Flapping flight has been the focus of research investigations for al- most a century. The early studies were concerned with birds and in- sect flights and mainly carried out by biologists; more recently, the- re has been a significant interest in the modeling and simulation of flapping flights for design of Micro Air Vehicles (MAVs). A tight cou- pled Aerodynamic-Structure-Flight Dynamic model is here presented to analyze flapping wing Micro Air Vehicles’ flight in hovering con- dition. The three sides of the problem interact together influencing each other, generating a full-coupled aeroelastic system. The unstea- dy model developed by Taha et al. is used to describe the aerody- namics: this formulation is able to capture unsteadiness along with non-conventional lift mechanisms typical of flapping flight, such as leading edge vortexes and rotational effects. The wings are described with Euler-Bernoulli beam model, which allows vertical and rotatio- nal displacement at each wing section. Modal expansion is employed to assess the section displacements and Rayleigh-Ritz method is used to approximate the structural natural mode shapes and frequencies. A brief comparison between flexible and rigid model is performed to detect the role of elasticity. Only longitudinal flapping flight dynamic near hover is considered: under specific assumptions, the equations of the longitudinal body motion can be written similarly to those of a conventional aircraft. The simulation is carried out over multi- ple cycles to access the system behave in time. Then, the Optimized Shooting Method is used to find the periodic equilibrium solution of the nonlinear time-periodic system, over which Floquet theory is performed to discuss stability. Finally, a simple feedback control sy- stem is developed on the associated linear time-invariant problem and then applied on the original one to guarantee the target mission (hovering).
Il volo ad ala battente è stato oggetto di ricerca per quasi un secolo. I primi a studiare il volo di uccelli e insetti furono principalmente i biologi; recentemente invece si è sviluppato un notevole interesse verso la modellazione e simulazione di questa tecnica di volo mira- to alla progettazione di Micro Air Vehicles (MAVs). Nella trattazione proposta è presentato un modello aeroelastico e di dinamica del vo- lo accoppiato in senso stretto con lo scopo di analizzare un MAV in configurazione di hovering. I tre lati del problema (aerodinamica, struttura e dinamica del corpo) interagiscono tra di loro influenzan- dosi a vicenda, dando vita ad un problema aeroelastico completo. Il modello instazionario di Taha et al. è utilizzato per descrivere l’aero- dinamica: questa formulazione è in grado di catturare sia l’instazio- narietà che i meccanismi di portanza non convenzionali che caratte- rizzano il volo ad ala battente, come ad esempio i vortici di bordo d’attacco e gli effetti di rotazione. Le ali sono descritte tramite il mo- dello di trave di Eulero-Bernoulli, il quale consente deformazioni fles- sionali e torsionali ad ogni stazione alare in apertura. L’espansione modale è impiegata per stimare le deformazioni, mentre modi e fre- quenze proprie strutturali sono approssimati facendo uso del metodo Rayleigh-Ritz. Per quanto riguarda la dinamica del volo, si considera soltanto il movimento longitudinale del corpo: sotto particolari ipote- si, le equazioni di governo possono essere scritte in analogia a quelle di un veivolo convenzionale. La simulazione è condotta sopra diver- si cicli in modo da poter studiare il comportamento del sistema nel tempo. L’analisi di stabilità è eseguita ricercando inizialmente l’orbita periodica di equilibrio del sistema completo (non lineare e instazio- nario) attraverso il metodo numerico “Optimized Shooting Method”, per poi applicarne la teoria di Floquet. Infine, un semplice sistema di controllo in feedback è progettato per garantire il raggiungimento della configurazione desiderata (hovering).
Accoppiamento aeroelastico e di dinamica del volo per un MAV ad ala battente in configurazione di hovering
SCALCERLE, VALERIO
2016/2017
Abstract
Flapping flight has been the focus of research investigations for al- most a century. The early studies were concerned with birds and in- sect flights and mainly carried out by biologists; more recently, the- re has been a significant interest in the modeling and simulation of flapping flights for design of Micro Air Vehicles (MAVs). A tight cou- pled Aerodynamic-Structure-Flight Dynamic model is here presented to analyze flapping wing Micro Air Vehicles’ flight in hovering con- dition. The three sides of the problem interact together influencing each other, generating a full-coupled aeroelastic system. The unstea- dy model developed by Taha et al. is used to describe the aerody- namics: this formulation is able to capture unsteadiness along with non-conventional lift mechanisms typical of flapping flight, such as leading edge vortexes and rotational effects. The wings are described with Euler-Bernoulli beam model, which allows vertical and rotatio- nal displacement at each wing section. Modal expansion is employed to assess the section displacements and Rayleigh-Ritz method is used to approximate the structural natural mode shapes and frequencies. A brief comparison between flexible and rigid model is performed to detect the role of elasticity. Only longitudinal flapping flight dynamic near hover is considered: under specific assumptions, the equations of the longitudinal body motion can be written similarly to those of a conventional aircraft. The simulation is carried out over multi- ple cycles to access the system behave in time. Then, the Optimized Shooting Method is used to find the periodic equilibrium solution of the nonlinear time-periodic system, over which Floquet theory is performed to discuss stability. Finally, a simple feedback control sy- stem is developed on the associated linear time-invariant problem and then applied on the original one to guarantee the target mission (hovering).File | Dimensione | Formato | |
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https://hdl.handle.net/10589/135238