Modal parameter identification using mode isolation

Multiple degree of freedom (MDOF) methods for modal parameter identification in current use deal with all of the modal parameters in a simultaneous fashion in the process of matching measured data to analytical forms. In contrast, the mode isolation algorithm exploits the fact that each mode has unique characteristics that can be used to isolate it from the contribution of other modes. The thesis describes how modal parameters are identified and then refined in a recursive manner. This feature allows the mode isolation method to offer a simple and consistent modal identification methodology that is inherently automatic in nature.; The present work begins by developing the algorithm in an undamped modal formulation. A numerical example of the mode isolation method is presented for a system that was previously studied with the Eigensystem Realization Algorithm (ERA) and Enhanced ERA. Eigenvalues and mode shapes are compared for each algorithm. The results suggest that the mode isolation method is more robust in the treatment of noisy data.; Development of the algorithm continues by extending it to use state space modes as the analytical foundation. This provides the algorithm the ability to cope with generalized damping. Prototypical systems are used to demonstrate that the algorithm is not limited by the presence of modal coupling. A cantilever beam with three attached spring-mass-damper systems is tuned such that the bandwidths of two resonances are commensurate with the natural frequency separation. In addition, a frame structure is constructed to have flexural and rotational natural frequencies that are closely spaced. The addition of damping elements creates bandwidths that blur the individuality of the resonance peaks. Differing levels of noise are imposed on the simulated time-domain response, which is then transformed to the frequency domain. The simulated data is used to illustrate the results of the algorithmic steps. The natural frequencies and damping ratios that result from the procedure are found to match the analytical system properties, with an error that is less than the noise level that was added.