The sensitivity of structural acoustic response to attachment feature scale representation

Abstract

This paper presents a technique to assess the impact on model fidelity introduced through discretization of attachments on harmonically forced fluid-loaded structural acoustic models. While fluid loading is included, it is not a requirement or restriction to the methods presented. 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 with increasing resonance frequency. For frequencies within ±5% of a resonance frequency, the amount of damping in the system determines and limits the magnitude of the response perturbation. The perturbation outside the range of ±5% of the resonance frequency is relatively insensitive to damping. The SDOF analysis method is limited by its assumption of constant modal forcing between the reference and perturbed states.