wings. Embedding the full aeroelastic description into an optimal control framework is shown to expand the space of achievable manoeuvres, such as quick wing response with low structural vibrations or large lateral forces with minimal lift losses. It is also seen to provide a general methodology to identify unconventional manoeuvres that utilize large wing geometry changes to meet multiple simultaneous control objectives.
Palacios R, Simpson RJS, Maraniello S, 2017, State-space realizations and model reduction of potential-flow unsteady aerodynamics with arbitrary kinematics
We introduce a nondimensional state-space formulation of the unsteady vortex-lattice method for time-domain aerodynamics. It deals with 2- or 3-dimensional geometries, resolves frequencies up to a spatio-temporal Nyquist limit defined by the wake discretization, and has a convenient form for linearization, model reduction and coupling with structural dynamics models. No assumptions are made relating to the kinematics of the fluid-structure interface (inputs) and use of Joukowski’s theorem to compute forces naturally resolves all components of the unsteady aerodynamic forcing (outputs). Linearized expressions are written about arbitrary non-zero reference geometries, velocities and loading distributions and as such yield models that are as general as possible given the assumptions in the underlying fluid mechanics. The implementation is verified against classical solutions in the unsteady aerodynamics, and in aeroelastic stability analysis of cantilever wing configurations.
Wang Y, wynn A, Palacios R, 2016, Nonlinear modal aeroservoelastic analysis framework for flexible aircraft, AIAA Journal: devoted to aerospace research and development, Vol: 54, Pages: 3075-3090, ISSN: 0001-1452
A nonlinear formulation in modal coordinates of the equations of motion of a flexible aircraft is presented. It relies on the projection of the intrinsic equations of geometrically nonlinear composite beams on the linear normal modes at a reference condition, which are coupled with two-dimensional unsteady aerodynamics. The resulting description is suitable for nonlinear dynamic analysis and control design, whereas the description in modal coordinates links directly to linear aeroservoelastic analysis methods. Results are presented on and compared to cantilever wings and full aircraft configurations previously studied in the literature. Linear H∞H∞ control synthesis and closed-loop nonlinear simulations are finally explored on a highly flexible flying wing under large-amplitude discrete gusts. Results show the ability of the proposed framework to capture the nonlinear dynamics of the aeroelastic system, while providing a seamless integration with linear methods, as well as its strength in identification of the dominant contributors to the nonlinear response.
Sanchez R, Kline HL, Thomas D, et al., 2016, Assessment of the fluid-structure interaction capabilities for aeronautical applications of the open-source solver SU2, ECCOMAS Congress 2016, Publisher: Institute of Structural Analysis and Antiseismic Research, Pages: 1498-1529
We report on an international effort to develop an open-source computational environmentfor high-fidelity fluid-structure interaction analysis. In particular, we will focus onverification of the implementation for application in computational aeroelasticity. The capabilitiesof the SU2 code for aeroelastic analysis have been further enhanced both by developingnatively embedded tools for the study of largely deformable solids, and by wrapping it usingPython tools for an improved communication with external solvers. Both capabilities will bedemonstrated on relevant test cases, including rigid-airfoil solutions with indicial functions,the Isogai Wing Section, test cases from the AIAA 2nd Aeroelastic Prediction Workshop, andthe vortex-induced vibrations of a flexible cantilever in the wake of a square cylinder. Resultsshow very good performance both in terms of accuracy and computational efficiency. The modularityand versatility of the baseline suite allows for a flexible framework for multidisciplinarycomputational analysis. The software libraries have been freely shared with the community toencourage further engagement in the improvement, validation and further development of thisopen-source project.
Broughton-Venner JJ, Wynn A, Palacios R, 2016, Aeroservoelastic optimisation of an aerofoil with active compliant flap via reparametrisation and variable selection, 17th AIAA/ISSMO Multidisciplinary Analysis and Optimization Conference, Publisher: AIAA
To aid in the investigation of new simultaneous optimisation strategies for exible vehicles and their control systems, a two-dimensional aerofoil optimisation which demands minimal computational effort is studied. The aeroservoelastic system consists of a two-dimensional, potential flow over a deforming aerofoil; an actively controlled, but saturated compliant trailing edge; a dynamic observer that uses a series of pressure sensors on the aerofoil; and a heave/pitch linear spring model. Although computationally simple, the design allows for optimisation over multiple disciplines: the structure can be designed by varying the stiffness of the springs; the control architecture through weightings in a LQR controller; the observer by means of the placement of pressure sensors; and the aerodynamics via the shaping of the compliant trailing edge. Optimising the weight and a metric of performance over all these fields simultaneously is compared to a sequential methodology of optimising the open-loop characteristics first and subsequently adding a closed-loop con-troller. Parametrisation of the design vector and variable selection often require user input and are fixed during optimisation. Our research aims to automate this process. Further-more, we investigate whether varying the parametrisation and number of design variables during the optimisation can lead to improvements in the final design. To accomplish this, a new basis for the design vector is created via Proper Orthogonal Decomposition (POD) using the trajectories of initial optimisation paths as a “training set". This parametrisation is shown to make the optimisation more robust with respect to the initial design, and facilitate an automated variable selection methodology. This variable selection allows for the dimension of the problem to be reduced temporarily and it is shown that this makes the optimisation more robust.
Bao Y, Palacios R, Graham JMR, et al., 2016, Generalized thick strip modelling for vortex-induced vibration of long flexible cylinders, Journal of Computational Physics, Vol: 321, Pages: 1079-1097, ISSN: 1090-2716
We propose a generalized strip modelling method that is computationally efficient for the VIV prediction of long flexible cylinders in three-dimensional incompressible flow. In order to overcome the shortcomings of conventional strip-theory-based 2D models, the fluid domain is divided into “thick” strips, which are sufficiently thick to locally resolve the small scale turbulence effects and three dimensionality of the flow around the cylinder. An attractive feature of the model is that we independently construct a three-dimensional scale resolving model for individual strips, which have local spanwise scale along the cylinder's axial direction and are only coupled through the structural model of the cylinder. Therefore, this approach is able to cover the full spectrum for fully resolved 3D modelling to 2D strip theory. The connection between these strips is achieved through the calculation of a tensioned beam equation, which is used to represent the dynamics of the flexible body. In the limit, however, a single “thick” strip would fill the full 3D domain. A parallel Fourier spectral/hp element method is employed to solve the 3D flow dynamics in the strip-domain, and then the VIV response prediction is achieved through the strip-structure interactions. Numerical tests on both laminar and turbulent flows as well as the comparison against the fully resolved DNS are presented to demonstrate the applicability of this approach.
Maraniello S, Palacios Nieto R, 2016, Optimal vibration control and co-design of very flexible actuated structures, Journal of Sound and Vibration, Vol: 377, Pages: 1-21, ISSN: 1095-8568
The single shooting method is applied to the optimal control and combined structural and control design (co-design) of very flexible beams. The objective is to assess feasibility, advantages and limitations of an integrated design approach when dealing with actuated structures exhibiting large oscillations and, more generally, strongly nonlinear couplings. A gradient based approach is proposed for the large design space defined by both the optimal control and co-design problems. Numerical studies are presented for the case of a very flexible actuated pendulum with large rigid-body motion. The impact of local (B-splines) and global (discrete sines) set of basis functions is investigated for increasing levels of actuation authority, showing the importance of the time–frequency resolution of the parametrisation on the convergence properties and outcome quality of the process. Locking between control and structural disciplines around specific design points is found, thus highlighting the disadvantage of a sequential design approach. Simultaneous designing of control law and structure is seen, instead, to explore efficiently larger regions of the design space.
Hesse H, Palacios R, 2016, Dynamic Load Alleviation in Wake Vortex Encounters, Journal of Guidance Control and Dynamics, Vol: 39, Pages: 801-813, ISSN: 1533-3884
Buoso S, Palacios R, 2016, High-fidelity simulation and reduced-order modelling of integrally-actuated membrane wings with feedback control, SPIE 9799, Active and Passive Smart Structures and Integrated Systems 2016
Ng BF, New TH, Palacios R, 2016, Effects of Leading-Edge Tubercles on Wing Flutter Speeds, Bioinspiration & Biomimetics, Vol: 11, ISSN: 1748-3190
The dynamic aeroelastic effects on wings modified with bio-inspired leading-edge (LE) tubercles are examined in this study. We adopt a state-space aeroelastic model via the coupling of unsteady vortex-lattice method and a composite beam to evaluate stability margins as a result of LE tubercles on a generic wing. The unsteady aerodynamics and spanwise mass variations due to LE tubercles have counteracting effects on stability margins with the former having dominant influence. When coupled, flutter speed is observed to be 5% higher, and this is accompanied by close to 6% decrease in reduced frequencies as an indication of lower structural stiffness requirements for wings with LE tubercles. Both tubercle amplitude and wavelength have similar influences over the change in flutter speeds, and such modifications to the LE would have minimal effect on stability margins when concentrated inboard of the wing. Lastly, when used in sweptback wings, LE tubercles are observed to have smaller impacts on stability margins as the sweep angle is increased.
Buoso S, Palacios R, 2016, Viscoelastic effects in the aeromechanics of actuated elastomeric membrane wings, Journal of Fluids and Structures, Vol: 63, Pages: 40-56, ISSN: 1095-8622
This work is a numerical investigation on the influence of viscoelastic effects on the aerodynamics of integrally actuated membrane wings. For that purpose, a high-fidelity electro-aeromechanical computational model of wings made of dielectric elastomers has been developed. The structural model is based on a geometrically non-linear description and a non-linear electro-viscoelastic constitutive material law. It is implicitly coupled with a fluid solver based on a finite-volume discretisation of the unsteady Navier–Stokes equations. The resulting framework is used for the evaluation of the dynamics of passive and integrally actuated membrane wings at low Reynolds numbers under hyperelastic and viscoelastic assumptions on the constitutive model. Numerical simulations show that the damping introduced by viscoelastic stresses can significantly reduce the amplitude of membrane oscillations and modify key features in the coupled system dynamics. The estimated wing performance metrics are in good agreement with previous experimental observations and demonstrate the need of including rate-dependent effects to correctly capture the coupled system dynamics, in particular, for highly compliant membranes.
Sanchez R, Palacios R, Economon TD, et al., 2016, Towards a Fluid-Structure Interaction solver for Problems with Large Deformations within the Open-Source SU2 Suite, 57th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Publisher: AIAA/Aerospace Research Central
This paper describes a new framework for Fluid-Structure Interaction (FSI) modellingwithin the open-source code SU2. SU2 has been developed to solve complex, multi-physicsproblems described by Partial Differential Equations (PDEs), with an emphasis on problemsinvolving aerodynamic shape optimization. Due to its modularity, the code providesan appropriate infrastructure for the solution of physical problems in several disciplines.This work provides SU2 with new tools that expand its capabilities in the fields of structuralanalysis and FSI. The focus will be on geometrically-nonlinear deformable solids inlow-speed external flows.A Finite Element (FE) structural solver, able to deal with geometrical and materialnon-linearities in a static and a dynamic setting, has been built within the frameworkof SU2 alongside the existing solvers. Following the original object-oriented architecturein C++, a new structure compliant with the CFD solver has been developed. These newfeatures will serve as a basis for future developments of FE-based strategies for the solutionof PDEs. The structural solver has been coupled with the original fluid solver in SU2 usinga partitioned approach. The structure of the code was fully recast to allow analysis acrossmultiple zones and physical problems, currently limited to problems involving fluid andstructural analysis. Both loosely- and strongly-coupled strategies are available for thesolution of the coupled FSI problem.Finally, the validity of the implementations is assessed by studying the behavior ofa rigid square with a flexible cantilever at low Reynolds number. The results obtaineddemonstrate the capabilities of these new developments and further address the physicsbehind this benchmark problem.
Wang Y, Wynn A, Palacios R, 2016, Model-Predictive Control of Flexible Aircraft using Nonlinear Reduced-Order Models, 57th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Publisher: AIAA
This paper introduces an optimization-based load control strategy suitable for flexiblevehicles with very flexible wings. A model for the coupled flight dynamics/aeroelasticresponse of the vehicle is built from geometrically-nonlinear beams using an intrinsic descriptionand a simple linear 2-D unsteady aerodynamic with no spanwise couplings. Theresulting model has only quadratic nonlinearities and a balanced projection of the dynamicequations is then practicable and results in a much smaller model that retains the relevantnonlinear couplings. This is finally used to drive a model-predictive control designed tosuppress wing oscillations in the response to atmospheric gusts. Results are presented onhigh-aspect-ratio flying wing undergoing moderately large excursions in the presence ofdiscrete gusts. They demonstrate the performance of the nonlinear MPC in comparison toequivalent linear control schemes.
Buoso S, Palacios R, 2016, Feedback Control of Integrally Actuated Membrane Wings: A Computational Study, 57th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Publisher: AIAA
The paper is an investigation on computational modelling and control system designof integrally actuated membrane wings. A high-fidelity electro-aeromechanical model isused for the simulation of the dynamic fluid-structure interaction between a low-Reynoldsnumberflow and a dielectric elastomer wing. A reduced-order model (ROM) is obtainedcoupling a modal structural description with a linearisation of the fluid equations based onthe Proper Orthogonal Decomposition (POD). The low-order system is then used for thedesign of Proportional-Integral-Derivative (PID) and Linear Quadratic Gaussian (LQG)feedback schemes for the control of the wing lift coefficient. Their implementation in thehigh-fidelity model shows very good agreement with the reduced-order model, demonstratingthe suitability of the approach for the initial design of control systems on integrallyactuated membranes. Finally, the designed controllers are used to track required aerodynamicperformance and compensate for prescribed disturbances of the inlet flow conditions.Numerical results demonstrates the potential for the aerodynamic control of membranewings in outdoor flight using dielectric elastomers.
Maraniello S, Simpson RJS, Palacios R, 2016, Optimal Manoeuvres with Very Flexible Wings, 57th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Publisher: AIAA
The single shooting method is used identify optimal manoeuvres in the lateral dynamicsof partially-supported wings of very low stiffness. The aim is to identify actuationstrategies in the design of aircraft manoeuvres in which large wing deflections can substantiallymodify the vehicle structural and aerodynamic features. Preliminary studies arepresented for a representative high-altitude long-endurance aircraft wing in hinged confi-guration. Nonlinear effects due to large deflections are captured coupling a geometricallyexact beam model with an unsteady vortex lattice method for the aerodynamics. Theoptimal control problem is solved via a gradient-based algorithm. When lowering the wingstiffness, the nonlinearities connected to the system — such as the fore-shortening effectdue to large bending deflections — increase the wing lateral stability but at the same timethey also reduce aileron authority. The single-shooting optimisation is shown to capturethese features and to provide satisfactory results, not only when refining a predeterminedactuation law but also when designing it from zero.
Buoso S, Palacios R, 2015, Electro-aeromechanical modelling of actuated membrane wings, Journal of Fluids and Structures, Vol: 58, Pages: 188-202, ISSN: 0889-9746
This paper presents a numerical investigation on the aeromechanical performance of dynamically actuated membrane wings made of dielectric elastomers. They combine the advantages of membrane shape adaptability, which produces increased lift and delayed stall, with the benefits of simple, lightweight but high-authority control mechanism offered by integral actuation. High-fidelity numerical models have been developed to predict their performance and include a fluid solver based on the direct numerical integration of the unsteady Navier-Stokes equations, an electromechanical constitutive material model and a non-linear membrane structural model. Numerical results show that harmonic actuation can either increase or reduce the overall aerodynamic efficiency of the wing, measured as the mean lift-to-drag ratio, depending on the ratio between the actuation frequency and the natural frequency of the membrane. In addition, the definition of a reduced-order model based on POD modes of the complete high-fidelity system provides an insight of the main characteristics of the dynamics of the coupled system.
Jaswantlal RJ, Marzocca P, Palacios R, 2015, Unsteady Aerodynamics of a 3D Wing Hosting Synthetic Jet Actuators
The implementation of Synthetic Jet Actuators (SJAs) on Unmanned Aerial Vehicles (UAVs) provides a safe test-bed for analysis of improved performance, in the hope of certification of this technology on commercial aircraft in the future. The use of high resolution numerical methods (i.e. CFD) to capture the details of the effects of SJAs on flows and on the hosting lifting surface are computationally expensive and time-consuming, which renders them ineffective for use in real-time flow control implementations. Suitable alternatives include the use of Reduced Order Models (ROMs) to capture the lower resolution overall effects of the jets on the flow and the hosting structure. This research paper analyses the effects of SJAs on aircraft wings using a ROM for the purpose of determining the unsteady aerodynamic forces modified by the presence of the SJAs. The model developed is a 3D unsteady panel code where the jets are represented by source panels. This code has the ability to model thick 3D trapezoidal wings with sweep and dihedral, accepting any aerofoil coordinate file. Multiple rows of SJAs can also be applied where desired. In order to validate the panel code, comparisons are made with past experimental data and other numerical methods like the vortex lattice method and CFD. There is avenue for further work in implementing a robust control architecture around SJA technologies, which in the future could serve as replacements for traditional hinged flight control surfaces and flutter suppression solutions.
Ng BF, Palacios R, Graham JMR, 2015, Model-based aeroelastic analysis and blade load alleviation of offshore wind turbines, International Journal of Control, Vol: 90, Pages: 15-36, ISSN: 1366-5820
Offshore wind turbines take advantage of the vast energy resource in open waters but face structural integrity challenges specific to their operating environment that require cost-effective load alleviation solutions. This paper introduces a computational methodology for model-based two- and three-dimensional design of load alleviation systems on offshore wind turbines. The aero-hydro-servoelastic model is formulated in a convenient state-space representation, coupling a multi-body composite beam description of the main structural elements with unsteady vortex-lattice aerodynamics and Morison's description of the hydrodynamics. The aerodynamics does not require empirical corrections and focuses on a control-oriented approach to the modelling. Numerical results show that through trailing-edge flaps actuated by a robust controller, more than 60% reduction in dynamic loading due to atmospheric turbulence can be achieved for the sectional model and close to 13% reduction in blade loads is obtained for the complete three-dimensional floating turbine.
Wang Y, Palacios R, Wynn A, 2015, A method for normal-mode-based model reduction in nonlinear dynamics of slender structures, Computers & Structures, Vol: 159, Pages: 26-40, ISSN: 0045-7949
This paper introduces a nonlinear reduced-order modelling methodology forfinite-element models of structures with slender subcomponents and inertiarepresented by lumped masses along main load paths. The constructed modelshave dynamics described by 1-D intrinsic equations of motion, which arefurther written in modal co-ordinates. This yields finite-dimensional approximationsof the system dynamics with only quadratic nonlinearities. Evaluationof the problem coefficients is performed from static condensation of theoriginal model on the lumped masses. The method exploits the multi-pointconstraints typically used to obtain sectional loads in aircraft aeroelasticanalysis. The technique is illustrated on simple 3D structural models builtusing solid elements.
Hesse H, Palacios R, 2015, Dynamic Load Alleviation of Flexible Aircraft in Wake Vortex Encounters, International Forum of Aeroelasticity and Structural Dynamics (IFASD) 2015
Buoso S, Palacios R, 2015, Reduced-order modelling and feedback control of integrally actuated membrane wings, International Forum of Aeroelasticity and Structural Dynamics (IFASD) 2015
Maraniello S, Palacios R, 2015, Co-design of very flexible actuated structures, International Forum of Aeroelasticity and Structural Dynamics (IFASD) 2015
Ng BF, Palacios R, Kerrigan EC, et al., 2015, Aerodynamic load control in horizontal axis wind turbines with combined aeroelastic tailoring and trailing-edge flaps, Wind Energy, Vol: 19, Pages: 243-263, ISSN: 1095-4244
This paper presents an aeroservoelastic modeling approach to investigate dynamic load alleviation in large wind turbines with composite blades and trailing-edge aerodynamic surfaces. The tower and rotating blades are modeled using geometrically non-linear composite beams and linearized about reference rotating conditions with potentially arbitrarily large structural displacements. The aerodynamics of the rotor are represented using a linearized unsteady vortex lattice method, and the resulting aeroelastic system is written in a state-space description that is both convenient for model reductions and control design. A linear model of a single blade is then used to design an inline image regulator, capable of providing load reductions of up to 13% in closed loop on the full wind turbine non-linear aeroelastic model. When combined with passive load alleviation through aeroelastic tailoring, dynamic loads can be further reduced to 35%. While the separate use of active flap controls and passive mechanisms for load alleviation has been well-studied, an integrated approach involving the two mechanisms has yet to be fully explored and is the focus of this paper. Finally, the possibility of exploiting torsional stiffness for active load alleviation on turbine blades is also considered.
Buoso S, Palacios R, 2015, Electro-aeromechanical modelling and feedback control of actuated membrane wings, 23rd AIAA/ASME/AHS Adaptive Structures Conference, Publisher: Aerospace Research Central
This paper presents a numerical investigation on the potential for unsteady aerodynamiccontrol on integrally-actuated membrane wings made of dielectric elastomers (DEs). Theycombine the advantages of membrane shape adaptability, which produces increased lift anddelayed stall, with the benefits of simple, lightweight but high-authority control mechanismoffered by integral actuation. High-fidelity numerical models have been developed to predicttheir performance and include a fluid solver based on the direct numerical integrationof the unsteady Navier-Stokes equations, an electromechanical constitutive material modeland a non-linear three-dimensional membrane structural model. Numerical results showthat harmonic actuation of 5.0 kV gives an overall increase in the aerodynamic efficiencya fixed wing configuration the wing of up to 6.0%, measured as the lift-to-drag ratio. Inaddition, the definition of a reduced order model based on POD modes of the completehigh-fidelity system allows the synthesis of a feedback control system to obtain on-demandaerodynamic performance.
Wang Y, Wynn A, Palacios R, 2015, Nonlinear Aeroservoelastic Analysis of Flexible Aircraft Described by Large Finite-Element Models, 56th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials
Simpson RJS, Palacios R, 2015, Integrated flight dynamics and aeroelasticity of flexible aircraft with application to swept flying wings
© 2015, American Institute of Aeronautics and Astronautics Inc. All Rights Reserved. The dynamics of flexible, swept flying wing (SFW) aircraft are described by a set of nonlinear, multi-disciplinary equations of motion. Aircraft structures are modeled using a geometrically-exact composite beam model which can, in general, capture large dynamic deformations and the interaction between rigid-body and elastic degrees-of-freedom. In addition, an implementation of the unsteady vortex-lattice method capable of handling arbitrary kinematics is used to capture the unsteady, three-dimensional flow-field around the aircraft as it deforms. Linearization of this coupled nonlinear description, which can in general be around a nonlinear equilibrium, is performed to yield linear time-invariant state-space models. Verification of aeroelastic stability analyses using these models is carried out. Subsequently, a set of SFW models are developed and the dynamic stability characteristics of these aircraft are investigated for a range of flight velocities and vehicle parameters.
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Tantaroudas ND, Badcock KJ, DaRonch A, et al., 2015, Model order reduction for control design of flexible free-flying aircraft
This paper describes a systematic approach to the nonlinear model order reduction of free-flying flexible aircraft and the subsequent flight control system design. System non- linearities arise due to large wing deformation and the coupling between flexible and rigid body dynamics. The nonlinear flight dynamics equations are linearised and the approach uses information on the eigenspectrum of the resulting coupled system Jacobian matrix and projects it through a series expansion onto a small basis of eigenvectors representative of the full-order model dynamics. A very flexible aircraft representative of a HALE aircraft is implemented and the aeroelastic solver is validated against other frameworks for trimming cases when gravitational forces are also included. Furthermore, a very large flexible wing of high aspect ratio is built and the flexibility effects on the flight dynamic response are in- vestigated. The reduced order model eigenvalue basis is identified and convergence studies are performed. Reduced order models are generated and used for faster parametric worst case gust searches of the full order nonlinear flight dynamic response and are exploited for complex robust control methodologies such as H∞ for the loads alleviation. Finally, a comparison of the control performance with respect to the controllers gains when applied on the nonlinear full order model is discussed.
Simpson RJS, Palacios R, 2015, Integrated flight dynamics and aeroelasticity of flexible aircraft with application to swept flying wings
The dynamics of flexible, swept flying wing (SFW) aircraft are described by a set of nonlinear, multi-disciplinary equations of motion. Aircraft structures are modeled using a geometrically-exact composite beam model which can, in general, capture large dynamic deformations and the interaction between rigid-body and elastic degrees-of-freedom. In addition, an implementation of the unsteady vortex-lattice method capable of handling arbitrary kinematics is used to capture the unsteady, three-dimensional flow-field around the aircraft as it deforms. Linearization of this coupled nonlinear description, which can in general be around a nonlinear equilibrium, is performed to yield linear time-invariant state-space models. Verification of aeroelastic stability analyses using these models is carried out. Subsequently, a set of SFW models are developed and the dynamic stability characteristics of these aircraft are investigated for a range of flight velocities and vehicle parameters.
Murua J, Martinez P, Climent H, et al., 2014, T-Tail Flutter: Potential-Flow Modelling, Experimental Validation and Flight Tests, Progress in Aerospace Sciences, Vol: 71, Pages: 54-84
Hesse H, Palacios R, 2014, Reduced-order aeroelastic models for the dynamics of maneuvering flexible aircraft, AIAA Journal: devoted to aerospace research and development, Vol: 52, Pages: 1717-1732, ISSN: 0001-1452
This paper investigates the model reduction, using balanced realizations, of the unsteady aerodynamics of maneuvering flexible aircraft. The aeroelastic response of the vehicle, which may be subject to large wing deformations at trimmed flight, is captured by coupling a displacement-based flexible-body dynamics formulation with an aerodynamic model based on the unsteady vortex lattice method. Consistent linearization of the aeroelastic problem allows the projection of the structural degrees of freedom on a few vibration modes of the unconstrained vehicle, but preserves all couplings between the rigid and elastic motions and permits the vehicle flight dynamics to have arbitrarily-large angular velocities. The high-order aerodynamic system, which defines the mapping between the small number of generalized coordinates and unsteady aerodynamic loads, is then reduced using the balanced truncation method. Numerical studies on a representative high-altitude, long-endurance aircraft show a very substantial reduction in model size, by up to three orders of magnitude, that leads to model orders (and computational cost) similar to those in conventional frequency-based methods but with higher modeling fidelity to compute maneuver and gust loads. Closed-loop results for a cantilever wing finally demonstrate the application of this approach in the synthesis of a robust stability augmentation system.
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