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A feedback controller bas been developed using robust control techniques to control the sound radiated from turbulent flow driven plates. The control design methodology uses frequency domain loop shaping techniques. System uncertainty, sound pressure level reductions, and actuator constraints are included in the design process. For the wind noise problem, weighting factors have been included to distinguish between the importance of modes that radiate sound and those that do not radiate. The wind noise controller has been implemented in the quiet wind tunnel facility at the Ray W. Herrick Laboratories at Purdue University. A multiple-input, multiple-output controller using accelerometer feedback and shaker control was able to achieve control up to 1000 Hz. Sound pressure level reductions of as much as 15 dB were achieved at the frequencies of the plates modes. Overall reductions over the 100-1000 Hz band were approximately 5 dB.

Wavenumber domain methods have been developed to experimentally determine the flexural group speeds and loss factors in beam elements and the flexural power transmission and reflection coefficients of joints in a structure. These techniques are used in this paper to measure uncertain information for an Energy Finite Element Method (EFEM) model of a ladder frame structure. The loss factors and group speeds in each element in the structure were measured and found to compare well with the analytical predictions. However, the flexural power transmission and reflection coefficients of the joints in the structure were found to be significantly different from analytically predicted values. EFEM predictions and measured velocities for several components are compared.

Two structure-borne and two airborne paths were measured on 99 “identical” Isuzu RODEOs and 57 “identical” Isuzu pickup trucks. Significant effort was made to control measurement variability but not environmental (climate) variations. A record was kept of the tests of a reference vehicle over the variation of environmental factors. The frequency response functions (FRFs) of the reference vehicle varied by approximately 2-4 dB over the frequency range 0-500 Hz for the structure-borne paths and over 0-1000 Hz for the airborne paths due to measurement and environmental variations. The FRFs of the fleet varied by as much as 5-10 dB over the same frequency range. In this paper, the vehicle tests are described. The reference and the fleet data are shown in raw form. Reduced data and implications of the results are also discussed.

The mobility modeling technique is applied to the structure-borne noise path through a vehicle suspension. The model is developed using measured FRF data taken on the isolated components of the suspension and body structure of a midsize sedan. Several important modeling issues of suspensions are resolved. It was determined that multiple degrees of freedom are required to model the coupling at joints between the suspension and body structure. The investigation also demonstrated that bushings should not be included in the measurements used to develop these models and should be added later using simplified bushing parameters. The importance of transfer mobility information between the various suspension attachments was also investigated. The agreement between the mobility model predictions and the measured FRF data for the overall system is better than similar data published in the literature to date.

Active noise control is a potential method for controlling troublesome low frequency road noise in the passenger cabin of automobiles. In this investigation, the control of simulated road noise in a four door automobile is studied. Active control of road noise requires that the inputs to the controller sense a significant part of the energy causing the noise. Only the coherent energy between the input sensors and the performance microphone is controllable. An investigation is conducted of the control achievable using accelerometers mounted at various positions near the rear wheel of the vehicle as inputs to the controller. The best input sensor location was used with a commercial active noise controller to reduce simulated road noise near the driver's head location. The measured reduction is compared with the results predicted using the coherence.

An experimental verification study was done of the numerical predictions of sound radiation from an automotive valve cover. The valve cover was mounted on the floor of a semi-anechoic chamber with a mechanical shaker attached to the inside of the cover. Transfer functions between the excitation force and the surface motion of the cover surfaces and the radiated sound pressure were measured. The surface motion of the valve cover was input to a numerical radiation prediction program which was used to predict the acoustic radiation using both the Helmholtz integral equation and the Rayleigh integral equation. The predicted and measured sound pressure levels were compared at 25 field points. The verification study showed that the Helmholtz integral equation prediction is good at all locations for this frequency band. The Rayleigh integral equation predictions were reasonable at some frequencies at some points but are not good in general.

A numerical technique is developed to find and evaluate the optimal active noise controller in three dimensional cavities. The technique finds the volume velocity of multiple specified secondary sources which minimize a design objective function. The design objective function may emphasize either local or global control of the sound field. The noise sources in the cavity may be either compact or distributed. Results for global and local control in spherical and rectangular cavities are discussed.

In this paper, the acoustical finite element method is reformulated to make geometric shape parameters, explicit variables of the resultant matrix equation. Since the acoustical design of mufflers and enclosures is largely dependent on geometric shape, such a formulation may be usefully applied. The paper includes several different illustrations of acoustical design using the new formulation; the synthesis of an appropriate shape to get a desired response, the computation of shape sensitivity information, and automated shape optimization for minimization of a given objective function.