On the calculation of dynamic derivatives using computational fluid dynamics

In this thesis, the exploitation of computational fluid dynamics (CFD) methods for the flight dynamics of manoeuvring aircraft is investigated. It is demonstrated that CFD can now be used in a reasonably routine fashion to generate stability and control databases. Different strategies to create CFD-derived simulation models across the flight envelope are explored, ranging from combined low-fidelity/high-fidelity methods to reduced-order modelling. For the representation of the unsteady aerodynamic loads, a model based on aerodynamic derivatives is considered. Static contributions are obtained from steady-state CFD calculations in a routine manner. To more fully account for the aircraft motion, dynamic derivatives are used to update the steady-state predictions with additional contributions. These terms are extracted from small-amplitude oscillatory tests. The numerical simulation of the flow around a moving airframe for the prediction of dynamic derivatives is a computationally expensive task. Results presented are in good agreement with available experimental data for complex geometries. A generic fighter configuration and a transonic cruiser wind tunnel model are the test cases. In the presence of aerodynamic non-linearities, dynamic derivatives exhibit significant dependency on flow and motion parameters, which cannot be reconciled with the model formulation. An approach to evaluate the sensitivity of the non-linear flight simulation model to variations in dynamic derivatives is described. The use of reduced models, based on the manipulation of the full-order model to reduce the cost of calculations, is discussed for the fast prediction of dynamic derivatives. A linearized solution of the unsteady problem, with an attendant loss of generality, is inadequate for studies of flight dynamics because the aircraft may experience large excursions from the reference point. The harmonic balance technique, which approximates the flow solution in a Fourier series sense, retains a more general validity. The model truncation, resolving only a small subset of frequencies typically restricted to include one Fourier mode at the frequency at which dynamic derivatives are desired, provides accurate predictions over a range of two- and three-dimensional test cases. While retaining the high fidelity of the full-order model, the cost of calculations is a fraction of the cost for solving the original unsteady problem. An important consideration is the limitation of the conventional model based on aerodynamic derivatives when applied to conditions of practical interest (transonic speeds and high angles of attack). There is a definite need for models with more realism to be used in flight dynamics. To address this demand, various reduced models based on system-identification methods are investigated for a model case. A non-linear model based on aerodynamic derivatives, a multi-input discrete-time Volterra model, a surrogate-based recurrence-framework model, linear indicial functions and radial basis functions trained with neural networks are evaluated. For the flow conditions considered, predictions based on the conventional model are the least accurate. While requiring similar computational resources, improved predictions are achieved using the alternative models investigated. Furthermore, an approach for the automatic generation of aerodynamic tables using CFD is described. To efficiently reduce the number of high-fidelity (physics-based) analyses required, a kriging-based surrogate model is used. The framework is applied to a variety of test cases, and it is illustrated that the approach proposed can handle changes in aircraft geometry. The aerodynamic tables can also be used in real-time to fly the aircraft through the database. This is representative of the role played by CFD simulations and the potential impact that high-fidelity analyses might have to reduce overall costs and design cycle tim

The European Monetary Union: an optimal currency area?

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Adaptive feedforward control design for gust loads alleviation and LCO suppression

An 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

Adaptive feedforward control design for gust loads alleviation and LCO suppression

An 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

On the calculation of dynamic derivatives using computational fluid dynamics

In this thesis, the exploitation of computational fluid dynamics (CFD) methods for the flight dynamics of manoeuvring aircraft is investigated. It is demonstrated that CFD can now be used in a reasonably routine fashion to generate stability and control databases. Different strategies to create CFD-derived simulation models across the flight envelope are explored, ranging from combined low-fidelity/high-fidelity methods to reduced-order modelling. For the representation of the unsteady aerodynamic loads, a model based on aerodynamic derivatives is considered. Static contributions are obtained from steady-state CFD calculations in a routine manner. To more fully account for the aircraft motion, dynamic derivatives are used to update the steady-state predictions with additional contributions. These terms are extracted from small-amplitude oscillatory tests. The numerical simulation of the flow around a moving airframe for the prediction of dynamic derivatives is a computationally expensive task. Results presented are in good agreement with available experimental data for complex geometries. A generic fighter configuration and a transonic cruiser wind tunnel model are the test cases. In the presence of aerodynamic non-linearities, dynamic derivatives exhibit significant dependency on flow and motion parameters, which cannot be reconciled with the model formulation. An approach to evaluate the sensitivity of the non-linear flight simulation model to variations in dynamic derivatives is described. The use of reduced models, based on the manipulation of the full-order model to reduce the cost of calculations, is discussed for the fast prediction of dynamic derivatives. A linearized solution of the unsteady problem, with an attendant loss of generality, is inadequate for studies of flight dynamics because the aircraft may experience large excursions from the reference point. The harmonic balance technique, which approximates the flow solution in a Fourier series sense, retains a more general validity. The model truncation, resolving only a small subset of frequencies typically restricted to include one Fourier mode at the frequency at which dynamic derivatives are desired, provides accurate predictions over a range of two- and three-dimensional test cases. While retaining the high fidelity of the full-order model, the cost of calculations is a fraction of the cost for solving the original unsteady problem. An important consideration is the limitation of the conventional model based on aerodynamic derivatives when applied to conditions of practical interest (transonic speeds and high angles of attack). There is a definite need for models with more realism to be used in flight dynamics. To address this demand, various reduced models based on system-identification methods are investigated for a model case. A non-linear model based on aerodynamic derivatives, a multi-input discrete-time Volterra model, a surrogate-based recurrence-framework model, linear indicial functions and radial basis functions trained with neural networks are evaluated. For the flow conditions considered, predictions based on the conventional model are the least accurate. While requiring similar computational resources, improved predictions are achieved using the alternative models investigated. Furthermore, an approach for the automatic generation of aerodynamic tables using CFD is described. To efficiently reduce the number of high-fidelity (physics-based) analyses required, a kriging-based surrogate model is used. The framework is applied to a variety of test cases, and it is illustrated that the approach proposed can handle changes in aircraft geometry. The aerodynamic tables can also be used in real-time to fly the aircraft through the database. This is representative of the role played by CFD simulations and the potential impact that high-fidelity analyses might have to reduce overall costs and design cycle time

Anna Banti da «Paragone» all’«Approdo letterario». Venticinque anni di critica cinematografica d’autrice

L’analisi si propone di testimoniare, attraverso l’esame degli articoli di critica cinematografica di Anna Banti, un caso di pratica intellettuale d’autrice nel quadro italiano del medio Novecento. L’attiva partecipazione della scrittrice — oggi conosciuta come romanziera, ma non altrettanto per il suo ruolo di voce critica — al dibattito critico, cinematografico e letterario dello scorso secolo dimostra il ruolo di operatrice culturale da lei svolto. L’articolo esamina gli scritti di critica cinematografica di Anna Banti considerando le peculiari modalità di analisi utilizzate e il nodo problematico fondamentale che attraversa tali testi — l’indagine sul rapporto tra la rappresentazione artistica e il reale —, allo scopo di indicarne le caratteristiche fondamentali. L’intento è di illustrare la specificità del pensiero critico di quest’intellettuale e, contestualmente, di metterne in luce la partecipazione al dibattito cinematografico e letterario del periodo.À travers l’étude des articles de critique cinématographique écrits par Anna Banti, cette étude examine un cas d’activité intellectuelle d’auteure, dans le panorama culturel italien du milieu du xxe siècle. Anna Banti est aujourd’hui reconnue comme une romancière importante, mais moins en tant que voix critique. Ses articles de critique cinématographique illustrent son rôle d’acteur culturel dans le débat cinématographique et littéraire du siècle dernier. Cet essai se focalise sur la méthode d’analyse de l’écrivaine ainsi que sur le thème qui revient le plus souvent dans ses écrits de critique cinématographique, la relation entre la représentation artistique et le réel. Le but principal est de faire ressortir la spécificité de son approche critique, ainsi que sa participation au débat cinématographique et littéraire de l’époque.Through the examination of Anna Banti’s film criticism, this essay aims at testifying to the intellectual practice of a female author within the Italian context of the mid-twentieth century. Banti is today widely recognized as an important novelist, much less as a critical voice. Her active participation in the critical, cinematographic and literary debate of the last century demonstrates the role she played as a cultural operator. The article examines Banti’s writings on film criticism, considering the peculiar modes of analysis she used and the main problematic node that runs through these texts—the investigation of the relationship between artistic representation and reality. The intent is to illustrate the specificity of her critical thought and, at the same time, to highlight her participation in the cinematographic and literary debate of that period

The role of different lifestyles on elderly’s Health. Data from the MentDis_ICF65+ Study

Due to demographic change mental health of the elderly increasingly becomes a focus of interest. Specifically aging can bear considerable consequences for physical and mental health, since it comprises numerous stress factors (e.g. social isolation, reduced functional capacity, somatic comorbidity). Sedentary habits, especially TV viewing, have been identified as potential risk factors for people’s health. The present research project is part of a broader international research project called MentDis_ICF65+, funded by the European Community, on the prevalence and incidence of Mental Disorders in the elderly. The MentDis_ICF65+ research group comprises 7 partners from 6 different European Countries and associated states (Italy – University of Ferrara, Germany – University of Hamburg and University of Dresden, UK - Royal College of Psychiatrists, London, Switzerland – University of Geneva, Spain- Complutense University, Madrid, Israel – Jerusalem University) and has collected data from around 3000 people in the general population between 65 and 84 years old. From these data we analyzed the association between physical and mental health and sedentary habits, in particular TV viewing, in a subsample of 1383 elderly people. There are indeed associations between TV viewing and medical and mental health problems. Results support therefore the emerging indication that as well as promoting programs for increasing physical activity levels in the elderly, it would be also extremely important to raise awareness of the negative consequences of sedentary habits, TV viewing in particular, and design programs to help people reducing the time spent in such in-activity

A modified airfoil-based piezoaeroelastic energy harvester with double plunge degrees of freedom

In this letter, a piezoaeroelastic energy harvester based on an airfoil with double plunge degrees of freedom is proposed to additionally take advantage of the vibrational energy of the airfoil pitch motion. An analytical model of the proposed energy harvesting system is built and compared with an equivalent model using the well-explored pitch-plunge configuration. The dynamic response and average power output of the harvester are numerically studied as the flow velocity exceeds the cut-in speed (flutter speed). It is found that the harvester with double-plunge configuration generates 4%–10% more power with varying flow velocities while reducing 6% of the cut-in speed than its counterpart

Extension of analytical indicial aerodynamics to generic trapezoidal wings in subsonic flow

Analytical indicial aerodynamic functions are calculated for several trapezoidal wings in subsonic flow, with a Mach number 0.3≤ Ma≤ 0.7. The formulation herein proposed extends well-known aerodynamic theories, which are limited to thin aerofoils in incompressible flow, to generic trapezoidal wing planforms. Firstly, a thorough study is executed to assess the accuracy and limitation of analytical predictions, using unsteady results from two state-of-the-art computational fluid dynamics solvers as cross-validated benchmarks. Indicial functions are calculated for a step change in the angle of attack and for a sharp-edge gust, each for four wing configurations and three Mach numbers. Then, analytical and computational indicial responses are used to predict dynamic derivatives and the maximum lift coefficient following an encounter with a one-minus-cosine gust. It is found that the analytical results are in excellent agreement with the computational results for all test cases. In particular, the deviation of the analytical results from the computational results is within the scatter or uncertainty in the data arising from using two computational fluid dynamics solvers. This indicates the usefulness of the developed analytical theories