Frequency based model mixing for machine condition monitoring

Creating holistic, efficient models for vibration-based monitoring applications containing rotor systems is still challenging. Reasons for these difficulties are application-dependent housing peripheries and inaccessible measurement points. Due to the complexity of these systems, numerical modeling is cumbersome and the application of experimental techniques only is restricted. With this contribution, we propose a solution approach for combining the experimental determined housing dynamics with a numerical rotor model. The method performs in the frequency domain, based on Lagrange Multiplier Frequency Based Substructuring (LM FBS) and System Equivalent Model Mixing (SEMM) as a closely related method. Our technique rests upon three parts: Firstly, a finite elements rotor model with reduced degrees of freedom (DoF) is created and the complete Frequency Response Function (FRF) matrix for all interface and input DoF is calculated. Secondly, the entire FRF-matrix is coupled with the simulatively determined transfer functions of the housing. Thirdly, FRFs of a collocated subset DoF of the rotor-assembly are experimentally measured. These are expanded to the FRF-matrix of the coupled model using the SEMM method. As a result, we get the complete FRF-matrix being full rank and containing dynamics of the entire, coupled system. Finally, the proposed methodology is experimentally validated based on an exemplary transfer function.