1,721,028 research outputs found
Linear reduced order modelling for gust response analysis using the DLR-TAU code
No full textA unified modelling approach, using computational fluid dynamics, to calculate the flutter stability and dynamic gust response of realistic aircraft models is outlined. The approach uses an eigenmode decomposition of the coupled problem combined with a (linear or nonlinear) Taylor expansion of the nonlinear, full order residual function. The necessary information for the flutter stability analysis, aerodynamic influence coefficients, is readily calculated. The aerodynamic influence is presented in a form which is in line with industrial practice using corrected doublet lattice method aerodynamics. Based on the stability analysis, eigenmodes are used to produce a reduced model for the gust response analysis. With the projection of the full order system on the eigenmode basis, a small set of equations governing the dominant dynamics is found. The approach is general to work with a variety of numerical schemes for the different physics involved in the coupled problem. In addition, arbitrary parameter variations can be included in the reduced model. The methods are used herein for the computational fluid dynamics solver DLR–TAU, which is adopted by industry throughout Europe, for aerodynamics. Structures are described by the standard modal form of a finite–element model. While pre–computations to evaluate the reduced order model require heavy computational resources, the reduced model can be solved in a matter of seconds on a desktop machine. The test cases presented to demonstrate the modelling capability include a wing structure and a realistic passenger aircraf
A nonlinear controller for flutter suppression: from simulation to wind tunnel testing
No full textActive control for flutter suppression and limit cycle oscillation of a wind tunnel wing section is presented. Unsteady aerodynamics is modelled with strip theory and the incompressible two-dimensional classical theory of Theodorsen. A good correlation of the stability behaviour between simulation and experimental data is achieved. The paper focuses on the introduction of a nonlinearity in the plunge degree of freedom of an experimental wind tunnel test rig and the design of a nonlinear controller based on partial feedback linearization. To demonstrate the advantages of the nonlinear synthesis on linear conventional methods, a linear controller is implemented for the nonlinear system that exhibits limit cycle oscillations above the linear flutter speed. The controller based on partial feedback linearization outperforms the linear control strategy based on pole placement. Whereas feedback linearization allows to suppress fully the limit cycle oscillations, the pole placement fails to achieve any significant reduction in amplitude
Adaptive feedforward control design for gust loads alleviation and LCO suppression
No full textAn adaptive feedforward controller is designed for gust loads alleviation and limit cycle oscillations suppression. Two sets of basis functions, based on the finite impulse response and modified finite impulse response approaches, are investigated to design the controller for gust loads alleviation. Limit cycle oscillations suppression is shown by using the modified finite impulse response controller. Worst case gust search is performed by using a nonlinear technique of model reduction to speed up the costs of calculations. Both the “one–minus–cosine” and Von Kármán continuous turbulence gusts of different intensities were generated to examine the performance of controllers. The responses of these two types of gust can be reduced effectively by finite impulse response controller in the whole process, while the modified finite impulse response controller is found to increase the loads during the initial transient response. The above two types of gust induced limit cycle oscillations were used to test the modified finite impulse response controller. Results show that it can suppress limit cycle oscillations to some exten
Modeling of unsteady aerodynamic loads
No full textTime-accurate solutions of the Euler or Navier-Stokes equations are still nowadays a computationally expensive approach for applications where a magnitude of parameters has to be investigated. This work focuses on flight dynamics-related studies. The generation of several low-order models for the evaluation of unsteady and non-linear aerodynamic loads are investigated. The validity of low-order models presented is assessed by comparing the model output with unsteady time-accurate Computational Fluid-Dynamics (CFD) simulations. The test case is the NACA 0012 airfoil. The low-order models considered are: a non-linear model based on aerodynamic derivatives, a Volterra model, a surrogate-based recurrence-framework model, linear indicial functions and radial basis functions trained with neural networks
Investigating the Piaggio Avanti design using CEASIOM
No full textIn early steps of aircraft design the unification of configuration definition is important to avoid user–input errors. Also coupling with each other can strengthen different tools with different specifications simultaneously provided that the geometry definition is transferred with minimum data loss. This is vitally useful especially when geometry data is transferred in order to perform high–fidelity analysis. This paper reports the analysis for the pitch control of a three–lifting–surface aircraft Piaggio Avanti using CEASIOM, a tool–chain software for aircraft preliminary design, with the baseline configuration coming from the conceptual design code AAA, linked by a common name–space CPACS for the means of data collaboratio
Assessing the impact of aerodynamic modelling on manoeuvring aircraft
No full textThis paper investigates the impact of aerodynamic models on the dynamic response of a free-flying aircraft wing. Several options for the aerodynamics are evaluated, from two-dimensional thin aerofoil aerodynamics and unsteady vortex-lattice method up to computational fluid dynamics. A nonlinear formulation of the rigid body dynamics is used in all cases. Results are generated using a numerical framework that will allow in the near future multi-disciplinary fluid/structure/flight analysis. In this paper, flexibility effects are neglected. A validation for fluid/flight models is presented. The well-established approach based on stability derivatives is also used, and is found in good agreement with solutions obtained from linear aerodynamic models. The uncertainties in predicted trajectories of the free-flying wing are, in general, large and attributed to the aerodynamics only. This suggests that a careful control law synthesis should be done to account for uncertainties from modelling technique
GUESS: Generic unknowns estimator for aircraft structural sizing
No full textThis document constitutes a summary of work for eligibility of a MSc degree from the Department of Aerospace Engineering, Politecnico di Milano (POLIMI), Italy, and Department of Aeronautics (Flygteknik), Royal Institute of Technology (KTH), Stockholm, Sweden. The work has been performed over the period of one year, from September 2007 to October 2008. It is with great fortune I have had the opportunity to join the 6th European Framework SimSAC for preliminary structural sizing and aeroelastic analysis for fixed-wing aircrafts. During the time I spent giving my own contribution to the project, I had the opportunity to meet excellent persons and accomplishing professional and pedagogicalabilities.Expressions of gratitude are forwarded to my supervisor Professor Sergio Ricci (POLIMI) and Arthur Rizzi (KTH) for their invaluable advice and insight during the course of this degree. I have to recognize the helps given by several PhD students, just to remember some of them: Luca Cavagna (POLIMI), Adrien Berard (KTH) and last, but not least, Simone Crippa (KTH). After the work performed within the project, I decided to apply for a PhD position. It is with great happiness that I will move in University of Liverpool, UK, to became a PhD student with Professor Badcock, K.J.A final word of profound thanks goes to my family for the untold amount of patience, understanding and support exhibited by them during the protracted period of accomplishing this milestone
Reduction of nonlinear models for control applications
No full textA systematic approach to the model reduction of high-fidelity fluid-structure-flight models and the subsequent flight control design for very flexible aircraft is considered. The test case is for an unmanned aerial vehicle. The full order model involves the geometrically-exact nonlinear beam equations coupled with a linear aerodynamic model. A nonlinear reduced order model is derived to reduce the computational cost and dimension of the full order nonlinear system while retaining the ability to predict nonlinear effects. The approach uses information on the eigenspectrum of the coupled system Jacobian matrix and projects the system through a series expansion onto a small basis of eigenvectors representative of the full order dynamics. The small dimension model is then used to design control laws for applications sush as load alleviation. Results are presented for an aerofoil section and an unmanned aerial vehicle model to illustrate the approach
Active control for flutter suppression: an experimental investigation
No full textThis paper describes an experimental study involving the implementation of the method of receptances to control binary flutter in a wind-tunnel aerofoil rig. The aerofoil and its suspension were designed as part of the project. The advantage of the receptance method over conventional state-space approaches is that it is based entirely on frequency response function measurements, so that there is no need to know or to evaluate the system matrices describing structural mass, aeroelastic and structural damping and aeroelastic and structural stiffness. There is no need for model reduction or the estimation of unmeasured states, for example by the use of an observer. It is demonstrated experimentally that a significant increase in the flutter margin can be achieved by separating the frequencies of the heave and pitch modes. Preliminary results from a complementary numerical programme using a reduced-order model, based on linear unsteady aerodynamics, are also presente
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