Application of the wavelet based FRFs to the analysis of nonstationary vehicle data

A traditional difficulty in vehicle road at testing is the nonstationary nature of the data. Frequency Response Functions (FRF) and other classical input/output relationships care difficult to obtain accurately due to the uncontrolled time and energy characteristics of the road input to the vehicle. Time-variant methods can be useful in this analysis. This paper presents a new FRF approach based on the wavelet transform. The procedure employs the continuos Grossman-Morlet wavelets calculated in the frequency domain. The method is used to analyse acceleration transmissibilities across an automobile seat in the vertical direction. The study involves transient road data from a speedbump and nonstationary road data from a pave' surface. The method provides new insights with respect to classical time-invariant approaches and would thus seem promising for a wide range of vehicle testing applications. Several observations are made regarding the dynamics of the person/seat system.