Publications
197 results found
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.
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
Artola M, Goizueta N, Wynn A, et 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.
Goizueta N, Wynn A, Palacios R, et 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.
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.
Sherwin S, Lahooti M, Bao Y, et al., 2021, The thick strip method for slender body fluid structure interaction
For slender body fluid structure interaction which arise in problems such as the vortex induced vibration of oil riser pipes[1], flexible wings [2] or parked wind turbine blades, there is a natural separation of spatial scales between the fluid and structural problem. Nevertheless the large scale dynamics of the structure can have a notable impact on the fluid flow, for example leading to large scale separation which then modify the fluid forces applied to the structure. To resolve the full scale fluid structure interaction problem at realistic flow conditions/Reynolds number is typically prohibitive even on the largest HPC systems currently available. A reasonable modelling approach to address these challenging problems is to leverage the scale separation between the fluid and structural problem and only model the fluid on a strip at a series of locations along the slender body. Earlier approaches to this type of modelling used potential flow, two-dimensional U-RANS or even empirical data, in "thin" strip approximations. However these approaches were unable to capture the near body anisotropic or transitional flow features which are often responsible for energising the slender body dynamics. In [1] we proposed a generalized "thick" strip method where we adopt a finite thickness strip, which is still thin compared to the slender body, within which we apply an under-resolved Direct Numerical Simulation uDNS or implicit Large Eddy Simulation iLES modelling to capture the anisotropic flow behaviour and if sufficiently resolved the transitional nature of the flow. Within each strip we apply a high fidelity spectral/hp element-Fourier approximation using the Nektar++ package [3]. In this presentation we will outline the development and application of the thick strip modelling method for vortex induced problem of riser pipes and wind turbine blades. We will also discuss the challenges of the high fidelity modelling using spectral/hp element approximati
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.
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.
Wang Y, Zhao X, Palacios R, et 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.
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".
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.
Wang C, Muñóz-Simon A, Deskos G, et al., 2020, Code-to-code-to-experiment validation of LES-ALM wind farm simulators, Journal of Physics: Conference Series, Vol: 1618, Pages: 1-8, ISSN: 1742-6588
The aim of this work is to present a detailed code-to-code comparison of two Large-Eddy Simulation (LES) solvers. Corresponding experimental measurements are used as a reference to validate the quality of the CFD simulations. The comparison highlights the effects of solver order on the solutions, and it tries to answer the question of whether a high order solver is necessary to capture the main characteristics of a wind farm. Both solvers were used on different grids to study their convergence behavior. While both solvers show a good match with experimental measurements, it appears that the low order solver is more accurate and substantially cheaper in terms of computational cost.
Muñoz-Simón A, Palacios R, Wynn A, 2020, Benchmarking different fidelities in wind turbine aerodynamics under yaw, The Science of Making Torque from Wind (TORQUE 2020), Publisher: IOP Publishing, Pages: 1-11, ISSN: 1742-6588
This paper analyses the aerodynamics of wind turbines under yaw with different modelling fidelities (BEM, BEM with skewed wake model, UVLM and LES-AL). First of all, models are compared in a zero-yaw case to demonstrate their accuracy in prediction of out-of-plane loads and the discrepancy of UVLM in the in-plane loads due to the lack of viscous drag. Secondly, the yaw aerodynamics are described through the advancing/retreating and skewed wake effects, which are appropriately captured by UVLM and LES-AL and lead to an incorrect prediction of the location of maximum and minimum loading along a revolution by BEM. Further, when a skew-wake model is included in BEM, it predicts the correct locations but exhibits overly large loading variations. These predictions are consistent for all yaw angles studied (γ = 10° − 30°). All solvers predict similar decrease of root-bending moments, rotor power and thrust coefficients up to a yaw angle of 10°. However, at larger yaw angles, BEM overpredicts this decrease of coefficients with the yaw angle due to the unsuccessful performance of yaw corrections as opposed to UVLM that inherently accounts for three-dimensional effects. This study demonstrates the need to use computational models that can account for three-dimensional effects in the computation of aerodynamic loads for yaw angles above 10°.
Del Carre de la Portilla A, Palacios R, 2020, Simulation and optimization of takeoff maneuvers of very flexible aircraft, Journal of Aircraft: devoted to aeronautical science and technology, Vol: 57, Pages: 1097-1110, ISSN: 0021-8669
A generic framework for the simulation of transient dynamics in nonlinear aeroelasticity is presented that is suitable for flexible aircraft maneuver optimization. Aircraft are modeled using a flexible multibody dynamics approach built on geometrically nonlinear composite beam elements, and the unsteady aerodynamics on their lifting surfaces is modeled using vortex lattices with free or prescribed wakes. The open loop response to commanded inputs and external constraints is then fed into a Bayesian optimization framework, which adaptively samples the configuration space to identify optimal maneuvers. As a representative example, the proposed approach is demonstrated on a catapult-assisted takeoff. The specific modeling challenges associated to that problem are first discussed, including the effect of aircraft flexibility. An optimality measure based on ground clearance and wing root loads is then defined. It is finally shown that the link that ramp-length constraints introduce between acceleration, release speed, and wing root loads is the main driver in the optimal solution.
Deskos G, Del Carre de la Portilla A, Palacios R, 2020, Assessment of low-altitude atmospheric turbulence models for aircraft aeroelasticity, Journal of Fluids and Structures, Vol: 95, Pages: 1-19, ISSN: 0889-9746
We investigate the dynamic aeroelastic response of large but slow aircraft in low-altitude atmospheric turbulence. To this end, three turbulence models of increasing fidelity, namely, the one-dimensional von Kármán model, the two-dimensional Kaimal model and full three-dimensional wind fields extracted from large-eddy simulations (LES) are used to simulate ambient turbulence near the ground. Load calculations and flight trajectory predictions are conducted for a representative high-aspect-ratio wing aircraft, using a fully coupled nonlinear flight dynamics/aeroelastic model, when it operates in background atmospheric turbulence generated by the aforementioned models. Comparison of load envelopes and spectral content, on vehicles of varying flexibility, shows strong dependency between the selected turbulence model and aircraft aeroelastic response (e.g. 58% difference in the predicted magnitude of the wing root bending moment between LES and von Kármán models). This is mainly due to the presence of large flow structures at low altitudes that have comparable dimensions to the vehicle, and which despite the relatively small wind speeds within the Earth boundary layer, result in overall high load events for slow-moving vehicles. Results show that one-dimensional models that do not capture those effects provide fairly non-conservative load estimates and are unsuitable for very flexible airframe design.
Deskos G, del Carre A, Palacios R, 2020, Assessment of low-altitude atmospheric turbulence models for aircraft aeroelasticity, Publisher: ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
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Deskos G, Laizet S, Palacios R, 2020, WInc3D: a novel framework for turbulence-resolving simulations of wind farm wake interactions, Wind Energy, Vol: 23, Pages: 779-794, ISSN: 1095-4244
A fast and efficient turbulence‐resolving computational framework, dubbed as WInc3D (Wind Incompressible 3‐Dimensional solver), is presented and validated in this paper. WInc3D offers a unified, highly scalable, high‐fidelity framework for the study of the flow structures and turbulence of wind farm wakes and their impact on the individual turbines' power and loads. Its unique properties lie on the use of higher‐order numerical schemes with “spectral‐like” accuracy, a highly efficient parallelisation strategy which allows the code to scale up to O(104) computing processors and software compactness (use of only native solvers/models) with virtually no dependence to external libraries. The work presents an overview of the current modelling capabilities along with model validation. The presented applications demonstrate the ability of WInc3D to be used for testing farm‐level optimal control strategies using turbine wakes under yawed conditions. Examples are provided for two turbines operating in‐line as well as a small array of 16 turbines operating under “Greedy” and “Co‐operative” yaw angle settings. These large‐scale simulations were performed with up to 8192 computational cores for under 24 hours, for a computational domain discretised with O(109) mesh nodes.
Del Carre de la Portilla A, Goizueta N, Muñoz-Simón A, et al., 2020, SHARPy: A dynamic aeroelastic simulation toolbox for very flexible aircraft and wind turbines
SHARPy v1.1.1 is the latest release, consolidating v1.1 with some minor bug fixes and features.Changelog 1.1.1 (2020-02-03)
Maraniello S, Palacios R, 2020, Parametric reduced-order modelling of the unsteady vortex-lattice method, AIAA Journal: devoted to aerospace research and development, Vol: 58, Pages: 2206-2220, ISSN: 0001-1452
A method for frequency-limited balancing of the unsteady vortex-lattice equations is introduced that results in compact models suitable for computational-intensive applicationsin load analysis, aeroelastic optimisation, and control synthesis. The balancing algorithmrelies on a frequency-domain solution of the vortex-lattice equations that effectively eliminates the cost associated to the wake states. It is obtained from a Z-transform of theunderlying discrete-time equations, and requires no additional geometrical or kinematicassumptions for the lifting surfaces. Parametric reduced-order modelling is demonstratedthrough interpolation over (a) projection matrices, (b) state-space realisations and (c)transfer functions, which trade accuracy, robustness and cost. Methods are finally exemplified in the dynamic stability of a T-tail configuration with varying incidence. Numericalstudies show that a very small number of balanced realisations is sufficient to accuratelycapture the unconventional aeroelastic response of this system, which includes in-planekinematics and steady loads, over a wide range of operation conditions.
Artola M, Goizueta N, Wynn A, et al., 2020, Modal-based nonlinear estimation and control for highly flexible aeroelastic systems, AIAA Scitech 2020 Forum, Publisher: American Institute of Aeronautics and Astronautics, Pages: 1-23
Modal-based, nonlinear Moving Horizon Estimation (MHE) and Model Predictive Control (MPC) strategies for highly flexible aeroelastic systems are presented. The aeroelastic model is 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 equilibrium 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's continuous-time adjoints efficiently to compute sensitivities, lays the foundations for real-time estimation and control of highly flexible aeroelastic systems.
Muñoz-Simón A, Wynn A, Palacios R, 2020, Unsteady and three-dimensional aerodynamic effects on wind turbine rotor loads, AIAA Scitech 2020 Forum, Publisher: American Institute of Aeronautics and Astronautics, Pages: 1-22
The paper investigates the use of vortex methods in the computation of important flows for wind turbine aerodynamics. These flows are characterised by inflow velocity unsteadiness, spatial variations and non-zero spanwise component. First, computational vortex methods are shown to match analytical solutions on simple geometries. Second, these geometries will be studied to reveal the effects of these flows on airfoil aerodynamics: unsteady damping and load reduction when subjected to side slip or spanwise inflow velocity variations. Finally, vortex methods will be compared with traditional BEM methods in full wind turbine configurations under real operating inflows such as shear, yaw and turbulence which are characterised by unsteadiness and three-dimensional effects. Vortex methods allow quantifying the error of BEM methods for these conditions.
Venkatesan-Crome C, Palacios R, 2020, A discrete adjoint solver for time-domain fluid-structure interaction problems with large deformations
Progress in the development of computational methodology for time-accurate, non-linear, fluid-structure interaction problems including sensitivity determination using discrete adjoint analysis is presented. Three-field partitioned FSI solver structure, made up of the fluid, structural and mesh domain, is employed. For both the primal and discrete adjoint analysis, the individual domains are initially discussed ahead of the fully coupled FSI solver. Single domain results for structural and fluid problems are initially presented for an axially loaded bar and pitching NACA 0012 airfoil respectively. Dynamic coupled FSI problem proposed in this work is a flexible NACA 0012 airfoil under unsteady aerodynamic load resulting in shock induced vibrations.
Burghardt O, Gauger NR, Gomes P, et al., 2020, Coupled discrete adjoints for multiphysics in su2, Pages: 1-12
Many optimization problems in fluid dynamics are naturally constituted in a larger multiphysics setting, the most prominent ones nowadays being fluid-structure interaction and conjugate heat transfer or combinations of them. In the context of partitioned solution approaches, and from a software perspective, this means that two or more solvers are coupled by exchanging data at common physical boundaries during the simulation. Optimization methods relying on discrete adjoint solutions have to consider such couplings in order to give accurate gradients. This article presents a methodology for how coupled multiphysics adjoints can be computed efficiently in a way that is also independent of the choice or configuration of the underlying physical problem. Based on an implementation in SU2 (an open-source multiphysics simulation and design software1 ) we demonstrate how the same algorithm can be applied for shape sensitivity analysis on a conjugate heat transfer as well as a fluid-structure interaction test case.
Gomes P, Palacios R, 2020, Aerodynamic driven multidisciplinary topology optimization of compliant airfoils
We propose a strategy for density-based topology optimization of fluid structure interaction problems that deals with some short-comings associated with non stiffness-based design problems. The method is demonstrated on a problem where we seek to improve the passive load alleviation characteristics of a highly compliant airfoil at high speed while producing sufficient lift at a lower speed. The fluid structure interaction is simulated with the multi-physics suite SU2, which includes RANS modelling of the fluid and hyper-elastic material behaviour of the geometrically-nonlinear structure. Gradient-based optimization is used with the coupled aerostructural sensitivities being obtained via an algorithmic differentiation-based coupled discrete adjoint solver.
Ng BF, Ong EJG, Palacios R, et al., 2020, Effects of Leading-Edge Tubercles on Structural Dynamics and Aeroelasticity, Flow Control Through Bio-inspired Leading-Edge Tubercles: Morphology, Aerodynamics, Hydrodynamics and Applications, Pages: 147-173, ISBN: 9783030237912
The design of tubercles has both aerodynamics and structural considerations. In this chapter, we discuss structural design, stability and aeroelasticity of lifting surfaces that are modified with leading-edge (LE) tubercles. With LE tubercles, bending and torsional frequencies are slightly lower due to the combined effects of spanwise stiffness and inertia variations from spanwise chord length variation and mass redistribution. In the pre-stall regime, lifting surfaces are likely to encounter instability (flutter) due to flexibility and rear placement of the centre-of-gravity. The structural dynamics and unsteady aerodynamics with LE tubercles have opposite influence on margins-of-stability with the latter having the dominant effect. Numerical investigations show that the flutter speed is consistently mildly higher with LE tubercles and they have reduced effect on themargins for stability when concentrated inboard of the wing or on sweptback wings as the sweep angle is increased.
Del Carre A, Deskos G, Palacios R, 2020, Realistic turbulence effects in low altitude dynamics of very flexible aircraft
The focus are the challenges associated with the low-altitude part of the mission of very flexible aircraft, namely the launching procedure and the atmospheric boundary layer response. First, the robustness of a catapult-assisted take off to changes in incoming flow velocity and sideslip angle is assessed. Results show how the sideslip angle affects the launch manoeuvre, defining a safe range and analysing how an increasing sideslip alters the structural dynamics and trajectory of the aircraft. Next, continuous turbulence response of the X-HALE, a multi-tail, span-loaded nonlinear aeroelasticity testbed is computed for a classic von kármán spectrum and a time-varying high-fidelity LES simulation of the atmospheric boundary layer. It is shown that the structural responses obtained with the two statistically equivalent flow fields (same mean velocity and turbulent intensity) differ by an order of magnitude, highlighting the importance of span-varying gust load analysis on very flexible aircraft.
Palacios Nieto R, Cea A, 2019, Nonlinear modal condensation of large finite element models: An application of Hodges’ intrinsic theory, AIAA Journal, Vol: 57, Pages: 4255-4268, ISSN: 0001-1452
A method to obtain geometrically nonlinear reduced-order descriptions of structures defined by a large finite element model is presented. The full model is used to identify all the coefficients in a modal projection of Hodges’s intrinsic beam equations, with the geometric reduction introduced through static or dynamic condensation along the main load paths on the original structure. The only information retrieved from the full model is the linear normal modes as well as condensed mass and stiffness and nodal coordinates. The approach aims to solve geometrically nonlinear problems of industrial complexity in an efficient manner, while preserving the linear model under small displacements. Examples of increasing complexity will be shown with the built-up finite element models made with beams and shells and both lumped and distributed masses. Nonlinear static and dynamic analyses, including rigid-body dynamics, are then demonstrated using the resulting nonlinear modal description.
Artola M, Wynn A, Palacios R, 2019, A nonlinear modal-based framework for low computational cost optimal control of 3D very flexible structures, 2019 18th European Control Conference (ECC), Publisher: Institute of Electrical and Electronics Engineers
A nonlinear modal-based reduced-order model, equipped with an efficient adjoint-sensitivity analysis, is presented as a low computational cost framework for optimal control of very flexible structures, with particular focus on efficiently computing finite rotations. Multiple shooting is shown to improve convergence of a highly nonlinear problem when compared to the single shooting case, with optimisation further accelerated via parallelisation, which suggests the presented approach may be employed for real-time control of very flexible structures.
Venkatesan-Crome C, Palacios R, Kattmann T, et al., 2019, Discrete Adjoint for Unsteady Incompressible Flows Using a Density-based Formulation, AIAA AVIATION Forum, Publisher: American Institute of Aeronautics and Astronautics
Maraniello S, Palacios R, 2019, State-space realizations and internal balancing in potential-flow aerodynamics with arbitrary kinematics, AIAA Journal, Vol: 57, Pages: 2308-2321, 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.
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