Εξάλειψη διακλαδώσεων σε συστήματα αξόνων αεροεδράνων, εφαρμόζοντας αριθμιτκή συνέχιση με ενσωματωμένη βελτιστοποίηση σχεδιασμού

Παπαφράγκος, Παναγιώτης; Papafragkos, Panagiotis

dc.contributor.author	Παπαφράγκος, Παναγιώτης	el
dc.contributor.author	Papafragkos, Panagiotis	en
dc.date.accessioned	2022-12-13T09:18:15Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/56433
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.24131
dc.rights	Αναφορά Δημιουργού-Μη Εμπορική Χρήση-Όχι Παράγωγα Έργα 3.0 Ελλάδα	*
dc.rights.uri	http://creativecommons.org/licenses/by-nc-nd/3.0/gr/	*
dc.subject	Εξάλειψη διακλαδώσεων	el
dc.subject	Άξονες	el
dc.subject	Αεροέδρανα	el
dc.subject	Αριθμητική συνέχιση	el
dc.subject	Βελτιστοποίηση σχεδιασμού	el
dc.subject	Bifurcation elimination	en
dc.subject	Rotor	en
dc.subject	Gas foil bearings	en
dc.subject	Numerical continuation	en
dc.subject	Design optimization	en
dc.title	Εξάλειψη διακλαδώσεων σε συστήματα αξόνων αεροεδράνων, εφαρμόζοντας αριθμιτκή συνέχιση με ενσωματωμένη βελτιστοποίηση σχεδιασμού	el
dc.title	Bifurcation elimination in rotor gas bearing systems applying numerical continuation with embedded design optimization scheme	en
heal.type	bachelorThesis
heal.classification	Δυναμική μηχανών	el
heal.classification	Rotordynamics	en
heal.dateAvailable	2023-12-12T22:00:00Z
heal.language	en
heal.access	embargo
heal.recordProvider	ntua	el
heal.publicationDate	2022-07-28
heal.abstract	This thesis investigates the quality of bifurcations presented in a dynamic system consisting of a balanced or unbalanced elastic Jeffcott rotor mounted on gas-foil bearings, and assesses the stability of limit cycle motions for specific values of operating parameters and key design properties of the system, like rotor stiffness, foil stiffness and damping. The study aims to the design optimization of gas bearings in order to eliminate bifurcations, as they may compromise the operability of rotating systems, or increase noise level. This work applies the pseudo arc length continuation in combination with collocation method for the evaluation of limit cycles (periodic motions) as the bifurcation parameter changes (this being operating parameter or design property) of the non-autonomous system. The energy flow among the components of the system is evaluated for various design sets of bump foil properties, rotor stiffness and unbalance magnitude. The project presents a methodology to retain the dissipating work at positive values during the periodic limit cycle motions caused by unbalance. An optimization technique is embedded in the pseudo arc length continuation of limit cycles, those evaluated (when exist) utilizing an orthogonal collocation method. The optimization scheme considers the bump foil stiffness and damping as the variables for which bifurcations do not appear in a certain speed range. It is found that secondary Hopf (Neimark-Sacker) bifurcations, which trigger large limit cycle motions, do not exist in the unbalanced rotors when bump foil properties follow the optimization pattern. Period doubling (flip) bifurcations are possible to occur, without driving the rotor in high response amplitude. Different design sets of rotor stiffness and unbalance magnitude are investigated for the efficiency of the method to eliminate bifurcations. Aiming to adjustable gas bearings as a future technology, the quality of the optimization pattern allows real time optimization, and in this way gas foil properties may shift values during operation, eliminating bifurcations and allowing operation in higher speed margins. The present study is considered as precursor for smart gas bearing applications under development.	en
heal.advisorName	Χασαλεύρης, Αθανάσιος	el
heal.committeeMemberName	Σπιτάς, Βασίλειος	el
heal.committeeMemberName	Αντωνιάδης, Ιωάννης	el
heal.academicPublisher	Εθνικό Μετσόβιο Πολυτεχνείο. Σχολή Μηχανολόγων Μηχανικών	el
heal.academicPublisherID	ntua
heal.numberOfPages	57 σ.	el
heal.fullTextAvailability	false