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This paper considers two questions: how does one know when a boundary element mesh is reliable, and what are the advantages and potential pitfalls of various methods for sound radiation prediction. To answer the first question, a mesh checking method is used. With this method velocity boundary conditions are calculated on the nodes of the mesh using a point source or sources placed inside the mesh. A boundary element program is then used to calculate the sound power due to these boundary conditions. The result is compared to the known sound power of the point source or sources. This method has been used to determine the maximum frequency of a mesh, how many CHIEF points to use, etc. The second question is answered by comparing the results of several numerical methods to experimental results for a running diesel engine. The methods examined include the direct and indirect boundary element methods and the Rayleigh integral.

The Boundary Element Method (BEM) is a computational method for solving the acoustic wave equation when the acoustic domain has an irregular or arbitrary shape. The BEM is distinguished from other numerical methods such as the finite element method in that with the BEM only the surface or the boundary of the acoustic domain needs to be discretized. In this paper some examples are presented concerning problems in automotive industry involving the radiation of sound from engines and other vibrating structures, the acoustical response of passenger compartments of vehicles and the attenuation of mufflers and other exhaust or intake system components.

This paper examines the feasibility of using the boundary element method (BEM) and the Rayleigh integral to assess the sound radiation from engine components such as oil pans. Two oil pans, one cast aluminum and the other stamped steel, are used in the study. All numerical results are compared to running engine data obtained for each of these oil pans on a Cummins engine. Measured running-engine surface velocity data are used as input to the BEM calculations. The BEM models of the oil pains are baffled in various ways to determine the feasibility of analyzing the sound radiated from the oil pan in isolation of the engine. Two baffling conditions are considered: an infinite baffle in which the edge of the oil pan are attached to an infinite, flat surface; and a closed baffle in which the edge of the oil pan is sealed with a rigid structure. It is shown that either of these methods gives satisfactory results when compared to experiment.

Numerical acoustics has traditionally been relegated to a prediction only role. However, recent work has shown that numerical acoustics techniques can be used to diagnose noise problems. The starting point for these techniques is the acoustic transfer vector (ATV). First of all, ATV's can be used to conduct contribution analyses which can assess which parts of a machine are the predominant noise sources. As an example, the sound power contribution and radiation efficiency from parts of a running diesel engine are presented in this paper. Additionally, ATV's can be used to reliably reconstruct the vibration on a machine surface. This procedure, commonly called inverse numerical acoustics (INA), utilizes measured sound pressures along with ATV's to reconstruct the surface velocity. The procedure is demonstrated on an engine cover for which the reconstructed vibration had excellent agreement with experimental results.

An advanced computational method is presented for calculating the sound radiated by vibrating engine of arbitrary shape. The method is based on the numerical evaluation of the Helmholtz Integral Equation. In particular an isoparametric element formulation is introduced in which both the surface geometry and the acoustic variables on the surface of the vibrating body are represented by second order shape functions within the local coordinate system. The formulation includes the case where the surface may have a non-unique normal (e.g. at edges or corners). A general result for the surface and field velocity potential is derived. Test cases involving spherical geometry are given for a pulsating sphere and for an oscillating sphere in which the analytical solutions are known. Examples for bodies with edges and corners are shown for the problems of radiation from a circular cylinder and from a pulsating cube.

The objective of this study was to determine whether standard modeling packages could be used to predict the acoustical response of an IC-engine induction system. To determine the answer to this question, we constructed from acrylic plastic a “prototype” induction system for a four-cylinder engine. Two modeling packages were used. The first package used was BEMAP, a boundary element program designed specifically for acoustical modeling. The second package used was ANSYS, a general purpose finite element program. For both BEMAP and ANSYS, a radiation boundary condition was used at the air intake of the induction system. Results from BEMAP and ANSYS are compared to experimental data. The experimental results were obtained by exciting one of the induction system intake ports with a small loudspeaker and measuring the transfer function between the sound pressure at the air inlet and the sound pressure at the intake port. All three sets of results exhibit good agreement.

In this article we discuss the boundary element method as it may be used in the automotive industry for acoustical modeling and prediction for noise control design. The boundary element method is used to calculate the sound pressure level at a prescribed distance from a vibrating engine block, the sound intensity on the surface of the engine block and the sound radiation efficiency of the block mode. The boundary element method is also used to determine the performance of a partial enclosure. The boundary element method is used to determine the sound intensity field inside and outside of the enclosure, both for unlined and lined cases. The sound pressure directivity pattern is also determined for each case. For verification of the boundary element method, we compare the results to experimental results for two test cases: radiation of sound from a vibrating structure and the acoustical response of a cavity.

In this paper the application of the Boundary Element Method (BEM) to problems in acoustics and noise control will be reviewed. The BEM is a computational method for solving the acoustic wave equation when the acoustic domain has an irregular or arbitrary shape. Examples of such problems in the automotive industry include the radiation of sound from engines and other vibrating structures, the scattering (diffraction) of sound from irregular surfaces and obstacles, the acoustical response of passenger compartments of vehicles and the attenuation of mufflers and other exhaust or intake system components. The BEM is distinguished from other numerical methods such as the finite element method in that with the BEM only the surface or boundary of the acoustic domain must be discretized. This is an important feature in solving radiation problems, where the domain is infinite or semi-infinite, but is also beneficial for cavity and muffler problems as well.