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A number of researchers [3],[4] have shown that Statistical Energy Analysis[1] provides a useful framework for test-based noise path analysis - as well purely analytical models. This paper describes the results of a comparative study of two such models - an analytic SEA model and a test-based SEA parameter model - for predicting the Noise Reduction performance of a light truck body. First, the different power balance matrix solutions and SEA subsystem definitions are reviewed. Second the results of the two independent models are compared. For some specific cases of structure-borne noise, the test-based method is shown to be more accurate than the analytic model. Third, means by which individual measured SEA parameters can be integrated into an analytic SEA model are proposed and evaluated. Results indicate that the scope for analytical model improvement, but also highlight the need for more rigorous “consistency” in the way test-based SEA parameters are measured.

A simple mathematical model was developed and experimentally validated to evaluate how the materials and construction of an automobile tire affect its vibration-radiated noise performance. The mathematical model uses Statistical Energy Analysis (SEA) with modal joint acceptance formulations for wavespeed and radiation efficiency of orthotropically-stiffened and pressurized cylindrical shells. Experimental validation of the model included wavenumber decomposition to determine the dispersion characteristics of an inflated, non-rolling tire in the laboratory. The model is used to conduct a preliminary study into how the various tire constituent materials and construction parameters influence the vibration-radiated noise performance.

Automakers have reported that passenger perception of vehicle interior wind noise is strongly correlated to the non-Gaussian and non-stationary character of the exterior aero-acoustic wind loading. Researchers in other domains have shown that leptokurtic non-Gaussian loading (Kurtosis κ>3) can be synthesized by non-stationary modulation of otherwise Gaussian random loading. This paper introduces a transient statistical energy analysis (SEA) model for the aero-vibro acoustic transmission of non-stationary wind noise which uses the same approach - a modulation of otherwise Gaussian random fluctuating pressure loading, in each one third octave band. The authors have previously shown that the non-stationary character of random wind loading can be measured in a wind tunnel or on the road with a suitable surface pressure microphone array.

It has been shown that internal transmission of wind noise is dependent on the external aerodynamic and acoustic excitation around the automobile. Flow over the A-pillar and side-view mirror induces strongly convecting turbulence and associated acoustics which excite the side-glass. A useful tool to understand and quantify these physics is to perform temporal Fourier analysis (auto-spectra) and spatial Fourier analysis (cross-spectra and wave-number decomposition). This study demonstrates the uses of wave-number decomposition to quantify the mechanisms associated with turbulent convection and acoustical propagation. A CFD computation using the commercial codes STAR-CCM+ is performed for the flow over a generalized side-view mirror in a freestream of 38m/s. LES-enabled turbulence is solved in a fully compressible framework so as to capture all the local acoustical propagation well beyond 3kHz.

Measurements of interior wind noise sound pressure level have shown that dBA and Loudness are not adequate metrics of wind noise sound quality due to non-stationary characteristics such as temporal modulation and impulse. A surface microphone array with high spatio-temporal resolution has been used to measure and analyze the corresponding non-stationary characteristics of the exterior aero-acoustic loading. Wavenumber filtering is used to observe the unsteady character of the low wavenumber aero-acoustic loading components most likely to be exciting glass vibration and transmitting sound.

Low frequency interior wind noise is typically dominated by underfloor flow noise. The source mechanisms are fluctuating surface pressure loading from both flow turbulence and acoustic field levels developed in the semi-reverberant cavity between floor and road. Previous studies have used computation fluid dynamics (CFD) to estimate the aero-acoustic loading applied to a vibro-acoustic model, which is then used to predict the transmitted interior wind noise. This paper reports a new perspective in two respects. First it uses novel surface pressure microphone arrays to directly measure the underfloor aero-acoustic loading in the wind tunnel. Second, it considers two different underfloor aerodynamic configurations - with and without lightweight aero cover panels, which are installed primarily to reduce aerodynamic drag.

Surface pressure measurements using microphone arrays are still challenging, especially in an automotive context with cruising speeds around Mach 0.1. The separated turbulent boundary layer excitation and the side mirror wake flow generate both acoustic and aerodynamic components, which have wavenumbers that differ by a factor of approximately 10. This calls for high spatial resolution measurements to fully resolve the wavenumber-frequency spectrum. In a previous publication [1], the authors reported a micro-electro-mechanical (MEMS) surface microphone array that successfully used wavenumber analysis to quantify acoustic versus turbulence loading. It was shown that the measured surface pressure at each microphone could be strongly influenced by self-noise induced by the microphone “packaging”, which can be attenuated with a suitable windscreen.

A fully analytical method for the evaluation of noise reduction in a vehicle interior furnished with layered acoustic trim is presented. The method combines calculation of trim Transmission Loss (TL) and Absorption Coefficient with a Statistical Energy Analysis (SEA) calculation of trimmed panel Noise Reduction (NR). This allows for the evaluation of the trim package performance in real operating conditions and ranking of the different air-borne and structure-borne transmission paths.

A mathematical model was developed to evaluate design options for control of road noise transmission into the interior of a passenger car. Both air-borne and structure-borne road noise over the frequency range of 200-5000 Hz was able to be considered using the Statistical Energy Analysis (SEA) method. Acoustic and vibration measurements conducted on a laboratory rolling road were used to represent the tire noise “source” functions. The SEA model was correlated to in car sound pressure level measurements to within 2-4 db accuracy, and showed that airborne noise dominated structure-borne noise sources above 400 Hz. The effectiveness of different noise control treatments was simulated and in some cases evaluated with tests.