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As an alternative method to Statistical Energy Analysis (SEA), Energy Finite Element Method (EFEM) offers several unique advantages for vibro-acoustic analysis of structural-acoustic systems. In this paper, the theory of the energy finite element method is overviewed. The main developments of a recently available EFEM code are presented. This is followed by the investigation of several example problems using EFEM; (a) the acoustic pressure computation in an acoustical duct, (b) the sound transmission loss of an automotive dash, and (c) the vibro-acoustic analysis of a truck cab. The EFEM predictions are compared to the analytical solutions, SEA predictions or test data and good correlations are observed. Further, the advantages of EFEM in the solution of high and middle frequency vibro-acoustic problems are discussed.

A hybrid method is developed by combining energy finite element method (EFEM) and energy boundary element method (EBEM) to predict interior noise of structural-acoustic systems at high frequencies. In the hybrid EFEM/EBEM method, the structural domain of the system is modeled by structural finite elements, and the acoustic domain is modeled by acoustic boundary elements. The structural vibration response is computed from EFEM. The interior sound pressure level in the acoustic domain is recovered using EBEM. To validate the hybrid method, the interior noise levels in simplified airplane cabin and van models are computed and compared with that of EFEM only model. Good correlations are observed.

Energy Finite Element Method (EFEM) is an alternative method to currently practiced Statistical Energy Analysis (SEA) for the solution of high frequency vibro-acoustic problems. In this paper, the theory of the energy finite element method for interior noise prediction is reviewed first. This is followed by the investigation of two example problems using EFEM; (a) the interior noise of an airplane cabin and (b) the sound transmission loss of a dash. In both case EFEM results are compared to SEA predictions. The EFEM and SEA results using different mesh density are also investigated. Further, the advantages of EFEM in the solution of high frequency vibroacoustic problems are discussed.

The identification/localization of propulsion noise in turbo machinery plays an important role in its design and in noise mitigation techniques. Near field acoustic holography (NAH) is the process by which all aspects of the sound field can be reconstructed based on sound pressure measurements in the near field domain. Identification of noise sources, particularly in turbo-machinery applications, efficiently and accurately is difficult due to complex noise generation mechanisms. Backward prediction of the sound field closer to the source than the measurement plane is typically an unstable “ill-posed” inverse problem due to the presence of measurement noise. Therefore regularized inversion techniques are typically implemented for noise source reconstruction. Another major source of ill-posedness in NAH inverse problems is a larger number of unknowns (sources) than available pressure measurements. A model reduction technique is proposed in this paper to address this issue.

This paper discusses the approach and application of controlling material and manufacturing parameters in development of lightweight acoustic interior systems. First addressed is the theoretical premise of noise control mechanisms and their relationship to material property/process sensitivity through poroelastic model simulation. The optimal balance of sound transmission loss and absorption in achieving optimally tuned acoustic performance is then presented along with material sample and in-vehicle experimental results. The ability to acoustically tune the vehicle interior to a desired sound level and frequency content through proper design & control of the elastic porous properties achieved by unique acoustic material/process flexibility & capability is demonstrated.

Nearfield Acoustical Holography (NAH) has traditionally been utilized in the identification of noise sources on separable geometry of the wave equation. Recent advances have utilized the Boundary Element Method (BEM) to extend the source identification to noise sources with arbitrary geometry. However, this generalized NAH leads to the solution of a discrete ill-posed problem that requires solution through Singular Value Decomposition (SVD) in conjunction with numerical regularization. Robust numerical regularization schemes have recently been implemented in commercial software COMET/Acoustics® [1, 2] so as to fully automate the noise source identification procedure, and render it applicable to complex, practical problems. An application involving noise source identification on the interior of an earthmoving equipment cab is presented to demonstrate the capability of generalized NAH. The NAH reconstructed velocities on the surface of the cab are compared with the input velocities.

The designs of vehicle seats have significant impact on interior acoustic modes as well as sound pressure level inside the vehicles. Seats trimmed with elastic porous materials are especially critical to the acoustic behavior of the vehicles due to the sound absorption of the materials. This paper demonstrates how seating materials affect the acoustic performance of an earh-moving cab. To accurarely simulate the sound absorption of the seat, the seat was modeled as a bulk reactive absorber instead of a local reactive absorber.

Nearfield Acoustical Holography (NAH) has traditionally been utilized in the identification of noise sources on planar structures. The planar NAH was subsequently extended to handle noise source identification on separable geometry such as cylindrical and spherical surfaces using measurements taken on a conforming surface. Recent advances have replaced the mathematics of separable wave propagation with a Boundary Element Method (BEM) based numerical formulation, enabling NAH to reconstruct sources on arbitrarily complex geometry with arbitrarily shaped measurement surfaces. However, this generalized NAH leads to the solution of a discrete ill-posed problem that requires solution through singular value decomposition (SVD) or iterative strategies. Various regularization schemes have been proposed in the literature of inverse problems to be used in conjunction with SVD for robust inversion. Applications of these schemes to generalized NAH problems are beginning to appear in literature.

Formulation of a fast algorithm for evaluating the Nearfield Acoustic Holography (NAH) transfer functions based on boundary integral equations is presented. The new algorithm overcomes some of the well known numerical difficulties exhibited in the traditional Boundary Element Method (BEM) based NAH transfer function formulations such as excessive computational cost, non-uniqueness problem, and regularization of hypersingular integrals. The formulation is based on deriving transfer functions between acoustic field pressure and surface layer potentials using modified Helmholtz/Kirchhoff integral equations. Example problems are analyzed using both traditional and new algorithms. Solution time and NAH reconstruction results are compared to validate and demonstrate the effectiveness of the new algorithm. Finally, the acoustic holography reconstruction is applied for an automotive powerplant.

An application involving noise source reconstruction on a full automotive powerplant including the engine, manifolds and the transmission is considered herein, to demonstrate the versatility of modern generalized acoustical holography. The complex source geometry necessitates measurements on non-conforming surfaces. The acoustic pressures were experimentally acquired at three different engine excitations. Accelerometers were mounted at select locations on the powerplant in order to study the accuracy of the reconstructed vibrations from acoustical holography. Through a series of synthetically generated holograms with added random noise, it is conclusively demonstrated that the error margins in the reconstructed vibrations on the powerplant are consistent with errors in reconstructed vibrations from numerically synthesized holograms of a similar Signal to Noise Ratio (SNR).

Biot's theory provides a framework for the numerical modeling of propagating stress waves in elastic porous materials. A finite element method technique based on the adaptation of Biot's theory [1, 2] to acoustic porous material that is applicable for the solution of complex systems consisting of porous, fluid and structural media is described. Acoustic indicators such as absorption coefficient and transmission loss are calculated for flat samples and these results are compared to known solutions. Finally the transmission loss of a complex dash system is computed and contrasted with the corresponding planar multi-layer results.

A general numerical formulation based on the Boundary Element Method (BEM) for computing radiated sound power sensitivity is presented in this paper. The total radiated sound power is computed using surface acoustic pressure and velocity information. Explicit analytical differentiation of the sound power with respect to acoustic normal velocities is performed on the boundary integral equations to obtain sound power sensitivity information. The formulation is applicable to structures with arbitrary geometries, free edges, openings, and multiple connections. Acoustic absorption materials applied on the structure surface can also be modeled as impedance boundary conditions. The developed formulation is validated and its application is demonstrated.

The boundary element solution procedure for exterior periodic acoustic problems fails at frequencies associated with the eigenfrequencies of the corresponding interior problems. A new technique is developed to overcome this problem in the indirect boundary element method by expanding the integral equations through the application of multi-valued impedance boundary conditions. The effectiveness of this newly developed UNequal Impedance technique for Qualitative Evaluation of acoustic response (UNIQUE) is demonstrated by applying this procedure for the solution a series of exterior acoustic problems.

An integrated experimental/numerical technique based on nearfield acoustical holography (NAH) is developed to identify aeroacoustic noise sources associated with turbomachinery noise sources. An efficient enhanced surface potential formulation that is applicable for the resolution of complex noise source identification is developed for this purpose. Numerical examples are presented to validate the applicability of the presently developed formulation for the identification of aeroacoustic noise sources.

A new Energy Finite Element Formulation was developed for interior noise prediction that includes not only ‘the indirect transmission path associated but also the direct transmission path. The formulation was subsequently extended to model noise control treatments by incorporating appropriate modifications to structural-acoustic and acoustic-acoustic joint matrices. The formulations developed are implemented and the resulting computer program was validated by comparing the predictions from the present development to the results from alternative methods.

The relationship between the acoustical performance and macroscopic material properties of elastic porous materials, based on modified Biot's theory, is used to develop sensitivity relationship among acoustic and macroscopic material properties. The sensitivity information are normalized (scaled) and subsequently used to improve and tune the acoustical performance of elastic porous materials. Example problems are used to demonstrate the applicability of the technique.