1,720,972 research outputs found
Clustering Inverse Beamforming and multi-domain acoustic imaging approaches for vehicles NVH
Full text linkIl rumore percepito all’interno della cabina di un veicolo è un aspetto molto rilevante nella valutazione della sua qualità complessiva. Metodi sperimentali di acoustic imaging, quali beamforming e olografia acustica, sono usati per identificare le principali sorgenti che contribuiscono alla rumorosità percepita all’interno del veicolo. L’obiettivo della tesi proposta è di fornire strumenti per effettuare dettagliate analisi quantitative tramite tali tecniche, ad oggi relegate alle fasi di studio preliminare, proponendo un approccio modulare che si avvale di analisi dei fenomeni vibro-acustici nel dominio della frequenza, del tempo e dell’angolo di rotazione degli elementi rotanti tipicamente presenti in un veicolo. Ciò permette di ridurre tempi e costi della progettazione, garantendo, al contempo, una maggiore qualità del pacchetto vibro-acustico. L’innovativo paradigma proposto prevede l’uso combinato di algoritmi di pre- e post- processing con tecniche inverse di acoustic imaging per lo studio di rilevanti problematiche quali l’identificazione di sorgenti sonore esterne o interne all’abitacolo e del rumore prodotto da dispositivi rotanti. Principale elemento innovativo della tesi è la tecnica denominata Clustering Inverse Beamforming. Essa si basa su un approccio statistico che permette di incrementare l’accuratezza (range dinamico, localizzazione e quantificazione) di una immagine acustica tramite la combinazione di soluzioni, del medesimo problema inverso, ottenute considerando diversi sotto-campioni dell’informazione sperimentale disponibile, variando, in questo modo, in maniera casuale la sua formulazione matematica. Tale procedimento garantisce la ricostruzione nel dominio della frequenza e del tempo delle sorgenti sonore identificate. Un metodo innovativo è stato inoltre proposto per la ricostruzione, ove necessario, di sorgenti sonore nel dominio dell’angolo. I metodi proposti sono stati supportati da argomentazioni teoriche e validazioni sperimentali su scala accademica e industriale.The interior sound perceived in vehicle cabins is a very important attribute for the user. Experimental acoustic imaging methods such as beamforming and Near-field Acoustic Holography are used in vehicles noise and vibration studies because they are capable of identifying the noise sources contributing to the overall noise perceived inside the cabin. However these techniques are often relegated to the troubleshooting phase, thus requiring additional experiments for more detailed NVH analyses. It is therefore desirable that such methods evolve towards more refined solutions capable of providing a larger and more detailed information. This thesis proposes a modular and multi-domain approach involving direct and inverse acoustic imaging techniques for providing quantitative and accurate results in frequency, time and angle domain, thus targeting three relevant types of problems in vehicles NVH: identification of exterior sources affecting interior noise, interior noise source identification, analysis of noise sources produced by rotating machines. The core finding of this thesis is represented by a novel inverse acoustic imaging method named Clustering Inverse Beamforming (CIB). The method grounds on a statistical processing based on an Equivalent Source Method formulation. In this way, an accurate localization, a reliable ranking of the identified sources in frequency domain and their separation into uncorrelated phenomena is obtained. CIB is also exploited in this work for allowing the reconstruction of the time evolution of the sources sought. Finally a methodology for decomposing the acoustic image of the sound field generated by a rotating machine as a function of the angular evolution of the machine shaft is proposed. This set of findings aims at contributing to the advent of a new paradigm of acoustic imaging applications in vehicles NVH, supporting all the stages of the vehicle design with time-saving and cost-efficient experimental techniques. The proposed innovative approaches are validated on several simulated and real experiments
Sound source identification in time domain exploiting the clustering inverse beamforming
Full text linkAcoustic imaging techniques allow the user to see what he/she is listening to. This paper aims at proposing an inverse procedure that allows for retrieving the evolution of the noise source identified in a beamforming map. Such approach overcomes the limit of frequency domain strategies, and opens up different application fields such as auralization, coherence analyses, etc. The source localization step is performed in frequency domain with the goal of accurately identifying the source coordinates. The corresponding time signals are subsequently obtained by convolving in time domain the microphones data with multiple input-multiple output impulse responses corresponding to the back-propagating functions identifying the receiver-source link. The formulation of the algorithm is presented in this paper and its main strengths and limitations are discussed. Applications are shown in simulated and real experiments
Clustering inverse beamforming for vehicles NVH
No full textClustering Inverse Beamforming is an array-based acoustic imaging technique to solve inverse problems formulated by discretizing the source region into elementary equivalent sources. It is based on a statistical processing of multiple realizations of the acoustic image, related to the investigated source region, iteratively obtained solving the corresponding inverse problem on different clusters of microphones, taken from the same microphones array. The result of such statistical processing is stored in the so-called "clustering mask matrix". This function is defined, in the source region, where it is interpretable as the confidence level of finding a physical source in each location within the domain. The inner statistical nature of such approach prevents the occurrence of numerical issues related to the solution of the inverse problem. It allows accurate localization and optimal quantification by enabling to focus on those sub-regions most likely to be the location of physical sources. Moreover, if combined with Principal Component Analysis, the method provides a robust criterion for uncorrelated noise source separation with no need of reference sensors in the proximity of the investigated object. Clustering Inverse Beamforming is applicable to exterior as well as to interior acoustic imaging problems. It does not require any special geometrical configuration of the microphones array. The technique is presented both on numerical simulations and on experiments related to vehicles NVH applications
Emissions, Performance and Vibro-Acoustic Analysis of a Compression-Ignition Engine Running on Hydrotreated Vegetable Oil (HVO)
No full textTo meet future energy sustainability and carbon neutrality requirements, disruptive changes to the current energy mix are expected. Renewable fuels, such as hydrotreated vegetable oil (HVO), could play an important role in this context. To assess the potential of HVO, further quantitative research analyses are still required in order to emphasize the benefits (and drawbacks, if any) from a global perspective, rather than limiting the investigation to a single topic (e.g., emissions).
For this purpose, HVO and conventional diesel were compared, in this study, running initially the engine with the same (diesel-oriented) calibration, before being optimized using purposely developed fuel-specific calibrations.
In terms of exhaust pollutant emissions, HVO showed the potential to substantially reduce engine-out emissions of soot, HC and CO at low loads, while differences in exhaust emissions at higher loads proved to be mainly determined by the amount of oxygen available in the combustion chamber, rather than the specific characteristics of the fuels. HVO also demonstrated reductions in tank-to-wheel CO2 emissions, due to lower fuel consumption, even though the primary benefit of renewable fuels should be highlighted in a larger well-to-wheel analysis.
In addition to emission analyses, since extensive investigations on the area of vibroacoustic behavior of engines running on renewable fuels are rare in the literature, a thorough comparison between regular diesel and HVO was carried out on this aspect. In this preliminary activity, the acoustic analysis focused solely on combustion noise, which was extracted by using dedicated signal processing techniques. This approach allowed the authors to focus on the noise contribution that is specifically influenced by the fuel characteristics. Furthermore, the vibrations of the engine block were evaluated. The results showed slightly lower levels of HVO in terms of both noise and vibrations
Uncorrelated noise sources separation using inverse beamforming
No full textThe separation of a measured sound field in uncorrelated sources distributions can be very useful when dealing with sound source localization problems. The use of the Principal Component Analysis (PCA) principle, combined with a Generalized Inverse Beamforming (GIBF) technique, offers the possibility to resolve complex and partially correlated sound sources distributions. Despite very promising, this approach appears still to be optimized and the influence of a number of potentially influent parameters is to be understood. In this paper a developed GIBF algorithm is combined with a PCA and firstly tested on a simulated problem, then applied on gradually more complex real cases. A sensitivity analysis on some relevant parameters is carried out in order to evaluate the robustness of the developed algorithm and the effectiveness of the used PCA
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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