Imperial College London

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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185 results found

Gomes P, Palacios R, 2022, Aerostructural topology optimization using high fidelity modeling, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, Vol: 65, ISSN: 1615-147X

We investigate the use of density-based topology optimization for the aeroelastic design of very flexible wings. This is achieved with a Reynolds-averaged Navier–Stokes finite volume solver, coupled to a geometrically nonlinear finite element structural solver, to simulate the large-displacement fluid-structure interaction. A gradient-based approach is used with derivatives obtained via a coupled adjoint solver based on algorithmic differentiation. In the example problem, the optimization uses strong coupling effects and the internal topology of the wing to allow mass reduction while maintaining the lift. We also propose a method to accelerate the convergence of the optimization to discrete topologies, which partially mitigates the computational expense of high-fidelity modeling approaches.

Journal article

Wang Y, Zhao X, Palacios R, Otsuka Ket al., 2022, Aeroelastic simulation of high-aspect ratio wings with intermittent leading-edge separation, AIAA Journal, Vol: 60, Pages: 1769-1782, ISSN: 0001-1452

We present a medium-fidelity aeroelastic framework for computing intermittently separating three-dimensional (3-D) flows around high-aspect ratio wings with a significantly reduced computational cost compared to the computational-fluid- dynamics-based method. To achieve that, we propose a modified three-dimensional vortex panel method with leading-edge separation controlled by leading-edge suction parameter theory, and its incorporation in a coupled aeroelastic solver for the dynamic response of these systems. Numerical verifications and simulations are presented on both attached and separated aeroelastic test cases, demonstrating the method on postflutter limit-cycle oscillation of a cantilever wing, and leading-edge separation on a deploying wing, a complex kinematic response. In both cases we were able to capture three-dimensional interactions on intermittently separating dynamic flowfields using a low computational cost.

Journal article

Gomes P, Palacios R, 2022, Pitfalls of discrete adjoint fixed-points based on algorithmic differentiation, AIAA Journal, Vol: 60, Pages: 1251-1256, ISSN: 0001-1452

Journal article

Muñoz-Simón A, Wynn A, Palacios R, 2022, Some modelling improvements for prediction of wind turbine rotor loads in turbulent wind, Wind Energy, Vol: 25, Pages: 333-353, ISSN: 1095-4244

This paper investigates the accuracy of three aerodynamic models to compute loads on wind turbine rotors under turbulent inflow: Blade Element Momentum (BEM); Unsteady Vortex LatticeMethod (UVLM) and Large Eddy Simulation with Actuator Line (LES-AL). Turbulent inflow conditions are numerically generated with a new approach that combines control of turbulence andrealistic velocity spectrum by using Mann boxes and LES simulations, respectively. Several deficiencies of the tested models are found and overcome through proposed improvements. First,the BEM assumption of independent radial sections does not hold in turbulent cases with longblades. Thus, a spatial filter to account for the interaction of radial sections in BEM is designedthrough the analysis of these interactions with UVLM. Second, the absence of viscous drag inUVLM is observed to lead to a very high rotor power coefficient, and it is shown that this canbe mitigated by including drag in UVLM with a BEM-like-approach through look-up tables. Third,the free wake model in UVLM, required to accurately capture rotor thrust, significantly increasescomputational cost. For this reason, a new wake discretisation scheme for the wake convectionequation in UVLM is proposed, in which a coarse discretisation is employed far from the solidsurfaces, which significantly reduces the computational time. Finally, these improvements andthe performance of the three fidelities are analysed in a reference 10 MW wind turbine rotordemonstrating, in general, good agreement.

Journal article

Goizueta N, Wynn A, Palacios R, Drachinsky A, Raveh DEet al., 2022, Flutter predictions for very flexible wing wind tunnel test, Journal of Aircraft: devoted to aeronautical science and technology, ISSN: 0021-8669

The stability boundaries of a very flexible wing are sought to inform a wind-tunnel flutter test campaign. The objective is twofold: to identify via simulation the relevant physical processes to be explored while ensuring safe and non-destructive experiments, and to provide a benchmark case for which computational models and test data are freely available. Analyses have been independently carried out using two geometrically nonlinear structural models coupled with potential flow aerodynamics. The models are based on a prototype of the wing for which static load and aeroelastic tests are available, and the experimental results have been successfully reproduced numerically. The wing displays strong geometrically nonlinear effects with static deformations as high as 50% of its span. This results in substantial changes to its structural dynamics, which display several mode crossings that cause the flutter mechanisms to change as a function of deformation. Stability characteristics depend on both the free-stream velocity and the angle of attack. A fast drop of the flutter speed is observed as the wing deforms as the angle of attack is increased, while a large stable region is observed for wing displacements over 25%. The corresponding wind tunnel dynamic tests have validated these predictions.

Journal article

Düssler S, Goizueta N, Muñoz-Simón A, Palacios Ret al., 2022, Modelling and numerical enhancements on a UVLM for nonlinear aeroelastic simulation, AIAA SCITECH 2022 Forum, Publisher: American Institute of Aeronautics and Astronautics, Pages: 1-20

This work presents various improvements made to the Unsteady Vortex Lattice Method (UVLM) integrated into the open-source, nonlinear aeroelastic simulation environment SHARPy. The UVLM is extended by non-lifting body effects, polar corrections, and a new wake discretization scheme. The theory behind these enhancements is discussed and successfully verified. Finally, some of these enhancements are employed on a flexible aircraft demonstrator model. The results indicate an influence of the fuselage on the aeroelastic behavior of the wing, which becomes increasingly important for larger wing deformations and fuselage diameters. The polar corrections provide valuable refinements to the aerodynamic forces and moments, and the new wake discretization scheme significantly speeds up the simulations.

Conference paper

Otsuka K, Wang Y, Palacios R, Makihara Ket al., 2022, Strain-Based Geometrically Nonlinear Beam Formulation for Multibody Dynamic Analysis

The geometrically nonlinear strain-based beam formulation has the potential to analyze flexible multibody systems efficiently due to the minimum number of variables and the constant stiffness matrix. The objective of this paper is to extend the strain-based beam formulation to a generic multibody dynamic analysis. To achieve this objective, we describe the constraint equation by using the vector variables of the absolute nodal coordinate formulation that has a velocity-transformation relationship with the strain-based formulation. Then, we divide the Jacobian of the constraint equation into two terms. One term is equivalent to the velocity transformation matrix that has been implemented in the existing strain-based analysis framework. Therefore, additional programming effort and calculation are not needed. The other term is a simple constant or linear Jacobian defined by the orthonormal vectors of the absolute nodal coordinate formulation. This simple Jacobian description enables not only efficient analysis but also various choice of a time-integration method. We demonstrated that the proposed framework can be used with the explicit Runge-Kutta method and the implicit generalized-α method. The proposed strain-based multibody dynamic analysis method exhibited good agreement with and a better convergence than a conventional flexible multibody dynamic analysis method.

Conference paper

Simiriotis N, Palacios R, 2022, Correction to: A Flutter Prediction Framework in the OpenSource SU2 Suite (AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022)

Correction Notice Email address in footnote, first page, for first author Nikolaos Simiriotis should be corrected. Correct email address is: n.simiriotis@imperial.ac.uk.

Conference paper

Burghardt O, Gomes P, Kattmann T, Economon TD, Gauger NR, Palacios Ret al., 2022, Discrete adjoint methodology for general multiphysics problems A modular and efficient algorithmic outline with implementation in an open-source simulation software, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, Vol: 65, ISSN: 1615-147X

Journal article

Wynn A, Artola M, Palacios R, 2021, Nonlinear optimal control for gust load alleviation with a physics-constrained data-driven internal model, AIAA SCITECH 2022 Forum, Publisher: American Institute of Aeronautics and Astronautics, Pages: 1-22

A data-driven strategy is developed to improve the internal models used for predictive control in nonlinear aeroelastic applications. A nonlinear modal formulation of the structure is retained, while an identified quadratic model for both the gravitational forces and the aerodynamics are obtained from a least-squares fit with LASSO regularisation from simulated flights. This is first seen to improve the accuracy of the resulting reduced-order model for open-loop predictions on both gust response and a payload drop problem. Its superior performance as internal model for nonlinear control and estimation is finally demonstrated numerically.

Conference paper

Cea A, Palacios R, 2021, Parametric reduced order models for aeroelastic design of very flexible aircraft, AIAA Scitech, Publisher: ARC, Pages: 1-28

A description for flutter and dynamic loads prediction is laid out based on state-space systems around a nonlinear equilibrium. In order to reduce the computational times associated with building and manipulating these systems, a newmethodology is proposed to build parametric reduced-order models of the unsteady aerodynamic systems from optimal Latin-Hypercube design of experiments, frequency-limited balancing techniques and interpolation on the transfer functions of the resulting reduced systems. Optimization of the kernels encapsulating the parametric dependence is also studied. The developed tools are employed for the aeroelastic design optimization of a very flexible strut-braced wing with flutter constraints. Results show a promising approach to be deployed in design problems where dynamics and stability are to be included in the analysis and geometrically nonlinear effects are to be accounted for.

Conference paper

Goizueta N, Wynn A, Palacios R, 2021, Fast flutter evaluation of very flexible wing using interpolation on an optimal training dataset, AIAA SCITECH 2022 Forum, Publisher: American Institute of Aeronautics and Astronautics, Pages: 1-21

Machine learning strategies can be efficiently used to accelerate the exploration of the design space or flight envelope of highly flexible aeroelastic systems. In this paper, we explore the use of interpolation between parametric state-space realizations to, with few true systems sampled in the parameter space, produce with adequate accuracy a state-space model anywhere in the parameter space. The location of the sampling points is shown to be decisive thus the selection of these points takes the focus in this work. Several approaches are explored, putting emphasis on adaptive schemes that locate the optimal points in the parameter space that are needed to capture the changing system dynamics. Since the evaluation of the true system is costly, optimization techniques based on statistical surrogate models are sought, which need to be trained but are effective in locating the best locations to use as sampling data. A novel method inspired by Bayesian optimization is used to make the most out of a limited number of known state-spaces by taking different combinations as training and testing data of the statistical surrogate, leading to not only an accurate interpolation framework but also to a reduction of 50% of the number of costly full system evaluations compared to a standard Bayesian optimization set-up. These methods are demonstrated on the Pazy wing, a very flexible wing with a complex stability envelope, whereby we produce a very accurate representation of the flutter envelope at a reduced computational cost.

Conference paper

Simiriotis N, Palacios R, 2021, A flutter prediction framework in the open-source SU2 suite, AIAA SCITECH 2022 Forum, Publisher: American Institute of Aeronautics and Astronautics, Pages: 1-15

The paper reports on the development of a direct flutter-onset prediction framework, based on CFD frequency-domain techniques, for a robust and efficient search of the flutter boundary across the flight envelope. The implementation was carried out in the open-source SU2 solver. The complete methodology is examined in this contribution. The existing harmonic balance formulation was extended to treat arbitrarily deforming surfaces. A dedicated native solver was developed to integrate the linear structural equations of motion. Reduced order structural equations are built based on input modal shapes from external FE solvers. To this end, suitable interpolation schemes have been included to transfer data across the fluid-structure interface. This paper provides numerical results from the application of the developed approach to well-established 2D and 3D test cases operating in the transonic regime. The accuracy of the chosen strategy is shown, and the robustness and computational efficiency of the implementation are discussed.

Conference paper

Artola M, Rodriguez C, Wynn A, Palacios R, Leugering Get al., 2021, Optimisation of Region of Attraction Estimates for the Exponential Stabilisation of the Intrinsic Geometrically Exact Beam Model, 2021 60th IEEE Conference on Decision and Control (CDC), Publisher: IEEE

Conference paper

Otsuka K, del Carre A, Palacios R, 2021, Nonlinear Aeroelastic Analysis of High-Aspect-Ratio Wings with a Low-Order Propeller Model, Journal of Aircraft, Pages: 1-14

Journal article

Artola M, Goizueta N, Wynn A, Palacios Ret al., 2021, Aeroelastic control and estimation with a minimal nonlinear modal description, AIAA Journal: devoted to aerospace research and development, Vol: 59, Pages: 2697-2713, ISSN: 0001-1452

Modal-based, nonlinear Moving Horizon Estimation (MHE) and Model Predictive Control(MPC) strategies for very flexible aeroelastic systems are presented. They are underpinned by an aeroelastic model built from a 1D intrinsic (based on strains and velocities) description of geometrically-nonlinear beams and an unsteady Vortex Lattice aerodynamic model. Construction of a nonlinear, modal-based, reduced order model of the aeroelastic system, employing a state-space realisation of the linearised aerodynamics around an arbitrary reference point, allows us to capture the main nonlinear geometrical couplings at a very low computational cost. Embedding this model in both MHE and MPC strategies, which solve the system continuous-time adjoints efficiently to compute sensitivities, lays the foundations for real-time estimation and control of highly flexible aeroelastic systems. Finally, the performance and versatility of the framework operating in the nonlinear regime is demonstrated on two very flexible wing models, with notably different dynamics, and on two different control setups: a gust-load alleviation problem on a very high aspect ratio wing with slower dynamics, which involves substantial deflections; and flutter suppression on a flexible wing with significantly faster dynamics, where an unconventional nonlinear stabilisation mechanism is unveiled.

Journal article

Artola M, Wynn A, Palacios R, 2021, Modal-based model predictive control of multibody very flexible structures, 21st IFAC World Congress on Automatic Control - Meeting Societal Challenges, Publisher: Elsevier, Pages: 7472-7478, ISSN: 2405-8963

A model predictive control strategy for flexible multibody structures undergoing large deformations is presented. The dynamics of such structures are highly nonlinear, with local effects introduced by the joint constraints and distributed effects arising from the structure’s increased flexibility, from which arbitrary large deflections and rotations can be expected. A modal-based nonlinear reduced order model of an intrinsic description (based on velocities and strains) of geometrically-exact beams is used to underpin the internal model. This low-order model, constructed using the linearised eigenfunctions of the constrained structures, is a set of nonlinear ordinary differential equations in time (i.e. no algebraic equations are present) thus facilitating analysis and demonstrating successful control. Numerical examples are presented based on a very flexible hinged two-link manipulator.

Conference paper

Artola M, Wynn A, Palacios R, 2021, Modal-based nonlinear model predictive control for 3D very flexible structures, IEEE Transactions on Automatic Control, Vol: 67, ISSN: 0018-9286

In this paper a novel NMPC scheme is derived, which is tailored to the underlying structure of the intrinsic description of geometrically exact nonlinear beams (in which velocities and strains are primary variables). This is an important class of PDE models whose behaviour is fundamental to the performance of flexible structural systems (e.g., wind turbines, High-Altitude Long-Endurance aircraft). Furthermore, this class contains the much-studied Euler-Bernoulli and Timoshenko beam models, but has significant additional complexity (to capture 3D effects and arbitrarily large displacements) and requires explicit computation of rotations in the PDE dynamics to account for orientation-dependent forces such as gravity. A challenge presented by this formulation is that uncontrollable modes necessarily appear in any finite dimensional approximation to the PDE dynamics. We show, however, that an NMPC scheme can be constructed in which the error introduced by the uncontrollable modes can be explicitly controlled. Furthermore, in challenging numerical examples exhibiting considerable deformation and nonlinear effects, it is demonstrated that the asymptotic error can be made insignificant (from a practical perspective) usingour NMPC scheme and excellent performance is obtained evenwhen applied to a highly resolved numerical simulation of thePDEs. We also present a generalisation of Kelvin-Voigt dampingto the intrinsic description of geometrically-exact beams. Finally,special emphasis is placed on constructing a framework suitablefor real-time NMPC control, where the particular structure ofthe underlying PDEs is exploited to obtain both efficient finite-dimensional models and numerical schemes.

Journal article

Cea A, Palacios R, 2021, A non-intrusive geometrically nonlinear augmentation to generic linear aeroelastic models, Journal of Fluids and Structures, Vol: 101, ISSN: 0889-9746

A new approach to build geometrically-nonlinear dynamic aeroelastic models is proposed that only uses information typically available in linear aeroelastic analyses, namely a generic (linear) finite-element model and frequency-domain aerodynamic influence coefficient matrices (AICs). Good computational efficiency is achieved through a two-step process: Firstly, a geometric reduction of the structure is carried out through static or dynamic condensation on nodes along the main load paths of the vehicle. Secondly, manipulation of the resulting linear normal modes (LNMs), the condensed stiffness and mass matrices, and the nodal coordinates provides the modal coefficients of the intrinsic beam equations along these load paths. This preserves the LNMs of the original problem and augments them with the geometrically nonlinear terms of beam theory. The structural description is in material coordinates and modal AICs are thus naturally included as follower forces. Numerical examples include cantilever wings built using detailed models, for which effects such as nonlinear aeroelastic equilibrium, nonlinear dynamics and structural-driven limit-cycle oscillations are shown. Results demonstrate the ability of the methodology to seamlessly and efficiently incorporate critical nonlinear effects to (linear) arbitrarily large aeroelastic models of high aspect ratio wings.

Journal article

Cea A, Palacios R, 2021, A non-intrusive nonlinear aeroelastic extension of loads packages with application to long range transport aircraft configuration, AIAA Scitech 2021 Forum, Publisher: American Institute of Aeronautics and Astronautics

A new method for constructing geometrically-nonlinear aeroelastic systems from standard linear models is applied to an industry-level aircraft configuration. The new approach seamlessly integrates with current aeroelastic load packages performing linear analysis based on generic finite-element models (FEMs) and aerodynamic influence coefficient matrices (AICs). We generalize the methodology to incorporate control inputs, find the trimmed aircraft state, or generate gusts disturbances, which can be employed separately or combined to obtain a simplified flight dynamics model for load analysis. An initial study of the aeroelastic response of a long range aircraft is presented. Linear and nonlinear results are introduced in static and dynamic computations of manoeuvres, trim, and gust disturbances. These are compared to commercial software calculations, showing the need for geometrically nonlinear analysis in the production environment of airplanes with ultra high aspect ratio wings.

Conference paper

Goizueta N, Wynn A, Palacios R, 2021, Parametric Krylov-based order reduction of aircraft aeroelastic models, AIAA Scitech 2021 Forum, Publisher: American Institute of Aeronautics and Astronautics, Pages: 1-25

We present an interpolation-based scheme to obtain in real-time linearised aeroelastic models of very flexible aircraft at any flight condition within the flight envelope. First, in an offline phase, a library of reduced-order linear aeroelastic models is computed by finding the nonlinear equilibrium (trimmed aircraft) using a nonlinear, geometrically-exact beam formulation coupled with an Unsteady Vortex Lattice Method. Subsequent linearisation is achieved analytically and followed by reduction using Krylov subspace methods. The interpolation is performed directly on the reduced-order system matrices, which are projected onto a congruent coordinate system for compatibility. Any interpolation scheme of choice can be used, and the size of the models permits real-time computation.

Conference paper

Lahooti M, Palacios R, Sherwin SJ, 2021, Thick strip method for efficient large-eddy simulations of flexible wings in stall, AIAA Scitech 2021 Forum, Publisher: American Institute of Aeronautics and Astronautics

An efficient computational method is presented based on the thick strip method for Large-Eddy simulation of flexible wings in stall. Fluid domain is break down into series of smaller 3D strips which one independently solved using implicit LES method. Force and moments are obtained from each strips and used to evolved the nonlinear dynamics of the structure. High deformation response of high-altitude long-endurance wing under several angle of attacks leading to the stall regions are presented to show the capability of proposed FSI method

Conference paper

Artola M, Goizueta N, Wynn A, Palacios Ret al., 2021, Proof of concept for a hardware-in-the-loop nonlinear control framework for very flexible aircraft, AIAA Scitech 2021 Forum, Publisher: https://arc.aiaa.org/doi/abs/10.2514/6.2021-1392, Pages: 1-26

Nonlinear Moving Horizon Estimation (MHE) and Model Predictive Control (MPC) strategies for very flexible aircraft are presented. They are underpinned by a nonlinear reduced-order model built upon the structure’s natural modes of vibration. This internal model aims for a minimal realisation of the aircraft which retains sufficient information to enable efficient real-time estimation and control. It is based on a modal intrinsic description of geometrically-nonlinear beams and a linearised unsteady vortex lattice aerodynamic model. Numerical evidence has shown that models of this form are able to capture the main nonlinear geometrical couplings at a very low computational cost. This opens the door to MHE and MPC strategies, which are naturally more computationally demanding than other linear conventional strategies, but are more versatile and able to provide control in the usually neglected nonlinear regime. The proposed control framework is tested on models built in an in-house open-source nonlinear aeroelasticity simulation and analysis package, to emulate the controller performance on a realistic plant model. Very satisfactory results are obtained in a flutter suppression problem involving a very flexible clamped wing, where the nonlinearity of the problem is leveraged by the internal model to achieve stabilisation, and a payload drop control of a very flexible HALE aircraft.

Conference paper

Goizueta N, Wynn A, Palacios R, Drachinsky A, Raveh DEet al., 2021, Flutter prediction for a very flexible wing wind tunnel test, AIAA Scitech 2021 Forum, Pages: 1-17

Two different nonlinear aeroelastic tool sets, SHARPy and the Modal Rotation Method (MRM), have been employed to predict and design a wind tunnel flutter test campaign of a very flexible wing, the Pazy Wing, as part of the 3rd Aeroelastic Prediction Workshop. The first method, SHARPy, uses geometrically exact beams coupled with an Unsteady Vortex Lattice, which is linearised about a deformed configuration, reduced by means of Krylov subspaces and analysed to compute the stability boundaries of the wing. The MRM is based on structural modal data, from either beam models or finite element models, coupled with a doublet-lattice aerodynamic model from ZAERO of the straight wing configuration. The excellent agreement between numerical and experimental data for structural-only and static aeroelastic analyses paves the way for predicting the stability boundaries of the Pre-Pazy wing with sufficient confidence for the safe design of a flutter wind tunnel test campaign.

Conference paper

Gomes P, Economon TD, Palacios R, 2021, Sustainable high-performance optimizations in su2, Pages: 1-18

Over a period of approximately 18 months, we have achieved an average 4-fold performance increase of the open source multiphysics suite SU2 through implementation optimizations (e.g. vectorization), and for some problems an additional 10-fold improvement via algorithmic changes. We have implemented a hybrid parallelization strategy (MPI + OpenMP) that improves the scalability of the code and allows key algorithms (such as multigrid) to maintain their effectiveness at small number of nodes per core. Our work has maintained the generality and versatility of the code by not relying on optimizations specific to given compilers, architectures, or physics. Furthermore, we maintain, or lower, the level of C++ knowledge needed for new developers. In this paper we document the implementation and algorithmic changes, give an overview of the details that allow implementing the hybrid parallel and vectorization frameworks in a way that hides the low-level complexity from high-level algorithm development. We demonstrate the improvements on benchmark problems known to the aeronautics community, and derive best practice guidelines to use the new capabilities.

Conference paper

Artola M, Wynn A, Palacios R, 2021, Generalized Kelvin–Voigt damping models for geometrically nonlinear beams, AIAA Journal: devoted to aerospace research and development, Vol: 59, Pages: 356-365, ISSN: 0001-1452

Strain-rate-based damping is investigated in the strong form of the intrinsic equations of three-dimensional geometrically exact beams. Kelvin–Voigt damping, often limited in the literature to linear or two-dimensional beam models, is generalized to the three-dimensional case, including rigid-body motions. The result is an elegant infinite-dimensional description of geometrically exact beams that facilitates theoretical analysis and sets the baseline for any chosen numerical implementation. In particular, the dissipation rates and equilibrium points of the system are derived for the most general case and for one in which a first-order approximation of the resulting damping terms is taken. Finally, numerical examples are given that validate the resulting model against a nonlinear damped Euler–Bernoulli beam (where detail is given on how an equivalent description using our intrinsic formulation is obtained) and support the analytical results of energy decay rates and equilibrium solutions caused by damping. Throughout the paper, the relevance of damping higher-order terms, arising from the geometrically exact description, to the accurate prediction of its effect on the dynamics of highly flexible structures is highlighted.

Journal article

Otsuka K, Carre AD, Palacios R, 2021, Nonlinear static and dynamic analysis framework for very flexible multibody aircraft with propellers, Pages: 1-23

A nonlinear static and dynamic aeroelastic analysis framework for high aspect ratio wings with propellers is described. The aerodynamic effect of propellers is considered. The high computational cost required for modeling aerodynamic interaction between the wing and propeller wake is reduced by taking advantage of the relatively slow dynamics of the wing. Consequently, the propeller wake is modeled as a straight vortex cylinder that does not require a computationally expensive wake updating process. By leveraging the smallness of the propeller, we propose an averaged vortex cylinder method that calculates the induced velocities of the propeller vortex cylinder efficiently without suffering from a numerical singularity and loss of accuracy. The induced velocities are considered in the wing aerodynamic force calculation using an unsteady vortex lattice method. We also propose an efficient propeller cylinder coordinate generation method modeling the propeller-attached wing by absolute nodal coordinate formulation with a multibody dynamic theory. The developed framework is validated by comparison with other frameworks and formulations. A nonlinear static analysis on a representative high-aspect-ratio wing demonstrates that the propeller-induced axial velocity has a larger effect on the increase in deflection than the tangential velocity. The nonlinear dynamic results show that the propeller may decrease the deflection amplitude.

Conference paper

Wang Y, Zhao X, Palacios R, Otsuka Ket al., 2021, Unsteady aeroelasticity of slender wings with leading-edge separation, Pages: 1-23

We present a medium-fidelity aeroelastic framework for computing intermittently separating 3D flows around slender aero-structures with a significantly reduced computational cost than CFD-based method. In which, we propose a modified 3D vortex panel method with leading-edge separation controlled by the leading-edge suction parameter theory, and demonstrate its incorporation in a coupled aeroelastic solver for the dynamic response of these systems. Numerical verifications and simulations are presented on both attached and separated aeroelastic test cases, demonstrating the capability of the proposed method.

Conference paper

Muñoz-Simón A, Palacios R, Wynn A, 2020, Scripts illustrating some modelling improvements for prediction of wind turbine rotor loads in turbulent wind

This repository contains some files to complement the publication "Some modelling improvements for prediction of wind turbine rotor loads in turbulent wind".

Software

Gomes P, Palacios R, 2020, Aerodynamic-driven topology optimization of compliant airfoils, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, Vol: 62, Pages: 2117-2130, ISSN: 1615-147X

A strategy for density-based topology optimization of fluid-structure interaction problems is proposed that deals with some shortcomings associated to non stiffness-based design. The goal is to improve the passive aerodynamic shape adaptation of highly compliant airfoils at multiple operating points. A two-step solution process is proposed that decouples global aeroelastic performance goals from the search of a solid-void topology on the structure. In the first step, a reference fully coupled fluid-structure problem is solved without explicitly penalizing non-discreteness in the resulting topology. A regularization step is then performed that solves an inverse design problem, akin to those in compliant mechanism design, which produces a discrete-topology structure with the same response to the fluid loads. Simulations are carried out with the multi-physics suite SU2, which includes Reynolds-averaged Navier-Stokes modeling of the fluid and hyper-elastic material behavior of the geometrically nonlinear structure. Gradient-based optimization is used with the exterior penalty method and a large-scale quasi-Newton unconstrained optimizer. Coupled aerostructural sensitivities are obtained via an algorithmic differentiation based coupled discrete adjoint solver. Numerical examples on a compliant aerofoil with performance objectives at two Mach numbers are presented.

Journal article

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