Victor Rastelli

Non-Linear Behaviors in the Motion of a Magnetically Supported Rotor on the Catcher Bearing During Levitation Loss:An Experimental Description

Recent developments improving load capacity foretell the practical implementation of Active Magnetic Bearings (AMB) on industrial level, pushed by the advantages of reduced wear and higher speeds that they make available. However, the possibility of an eventual power failure forces the use of back-up (catcher) bearings, which usually are of the ball bearing type. The back-up bearings present a clearance between the shaft and the inner race, such that there is not contact during normal operation. On a power failure or an emergency stop, the rotor is only supported by the catcher bearings. Thus, the rotor motion within the clearance results on a succession of impacts, contact and non-contact intervals producing a non-linear behavior of the system. The complexity of this non-linear behavior prevents the use of traditional methods for the design of the catcher bearings, calling for the need of extensive experimentation and previous experience in their dimensioning process. Here, the response of a rigid rotor, supported by a pivot on the drive side and a magnetic bearing on the other side, is measured during the emergency stop from several operating speeds. Non-linear analysis tools, such as Poincare Maps and Bifurcation Diagrams, are employed to demonstrate the non-linear characteristics of the motion, which in some conditions is shown to become chaotic with a vibration limit cycle. The rotor motion on the catcher bearings (with the magnetic bearing deactivated) is measured at constant running speeds. The limit cycles and chaotic attractors are described, showing the relation of the non-linear effects to the rotational speed.Copyright

Simple Model for a Magnetic Bearing System Operating on the Auxiliary Bearing

The present work studies the behavior of a magnetic bearing supported rotor when the flow of electric current to the magnetic actuator is suppressed In this condition the rotor is supported by the auxiliary bearing, which has looseness with the rotor, generating a series of impacts between these components. For the study of this state, a model of a flexible rotor is proposed, and the impacts are simulated using kinematical restitution coefficient theory. The results obtained from the theoretical model are compared with experimental data taken on a test rig using tools for non linear systems analysis such bifurcation diagrams. The comparison shows that, besides the simplification of the contact, the model predicts ranges chaotic, quasi-periodic, and periodic motions in the test rig.Copyright

A Test Rig for Air Bearings Rotordynamic Coeffcients Measurement

This paper describes the design and manufacturing of an experimental facility for measurement of equivalent stiffness and damping of air bearings. For these preliminary tests, the shaft moves only in two perpendicular directions, laying in the rotation plane, thus producing 2×2 characteristic matrices. However, the rig can be easily modified to measure rotordynamic characteristics related to angular motion of the journal and measuring 4×4 matrices. The testing facility uses an experimental magnetic bearing suspension system that allows imposing any given orbit to the shaft, during the testing experiments. All individual parts, as well as the assembly, were dynamically studied to determine their modal response and optimize it according to the test rig’s operating frequency range. The principle of operation is to produce a shaft orbit using the magnetic suspension system and measuring the forces generated on the test bearing housing. Then, the stiffness and damping coefficients are calculated using an iterative parameter identification algorithm (a modification of the IVF method). The force measurement is performed via three load cells placed in a triangle configuration around the test bearing housing. All data is gathered and processed using PC based data acquisition boards and software. The present design allows testing air bearings up to 44 mm in external diameter and a bandwidth of 0 Hz to 1.000 Hz. Preliminary testing was performed on this research that demonstrates the capability of the apparatus to measure the dynamic properties with ease and accuracy.© 2005 ASME

Burst mode dither control of automotive brake squeal

Brake squeal is an annoying phenomenon, generally occurring when vehicles brake at slow speeds. Significant effort is expended by the automotive industry to avoid squeal during the development of brake systems. Nonetheless, expensive warranty claims still occur when such efforts are not completely successful. Recent research demonstrated that introducing dither control into a brake is an effective means of suppressing squeal. Dither control is a method by which high‐frequency disturbances are introduced into a system. This suppresses the friction induced squeal response at lower frequencies, thus eliminating the audible brake squeal. Dither control, when applied at a 100% duty cycle, is an effective means of suppressing brake squeal. This presentation focuses on the potential to use burst mode dither control for squeal suppression. Burst mode dither control is characterized by duty cycles of less than 100%. Dither is introduced to a brake by placing a piezoelectric stack actuator in the piston of a floati...

A Test Rig for Air Bearings Dynamic Characterization

This paper describes the design and operation of an experimental facility for measurement of equivalent stiffness and damping of air bearings. The rig uses two magnetic bearings to impose any given orbit to the journal, including displacement in two perpendicular directions on the rotation plane and tilting on the conical mode. Dynamic forces are measured directly on the test bearing housing. Data is gathered and processed using PC based data acquisition boards and software. Only the stiffness and damping coefficients of the fluid film are calculated as a function of the excitation frequency, being it synchronous or not. The present design allows testing air bearings up to 44 mm in external diameter and at frequencies up to 1 KHz. Preliminary testing was performed on this research that demonstrates the capability of the apparatus to measure the dynamic properties with ease and accuracy.Copyright

A Simple Kinematic Model for the Behavior of a Magnetically Levitated Rotor Operating in Overload Regime

Currently, the use of magnetic levitation systems has incremented in lieu of the many advantages they present respect to conventional systems. They provide frictionless operation and thus, a wearless life, eliminate the need for lubricants and allow for active vibration control. However, there are some limitations to their use, the dynamic load capacity is restricted by the magnetic properties of the materials used in their constructions and, therefore, their tolerance to large dynamic loads, such as in the case of blade loss or similar sudden failures, is small. For these cases, as well as for the case of bearing power loss, all commercial magnetic suspensions contain a safety backup system, usually consisting of roller bearings that avoid contact between stationary and rotating parts. The present work analyses the behavior of a rotor supported by a magnetic radial bearing on the non-drive end, which is operated in an overload regime. In this regime, a series of impacts occurs between the rotor and the backup bearing, which results on a highly non-linear system that might become unstable depending on the geometry, the control algorithm, the speed and excitation conditions. A non-linear model is proposed. The equations are separated into two regimes, one when the rotor is levitated and one during contact with the backup bearings; the contact is modeled by kinematic conditions. The magnetic bearing forces are estimated using a non-linear model and a PID algorithm is considered as a system’s control strategy. Rigid body theory for planar collision is considered for description of impacts between the backup bearing and the rotor.Copyright

Environmental pollution and noise control of two power generator sets placed into a recreation area

This paper deals with the noise control of two power generator sets of 545 kW each, located in a Venezuelan resort. The generator sets made a noise level of 73 dB(A) at a distance of 47 m from the source, where are located the guest rooms. This level was far from the legal regulations for allowable environmental conditions. A noise enclosure with air silencers was proposed to reach a final level of 53 dB(A) at the guest accommodations. Two aspects must be taken into account, the noise reduction and the ventilation specifications of the generator sets, in order to keep the operational temperature. The final noise level was measured at 54 dB(A) and the pressure loss of the silencers was well placed into the ventilation specifications.

A mathematical model for the evaluation and prediction of the mean energy level of traffic noise in Caracas

The increase of the population in capital cities has provoked a serious increase in the acoustical pollution, where the real cause is the traffic noise. Over ten years, sound levels have been measured in several points in the city of Caracas. The main objective was to establish a mathematical model for the mean energy level of traffic noise. This model is a modification and improvement of the model that was used in Germany and Italy. Parameters of the fundamental equations were obtained by the use of large experimental data. In the particular case of Venezuela, an innovation was introduced by the consideration of the motorcycle noise. The obtained model can be used to predict noise pollution in cities and contour maps can be made as well.