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A new approach to the reduction of structure borne road noise inside car cabins is developed and verified experimentally. The experiments have been performed on a mid-size station wagon, in laboratory conditions with one wheel excitation. In the frequency range from 100 to 150 Hz, more than 10 dB noise reduction has been achieved using control forces applied to the car body. For maximum noise reduction the control configuration had to be tuned carefully to satisfy the causality constraints for the reduction of broadband disturbances.

This paper presents the design and experimental results of a novel test setup to measure the road impact response of a rotating tire. The test setup is based on a tire on tire principle and is used to analyse mechanisms of tire/road noise during road impact excitations, such as driving on cobbled roads, joints of a concrete road surface, railroad crossings,… A series of test are performed with different driving speeds, cleat dimensions and inflation pressures. Radiated noise, vibrations of the tire surface and spindle forces are measured on the test setup during impact excitations.

The reported investigations aimed at adopting and verifying numerical prediction methods for the determination of the efficiency of engine sound shields. An extended measurement series and parallel Boundary Element calculations were conducted on a simple engine simulator with various engine shields. The effect of the shields was expressed in terms of spatially averaged, narrow band Insertion Loss spectra. It was found that the efficiency of sound shields is determined by complex interactions between the source and its surroundings. These effects could be better understood and reasonably well predicted by using the BE method. The relative IL quantity can be calculated more accurately than the absolute sound field descriptors themselves.

In the context of the reduction of traffic-related noise the research reported in this paper provides tools that could be used to develop low noise tyres. Two measurement techniques have been analyzed for exterior noise radiation characterization of a loaded rotating slick tyre on a rough road surface. On one hand sound pressure measurements at low spatial resolution with strategically placed microphones on a half-hemisphere around the tyre/road contact point have been performed. This technique provides a robust solution to compute the (overall) sound power level. On the other hand sound intensity measurements at high spatial resolution by means of a scanning intensity probe have been performed. This technique allows a more detailed spatial visualization of the noise radiation and helps in getting more insight and better understanding of the acoustical phenomena.

The identification of the contributions of airborne noise sources in vehicles in operational driving conditions is still a cumbersome task. Whereas the measurement of the transfer path from possible noise sources to the observer ear locations is efficient and accurate in most conditions, the source strength identification is still a challenging task. This paper presents the basic concepts of a new source quantification technique based on acoustic pressure measurements close to the operating sources. The main goal of developing a new technique is to achieve a faster and more economic method as compared to existing methods.

A silencer to attenuate engine exhaust noise using active control methods has been developed. The device consists of an electrically driven valve, combined with a buffer volume, which is connected to the exhaust outlet. Using the mean flow through the valve and the pressure fluctuations in the volume, the valve regulates the flow in such a way that only the mean flow passes through the exhaust outlet. The fluctuations of the flow are temporally buffered in the volume. To carry out optimization and validation experiments, a cold engine simulator has been developed. This device generates realistic exhaust noise as well as the matching gas flow using compressed air. The simulator allows quick and reliable acoustic and fluid dynamic experiments on exhaust prototypes. The silencer is developed using electrical equivalent circuits, wherein at first instance a feedforward control is applied.

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.

This paper presents the results of an experimental test campaign carried out on a city bus powered by serial hybrid power train. The driveline system combines an Internal Combustion Engine with a battery pack and two electric motors. Tests were aimed at identifying the salient signal characteristics of the noise spectra recorded during operating conditions and to assess the acoustic comfort in the passenger compartment. Transfer Path Analysis technique was applied to identify airborne and structure borne vibro-acoustic loads, to measure transfer functions linking source locations to target locations and to estimate the internal vibro-acoustic comfort in operating conditions.

This paper presents a model updating method based on experimental receptances. The presented method minimises the so called ‘indirect receptance difference’. First, the reduced analytical dynamic stiffness matrix is expressed as an approximate, linearised function of the updating parameters. In a numerically stable, iterative procedure, this reduced analytical dynamic stiffness matrix is changed in such a way that the analytical receptances match the experimental receptances at the updating frequencies. The updating frequencies are a set of selected frequency points in the frequency range of interest. Some considerations about an optimal selection of the updating frequencies are given. Finally, a mixed static-dynamic reduction scheme is discussed. Dynamic reduction of the analytical dynamic stiffness matrix at each updating frequency is physically exact, but it involves a great computational effort.