Experimental analysis of the dynamic behaviour of a turbomachine foundation structure

The main reason for the development of the present cooperative work was the rising necessity of understanding the dynamic behavior of a specific turbine, rigidly coupled to a compressor, and both connected through hydrodynamic bearings to a concrete supporting structure of foundation. The dynamic response, obtained during the machine run up and run down, involves the mechanical behavior of three subsystems, as follow: the rotor system, the connection elements between rotor and foundation (bearings and seals) and, finally, the supporting pedestals and the foundation structure. An interaction between these subsystems is highly important in the analysis process, whether the concrete foundation structure presents some vibrational natural modes significantly participating into the operational frequency range of the machine. The foundation flexibility reacts to the excitation proceeding from the rotor vibration, which also dynamically reacts to a mass unbalancing external excitation force. The main objective of this work is to estimate the Frequency Response Functions on the bearings of the turbine. This estimation is based on some experimental data and on a finite element model of the foundation structure. These FRFs contain the necessary information to verify the influence of the foundation on the dynamic behavior of the rotating system.