Έλεγχος διακλαδώσεων ισορροπίας σημείων και οριακών κύκλων σε περιστρεφόμενους άξονες υψηλών ταχυτήτων με χρήση ενεργών αεροεδράνων

Παπαδόπουλος, Αναστάσιος; Papadopoulos, Anastasios

dc.contributor.author	Παπαδόπουλος, Αναστάσιος	el
dc.contributor.author	Papadopoulos, Anastasios	en
dc.date.accessioned	2023-01-24T09:26:01Z
dc.date.available	2023-01-24T09:26:01Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/56867
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.24565
dc.rights	Default License
dc.subject	Μη-Γραμμική Δυναμική	el
dc.subject	Ενεργά Αεροέδρανα	el
dc.subject	Περιστρεφόμενοι Άξονες	el
dc.subject	Έλεγχος	el
dc.subject	Ευστάθεια	el
dc.subject	Active Gas Foil Bearings	en
dc.subject	Nonlinear Dynamics	en
dc.subject	Rotating Shafts	en
dc.subject	Control	en
dc.subject	Stability	en
dc.title	Έλεγχος διακλαδώσεων ισορροπίας σημείων και οριακών κύκλων σε περιστρεφόμενους άξονες υψηλών ταχυτήτων με χρήση ενεργών αεροεδράνων	el
dc.title	Controlling bifurcations of fixed point and limit cycle equilibria in high - speed rotors utilizing active gas foil bearings	en
heal.type	bachelorThesis
heal.classification	Δυναμική	el
heal.language	en
heal.access	free
heal.recordProvider	ntua	el
heal.publicationDate	2022-10-20
heal.abstract	High speed rotors on gas foil bearings (>200kRPM) are applications of increasing interest due to their potential to increase the power to weight ratio in machines and also establish oil-free design solutions. The gas lubrication principles render lower – compared to oil – power losses and increase the threshold speed of instability in rotating systems. However, self-excited oscillations may still occur at DN (Diameter [mm] X Rotating Speed [RPM]) values much lower than the speed of sound [DN<6.5e6], these being usually triggered through Hopf bifurcation of a fixed point equilibrium (fully balanced rotor) or secondary Hopf (Neimark-Sacker) bifurcation of periodic limit cycles (unbalanced rotor). Bifurcation-free operation is a target in the dynamic design of high-speed machines like automotive turbosystems, turbopumps for rocket propulsion, small jet engines for drones or UAVs, and others; this is not always achievable with conventional rotor-bearing design. In this work, an active gas foil bearing is presented as a novel configuration including a number of piezoelectric actuators which shape the foil component through linear feedback control. At first, an enhanced finite element model for the thin foil mounted in a number of PZTs, is developed in order to avoid shear lock effect. Second, the gas-structure interaction (FSI) is modeled through Reynolds equation for compressible flow. A simple rotor model consisting of a rigid rotor and 2 gas foil bearings is then defined, and the dynamic system is composed with its unique source of nonlinearity to be the nonlinear impedance forces from the gas to the rotor and to the foil. The third milestone includes a linear feedback control scheme to stabilize (pole placement) the dynamic system, linearized around a speed depended equilibrium (balanced rotor). Linear control is found to be insufficient to stabilize the system when certain perturbations apply. Further to that, unbalanced rotor systems (most common case) follow trajectories which extend far from fixed point equilibria, emerging strong nonlinear impedance forces from the bearings. Linear feedback control is applied in the dynamic system utilizing polynomial feedback functions in order to overcome the problem of instability. Case studies include a small (30mm) and a large (100mm) bearing, both at operating range with upper bound of speed at DN = 6.5e6; different foil thickness is also included in the case study.	en
heal.advisorName	Χασαλεύρης, Αθανάσιος	el
heal.advisorName	Chasalevris, Athanasios	en
heal.committeeMemberName	Antoniadis, Ioannis	el
heal.committeeMemberName	Papadopoulos, Evangelos	el
heal.academicPublisher	Εθνικό Μετσόβιο Πολυτεχνείο. Σχολή Μηχανολόγων Μηχανικών. Τομέας Μηχανολογικών Κατασκευών και Αυτομάτου Ελέγχου	el
heal.academicPublisherID	ntua
heal.numberOfPages	55 σ.	el
heal.fullTextAvailability	false