Some experience with identification of the Caltech experimental space structure

It is shown that identification of modes with practically the same frequency but with different mode shapes can be carried out in experimental settings. Using multiple-input multiple-output data, distinct modes whose FRFs (frequency response functions) appear as single peaks can be distinguished from their input and output weights. When the peak is modeled with a single mode, some input/output channels may have good peaks, but others will not. Addition of more modes and use of multiple input data result in good fits for all channels if the system behaves in a linear modal manner.