Larry J. Howell

STRUCTURAL-ACOUSTIC FINITE ELEMENT ANALYSIS OF THE AUTOMOBILE PASSENGER COMPARTMENT: A REVIEW OF CURRENT PRACTICE

Abstract This paper contains a brief review of the formulation of the finite element method for structural-acoustic analysis of an enclosed cavity, and illustrations are given of the application of this analytical method at General Motors Corporation to investigate the acoustics of the automobile passenger compartment. Low frequency noise in the passenger compartment (in approximately the 20–200 Hz frequency range) is of primary interest, and particularly that noise which is generated by the structural vibration of the wall panels of the compartment. The topics which are covered in the paper include the computation of acoustic modes and resonant frequencies of the passenger compartment, the effect of flexible wall panels on the cavity acoustics, the methods of direct and modal coupling of the structural and acoustic vehicle systems, and forced vibration analysis illustrating the techniques for computing panel-excited noise and for identifying critical panels around the passenger compartment. The capabilities of the finite element method are illustrated by applications to the production automobile, and experimental verifications of the various techniques are presented to illustrate the accuracy of the method.

STRUCTURAL-ACOUSTIC FINITE ELEMENT ANALYSIS OF THE AUTOMOBILE PASSENGER COMPARTMENT

The objective of this paper is to give illustrative solutions for the types of combined structural and acoustic problems which arise in the finite element analysis of the automobile passenger compartment and to review related methodology. Analysis implementation using the NASTRAN (NASA STRuctural ANalysis) computer program is discussed briefly, including the use of modal compartment wall models and forced boundary conditions. The model is a two dimensional one, assuming a uniform pressue field in the cross-body direction. This simplification appears to be adequate for the frequency range of interest (20 to 80 Hz).

Automobile Interior Noise Reduction Using Finite Element Methods

Low-frequency interior noise in the automobile passenger compartment can be significantly affected by the vibration behavior of the body panels surrounding the enclosed cavity. An acoustic finite element method for computing panel-excited interior noise is reviewed and an approach outlined for identifying potentially noisy panels adjacent to the passenger compartment. To illustrate its potential, the analytical method is applied to a production automobile. A structural modification suggested by the procedure is shown to reduce significantly the low-frequency interior noise to which the occupant is exposed. Experimental verification of the method is presented.

DESIGN THROUGH ANALYSIS OF AN EXPERIMENTAL AUTOMOBILE STRUCTURE

It is evident that the use of impact simulation, static, and dynamic analyses in the pre-prototype phase of the design process can significantly improve the structural efficiency of the design process can significantly improve the structural efficiency of the automobile. As a result of this design project, the accuracy of the structural modeling and analysis was verified by experimental data obtained from a fabricated test vehicle, and the potential value of design through analysis was demonstrated by a significant reduction in structural weight of the project vehicle. /SAE/

Adapting GM research to a new corporate strategy

OVERVIEW: The business climate has changed tremendously for North American automobile manufacturers. Until the late 1970s, there was little foreign competition. Manufacturers could benefit by large economies of scale, and there was little incentive for radical innovation within the business. Today, manufacturers from all over the world compete in the United States. Customers have more than 600 vehicle options to choose from, and the intense competition has kept prices competitive and margins thin. Such changes have forced manufacturers to innovate as they never have before. In 1998, GM embarked on a corporate strategy of innovation and growth. As a result, GM Research transformed itself from a lab that had been working primarily to support an existing production system, to a lab focused on business innovation. The target was to put 30 percent of the labs resources on exploratory projects, but projects that could create wealth for the company. Changes required by the new emphasis included establishment of metrics at the lab level, increased research partnering with universities, and initiation of research programs with key suppliers and automotive alliance partners. Lessons learned: move fast, communicate well, keep some seasoned researchers involved, and make sure the companys top leaders support, if not demand, the new R&D focus.

STUDY OF VEHICLE STEERING AND RESPONSE CHARACTERISTICS IN SIMULATED AND ACTUAL DRIVING

Simulator characteristics were matched to those of the full-scale vehicle with respect to steering torque gradient, control sensitivity, and lateral acceleration response time; identical disturbance signals were applied to each facility. The influence of torque gradient was accentuated in the Simulator and at low levels of control sensitivity, with high levels of torque gradient producing smaller steering wheel and vehicle motion deviations. The effect of control sensitivity on steering wheel deviations was accentuated under actual driving conditions and for slower response times. A greater improvement in lateral position deviations with increased control sensitivity was noted for the slow response time configurations. Even though there were statistically significant interactions involving simulated versus actual driving conditions, examination of the data indicates that the performance trends are essentially the same in both facilities.