Imperial College London

Dr Rafael Palacios

Faculty of EngineeringDepartment of Aeronautics

Professor in Computational Aeroelasticity
 
 
 
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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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125 results found

Bao Y, Zhu HB, Huan P, Wang R, Zhou D, Han ZL, Palacios R, Graham M, Sherwin Set al., Numerical prediction of vortex-induced vibration of flexible riser with thick strip method, Journal of Fluids and Structures, ISSN: 0889-9746

We present numerical prediction results of vortex-induced vibration (VIV) of a long flexible tensioned riser subject to uniform currents. The VIV model of long length-to-diameter ratio is considered and ‘thick’ strip technique based on high-order spectral/hp element method is employed for computational simulation. The model parameter of the riser for the simulation is chosen according to the dimensional counterparts used in the experimental tests in Lehn (2003). The numerical results are displayed in terms of motion responses, hydrodynamic forces and wake patterns as well and compared and discussed with the available data in the literature.

JOURNAL ARTICLE

Maraniello S, Palacios R, State-space realizations and internal balancing in potential-flow aerodynamics with arbitrary kinematics, AIAA Journal, ISSN: 0001-1452

This paper presents a general state-space realization of the unsteady vortex-latticemethod together with a bespoke model-order reduction strategy. The aim is to providea computationally-efficient aerodynamic description suitable for integration in aeroelasti-city with arbitrary kinematics. The state-space realization is obtained from linearization,around arbitrary geometries and static loading conditions, of lifting surfaces and their freewakes. All components of the forces are evaluated in time domain using Joukowski’s the-orem. As the wake is also modelled, however, the state-space description has a large num-ber of states. High-order modelling of the apparent mass, projection on low-dimensionaldegrees-of-freedom, and balanced residualization are combined to reduce the system dimen-sionality. A parallelized low-rank square root algorithm for balancing is also introduced toreduce the computational cost. Numerical investigations on airfoils and cantilever wingslinearised around non-zero reference conditions are used to exemplify the approach.

JOURNAL ARTICLE

Palacios R, Cea A, 2018, Nonlinear Modal Condensation of Large Finite Element Models: Application of Hodges’s Intrinsic Theory, AIAA Journal, Pages: 1-14, ISSN: 0001-1452

JOURNAL ARTICLE

Qi P, Zhao X, Wang Y, Palacios R, Wynn Aet al., 2018, Automatic Landing Control of a Very Flexible Flying Wing, Pages: 2599-2604, ISSN: 0743-1619

© 2018 AACC. This paper investigates the landing control of a highly flexible flying wing model. An automatic landing control system is developed based on the reduced-order linear model, which employs a two-loop control scheme. The outer loop employs the LADRC (linear active disturbance rejection control) and PI control algorithms to track the reference landing trajectory and vertical speed respectively, and generate the attitude command based on which the inner loop uses H∞ control to compute the control inputs to the corresponding control surfaces. A landing trajectory generator is designed to generate real-time commands for the landing control system with a pre-compensator introduced to improve the dynamic tracking performance. Simulation results based on the full-order nonlinear model show that the automatic landing control system is able to land the flying wing effectively and safely, showing good performances in tracking and robustness against the wind disturbances.

CONFERENCE PAPER

Wang Y, Wynn A, Palacios R, 2018, Nonlinear Aeroelastic Control of Very Flexible Aircraft Using Model Updating, JOURNAL OF AIRCRAFT, Vol: 55, Pages: 1551-1563, ISSN: 0021-8669

JOURNAL ARTICLE

Maraniello S, Palacios R, 2018, State space realisation and model reduction of potential-flow aerodynamics for HAWT applications, 7th Conference on Science of Making Torque from Wind (TORQUE), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588

CONFERENCE PAPER

Palacios R, Venkatesan-Crome C, Sanchez R, Aerodynamic Optimization using FSI Coupled Adjoints in SU2, 6th European Conference in Computational Mechanics

CONFERENCE PAPER

Qi P, Zhao X, Wang Y, Palacios R, Wynn Aet al., 2018, Aeroelastic and Trajectory Control of High Altitude Long Endurance Aircraft, IEEE Transactions on Aerospace and Electronic Systems, ISSN: 0018-9251

IEEE We investigate the aeroelastic and trajectory control of an High Altitude Long Endurance (HALE) aircraft model in the presence of gust and turbulence disturbances. The model is derived from geometrically-nonlinear beam theory using intrinsic degrees of freedom and linear unsteady aerodynamics, which results in a coupled structural dynamics, aerodynamics and flight dynamics description. The control design employs a two-loop PI/LADRC (linear active disturbance rejection control) and H<formula><tex>$\infin$</tex></formula> control scheme in both the longitudinal and lateral channels, based on a reduced-order linearised model. In each channel, the outer loop (position control) employs a PI/LADRC technique to track the desired flight routes and generate attitude command to the inner loop, while the inner loop (attitude control) uses H<formula><tex>$\infin$</tex></formula> control to track the attitude command generated from the outer loop and computes the control inputs to the corresponding control surfaces. A Particle Swarm Optimization algorithm is employed for parameter optimization of the weighting matrices in the H<formula><tex>$\infin$</tex></formula> control design. The simulation tests conducted on the full-order nonlinear model show that the aeroelastic and trajectory control system achieves good performance with respect to robustness, trajectory tracking and disturbance rejection

JOURNAL ARTICLE

Broughton-Venner JJ, Wynn A, Palacios R, 2018, Aeroservoelastic Optimisation of Aerofoils with Compliant Flaps via Reparameterization and Variable Selection, 58th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Publisher: AMER INST AERONAUTICS ASTRONAUTICS, Pages: 1146-1157, ISSN: 0001-1452

CONFERENCE PAPER

Sanchez R, Albring T, Palacios R, Gauger NR, Economon TD, Alonso JJet al., 2018, Coupled adjoint-based sensitivities in large-displacement fluid-structure interaction using algorithmic differentiation, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Vol: 113, Pages: 1081-1107, ISSN: 0029-5981

JOURNAL ARTICLE

Bao Y, Palacios R, Graham M, Sherwin Set al., 2018, A strip modelling of flow past a freely vibrating cable, ERCOFTAC Series, Vol: 24, Pages: 221-227, ISSN: 1382-4309

© 2018, Springer International Publishing AG. Vortex-induced vibration of long flexible structures with cylindrical cross-section are widely encountered in various engineering fields.

JOURNAL ARTICLE

Qi P, Zhao X, Palacios R, 2018, Preview-based Altitude Control for a Very Flexible Flying Wing with Lidar Wind Measurements, 57th IEEE Conference on Decision and Control (CDC), Publisher: IEEE, Pages: 4289-4294, ISSN: 0743-1546

CONFERENCE PAPER

Buoso S, Dickinson BT, Palacios R, 2018, Bat-inspired integrally actuated membrane wings with leading-edge sensing, BIOINSPIRATION & BIOMIMETICS, Vol: 13, ISSN: 1748-3182

JOURNAL ARTICLE

Maraniello S, Palacios R, 2017, Optimal Rolling Maneuvers with Very Flexible Wings, AIAA JOURNAL, Vol: 55, Pages: 2964-2979, ISSN: 0001-1452

JOURNAL ARTICLE

Buoso S, Palacios R, 2017, On-Demand Aerodynamics in Integrally Actuated Membranes with Feedback Control, AIAA JOURNAL, Vol: 55, Pages: 377-388, ISSN: 0001-1452

JOURNAL ARTICLE

Palacios R, Simpson RJS, Maraniello S, 2017, State-space realizations of potential-flow unsteady aerodynamics with arbitrary kinematics

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. 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, re- solves 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 un- derlying uid mechanics. The implementation is verified against classical solutions in the unsteady aerodynamics, and in aeroelastic stability analysis of cantilever wing configurations.

CONFERENCE PAPER

Ng BF, New TH, Palacios R, 2017, Bio-inspired leading-edge tubercles to improve fatigue life in horizontal axis wind turbine blades

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Bio-inspired leading-edge tubercles are known to improve aerodynamic performances during stall but there could be additional advantages in other operating regimes and their effect on aeroelastic loadings is also less understood. In this study, the effect of leading-edge tubercles on fatigue loadings on wind turbine blades is investigated using an aeroelastic model that couples a composite beam to the unsteady vortex-lattice method. To accommodate the leading-edge tubercles, spanwise structural properties and aerodynamic geometries are varied, which resulted in a reduction in both torsional frequencies and aerodynamic lift despite keeping the same planform area. The reductions in structural frequencies and aerodynamics have counteracting effects on fatigue responses, with the former increasing and the latter reducing loads. On a turbine blade with tubercles (amplitude of 0.2c and wavelength of 0.5c) occupying 20% to 95% span of the leading-edge, flapwise root-bending moment was found to be 6% lower than the unmodified configuration, which can be further enhanced with a trough termination at the blade tip. Torsional moment was 17% lower due to the reduction in leading-edge suction along tubercle crests, which are further away from the elastic axis. In terms of tubercle positioning, having tubercles close to the blade tip enables performance enhancement during episodes of stall from large tip deflections and has significant contributions to root-bending moment due to a larger moment arm and higher relative flow speed. On the other hand, positioning tubercles close to the blade root may also be favoured as this region is prone to stall from low speeds, yet having little effect on fatigue responses.

CONFERENCE PAPER

González-Salcedo A, Aparicio-Sanchez M, Munduate X, Pires O, Méndez B, Palacios R, Graham JMRet al., 2017, A computationally-efficient panel code for unsteady airfoil modelling including dynamic stall

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. A new approach based on inviscid panel methods has been developed for airfoils undergoing unsteady kinematics. The model is tailored to practical applications related to wind turbines, taking into account accuracy and computational cost considerations. It is able to represent rigid or deformable airfoils, attached and separated flow focusing also on unsteady cases including dynamic stall. An extensive validation has been carried out including steady and unsteady conditions, while simulations of airfoils with trailing edge flaps have also been performed.

CONFERENCE PAPER

Qi P, Wang Y, Zhao X, Palacios R, Wynn Aet al., 2017, Trajectory Control of a Very Flexible Flying Wing, American Control Conference (ACC), Publisher: IEEE, Pages: 4480-4485, ISSN: 0743-1619

CONFERENCE PAPER

Ng BF, Palacios R, Graham JMR, 2017, Model-based aeroelastic analysis and blade load alleviation of offshore wind turbines, INTERNATIONAL JOURNAL OF CONTROL, Vol: 90, Pages: 15-36, ISSN: 0020-7179

JOURNAL ARTICLE

Palacios R, Simpson RJS, Maraniello S, 2017, State-space realizations and model reduction of potential-flow unsteady aerodynamics with arbitrary kinematics

Copyright 2018, IADC/SPE Drilling Conference and Exhibition. 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.

CONFERENCE PAPER

Sanchez R, Palacios R, 2017, Computing derivatives in nonlinear aeroelasticity using algorithm differentiation

Copyright 2018, IADC/SPE Drilling Conference and Exhibition. This paper introduces a new method to calculate design sensitivities in high-fidelity fluid-structural interactions problems. As the intended application is on aeroelastic systems, characterized by many design variables and a small number of objective functions, gradients are computed from the fully-coupled adjoint equation. This is cast here as an iterated sequence for which convergence is guaranteed. The system is finally obtained using algorithm differentiation on the fully-coupled primal problem and its solution is then sought using a block Gauss-Seidel method, which preserves the partitioned structure of the primal coupled solver. This solution architecture has been implemented in the open-source SU2 software suite for the solution of industrial-scale aeroelastic optimization problems with viscous fluids and structures with nonlinear geometric and material response.

CONFERENCE PAPER

Sanchez R, Palacios R, Economon TD, Alonso JJ, Albring T, Gaugerk NRet al., 2017, Optimal actuation of dielectric membrane wings using high-fidelity fluid-structure modelling

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. This paper describes a computational framework for the analysis and design of electromechanically actuated membrane wings operating at low flight speeds. A fluid-structure interaction formulation with large deformations and complex material behavior has been developed, which is suited for integrally-actuated wings built with dielectric elastomers. A coupled adjoint-based methodology based on algorithmic differentiation has also been developed to determine optimal actuation profiles. Coupled sensitivities are shown to be accurately computed on the wing response, both under constant pressure and immersed in a reattached laminar flow. A simple optimization problem on the equilibrium position of the membrane is finally solved to exemplify the proposed design methodology.

CONFERENCE PAPER

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.

CONFERENCE PAPER

Wang Y, Wynn A, Palacios R, 2016, Nonlinear Modal Aeroservoelastic Analysis Framework for Flexible Aircraft, AIAA JOURNAL, Vol: 54, Pages: 3075-3090, ISSN: 0001-1452

JOURNAL ARTICLE

Bao Y, Palacios R, Graham M, Sherwin Set al., 2016, Generalized thick strip modelling for vortex-induced vibration of long flexible cylinders, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 321, Pages: 1079-1097, ISSN: 0021-9991

JOURNAL ARTICLE

Maraniello S, Palacios R, 2016, Optimal vibration control and co-design of very flexible actuated structures, JOURNAL OF SOUND AND VIBRATION, Vol: 377, Pages: 1-21, ISSN: 0022-460X

JOURNAL ARTICLE

Ng BF, New TH, Palacios R, 2016, Effects of leading-edge tubercles on wing flutter speeds, BIOINSPIRATION & BIOMIMETICS, Vol: 11, ISSN: 1748-3182

JOURNAL ARTICLE

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: 0889-9746

JOURNAL ARTICLE

Hesse H, Palacios R, 2016, Dynamic Load Alleviation in Wake Vortex Encounters, JOURNAL OF GUIDANCE CONTROL AND DYNAMICS, Vol: 39, Pages: 801-813, ISSN: 0731-5090

JOURNAL ARTICLE

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