The methods employed to perform rotordynamics calculations of industrial machines are rather standard and usually allow forecasting the dynamic behavior of the considered machines. Anyhow, in some cases, in order to obtain high level of accuracy, the model has to be updated to fit experimental results, and standard modeling methods have to be improved. In this paper, the updating of the torsional model of a steam turbogenerator is presented. In order to fit the eigenfrequencies calculated using the standard model and the natural frequencies measured on-field, a modeling improvement is proposed, considering partially the dynamics of the components usually modeled as rigid disks. The proposed method has also the aim to preserve the physical meaning of the model. Finally, the new model is updated, and a very good fitting is obtained between eigenfrequencies and experimental natural frequencies.

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