On the Analysis of Rotor-Bearing-Foundation Systems

This work presents a methodology to analyse the influence of the foundation or supporting structure on the rotor-bearings system. A frequency response analysis of the complete system was accomplished by considering physical co-ordinates for the rotor-bearings system and principal co-ordinates for the foundation. The mathematical procedure applied a modal approach to the supporting structure, using modal parameters of generalised mass, damping ratio and natural frequency, which were calculated from the frequency response functions (FRF) of an actual structure. Convergence of the method was verified and the effect of the flexible foundation on the complete system response was analysed. A new formulation for the Mixed Co-ordinates method was presented to evaluate the influence of the supporting structure on the directional response of a rotor. An analysis of the directional frequency response function (dFRF) of the complete system was accomplished considering directional co-ordinates for the rotor-bearings system and principal co-ordinates for the foundation. These results were compared to the conventional FRF procedure.