Shung H. Sung

Comment on "On Dowell's simplification for acoustic cavity-structure interaction and consistent alternatives [J. Acoust. Soc. Am. 127, 22-32 (2010)]".

This Letter describes a correction to the equations used in Ginsberg [J. Acoust. Soc. Am. 127, 22-32 (2010)] to include the rigid-body (Helmholtz) cavity mode in the modal series solution when using Dowells method. While the correction is easy to implement, it significantly affects the results and the conclusions when using the modal series solution. Specifically, the correct formulation of Dowells method now predicts results that agree very well with the exact solution even to the lowest frequencies.

Validation of an Acoustic Finite Element Model of an Automobile Passenger Compartment

An acoustic finite-element model of an automobile passenger compartment that represents the more complicated vehicle interior acoustic characteristics is developed and experimentally assessed using loudspeaker excitation. The acoustic finite-element model represents the passenger compartment cavity, trunk compartment cavity, front and rear seats, parcel shelf, door volumes, and IP (Instrument Panel) volume. The model accounts for the coupling between the compartment cavity and trunk cavity through the rear seat and parcel shelf, and the coupling between the compartment cavity and the door and IP panel volumes. Modal analysis tests of a vehicle were conducted using loudspeaker excitation to identify the compartment cavity modes and sound pressure response at a large number of interior locations. Comparisons of the predicted versus measured mode frequencies, mode shapes, and sound pressure response at the occupant ear locations are made to assess the accuracy of the model to 400 Hz.

An Equivalent‐Acoustic Finite Element Method for Modeling Sound Absorbing Materials

An equivalent‐acoustic finite element method is developed for modeling sound absorbing materials, such as seats and interior trim in the automobile passenger compartment. The equivalent‐acoustic method represents the sound absorbing material using acoustic finite elements with frequency‐dependent material properties determined from the measured acoustic impedance of sound absorbing material samples. Solution of the equivalent‐acoustic model within the Nastran computer capability and coupling of the model with an acoustic finite element model of a surrounding enclosure, such as the passenger compartment, are developed. The accuracy of the equivalent‐acoustic method is assessed for modeling a sound absorbing material in a one‐dimensional impedance tube, a foam layer in a rectangular box enclosure, and an automotive seat in a semi‐reverberant enclosure.

Correlation of an Acoustic Finite Element Model of the Automobile Passenger Compartment Using Loudspeaker Excitation

An acoustic finite-element model of the automobile passenger compartment is developed and experimentally assessed for predicting the sound pressure response in the compartment. The acoustic finite-element model represents both the passenger compartment cavity and the trunk compartment cavity, with the coupling between them through the rear seats for which the acoustic properties are determined from a modified “heavy air” approximation. Measurements of the sound pressure response in the passenger compartment are obtained using a specially developed loudspeaker excitation device for assessing the accuracy of the model. Comparisons are made of the predicted versus measured sound pressure response to 300 Hz for loudspeaker excitation in both the passenger and trunk compartments.Copyright

A Regression-Based Energy Method for Estimating Vehicle Interior Noise in Road Tests

A regression-based energy method is developed for rapid estimation of the overall passenger-compartment interior noise (dBA) and Articulation Index (AI) in a vehicle of prescribed architecture when the vehicle travels on a particular road at a particular speed. The method is developed for use in the early vehicle design stage when only limited vehicle architecture design information are known. Regression analyses from a database of vehicle on-road tests and vehicle wind-tunnel tests are used to identify the energy transfer functions that represent the prescribed vehicle architecture. Energy excitation from both tire-road interaction and aerodynamic loads is then used to predict the interior dBA and AI responses. Comparisons of the predicted versus measured dBA and AI responses show reasonable agreement for car and wagon-type vehicles, although limited architecture data somewhat underestimates the actual response in certain vehiclesCopyright

A regression-based energy method for predicting structural vibration and interior noise

A regression-based energy method is developed for predicting the structural vibration and interior noise for prescribed loads applied to a structural-acoustic enclosure subject to differences in the structural or acoustic design. The formulation is based on the energy transfer functions that relate the applied load energy to the structural or acoustic response energy. The energy transfer functions are determined from a statistical regression analysis of the measured or predicted multiple responses that result from the differences in the structural or acoustic design. The applied load energy is determined analytically or experimentally for prescribed loading conditions. The energy method can then be used to estimate the mean-value and variation of the structural or acoustic response for different structural or acoustic designs and various prescribed loading inputs. A simple tube-mass-spring-damper system terminated with absorption material with variation is presented as an example. The practical applicatio...

Transfer Path Analysis of Body Panel Participation Using a Structural-Acoustic Finite Element Model

In transportation vehicles under operating conditions, interior noise frequently results from forces transmitted through the vehicle structure that excite body panel vibrations that couple with the body modes to radiate noise to the interior. The body panel participations to the interior noise that result from the force transfer paths can be identified using acoustic and structural-acoustic finite element models of the vehicle. This paper describes the transfer path analysis method to identify the body panel and modal participations for prescribed forcing excitations to the vehicle and to evaluate the effect of structural modifications. The theoretical development of the structural-acoustic finite element method and its example applications to two automotive vehicles are presented.Copyright

A Structural-Acoustic Finite Element Method for Predicting Automobile Vehicle Interior Road Noise

A structural-acoustic finite element model of an automotive vehicle is developed and experimentally evaluated for predicting the structural-borne interior noise in the passenger compartment when the vehicle travels over a randomly rough road at a constant speed. The structural-acoustic model couples a structural finite element model of the vehicle with an acoustic finite element model of the passenger compartment. Measured random road profile data provides the prescribed power spectral density excitation applied at the tire-patch contact points to predict the structural-borne interior road noise. Comparisons of the predicted and measured interior noise for laboratory shaker excitation, tire patch excitation, and vehicle travel over a randomly rough road are used to assess the accuracy of the model.Copyright

A Regression-Based Energy Method for Estimating Engine Noise in the Automobile Passenger Compartment

A regression-based energy method is developed for estimating the overall interior noise (dBA) and Articulation Index (AI) in the automobile passenger-compartment for engine operation at idle, 2500 rpm, and wide-open-throttle speeds. The method is developed for use in the early vehicle design stage for evaluating the effect of different vehicle and powertrain architecture designs on engine noise performance. Regression analyses from a database of standard vehicle chassis dynamometer tests are used to estimate the effect of vehicle and powertrain architectures on the acoustic energy response and resulting interior noise. Comparisons of the estimated versus measured dBA and AI responses show reasonable agreement for different powertrain types. However, the inclusion of only limited architecture details somewhat underestimates the actual response for certain engines and operating conditions.Copyright

Identification of Dynamic Rates of Elastomeric Vibration Isolators in Automotive Vehicles

Dynamic stiffness and damping rates of elastomeric vibration isolators used in automotive vehicles are identified from static isolator tests and the use of an isolator finite element model. Comparisons are made of the predicted versus measured dynamic stiffness and damping rates from 0 to 300 Hz of a rear suspension isolator to validate the technique. The identified dynamic rates of the elastomeric isolators of a representative vehicle are then input to the vehicle system finite-element model to compare the predicted versus measured vehicle vibration and interior noise response for laboratory shaker excitation.Copyright