Modal testing of mechanical structures subject to operational excitation forces

Operational Modal Analysis also known as Output Only Modal Analysis has in the recent years been used for extracting modal parameters of civil engineering structures and is now becoming popular for mechanical structures. The advantage of the method is that no artificial excitation need to be applied to the structure or force signals to be measured. All the parameter estimation is based upon the response signals, thereby mini-mising the work of preparation for the test. PCs test case is a controlled lab set-up enabling dyerent parame-ter estimation methods techniques to be used and compared to the Operational Modal Analysis. For Operational Modal Analysis two dyerent estimation techniques are used: a non-parametric technique based on Frequency Domain Decomposition (FDD), and a parametric technique working on the raw data in time domain, a data driven Stochastic Subspace Identijication (SSfl algorithm. These are compared to other methods such as traditional Modal Analysis. 1