Eventos Anais de eventos
COBEM 2017
24th ABCM International Congress of Mechanical Engineering
IDENTIFICATION OF DYNAMIC COEFFICIENTS IN A JOURNAL BEARING FROM EXPERIMENTAL UNBALANCE RESPONSES AND INVERSE PROBLEM
Submission Author:
Alcemir Miliavacca , PR
Co-Authors:
Carlos Alberto Bavastri, Alcemir Miliavacca
Presenter: Alcemir Miliavacca
doi://10.26678/ABCM.COBEM2017.COB17-0116
Abstract
Journal bearings have largely application in industrial turbomachinery. For most cases bearing stiffness and damping parameters governs the vibration characteristics in a rotor-bearing system. However, such coefficients are usually difficult to determine and this fact can produce inaccurate analysis in rotordynamic projects. In addition, during long term operation normal and abnormal machine conditions require its predictive monitoring. This work presents an experimental methodology to determine, simultaneously, the bearing dynamic coefficients and unbalance distribution by inverse problem based on unbalance response measurements and non-linear optimization techniques. The method adjusts the unbalance response simulated by a finite element model to measured curves at run-downs procedure. A hybrid method including genetic algorithm and a direct Nelder-Mead search was used for global optimization. A base formed by eigenvectors of an invariant primary system (real rotor and the initial constant bearing coefficients) was used to obtain the numerical unbalance response in the optimization environment. This base allows find the response of the real rotor (compound system), when bearing coefficients are changing in the optimization environment, in the equivalent way to structural modification techniques. This methodology allows solve the eigenvalue problem only once, reducing the computational time cost. An experimental rotor test rig was apply in this work. The rotor-bearing system include a flexible shaft supported by a plain journal bearing with fixed geometry. The collected data include phase and vibration amplitude for a rotation speed range passing through a critical rotation. The results for bearing parameters are compared to dynamic coefficients calculated by a commercial code. The unbalance magnitude and phase identified are compared to the trial mass applied and its position. The results are analyzed and discussed. Satisfactory results were obtained and the methodology shows to be applicable to identified, simultaneously, the bearing parameters and unbalance excitations.
Keywords
Journal Bearing, Optimization, Rotordynamics, Unbalance Response, identification
