Finite element model developed and modal analysis of large scale steam turbine rotor: Quantification of uncertainties and model updating

Abstract

In this work, the effectiveness of a computational framework to handle large scale linear and nonlinear models is presented by calibrating a high-fidelity FE model of a steam turbine rotor with several millions of degrees of freedom, using experimentally identified modal parameters. An extensible framework for Bayesian Uncertainty Quantification and Propagation of complex and computationally demanding physical models, was connected in an efficient way with a numerical code leading to an automated determination of dynamic response of linear and nonlinear mechanical systems. The effect of correlation in the prediction error models postulated in the Bayesian model selection and parameter estimation technique is investigated. First, using an integrated reverse engineering strategy, the digital shape of the three sections of a steam turbine rotor was developed and the final parametric CAD model was created. The finite element model of the turbine were created using tetrahedral solid elements. Due to complex geometry of the structure, the developed model consists of about fifty-five million DOFs. The identification of modal characteristics of the frame is based on acceleration time histories, which are obtained through an experimental investigation of its dynamic response in a support-free state by imposing impulsive loading. The developed computational framework with appropriate substructuring methods, are used for estimating the parameters (material properties) of the finite element model, based on minimizing the deviations between the experimental and analytical modal characteristics (modal frequencies and mode shapes). Direct comparison of the numerical and experimental data verified the reliability and accuracy of the methodology applied. The identified finite element model is representative of the initial structural condition of the turbine and is used to develop a simplified finite element model, which then used for the turbine rotordynamic analysis. Also, this model can be further used for structural health monitoring purposes of the rotor.