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In the design of an automobile, an important consideration is to minimize the amount of “boom” noise that the vehicle occupant could experience. Vehicles equipped with four cylinder engines can experience powertrain boom noise in the 40 to 200 Hz frequency range. Boom noise can also be generated by road input, and it is just as annoying. In this paper, a CAE methodology for predicting boom noise is demonstrated for a vehicle in the early design stage in which only 3-D CAD geometry exists. From the CAD geometry, a detailed finite element (FE) model is constructed. This FE model is then coupled with an acoustic model of the interior cavity. The coupled structural-acoustic model is used to predict acoustic response due to powertrain inputs. As a part of the detailed design process, various design modifications were considered and implemented in the vehicle system model. Many of these modifications proved successful at reducing the boom levels in the vehicle.

A new simulation-based method for design of powerplant mounting systems is presented. Unlike traditional methods, in which the objective is to obtain a set of powerplant rigid body modes found from experience to be favorable, this new method directly seeks minimal response in the vehicle passenger compartment, regardless of what powerplant modes are obtained. Therefore, the simulation objective exactly matches the design objective: minimal response. The new method, which uses optimization based on response sensitivities, has been implemented into software. Results show that the final response levels are significantly reduced from the baseline, and that typically the final mounting configuration is much different, and better, than the mounting system that would have resulted from application of the traditional method. POWERPLANT MOUNTING is one of the fundamental design characteristics of a motor vehicle.

The design of complex products such as automobiles and aircraft often requires performing repeated dynamic analyses using detailed finite element models. The high computational costs and long turnaround times associated with the use of these models can impede the design process. In this paper, a practical method for performing efficient design parameter studies using Eigensolution Reanalysis is discussed. Special purpose software has been developed which interfaces with commercial finite element analysis codes. The special purpose software uses the baseline modes to calculate new modes for each design change. The software can also compute forced response of the modified designs given user specified dynamic load cases. This method provides dramatic savings in CPU time compared to the traditional method of re-solving the full eigenproblem for the modified design modes. Typically, the reanalysis calculations use less than five percent of the CPU time required for the baseline analysis.

As vehicle development timeframes get continually shorter, the need for and use of computer simulation in the vehicle design and development cycle continues to increase. Computer simulation is used in almost all aspects of vehicle design, but with the current emphasis on vehicle comfort, it might be of greatest use for simulation of noise and vibration. This paper outlines new simulation methods aimed at producing design direction that is both timely and correct. The methods focus on efficient generation and use of full vehicle system models for noise and vibration evaluation.

In-vehicle noise can be simulated by structural-acoustic analysis. This is accomplished by constructing finite element models of the vehicle structure and the acoustic cavity, computing (separately) their modes of vibration, and then coupling the structure and acoustic modes to create a model of the vehicle with its contained air. With this model the analyst can predict the sound pressure level at any point in the passenger compartment due to input to the vehicle structure. Typical inputs are road input through the suspension or engine vibration input. This paper outlines the procedure for structural-acoustic analysis, including the software used and some methods for interpretation of the output. An example of an application of the procedure is documented as well.