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Operational Modal Analysis -the technique where modal parameters are estimated without known input forces- has been an accepted tool in advanced mechanical engineering. The technique has its advantages were the modal parameters have to be estimated during the operational conditions as in flight ad on road testing. The paper will discuss the recent state of the art in vibration data acquisition as well as in modal parameter estimation enabling easy use of Operational Modal Analysis. A new data optimisation method, which will enhance the speed of calculation, will be shown Examples from both laboratory set-up and practical examples from automotive applications will be shown.

Operational Modal Analysis, also known as Output Only Modal Analysis or Ambient Modal Analysis, has for over a decade been used for extracting modal parameters from civil engineering structures and is now also being used for mechanical structures, such as on-road and in-flight testing. The advantage of this method is that no artificial excitation needs to be applied to the structure and if artificial loading is required, the force does not need to be measured. All parameter estimation is based on the response signals, thereby minimising the amount of work required for test preparation. As the loading force is unknown in Operational Modal Analysis, specially designed modal parameter estimation techniques need to be used. In classical modal analysis many validation tools are based upon the known force, but if this is not known, other validation tools must be implemented. In addition, different estimation techniques are used, so that results can be compared.