Simao Marques - Academia.edu (original) (raw)

Papers by Simao Marques

A Reduced-Order Model (ROM) for the prediction of aeroelastic instabilities is presented. The uns... more A Reduced-Order Model (ROM) for the prediction of aeroelastic instabilities is presented. The unsteady nonlinear aerodynamic system is characterised by an Artificial Neural Network (ANN) to a set of network weights. The system is trained on a time history of simultaneous forced oscillation of the normal modes as input and generalised forces as output. Network weights are then used to approximate the aerodynamic force in the structural equation of motion to obtain the structural response. Results from the 3D Goland wing are presented and compared against full order CFD. It is shown that the ROM can predict aeroelastic instabilities with reasonable accuracy at a cost of less than one typical unsteady aeroelastic computation.

53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference<BR>20th AIAA/ASME/AHS Adaptive Structures Conference<BR>14th AIAA, 2012

45th AIAA Aerospace Sciences Meeting and Exhibit, 2007

ABSTRACT

Aircraft design requires compromises between a myriad of disciplines in order to obtain an optimi... more Aircraft design requires compromises between a myriad of disciplines in order to obtain an optimized result. Typical TRMMs have treated multi-disciplinary problems as a single, monolithic problem and used a single trust region size. The Discipline Specific Trust Region Method presented in this paper allows the use of different size trust regions for each discipline, enabling more efficient use of the design space by the low-fidelity models. The method is demonstrated for an analytical function and an aero-structural problem, involving CFD aerodynamic, FE analysis for the high-fidelity models and a vortex lattice method and kriging response surface for the low fidelity models.

This paper describes an implementation of the popular method of Class-Shape Trans-formation for a... more This paper describes an implementation of the popular method of Class-Shape Trans-formation for aerofoil design within SU 2 software framework. To exploit the adjoint based methods for aerodynamic optimisation within the SU 2 , a formulation to obtain geomet-ric sensitivities from the new parameterisation is introduced, enabling the calculation of gradients with respect to new design variables. To assess the accuracy and efficiency of the alternative approach, two transonic optimisation problems are investigated: an inviscid problem with multiple constraints and a viscous problems without any constraints. Results show the new parameterisation obtaining reliable optimums, with similar levels of performance of the software native parameterisations.

The assimilation of discrete higher fidelity data points with model predictions can be used to ac... more The assimilation of discrete higher fidelity data points with model predictions can be used to achieve a reduction in the uncertainty of the model input parameters which generate accurate predictions. The problem investigated here involves the prediction of limit-cycle oscillations using a High-Dimensional Harmonic Balance method (HDHB). The efficiency of the HDHB method is exploited to enable calibration of structural input parameters using a Bayesian inference technique. Markov-chain Monte Carlo is employed to sample the posterior distributions. Parameter estimation is carried out on both a pitch/plunge aerofoil and Goland wing configuration. In both cases significant refinement was achieved in the distribution of possible structural parameters allowing better predictions of their true deterministic values.

The problem of linear flutter analysis in the presence of structural uncertainty is addressed. Fi... more The problem of linear flutter analysis in the presence of structural uncertainty is addressed. Firstly the sensitivity of the transient decay rate coefficient/damping ratio with resp ect to a large number of uncertain structural parameters is evaluated close to flutter speeds in the aeroelastic model of a heavy rectangular (Goland) wing and a transport wing. Aeroelastic sensitivity analysis enables us to select effective random parameters in the both wing models. Secondly, interval, fuzzy and perturbation methods are used to propagate the structural uncertainty through the aeroelastic analysis resulting in regions of flutter-boundary uncertainty characterised by intervals, fuzzy membership functions and probability density functions. Monte Carlo Simulation is also used for verification purposes. First-order perturbation is generally found to produce results in good agreement with MCS, although there are differences at the tails of the distributions, es pecially for the unstable mode...

Transonic aeroelasticity requires CFD level aerodynamics for first principals prediction. This al... more Transonic aeroelasticity requires CFD level aerodynamics for first principals prediction. This also brings a computational cost, which is overcome in the current paper by the use of eigenvalue based solution methods which avoid the need for time domain simulation. Simulation tools need to be able to predict the influence of variability from model components to be widely useful. In this paper the variability considered arises from the structural model. A systematic study is carried out for the significance of the routes of impact from structural variability, namely through the normal mode frequencies and mode shapes, and from the aerostatic solution. The Goland wing and a jet transport wing are used as test cases, and it is shown that most of the useful information can be obtained efficiently from the normal mode frequency variation if the analysis is done about the mean structural aerostatic solution.

44th AIAA Fluid Dynamics Conference, 2014

This work proposes a novel approach to compute transonic Limit Cycle Oscillations using high fide... more This work proposes a novel approach to compute transonic Limit Cycle Oscillations using high fidelity analysis. CFD based Harmonic Balance methods have proven to be efficient tools to predict periodic phenomena. This paper's contribution is to present a new methodology to determine the unknown frequency of oscillations, enabling HB methods to accurately capture Limit Cycle Oscillations (LCOs); this is achieved by defining a frequency updating procedure based on a coupled CFD/CSD Harmonic Balance formulation to find the LCO condition. A pitch/plunge aerofoil and delta wing aerodynamic and respective linear structural models are used to validate the new method against conventional timedomain simulations. Results show consistent agreement between the proposed and timemarching methods for both LCO amplitude and frequency, while producing at least one order of magnitude reduction in computational time. * Research Fellow, MAIAA † Lecturer, MAIAA

50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2009

Flutter prediction as currently practised is almost always deterministic in nature, based on a si... more Flutter prediction as currently practised is almost always deterministic in nature, based on a single structural model that is assumed to represent a fleet of aircraft. However, it is also recognised that there can be significant variability, even for different flights of the same aircraft. The ...

Flutter prediction as currently practiced is usually deterministic, with a single structural mode... more Flutter prediction as currently practiced is usually deterministic, with a single structural model used to represent an aircraft. By using interval analysis to take into account structural variability, recent work has demonstrated that small changes in the structure can lead to very large changes in the altitude at which flutter occurs (Marques, Badcock, et al., J. Aircraft, 2010). In this follow-up work we examine the same phenomenon using probabilistic collocation (PC), an uncertainty quantification technique which can efficiently propagate multivariate stochastic input through a simulation code, in this case an eigenvalue-based fluid-structure stability code. The resulting analysis predicts the consequences of an uncertain structure on incidence of flutter in probabilistic terms -information that could be useful in planning flight-tests and assessing the risk of structural failure. The uncertainty in flutter altitude is confirmed to be substantial. Assuming that the structural uncertainty represents a epistemic uncertainty regarding the structure, it may be reduced with the availability of additional information -for example aeroelastic response data from a flight-test. Such data is used to update the structural uncertainty using Bayes' theorem. The consequent flutter uncertainty is significantly reduced across the entire Mach number range.

The harmonic balance method is an attractive solution for the computation of periodic flows and c... more The harmonic balance method is an attractive solution for the computation of periodic flows and can be used as an alternative to classical time-marching methods, at a reduced computational cost. The current paper investigates using the Harmonic Balance (HB) method for LCO simulations under uncertainty. The HB formulation is used in conjuction with a non-intrusive polynomial-chaos (NIPC) approach to propagate variability in parameters. Results show the potential of the HB approach together with NIPC to represent uncertainty in nonlinear dynamical systems at a fraction of the cost of performing time accurate simulations.

Aircraft operating conditions and even design specifications can change considerably throughout t... more Aircraft operating conditions and even design specifications can change considerably throughout the design process and life of the aircraft. One cause of such changes are external stores. Wing tip stores can have a significant effect on the flutter boundary and their consequences are difficult to predict, specially in the transonic regime. In this paper, by applying modern aeroelastic stability analysis and uncertainty quantification methods, a wing structure is optimized for delaying the onset of flutter in the presence of tip stores variability. Stochastic information is used to build an objective function that allows the robust optimization of the wing structure against an uncertain wing tip store. Results for the Goland Wing + demonstrate the feasibility of the approach.

The effort integrates high order MP scheme into HB framework for Limit Cycle Oscillations (LCOs) ... more The effort integrates high order MP scheme into HB framework for Limit Cycle Oscillations (LCOs) prediction, with the goal of computational cost reduction. The work heavily relies on a novel approach for LCOs computation presented in previous work . The HB solver with high order MP scheme implementation or high order HB solver is first demonstrated by forced motion, AGARD CT5 case, and proven to have significant accuracy improvement in terms of lift/moment coefficients as well as flow field. A two-dimensional aero-elastic system further proves that high order HB solver is capable of predicting LCOs amplitude and frequency accurately with coarse grid, and at least two times faster than 2 nd order HB solver. Nomenclature b,c = semi chord and chord, respectively M ∞ = freeestream Mach number x m = Moment center α,h = pitch and plung displacement α m ,α 0 = mean angle of attack and pitch oscillation amplitude m = wing mass S α = first moment of inertia of airfoil about elastic axis I α = second moment of inertia of airfoil about elastic axis x α = airfoil static unbalance x α= S α /(mb) r α = Radius of gyration of airfoil about elastic axis, r α =√I α /(mb) C L ,C M = lift and moment coefficient, respectively ω h , ω α = pitch and plung natural frequency U ∞ = freestream velocity V = reduced freestream speed µ = mass ratio ω,κ = frequency and reduced frequency, respectively, κ=ω/ (U ∞ b) τ = Pseudo time step A = Harmonic Balance frequency domain matrix D = Harmonic Balance operator matrix * Research Fellow † Lecture

For the computation of limit cycle oscillations (LCO) at transonic speeds, CFD is required to cap... more For the computation of limit cycle oscillations (LCO) at transonic speeds, CFD is required to capture the nonlinear flow features present. The Harmonic Balance method provides an effective means for the computation of LCOs and this paper exploits its efficiency to investigate the impact of variability (both structural and aerodynamic) on the aeroelastic behaviour of a 2 dof aerofoil. A Harmonic Balance inviscid CFD solver is coupled with the structural equations and is validated against time marching analyses. Polynomial chaos expansions are employed for the stochastic investigation as a faster alternative to Monte Carlo analysis. Adaptive sampling is employed when discontinuities are present. Uncertainties in aerodynamic parameters are looked at first followed by the inclusion of structural variability. Results show the nonlinear effect of Mach number and it's interaction with the structural parameters on supercritical LCOs. The bifurcation boundaries are well captured by the polynomial chaos.

A Reduced-Order Model (ROM) for the prediction of aeroelastic instabilities is presented. The uns... more A Reduced-Order Model (ROM) for the prediction of aeroelastic instabilities is presented. The unsteady nonlinear aerodynamic system is characterised by an Artificial Neural Network (ANN) to a set of network weights. The system is trained on a time history of simultaneous forced oscillation of the normal modes as input and generalised forces as output. Network weights are then used to approximate the aerodynamic force in the structural equation of motion to obtain the structural response. Results from the 3D Goland wing are presented and compared against full order CFD. It is shown that the ROM can predict aeroelastic instabilities with reasonable accuracy at a cost of less than one typical unsteady aeroelastic computation.

53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference<BR>20th AIAA/ASME/AHS Adaptive Structures Conference<BR>14th AIAA, 2012

45th AIAA Aerospace Sciences Meeting and Exhibit, 2007

ABSTRACT

Aircraft design requires compromises between a myriad of disciplines in order to obtain an optimi... more Aircraft design requires compromises between a myriad of disciplines in order to obtain an optimized result. Typical TRMMs have treated multi-disciplinary problems as a single, monolithic problem and used a single trust region size. The Discipline Specific Trust Region Method presented in this paper allows the use of different size trust regions for each discipline, enabling more efficient use of the design space by the low-fidelity models. The method is demonstrated for an analytical function and an aero-structural problem, involving CFD aerodynamic, FE analysis for the high-fidelity models and a vortex lattice method and kriging response surface for the low fidelity models.

This paper describes an implementation of the popular method of Class-Shape Trans-formation for a... more This paper describes an implementation of the popular method of Class-Shape Trans-formation for aerofoil design within SU 2 software framework. To exploit the adjoint based methods for aerodynamic optimisation within the SU 2 , a formulation to obtain geomet-ric sensitivities from the new parameterisation is introduced, enabling the calculation of gradients with respect to new design variables. To assess the accuracy and efficiency of the alternative approach, two transonic optimisation problems are investigated: an inviscid problem with multiple constraints and a viscous problems without any constraints. Results show the new parameterisation obtaining reliable optimums, with similar levels of performance of the software native parameterisations.

The assimilation of discrete higher fidelity data points with model predictions can be used to ac... more The assimilation of discrete higher fidelity data points with model predictions can be used to achieve a reduction in the uncertainty of the model input parameters which generate accurate predictions. The problem investigated here involves the prediction of limit-cycle oscillations using a High-Dimensional Harmonic Balance method (HDHB). The efficiency of the HDHB method is exploited to enable calibration of structural input parameters using a Bayesian inference technique. Markov-chain Monte Carlo is employed to sample the posterior distributions. Parameter estimation is carried out on both a pitch/plunge aerofoil and Goland wing configuration. In both cases significant refinement was achieved in the distribution of possible structural parameters allowing better predictions of their true deterministic values.

The problem of linear flutter analysis in the presence of structural uncertainty is addressed. Fi... more The problem of linear flutter analysis in the presence of structural uncertainty is addressed. Firstly the sensitivity of the transient decay rate coefficient/damping ratio with resp ect to a large number of uncertain structural parameters is evaluated close to flutter speeds in the aeroelastic model of a heavy rectangular (Goland) wing and a transport wing. Aeroelastic sensitivity analysis enables us to select effective random parameters in the both wing models. Secondly, interval, fuzzy and perturbation methods are used to propagate the structural uncertainty through the aeroelastic analysis resulting in regions of flutter-boundary uncertainty characterised by intervals, fuzzy membership functions and probability density functions. Monte Carlo Simulation is also used for verification purposes. First-order perturbation is generally found to produce results in good agreement with MCS, although there are differences at the tails of the distributions, es pecially for the unstable mode...

Transonic aeroelasticity requires CFD level aerodynamics for first principals prediction. This al... more Transonic aeroelasticity requires CFD level aerodynamics for first principals prediction. This also brings a computational cost, which is overcome in the current paper by the use of eigenvalue based solution methods which avoid the need for time domain simulation. Simulation tools need to be able to predict the influence of variability from model components to be widely useful. In this paper the variability considered arises from the structural model. A systematic study is carried out for the significance of the routes of impact from structural variability, namely through the normal mode frequencies and mode shapes, and from the aerostatic solution. The Goland wing and a jet transport wing are used as test cases, and it is shown that most of the useful information can be obtained efficiently from the normal mode frequency variation if the analysis is done about the mean structural aerostatic solution.

44th AIAA Fluid Dynamics Conference, 2014

This work proposes a novel approach to compute transonic Limit Cycle Oscillations using high fide... more This work proposes a novel approach to compute transonic Limit Cycle Oscillations using high fidelity analysis. CFD based Harmonic Balance methods have proven to be efficient tools to predict periodic phenomena. This paper's contribution is to present a new methodology to determine the unknown frequency of oscillations, enabling HB methods to accurately capture Limit Cycle Oscillations (LCOs); this is achieved by defining a frequency updating procedure based on a coupled CFD/CSD Harmonic Balance formulation to find the LCO condition. A pitch/plunge aerofoil and delta wing aerodynamic and respective linear structural models are used to validate the new method against conventional timedomain simulations. Results show consistent agreement between the proposed and timemarching methods for both LCO amplitude and frequency, while producing at least one order of magnitude reduction in computational time. * Research Fellow, MAIAA † Lecturer, MAIAA

50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2009

Flutter prediction as currently practised is almost always deterministic in nature, based on a si... more Flutter prediction as currently practised is almost always deterministic in nature, based on a single structural model that is assumed to represent a fleet of aircraft. However, it is also recognised that there can be significant variability, even for different flights of the same aircraft. The ...

Flutter prediction as currently practiced is usually deterministic, with a single structural mode... more Flutter prediction as currently practiced is usually deterministic, with a single structural model used to represent an aircraft. By using interval analysis to take into account structural variability, recent work has demonstrated that small changes in the structure can lead to very large changes in the altitude at which flutter occurs (Marques, Badcock, et al., J. Aircraft, 2010). In this follow-up work we examine the same phenomenon using probabilistic collocation (PC), an uncertainty quantification technique which can efficiently propagate multivariate stochastic input through a simulation code, in this case an eigenvalue-based fluid-structure stability code. The resulting analysis predicts the consequences of an uncertain structure on incidence of flutter in probabilistic terms -information that could be useful in planning flight-tests and assessing the risk of structural failure. The uncertainty in flutter altitude is confirmed to be substantial. Assuming that the structural uncertainty represents a epistemic uncertainty regarding the structure, it may be reduced with the availability of additional information -for example aeroelastic response data from a flight-test. Such data is used to update the structural uncertainty using Bayes' theorem. The consequent flutter uncertainty is significantly reduced across the entire Mach number range.

The harmonic balance method is an attractive solution for the computation of periodic flows and c... more The harmonic balance method is an attractive solution for the computation of periodic flows and can be used as an alternative to classical time-marching methods, at a reduced computational cost. The current paper investigates using the Harmonic Balance (HB) method for LCO simulations under uncertainty. The HB formulation is used in conjuction with a non-intrusive polynomial-chaos (NIPC) approach to propagate variability in parameters. Results show the potential of the HB approach together with NIPC to represent uncertainty in nonlinear dynamical systems at a fraction of the cost of performing time accurate simulations.

Aircraft operating conditions and even design specifications can change considerably throughout t... more Aircraft operating conditions and even design specifications can change considerably throughout the design process and life of the aircraft. One cause of such changes are external stores. Wing tip stores can have a significant effect on the flutter boundary and their consequences are difficult to predict, specially in the transonic regime. In this paper, by applying modern aeroelastic stability analysis and uncertainty quantification methods, a wing structure is optimized for delaying the onset of flutter in the presence of tip stores variability. Stochastic information is used to build an objective function that allows the robust optimization of the wing structure against an uncertain wing tip store. Results for the Goland Wing + demonstrate the feasibility of the approach.

The effort integrates high order MP scheme into HB framework for Limit Cycle Oscillations (LCOs) ... more The effort integrates high order MP scheme into HB framework for Limit Cycle Oscillations (LCOs) prediction, with the goal of computational cost reduction. The work heavily relies on a novel approach for LCOs computation presented in previous work . The HB solver with high order MP scheme implementation or high order HB solver is first demonstrated by forced motion, AGARD CT5 case, and proven to have significant accuracy improvement in terms of lift/moment coefficients as well as flow field. A two-dimensional aero-elastic system further proves that high order HB solver is capable of predicting LCOs amplitude and frequency accurately with coarse grid, and at least two times faster than 2 nd order HB solver. Nomenclature b,c = semi chord and chord, respectively M ∞ = freeestream Mach number x m = Moment center α,h = pitch and plung displacement α m ,α 0 = mean angle of attack and pitch oscillation amplitude m = wing mass S α = first moment of inertia of airfoil about elastic axis I α = second moment of inertia of airfoil about elastic axis x α = airfoil static unbalance x α= S α /(mb) r α = Radius of gyration of airfoil about elastic axis, r α =√I α /(mb) C L ,C M = lift and moment coefficient, respectively ω h , ω α = pitch and plung natural frequency U ∞ = freestream velocity V = reduced freestream speed µ = mass ratio ω,κ = frequency and reduced frequency, respectively, κ=ω/ (U ∞ b) τ = Pseudo time step A = Harmonic Balance frequency domain matrix D = Harmonic Balance operator matrix * Research Fellow † Lecture

For the computation of limit cycle oscillations (LCO) at transonic speeds, CFD is required to cap... more For the computation of limit cycle oscillations (LCO) at transonic speeds, CFD is required to capture the nonlinear flow features present. The Harmonic Balance method provides an effective means for the computation of LCOs and this paper exploits its efficiency to investigate the impact of variability (both structural and aerodynamic) on the aeroelastic behaviour of a 2 dof aerofoil. A Harmonic Balance inviscid CFD solver is coupled with the structural equations and is validated against time marching analyses. Polynomial chaos expansions are employed for the stochastic investigation as a faster alternative to Monte Carlo analysis. Adaptive sampling is employed when discontinuities are present. Uncertainties in aerodynamic parameters are looked at first followed by the inclusion of structural variability. Results show the nonlinear effect of Mach number and it's interaction with the structural parameters on supercritical LCOs. The bifurcation boundaries are well captured by the polynomial chaos.