Simply structured controllers for vibration suppression in long rotors

Majid Aleyaasin

doi:10.1007/s40435-021-00787-3

Abstract

In this paper suppression of the transient flexural vibrational disturbances in long rotors, with fluid film bearings, is investigated. The rotor is described by a series of distributed shafts connected by the lumped discs, and the system is mounted on lumped fluid film bearings. Upon determination of the dynamic stiffness matrix of the system, the best approximate transfer function matrix description of the rotor, is determined. Initially vibration suppression by simple diagonal Proportional + Integral (PI) controllers is studied and via direct search optimisation techniques the PI parameters which exhibit fast vibration suppression is found. The resulted high integration rate, and low proportional gain PI controller, theoretically provided fast suppression time. However, it is shown that due to the strong coupling effect in the rotor system, and high rate of integration, the closed loop relative stability is weak, and feasibility of controller is questionable. Therefore, an alternative simple first order controller without integration action, that is named “attenuation filter “is suggested that can produce stronger stability and produces significant (not full) vibration suppression. The closed loop multivariable control of the rotor system comprising two vibration sensors and two magnetic actuators using such attenuation filter, is then simulated. The response to step disturbances, has provided 95% suppression with significantly fast response. It is concluded that although the attenuation filter may not provide 100% suppression, but it more reliable since the integration of the error, that results weak stability is avoided.

Highlights

It is nearly four decades that research on active vibration control is continuing to accommodate the needs for providing reliable aircraft engines and active anti-seismic structures
Hathout and Shafei [17] have considered a simple Jeffcott rotor model, they show that a Hybrid Squeeze Film Damper (HSFD) coupled to a servomechanism with Proportional + Integral (PI) controller can reduce the rotor vibration
This paper shows that in distributed-lumped rotor systems, vibrational disturbances can be suppressed by structured first order controllers

Summary

Introduction

It is nearly four decades that research on active vibration control is continuing to accommodate the needs for providing reliable aircraft engines and active anti-seismic structures. Hathout and Shafei [17] have considered a simple Jeffcott rotor model (a hypothetical distributed shaft with its mass concentrated in the middle), they show that a Hybrid Squeeze Film Damper (HSFD) coupled to a servomechanism with PI controller can reduce the rotor vibration The results of their simulation do not indicate a significant degree of rejection. By considering the location of the dominant closed loop pole as an objective function, and the closed loop system stability as a constraint, the range of PI parameters and attenuation filter are determined, that can reduce the suppression time and increase the suppression percentage This is applied to a system comprising two vibration sensors and two magnetic actuators. Since there is not integrator in the structure of alternative controller, the stability weakness, does not exist in attenuation filter

Multivariable models and transfer function estimation

Controller synthesis by optimisation

Numerical example and application

Findings

Gain k2