Subspace Identification Combined with New Mode Selection Techniques for Modal Analysis of an Airplane

Linear system identification is an important tool in experimental modal analysis. It allows for the extraction of resonance frequencies, damping ratios and mode shapes of a vibrating structure. In general, the model order is chosen quite high so as to catch all the important characteristics of the structure, even in the presence of large amounts of measurement noise. This often results in the appearance of non-physical, or so-called spurious modes. In this paper we will present a set of heuristic techniques to remove spurious modes from a previously identified model. The advantage of the techniques that will be presented is that they do not rely on statistical information, making them ideally suited for use in combination with subspace identification. The quality of the techniques will be assessed using simulated data and observations from in flight flutter tests. Copyright © 2002 IFAC