The sensitivity of structural acoustic response to attachment feature scale representation

This paper presents a technique to assess the impact on model fidelity intr oduced through discretization of attachments on harmonically forced fluid l oaded structural acoustic models. While fluid loading is included, it is no t a requirement or restriction to the methods presented. The perspective ta ken is one of knowledge of a reference state, with a desire to determine th e impact on the total radiated acoustic power due to perturbations in the r eference state. Such perturbations change the predicted resonance frequenci es of a structure under consideration and, hence, change the predicted resp onse 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 t he spatial representation of attached features (e.g., paint versus distribu ted attachments). Elements of the analysis method are not necessarily restr icted 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. Fo r frequencies within +/-5% of a resonance frequency, the amount of damping in the system determines and limits the magnitude of the response perturbat ion. 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 pertu rbed states. (C) 1999 Acoustical Society of America. [S0001-4966(99)01112-1 ].