Reducing scatter from derived rotational data to determine the frequency response function of connected structures

When two structures are connected together, the frequency response function (FRF) of the coupled system cannot be determined from the translational FRF of each substructure. Rotational FRFs are also needed. These quantities are not usually measured because of the lack of accurate rotational transducers, they can be obtained from the translational measured FRF through a finite difference computation. However errors in measurements and noise problems seriously affect the derived quantities and lead to inefficient estimates. Suggested improvements to the accuracy of rotational parameters derived from experimental translational data include mass correction, smoothing of data, estimates of low and high frequency residuals and appropriate selection of spacing between measurement locations. The results obtained for the assembled system following implementation of these actions are quite satisfactory.