Operational Modal Analysis For Automobile In Operating Conditions

Classically, the modal parameters of a automobile are derived from FRF measurements in well-controlled laboratory conditions using hammer of shaker excitation, this requires additional measurement costs and time. However, the modal vibro-acoustic behavior of an automobile on the road may differ significantly from the one during the laboratory test due to e.g. pre-stress and non-linear behavior of the suspension system in a classic modal analysis in laboratory more modes will be identified, some modes which are less important in the operational conditions. Hence, the need arises to identify a modal model of a automobile in driving condition. In this case, only response data are measurable while the actual loading condition is unknown.Aiming at the defects of classical modal parameter estimation approach, this article studies the technique for modal parameter extraction from structures under operation conditions. The method for system matrix determination is presented by using a block Hankel matrix of raw data and correlation functions. Subsequently, the performance of the methods is critically evaluated for cantilever beam. The results of experiment show that this methods possess the same accuracy as the classical modal estimation method.In this paper, the capabilities and limitations of the subspace identification techniques will be studied on response data on a microbus in driving conditions, The industrial applicability of using this kind of data for a modal analysis has been successfully investigated by doing some analysis on data measured in normal conditions. It has been shown how the modal parameters from in-operation output-only data can be extracted by using correlation-driven stochastic subspace techniques. In-operation modal analysis proves to be a valuable tool for identifying the actual dynamic characteristics of a structure of automobile in use.