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Maximizing the acoustic attenuation is one of the important design criteria of automotive exhaust systems. Although both analytical and numerical approaches exist to evaluate the acoustic transmission properties of exhaust systems, they are, at present, insufficient to model the full geometrical complexity and to accurately assess the influence of thermal and aerodynamic phenomena onto the acoustic attenuation characteristics. For this reason, an experimental test campaign is often still indispensable to evaluate the aeroacoustic performance of exhaust systems. One of the most commonly used experimental characterization techniques for flow duct systems is the two-port characterization.

In this paper, singular value decomposition, principle component analysis and multicoherence analysis is used to evaluate the number of important degrees of freedom in acceleration based road load data, which constitute the targets for road reproduction experiments on a hydraulic shaker table. It is therefore important to determine from this road data how many degrees of freedom need to be included in the road reproduction experiments. The multi-axial nature of the input and the suspension response is illustrated based on target data from different road surfaces, acquired on the road and on the road dynamometer, as well as on the reproduction results of these tracks using tire patch and spindle based excitation on the K.U.Leuven high frequency multi-axial shaker table.

Tire noise has become a predominant contributor in many traffic noise situations nowadays and hence, the demand for accurate tire noise prediction models is high. A rolling tire is experimentally characterized by means of the substitution monopole technique: the running tire is substituted by the non-operating tire covered by monopoles. All monopoles have mutual phase relationships and a well defined volume velocity distribution which is derived by means of an inverse Airborne Source Quantification technique; i.e. by combining static transfer function measurements with operational indicator pressure measurements close to the rolling tire. Models with varying amounts and locations of monopoles are discussed.

In many industrial applications, such as in the automotive and machine building industry, there is a continuous push towards lightweight materials motivated by material and energy savings. This increased use of lightweight materials, however, can strongly compromise the Noise, Vibration and Harshness (NVH) performance of the final products. Especially in times where the NVH performance not only receives a higher legislative attention, but also becomes a commercial differentiator, this also represents a key point of attention for designers and directs research activities towards new experimental and numerical techniques to accurately predict the NVH performance of lightweight systems as early as possible in the design process. The presented work discusses novel measurement setup, specifically developed for examining the vibro-acoustic behavior of lightweight structures. The test stand consists of a concrete cavity of 0.83 m₃.

The combination of lightweight design and performant Noise, Vibrations Harshness (NVH) solutions has gained a lot of importance over the past decades. Lightweight design complies with the ever more stringent environmental requirements, however conflicts with NVH performance, as low noise and vibration levels often require heavy and bulky systems, especially at low frequencies. To face this challenge, locally resonant metamaterials come to the fore as low mass, compact volume NVH solutions, beating the mass law in some tunable frequency zones, referred to as stopbands. Metamaterials are artificial materials made from assemblies of unit cells of non-homogeneous material composition and/or topology. The local interaction between unit cells leads to superior performance in terms of noise and vibration reduction with respect to the conventional NVH treatments. Previously the authors showed how wave propagation along one-dimensional structures can be reduced by metamaterial additions.