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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.

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.

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.

This paper presents the development of a structural model for passenger car tyres, based on a three-dimensional flexible ring on an elastic foundation. The ring represents the belt and the elastic foundation represents the tyre sidewall. The tyre model, which is implemented as a finite element model, is valid below the first treadband axial bending mode and includes a definition of the wheel flexibility and air cavity. The eigenfrequencies predicted by the model are within 5% of the measured eigenfrequencies. The model is validated by comparing predicted with measured responses for both an unloaded and loaded tyre.

A joint study was conducted between BMW and Goodyear with the objective of analysing the cause and identifying methods to reduce the structure-borne interior noise in a vehicle driving on rough road surfaces. A vibro-acoustic characterization of the car was performed by measuring the car vibro-acoustic transfer functions and by using a transfer path analysis technique to identify the main suspension parts affecting the interior noise at target frequencies. The vibration transmissibility characteristics of the tire were measured and also simulated by Finite Element in [1-200Hz] frequency range. The vibro-acoustic interaction between the tire and car sub-systems was examined. A Finite Element sensitivity analysis was used to define and build new prototype tires. A 3dB(A) interior noise improvement was obtained with these new tires at target frequencies.

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.

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.

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.

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.

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.

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.