On The Nonlinear Dynamics of Two Types of Backup Bearings — Theoretical and Experimental Aspects

Abstract

The possible contact between rotor and stator canfor some cases be considered a serious malfunction that may lead to catastrophic failure. Rotor rub is considered a secondary phenomenon caused by a primary source that leads to a disi'uption of the normal operational condition. It arises from sudden mass unbalance, instabilities generated by aerodynamic and hydrodynamic forces in seals and bearings among others. The contact event gives rise to normal and friction forces exerted on the rotor at impact events. The friction force plays a significant role by transferring some rotational energy of the rotor to lateral motion, impacting the stator. This event results in persistent coupled lateral vibration of the rotor and stator. This paper proposes a new unconventional backup bearing design in order to reduce the rub reiated severity in friction. The idea is to utilize pin connections that center the rotor during impacts. In this way, the rotor is forced to the center and the lateral motion is mitigated. The four pins are passively adjustable, which allows the clearance to be customized. A mathematical model has been developed to capture phenomena arising from impact for the conventional backup bearing (annular guide) and for the new disk-pin backup bearing. For the conventional annular guide setup, it is reasonable to superpose an impact condition to the rub, where the rotor spin energy can be fully transformed into rotor lateral movements. Using a nonideal drive, i.e., an electric motor without any kind of velocity feedback control, it is even possible to almost stop the rotor spin under rubbing conditions. All the rotational energy will be transformed in a kind of "self-excited" rotor lateral vibration with repeated impacts against the housing. The vibration of the housing is coupled through the interaction force. The experimental and numerical analysis shows that for the conventional annular guide setup, the rotational energy is fully transformed into lateral motion and the rotor spin is stopped. However, by employing the new disk-pin design the anaiysis shows that the rotor at impact is forced to the center of the backup bearing and the lateral motion is mitigated. As a result of this, the rotor spin is kept constant.

Dynamic characteristics analysis of a rotor–stator system under different rubbing forms

“…By a point-point contact model, Ma et al [2] investigated fault characteristics of a single span rotor system with two disks when the rubbing between a disk and an elastic rod occurs. In order to reduce the rub related severity in friction, Lahriri et al [3,4] developed a new unconventional backup bearing, which utilizes four pin connections to force the rotor to the center and mitigate the lateral motion. In this way, the full annular rubbing can be changed into four-point rubbing.…”

“…Under this condition, the rubbing force can change the motion direction of the rotor. Aiming at the point rubbing, lots of studies [1][2][3][4][5][6] have been carried out. Han et al [1] analyzed periodic motions of a rotor system with two disks where the rub-impacts occur at fixed limiter for a test rig with dual disks.…”

“…Sawicki et al [28] presented an analytical study of the dynamics and stability of rotors subjected to rubbing, taking account of associated thermal effects. Considering the rub-induced force impact and heat impact together, Tian and Yang [29] The mechanical model of the rotor-stator rubbing mostly adopts the piecewise-smooth model and the classical coulomb friction model [1,3,4,6,12,13,15,22,24]. In recent years, the rotor-stator rubbing simulated by the contact theory has become widely researched [2,5,9,[31][32][33][34][35].…”

Magnetically suspended flywheel in gimbal mount - Test bench design and experimental validation

“…3. The rotor consists of an inner steel shaft 24 with the axial permanent magnet bearing (PMB) 28 bolted onto one end and a compressor wheel 19 bolted onto the 1 Tilting frame, 2 Gimbal, 3 Housing, 4 Accelerometer, 5 Power Supplies for AMBs, 6 Pneumatic Supplies, 7 Pneumatic Actuator Position Sensor, 8 Pneumatic Actuator for Pitching, 9 Pneumatic Actuator for Surging, 10 Rail, 11 Translating Frame, 12 Proximity Probe Conditioners, 13 Electronic Cabinet. other end.…”

Analyzing the use of pins in safety bearings

“…A similar idea was given by Simon [16], who simulated and tested the disc collisions in different safety bearing geometries. The first attempt to introduce the idea of conscripted movement with pins was experimentally tested by Lahriri et al [11], in collaboration with PUC-Rio in 2011, which used an experimental test bench from the works of Alvarado [1] and Segayer [15]. Furthermore, an effective control that avoids a rotor to rub was proposed by Ginzinger [8] using active bearings and further developed by Jiang et al [10], whose works have shown that impacts were prevented and stabilization was achieved.…”