Imperial College London

Dr Rafael Palacios

Faculty of EngineeringDepartment of Aeronautics

Reader in Aeronautics
 
 
 
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Contact

 

+44 (0)20 7594 5075r.palacios CV

 
 
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Location

 

338City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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108 results found

Maraniello S, Palacios R, 2015, Co-design of very flexible actuated structures

A numerical investigation on open-loop control and combined structural and control design (co-design) of very flexible beams is presented. The objective is to allow for an efficient design of these systems by identifying design strategies that provide significant performance advantages with respect to conventional sequential design methods. The control vector parametrisation method, implemented for both a B-splines (local) and discrete sines (global) set of basis functions, is used in conjunction with a gradient based optimiser to solve first the open-loop control and then the co-design problems. Numerical results show the impact of the time-frequency resolution of the parametrisation on the outcome of the optimisation. Overall, B-splines can achieve higher performance as they better exploit the flexible, high frequency driven, behaviour of the structure, particularly as large deformations lead to changes in the natural frequencies of the system. The discrete sines based parametrisation, on the other hand, is found to be a more robust choice. The mutual influence between control and structural dynamics during the design process is showed and used to explain the ability of the optimiser to approach a global optimum. In particular, it was found that control and structural disciplines can freeze the design around specific characteristic frequencies (locking), limiting the advantages of a co-design approach based on gradient methods.

CONFERENCE PAPER

Ng BF, Hesse H, Palacios R, Graham JMR, Kerrigan ECet al., 2015, Aeroservoelastic state-space vortex lattice modeling and load alleviation of wind turbine blades, WIND ENERGY, Vol: 18, Pages: 1317-1331, ISSN: 1095-4244

JOURNAL ARTICLE

Sanchez R, Palacios R, Economon TD, Kline HL, Alonso JJ, Palacios Fet al., 2015, Towards a fluid-structure interaction solver for problems with large deformations within the open-source SU2 suite

© 2015 American Institute of Aeronautics and Astronautics. This paper describes a new framework for Fluid-Structure Interaction (FSI) modelling within the open-source code SU2. SU2 has been developed to solve complex, multi-physics problems described by Partial Differential Equations (PDEs), with an emphasis on problems involving aerodynamic shape optimization. Due to its modularity, the code provides an 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 structural analysis and FSI. The focus will be on geometrically-nonlinear deformable solids in low-speed external ows. A Finite Element (FE) structural solver, able to deal with geometrical and material non-linearities in a static and a dynamic setting, has been built within the framework of SU2 alongside the existing solvers. Following the original object-oriented architecture in C++, a new structure compliant with the CFD solver has been developed. These new features will serve as a basis for future developments of FE-based strategies for the solution of PDEs. The structural solver has been coupled with the original uid solver in SU2 using a partitioned approach. The structure of the code was fully recast to allow analysis across multiple zones and physical problems, currently limited to problems involving uid and structural analysis. Both loosely-and strongly-coupled strategies are available for the solution of the coupled FSI problem. Finally, the validity of the implementations is assessed by studying the behavior of a rigid square wit h a exible cantilever at low Reynolds number. The results obtained demonstrate the capabilities of these new developments and further address the physics behind this benchmark problem.

CONFERENCE PAPER

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.

CONFERENCE PAPER

Tantaroudas ND, Badcock KJ, Da Ronch A, Palacios Ret al., 2015, Model order reduction for control design of flexible free-flying aircraft

© 2015 by the American Institute of Aeronautics and Astronautics, Inc. 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.

CONFERENCE PAPER

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

JOURNAL ARTICLE

Wang Y, Wynn A, Palacios R, 2015, Nonlinear aeroservoelastic analysis of flexible aircraft described by large finite-element models

© 2015, American Institute of Aeronautics and Astronautics Inc. All Rights Reserved. We present a nonlinear reduced-order formulation for the simulation of geometrically- nonlinear responses of flexible aircraft and other aeroelastic systems. The method is based on a modal projection of the intrinsic description for beams coupled with a 2-D unsteady aerodynamic description. We also describe a method of obtaining coefficients of the nonlinear modal beam equations by means of a condensation process, based on the direct application of Guyan reduction of a high-fidelity 3D FE model. We then present structural and aeroelastic simulations and compare them against published results. Control design and closed-loop nonlinear simulations will also be demonstrated using the description in this work on a highly-flexible flying wing.

CONFERENCE PAPER

Buoso S, Palacios R, 2014, A NONLINEAR VISCOELASTIC MODEL FOR ELECTROACTIVE INFLATED MEMBRANES, 11th World Congress on Computational Mechanics (WCCM) / 5th European Conference on Computational Mechanics (ECCM) / 6th European Conference on Computational Fluid Dynamics (ECFD), Publisher: INT CENTER NUMERICAL METHODS ENGINEERING, Pages: 4300-4312

CONFERENCE PAPER

Cesnik CES, Palacios R, Reichenbach EY, 2014, Reexamined Structural Design Procedures for Very Flexible Aircraft, JOURNAL OF AIRCRAFT, Vol: 51, Pages: 1580-1591, ISSN: 0021-8669

JOURNAL ARTICLE

Da Ronch A, McCracken AJ, Tantaroudas ND, Badcock KJ, Hesse H, Palacios Ret al., 2014, Assessing the impact of aerodynamic modelling on Manoeuvring aircraft

This paper investigates the impact of aerodynamic models on the dynamic response of a free-flying aircraft wing. Several options for the aerodynamics are evaluated, from two-dimensional thin aerofoil aerodynamics and unsteady vortex-lattice method up to computational fluid dynamics. A nonlinear formulation of the rigid body dynamics is used in all cases. Results are generated using a numerical framework that will allow in the near future multi-disciplinary fluid/structure/flight analysis. In this paper, flexibility effects are neglected. A validation for fluid/flight models is presented. The well-established approach based on stability derivatives is also used, and is found in good agreement with solutions obtained from linear aerodynamic models. The uncertainties in predicted trajectories of the free-flying wing are, in general, large and attributed to the aerodynamics only. This suggests that a careful control law synthesis should be done to account for uncertainties from modelling techniques.

CONFERENCE PAPER

Hesse H, Palacios R, 2014, Reduced-Order Aeroelastic Models for the Dynamics of Maneuvering Flexible Aircraft, AIAA Journal, Vol: 52, Pages: 1717-1732

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.

JOURNAL ARTICLE

Hesse H, Palacios R, Murua J, 2014, Consistent Structural Linearization in Flexible Aircraft Dynamics with Large Rigid-Body Motion, Publisher: AMER INST AERONAUTICS ASTRONAUTICS, Pages: 528-538, ISSN: 0001-1452

CONFERENCE PAPER

Murua J, Martínez P, Climent H, Van Zyl L, Palacios Ret al., 2014, T-tail flutter: Potential-flow modelling, experimental validation and flight tests, Progress in Aerospace Sciences, Vol: 71, Pages: 54-84, ISSN: 0376-0421

© 2014 Elsevier Ltd. Flutter of T-tail configurations is caused by the aeroelastic coupling between the vertical fin and the horizontal stabiliser. The latter is mounted on the fin instead of the fuselage, and hence the arrangement presents distinct characteristics compared to other typical empennage setups; specifically, T-tail aeroelasticity is governed by inplane dynamics and steady aerodynamic loading, which are typically not included in flutter clearance methodologies based on the doublet lattice method. As the number of new aircraft featuring this tail configuration increases, there is a need for precise understanding of the phenomenon, appropriate tools for its prediction, and reliable benchmarking data. This paper addresses this triple challenge by providing a detailed explanation of T-tail flutter physics, describing potential-flow modelling alternatives, and presenting detailed numerical and experimental results to compensate for the shortage of reproducible data in the literature. A historical account of the main milestones in T-tail aircraft development is included, followed by a T-tail flutter research review that emphasises the latest contributions from industry as well as academia. The physical problem is dissected next, highlighting the individual and combined effects that drive the phenomenon. Three different methodologies, all based on potential-flow aerodynamics, are considered for T-tail subsonic flutter prediction: (i) direct incorporation of supplementary T-tail effects as additional terms in the flutter equations; (ii) a generalisation of the boundary conditions and air loads calculation on the double lattice; and (iii) a linearisation of the unsteady vortex lattice method with arbitrary kinematics. Comparison with wind-tunnel experimental results evidences that all three approaches are consistent and capture the key characteristics in the T-tail dynamics. The validated numerical models are then exercised in easy-to-duplicate canonical te

JOURNAL ARTICLE

Ng BF, Hesse H, Palacios R, Graham JMR, Kerrigan ECet al., 2014, Model-based Aeroservoelastic Design and Load Alleviation of Large Wind Turbine Blades, 32nd ASME Wind Energy Symposium

CONFERENCE PAPER

Ng BF, Hesse H, Palacios R, Kerrigan EC, Graham JMRet al., 2014, Efficient Aeroservoelastic Modeling and Control using Trailing-Edge Flaps of Wind Turbines, United-Kingdom-Automatic-Control-Council (UKACC) 10th International Conference on Control (CONTROL), Publisher: IEEE, Pages: 1-6

CONFERENCE PAPER

Simpson RJS, Palacios R, Hesse H, Goulart Pet al., 2014, Predictive control for alleviation of gust loads on very flexible aircraft

In this work the dynamics of very flexible aircraft are described by a set of non-linear, multi-disciplinary equations of motion. Primary structural components are represented by a geometrically-exact composite beam model which captures the large dynamic deformations of the aircraft 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-eld around the aircraft as it deforms. Linearization of this coupled nonlinear description, which can in general be about a nonlinear reference state, is performed to yield relatively high-order linear time-invariant state-space models. Subsequent reduction of these models using standard balanced truncation results in low-order models suitable for the synthesis of online, optimization-based control schemes that incorporate actuator constraints. Predictive controllers are synthesized using these reduced-order models and applied to nonlinear simulations of the plant dynamics where they are shown to be superior to equivalent optimal linear controllers (LQR) for problems in which constraints are active.

CONFERENCE PAPER

Tantaroudas ND, Da Ronch A, Gai G, Badcock KJ, Palacios Ret al., 2014, An adaptive aeroelastic control approach by using nonlinear reduced order models

A systematic approach to the model order reduction of high fidelity coupled fluid- structure/flight dynamics models and the subsequent control design is described. It uses information on the eigenspectrum of the coupled-system Jacobian matrix and projects the system through a series expansion onto a small basis of eigenvectors representative of the full-model dynamics. A nonlinear reduced order model is derived and is exploited for a worst case gust and adaptive control design. The investigation focuses on a flight control design based on the model reference adaptive control scheme via the Lyapunov stability approach. The novelty of this paper is two-fold. Firstly, it uses a single nonlinear reduced model for parametric worst case gust search. Secondly, it is shown that it makes feasible an implementation of a complex control methodology for a large nonlinear system. The adaptive controller is able to alleviate gust loads for a three degrees-of-freedom aerofoil and for an unmanned aerial vehicle. An investigation for the adaptation parameters is performed and their effect on control input actuation and aeroelastic closed-loop response is discussed.

CONFERENCE PAPER

Van Parys BPG, Ng BF, Goulart PJ, Palacios Ret al., 2014, Optimal control for load alleviation in wind turbines

Nowadays, trailing edge flaps on wind turbine blades are considered to reduce loading stresses in wind turbine components. In this paper, an optimal control synthesis methodology for the design of gust load controllers for large wind turbine blades is proposed. We discuss a control synthesis approach that minimises the power expenditure of the actuated trailing edge flap, while at the same time guaranteeing that certain blade load measures remain bounded in a probabilistic sense. To illustrate our proposed control design methodology, a standard NREL 5-MW reference turbine was considered. The obtained numerical results indicate that through the use of optimal feedback considerable reductions in loading stresses could be achieved for moderate actuation power.

CONFERENCE PAPER

Wang Y, Wynn A, Palacios R, 2014, Nonlinear model reduction for aeroelastic control of flexible aircraft described by large finite-element models

We describe a reduced-modal approach to modelling the nonlinear aeroservoelastic response of a flexible air vehicle, in which the geometrically-nonlinear structural response is characterised by a modal intrinsic form of the equations of motion. We use modal projections of sectional inertial velocities and stress resultants as primary degrees of freedom with the modes obtained from a condensation process by which a large aeroelastic model of the full vehicle is reduced into a nonlinear beam-type modal description. The 2-D aerodynamic model and any additional forces are subsequently projected onto the same set of modes, finally resulting in a set of equations with no nonlinear couplings of order higher than two. We validate this approach using a ying-wing configuration for which published data are available.

CONFERENCE PAPER

Arbos-Torrent S, Ganapathisubramani B, Palacios R, 2013, Leading- and trailing-edge effects on the aeromechanics of membrane aerofoils, JOURNAL OF FLUIDS AND STRUCTURES, Vol: 38, Pages: 107-126, ISSN: 0889-9746

JOURNAL ARTICLE

Cook RG, Palacios R, Goulart P, 2013, Robust Gust Alleviation and Stabilization of Very Flexible Aircraft, AIAA JOURNAL, Vol: 51, Pages: 330-340, ISSN: 0001-1452

JOURNAL ARTICLE

Dizy J, Palacios R, Pinho ST, 2013, Homogenisation of slender periodic composite structures, Publisher: PERGAMON-ELSEVIER SCIENCE LTD, Pages: 1473-1481, ISSN: 0020-7683

CONFERENCE PAPER

Dizy J, Palacios R, Pinho ST, 2013, Shear Effects in the Homogenisation of Slender Composite Beams, 5th European Conference for Aerospace Sciences (EUCASS), Munich, Germany

CONFERENCE PAPER

Fogell N, Sherwin SJ, Cotter CJ, Iannucci L, Palacios R, Pope DJet al., 2013, Fluid-structure interaction simulation of the inflated shape of ram-air parachutes

This paper explores the application of loosely coupled fluid-structure interaction simulations to the analysis of the equilibrium shape of a ram-air parachute during steady glide. Previous research has shown that consideration of the interaction between aerodynamics and structural dynamics in ram-air parachutes is a necessity for understanding how they behave. In this study the fabric membrane of the structure is modelled using the nonlinear Finite Element Method, and the fluid is characterized by the Reynolds-Averaged Navier-Stokes equations with a K-Epsilon turbulence model. In order to reduce computational cost the loosely coupled approach is applied to a single cell of an infinite ram-air canopy, using periodic boundary conditions to encourage a realistic response. The objective of the study is to investigate a means to computationally predict the flying shape of a ram-air canopy, as a step towards the computational derivation of its aerodynamic characteristics. This contributes towards an alternative to expensive and time-consuming test regimes, as well as providing a means to further the understanding of the performance of ram-air canopies. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

CONFERENCE PAPER

Gonzalez A, Munduate X, Palacios R, Graham JMRet al., 2013, Aeroelastic Tools for 2D Airfoils with Variable Geometry For Wind Turbine Applications, European Wind Energy Association Annual Event, Vienna, Austria

CONFERENCE PAPER

Hesse H, Palacios R, 2013, Model reduction in flexible-aircraft dynamics with large rigid-body motion

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 fiight 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 loads. Closed-loop results for the Goland wing finally demonstrate the application of this approach in the synthesis of a robust flutter suppression controller. © 2013 by Henrik Hesse and Rafael Palacios.

CONFERENCE PAPER

Hesse H, Palacios R, 2013, Reduced-order aeroelastic models for the dynamics of manoeuvring flexible aircraft

We investigate model reduction, using balancing methods, of the unsteady aerodynamics of flexible aircraft subject to asymmetric gust excitations. The aeroelastic response of the vehicle, with possibly large wing deformations at trim, is captured by coupling a geometrically-exact beam formulation with the three-dimensional unsteady vortex lattice method. Consistent linearisation of the structural degrees of freedom allows the projection on a few vibration modes of the unconstrained aircraft and permits the vehicle flight dynamics to have arbitrarily-large angular velocities. The linearised aerodynamic system, which defines the mapping between the small number of generalised coordinates and the aerodynamic loads, is then reduced through balanced truncation. Numerical studies on a representative high-altitude, long-endurance aircraft demonstrate the reduced-order modelling approach for spanwise non-uniform discrete gusts over a range of gust lengths and lateral placement.

CONFERENCE PAPER

Murua J, Martinez P, Climent H, van Zyl L, Palacios Ret al., 2013, T-tail Flutter: Potential-Flow Modelling and Experimental Validation, 16th International Forum of Aeroelasticity and Structural Dynamics

CONFERENCE PAPER

Ng BF, Hesse H, Palacios R, Graham JMR, Kerrigan ECet al., 2013, Aeroservoelastic Modelling and Robust Load Alleviation of Very Large Flexible Wind Turbine Blades, American Wind Energy Conference WINDPOWER 2013 Conference & Exhibition, Chicago, Illinois, USA

CONFERENCE PAPER

Palacios R, Wang Y, Wynn A, Karpel Met al., 2013, Condensation of large finite-element models for wing load analysis with geometrically-nonlinear effects

This paper describes a procedure to construct 1-D geometrically-nonlinear structural dynamics models from built-up 3-D linear finite-element solutions. The nonlinear 1-D model is based on an intrinsic form of the equations of motion, which uses sectional inertial velocities and stress resultants as primary degrees of freedom. It is further written in modal coordinates, which yields an finite-dimensional approximation of the geometrically-exact beam dynamics through ordinary differential equations with quadratic nonlinearities. We show that the evaluation of the coefficients in the resulting equations of motion does not actually require the generation of a finite-element model with beam elements. Instead, they are directly identified in the 3-D model through a process of static condensation on nodes defined along spanwise stations, as it is typically done in aircraft dynamic load analysis. In fact, the method exploits the multi-point constraints of linear load models that are normally used to obtain sectional loads. We illustrate the approach on simple aircraft-type structures modelled using shell elements.

CONFERENCE PAPER

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