A single-degree-of-freedom approach to response perturbation due to feature variability

Abstract

This paper presents a technique to assess the impact on model predictions due to feature perturbations on harmonically forced fluid-loaded structural acoustic models. The perspective taken is one of knowledge of a reference state, with a desire to determine the impact on the total radiated acoustic power due to perturbations in the reference state. Such perturbations change the predicted resonance frequencies of a structure under consideration, and hence, change the predicted response amplitudes. The method uses a single-degree-of-freedom response model in the local region of each fluid-loaded resonance, coupled with eigenvalue sensitivities, to estimate the perturbation impact. The sensitivity of the eigenvalues to changes in model detail is derived based on variations in the spatial representation of attached features (e.g., point versus distributed attachments). Elements of the analysis method are not necessarily restricted to model perturbations nor acoustic power, rather they may be used to assess the perturbation of any quadratic response quantity of interest due to changes in resonance frequency. The analysis reveals that the bandwidth of response perturbation increases directly with increasing resonance frequency. This ‘‘proportional bandwidth’’ has bearing upon the so-called midfrequency gap in structural acoustics.