529 research outputs found
Dataset for: Microphone array processing for sparse equivalent source representations of tyre noise
No full textData supports the PhD thesis entitled "Microphone array processing for sparse equivalent source representations of tyre noise", awarded to A Papaioanou, 2020 by the University of Southampton.
The data in this file are the raw and post-processed measured data which form the basis of the PhD thesis and were obtained by performing a number of measurements at the Southampton University Signal Processing and Control Lab, the semi-anechoic chamber in Applus IDIADA, Barcelona, Spain and the anechoic chamber in Siemens Digital Industries Software, Leuven, Belgium. To view and use the data, you will need the Matlab Software.</span
Microphone array processing for sparse equivalent source representations of tyre noise
No full textThe estimation of pass-by noise indoors, using a rolling road and a microphone array, has advantages over outdoor measurements in terms of the repeatability and robustness to the environmental conditions of the measurements. It also has the advantage of estimating the individual source contributions to pass-by noise, by placing additional microphone arrays close to each source. The in situ contribution of tyre noise is characterised here by discretising the tyre into a few equivalent sources, which are quantified using the measured near field spectra in an inverse problem and then used in a forward problem to synthesise the pressure in the far field. While the inverse method yields estimates of the source strengths acting simultaneously, the number and the position of the equivalent sources need to be known a priori. In this thesis, different techniques are investigated to choose the number and positioning of the equivalent sources for tyre noise synthesis using the sparsity promoting properties of the `1 norm regularisation. In the first instance, the methods are formulated and tested in a 2D tyre model, which models the tyre vibration up to 1 kHz. Two different `1 norm regularisation techniques are investigated, using frequency - dependent and frequency - averaged source positions. The `1 norm regularisation techniques are then used with the spectra measured from a rolling tyre at 50 km/h. While the frequency-dependent `1 norm regularisation delivers good representations of the directly measured far field spectra, an `2 norm regularisation is also needed when using a higher number of sources, to avoid ill-conditioning. Additional formulations of the `1 norm regularisation are also investigated, particularly a power-based approach for the frequency - averaged `1 norm regularisation, which gives good synthesised far field pressures with only 2 equivalent sources, near the leading and trailing edges of the tyre. The frequency - averaged `1 norm regularisation is then used to analyse the spectra measured from a tyre as it is accelerated, on a rolling road, from 5 to 60 km/h. Different cases are considered, where only tyre noise is present and where fully operational conditions are considered for an electric vehicle. It is shown that, in both cases, the regularisation can predict the number and position of the equivalent sources that give good representations of the measured far field spectra, which are valid for different acceleration rates. The power-based approach is also investigated in this case, again showing good results with only 2 equivalent sources. Omitting the phase and coherence information thus has advantages in reducing the number of equivalent sources needed for tyre noise synthesis
Approaches to the remote mapping of vehicle noise sources in a reverberant environment
No full textIn this paper, new methods for the remote acoustic source mapping of vehicle noise sources are considered. This work initially considers the effect of a wall reflection on conventional methods of processing the signals from a remote microphone array. The use of alternative array processing techniques to discriminate against the reflections are then considered, to produce a ‘heatmap’ of the array response as a noise source is moved around within the chamber. In a first step, an inverse impedance weighting strategy is considered, to distinguish the desired physical source location from the one created due to the reflections. In a second step, additional restrictions are also taken into account such as the ability of the microphone array to suppress the high levels for sources close to the microphones and an optimised weighting strategy is introduced and applied
Application of the 1-norm regularisation techniques in estimating the indoor tyre pass-by noise contribution with the inverse method
No full textThe indoor pass-by noise measurement can nowadays be realised in a laboratory environment with a microphone array and a stationary vehicle on a rolling road, according to ISO – 362-1:2016. Within this indoor testing procedure, the different contributions from the various noise sources on a car can be estimated using an inverse method with a set of microphones close to the various sources. This work assumes a 2D-tyre model to approximate the behaviour of a real car tyre at low frequencies. The inverse method is then adopted using this model for the tyre noise contribution synthesis and corresponding source strength and synthesised pressure estimates are calculated. A novel regularisation method is finally investigated to further optimise the far field pass-by noise pressure estimates through the frequency range of interest
L1 regularisation in the inverse method for the synthesis of indoor tyre pass-by noise
No full textThe indoor pass-by noise measurement can nowadays be realised in a laboratory environment with a stationary vehicle on a rolling road and a microphone array, according to ISO - 362-1:2016. Within this indoor testing procedure, there is also the option of evaluating the different contributions from the various noise sources on a car, for example using the inverse method with a number of sensors close to the various sources. This work assumes a 2D-tyre model to approximate the behaviour of a real car tyre at low frequencies. The inverse method is then adopted using this model for the tyre noise contribution synthesis and corresponding source strength and synthesised pressure estimates are calculated. A novel regularisation method is finally investigated to further optimise the far field pass-by noise pressure estimates
Application of ℓp norm regularisation techniques in the synthesis of indoor tyre pass-by noise with the inverse method
No full textPass-by noise measurements can nowadays be realised in a laboratory environment with a microphone array and a stationary vehicle on a rolling road, according to ISO – 362–1:2016. Within this indoor testing procedure, the contributions from the various noise sources in a car can be estimated, with a set of microphones close to the various sources, and the pass-by noise then synthesised. The methods described in this paper use measured near field pressure data close to a rolling tyre at 50 km/h to estimate virtual source strength, using the inverse method, and the synthesised far field tyre noise is then compared with the one measured directly at a far field microphone array. A combination of ℓ
1 norm and ℓ
2 norm regularisation methods are investigated to optimise the equivalent source position and strength and, subsequently, the far field pass-by noise pressure estimates through the frequency range of interest. It is shown that by optimising the positions of 4 equivalent sources, acceptable representations of the measured far field spectra can be synthesised.
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Approaching the serpentine factor at a local scale—a study in an ultramafic area in northern Greece
No full textWe explore factors responsible for vegetation differentiation in a small-scale serpentine area, and attempt to provide new insights in the complexity of the serpentine factor at community level. We sampled 49 quadrats. From each quadrat physical and chemical soil parameters were measured and species composition, altitude, inclination, aspect and coordinates were recorded. Quadrats were classified and ordination analyses were used to explore the environmental gradients and to estimate the explanatory power of the variables. Generalized linear models were used to investigate the response of species to environmental factors. Variance partitioning was applied to calculate the proportion of variance attributed to different groups of explanatory variables. The gradients revealed were related to soil texture, nutrient contents, calcium deficiency, chromium content, climatic parameters and grazing and disturbance intensity. Variance partitioning showed that the highest proportions of variance were attributed to the nutrients and physiographic (including soil texture) variables, while smaller but notable proportions of variance were attributed to geographical coordinates and to metal contents. Our study shows that vegetation differentiation at a local scale is determined by a complex factor of soil properties and climatic parameters, together with variation in disturbance and succession
Characteristics of the cosmic ray ground level enhancements on January 20, 2005, and December 13, 2006, as obtained from world-wide neutron monitor data
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