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An analytical model based on “vortex sound” theory was investigated for predicting the frequency, the relative magnitude, the onset, and the offset of self-sustained interior pressure fluctuations inside a vehicle with an open sunroof. The “buffeting” phenomenon was found to be caused by the flow-excited resonance of the cavity. The model was applied to investigate the optimal sunroof length and width for a mid-size sedan. The input parameters are the cavity volume, the orifice dimensions, the flow velocity, and one coefficient characterizing vortex diffusion. The analytical predictions were compared with experimental results obtained for a system which geometry approximated the one-fifth scale model of a typical vehicle passenger compartment with a rectangular, open sunroof. Predicted and observed frequencies and relative interior pressure levels were in good agreement around the “critical” velocity, at which the cavity response is near resonance.

With the implementation of digital signal processing, frequency response measurements are not limited to swept sine testing. With the discrete Fourier Transform, any physically realizable signal can be used for excitation. The best technique depends on the application, available equipment, the presence of measurement noise, the linearity of the test object, and the time available in which to execute the test. In this paper a number of excitation techniques have been described. All of these techniques have advantages and disadvantages which have been described in the text of this paper.

Numerical filtering is the smoothing of data by convolution of sampled data with a set of linear weights. Some novel applications of this technique to shock and vibration data analyses and impedance measurement are discussed and examples from existing programs are presented.