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For understanding the differences of the sound measured in a group of cars, one needs to be able to quantify independently from the type of engine and tires, the airborne transfer from these noise sources to the passenger compartment. State of the art methods use direct measurements, which are poorly suited to modern car congested engine bays, or require engine dismantling. Arbitrary positions of source are also questionable. In the reciprocal approach, no engine dismantling is necessary. A calibrated point source is located close to the ears of a clothing manikin. The resulting acoustic pressure over the radiating surfaces is measured. The transfer functions are frequency and space averaged, and then available in third octave bands from 400Hz to 4kHz.

The hybrid FEA method combines the conventional FEA method with the energy FEA (EFEA) for computing the structural vibration in vehicle structures when the excitation is applied on the load bearing stiff structural members. Conventional FEA models are employed for modeling the behavior of the stiff members in the vehicle. In order to account for the effect of the flexible members in the FEA analysis, appropriate damping and spring/mass elements are introduced at the connections between stiff and flexible members. Computing properly the values of these damping and spring/mass elements is important for the overall accuracy of the computations. Utilizing in these computations the analytical solutions for the driving point impedance of infinite or semi-infinite members introduces significant approximations.

In order to characterize the noise filtering performance of a vehicle with respect to both structure- and airborne transfer paths, a reciprocal transfer functions synthesis method is proposed. Simple, timesaving and repeatable, the procedure is an interesting alternative to the direct measurement. As part of the Vehicle Benchmarking acoustic expertise, the reciprocal transfer function synthesis method is well appropriate to rank different vehicles according to their sound attenuating performances, or to characterize the effectiveness of an acoustic package. As an application example, a sensitivity analysis of the rolling noise transmission with respect to the floor treatment of a vehicle is presented.

In order to characterize and summarize the structure-borne performance of the body and the NVH treatment of a group of vehicles independently from the type of powertrain, a reciprocal transfer function synthesis procedure is applied with respect to structure-borne noise. Structure-borne transfer functions or Noise Transfer Functions (NTF) are useful to quantify the vehicle acoustic sensitivity to structure-borne noise. Direct NTF measurements are difficult to perform on full vehicle configuration due to modern cars congested engine bays, and often require engine dismantling to take into account all the individual structure-borne routes; traditional impact testing is also time consuming and limited to low frequencies.

In the early stages of a vehicle program, sound package design is significantly complicated by numerous competing requirements including cost, weight, acoustical targets and packaging space. The problem is further convoluted due to a limited definition of the vehicle at this time. In this article, a Statistical Energy Analysis (SEA) model of the vehicle is created based on a gross description of the vehicle architecture. A large material database of commonly used sound package configurations is then linked to the SEA model. Genetic Algorithms (GA) are finally applied to optimize the sound package design to satisfy cost, weight, acoustical targets and packaging requirements in the vehicle design.

The Diffuse Field Absorption Coefficient (DFAC) is a physical quantity very often used in the automotive industry to assess the performance of sound absorbing multilayers. From a theoretical standpoint, such quantity is defined under rather ideal conditions: the multilayer is assumed to be infinite in extent and the exciting acoustic field is assumed to be perfectly diffuse. From a practical standpoint, in the automotive industry the DFAC is generally measured on samples having a relatively small size (of the order of 1m2) and using relatively small cabins (in the order of 6-7 m₃). It is well known that both these factors (the finite size of the sample and the small volume of the cabin) can have an influence on the results of the measurements, generating deviations from the theoretical DFAC.

The consistent measurement of airbag deployment noise places special demands on the enclosure in which the measurements are performed. The acoustical characteristics of the enclosure must be stable over long periods. It must also be sufficiently robust to withstand the loads involved. The use of a standardized enclosure provides a uniform basis for comparable measurements in different laboratories. The reasons for selecting a specific small cabin as the standard enclosure are discussed in this paper. Some examples of tests performed in the small cabin with a wide range of airbag systems are presented. High-speed film recordings of the deployment of the airbags were made simultaneously with the acoustic measurements. The stability of the acoustic environment and of the enclosure were important factors in obtaining reliable and comparable results.

Different solutions for trunk floors recently presented on the market have been collated and investigated in order to better define the possible features integrated and the acoustic performance of trunk load floors. A description protocol has been devised and applied to systematically categorize the whole set of features potentially characterizing a trunk floor, and the wide range of solutions used with respect to materials, processes and design configurations. The acoustic performance has been specifically addressed with the evaluation of the acoustic absorption on both sides and a specific testing procedure to evaluate the noise insulation capability provided by actual parts.

The present work explains an innovative design methodology that allows efficient optimizations of vehicle body panels and treatments towards shorter development time and improved vehicle Noise and Vibration Harshness (NVH) characteristics. This tool named GOLD (Genetic Optimization for Lighter Damping), internally developed by Rieter Automotive, can be embedded into vehicle Computer Aided Engineering (CAE) design flow and can be then used in providing design and platform component sharing guidance information before prototype vehicles are available. GOLD is able to detect the optimal design of vehicle panel shape and damping packages with respect to NVH targets, by means of vibro-acoustic simulations. The core of this tool are the Genetic algorithms (GAs) which are heuristic methods which have been already successfully used, in several research fields, to solve search and optimization problems with a very large number of variables.

This paper describes a new approach for modeling a trimmed vehicle body by blending FEA models of the BIW, the passenger compartment and each individual trim component. The approach bases on the update of modal matrices, transforming the untrimmed body-cavity modal representation into an updated modal model including the effect of the trim configuration on the local and global NVH indicators. Results on simple and more realistic models are presented and show that the methodology fulfills the efficiency and accuracy criteria and is thus to guide the NVH development process.

Porous materials are extensively used in the construction of automotive NVH parts. The sound package design during vehicle development requires simulation methods at vehicle level that can take into consideration the dynamical behavior of porous materials. This need has led to different numerical technologies based on Biot's equations. In particular, direct FE implementations of Biot's equations have been included into some commercial FE software programs. Such implementations, while giving good results, are time consuming and difficult to apply within the time constraints given by the timeline of vehicle development programs. This paper presents an alternative methodology, thanks to which it is possible to build the coupled vibro-acoustic model of a trimmed vehicle without modeling physically the trim components.

Typically, in the automotive industry, the design of the body damping treatment package with respect to NVH targets is carried out in such a way to achieve panel mobility targets, within given weight and cost constraints. Vibration mobility reduction can be efficiently achieved thanks to dedicated CAE FE tools, which can take into account the properties of damping composites, and also, which can provide their optimal location on the body structure, for a minimal added mass and a maximized efficiency. This need has led to the development of different numerical design and optimization strategies, all based on the modeling of the damping composites by mean of equivalent shell representations, which is a versatile solution for the full vehicle simulation with various damping layouts.