Calculation of Mass-Normalized Modes for Frequency Response Functions Using Acceleration Degrees of Freedom as References

Modal parameter estimation involves solving for mode shapes, damping, and natural frequency. Modal mass can be estimated if drive point acceleration over force (A/F) frequency response functions (FRFs) are available. This paper shows that force over acceleration (F/A) drive point FRFs are also required to calculate modal mass for FRFs with acceleration as references. In practice, F/A FRFs can be obtained either by using drive point accelerations as references or from modal survey tests performed alongside force-limited vibration qualification tests, where force links measure the interface forces. The process will be demonstrated on FRFs from both a simple, lumped-parameter system and on FRF data from test articles.