1,720,969 research outputs found
Properties of transparent sound-absorbing panels for use in noise barriers
No full textSound absorption and optical transparency are among the most useful properties of noise barriers.
While the latter is required to reduce visual impact and for aesthetical reasons, the former is required
whenever conditions of multiple reflections and presence of close, high receivers occur. The
technical feasibility of a transparent, sound-absorbing panel for outdoor antinoise devices is
investigated in this paper. An analysis of acoustical performance of multiple perforated plates is
performed employing an existing theory for microperforated absorbers under normal incidence and
diffused sound field. An optimization of the geometrical parameters is carried out on the basis of the
European classification criteria of noise barriers for roadways. An optimized three-layer
configuration can achieve sound-absorption properties similar to nontransparent products with only
a limited loss of visual transparency and appropriate mechanical strength. Experimental data
obtained with an impedance tube on small test samples made of transparent polycarbonate and in a
reverberation room on full-scale prototypes are reported, showing a rather good agreement with the
theoretical predictions. The optical performance of a multilayered configuration is evaluated also
Electromechanical actuation for landing gear application: A case study on end-stroke impact in case of high speed free-fall emergency extension
No full textCurrent widespread R&D trend in aeronautics is the use of electromechanical actuators for primary and secondary flight controls and for landing gear applications, often stepping up from an already existing hydraulic or electrohydraulic actuation (EHA) solution to an electromechanical one (EMA). While EMAs must always guarantee the compliance to similar performance requirements and equal safety requirements, they sometimes must also respect the envelope and integration constrains given by the direct substitution of an already existing hydraulic solution. In the context of the current "More Electric Aircraft" trend and within a project of the European Aeronautical R&D framework Clean Sky 2, named ASTIB, an innovative EMA architecture has been preliminarily designed for a regional aircraft landing gear application featuring embedded functions of extension/retraction, uplock and downlock. In such a scenario, the present paper is focused on describing the design loops that led to the definition and optimization of the EMA architecture, with a focus on the end-stroke impact issue which may occur in case of disconnection of the EMA for emergency extension and consequent free-fall at high speed of the landing gear. The estimated impact forces were investigated with three different approaches (analytical-numerical-FEM explicit) aimed to obtain as more accurate and reliable results as possible. The attained outcomes show how the three analyses methods converge to similar results even if with much different computational efforts. In an industrial context, such a difference may have a not negligible impact into design cost and schedule
Proprietà termofisiche di pannelli fonoassorbenti e trasparenti per barriere antirumore
No full textLa possibilità di coniugare, in un’unica soluzione costruttiva, delle buone prestazioni di assorbimento delle onde sonore con proprietà di trasparenza ottica si rivela importante in diverse applicazioni. Il contenimento dell’impatto visivo delle opere antirumore per infrastrutture di trasporto rappresenta infatti uno dei principali requisiti richiesti in fase di progettazione, sia in termini di sicurezza e comfort degli utenti dell’infrastruttura, sia in termini di “accettabilità” dell’opera da parte di coloro che vivono nell’ambiente circostante; l’impiego di materiali trasparenti è una delle soluzioni più comunemente adottate a questo scopo. D’altra parte, l’efficacia di un’opera antirumore può essere ridotta in presenza di superfici scarsamente fonoassorbenti e di riflessioni multiple. Il lavoro si propone di investigare, teoricamente e sperimentalmente, la realizzabilità tecnica di pannelli fonoassorbenti trasparenti, basati sull’impiego di lastre micro-perforate accoppiate ad intercapedini d’aria. Si sono considerate sorgenti di rumore a banda larga, in particolare le infrastrutture di trasporto su strada, optando quindi per configurazioni a più lastre, che consentono un significativo incremento delle prestazioni in un ampio range di frequenze. Oltre ad una breve disamina del modello teorico usato per la previsione delle prestazioni acustiche, sono riportati i risultati delle prove sperimentali condotte in condizioni di incidenza normale (mediante tubo di impedenza) e diffusa (in camera riverberante). Si è osservato un buon accordo tra il modello teorico e i dati sperimentali, che ha consentito un’ottimizzazione dei principali parametri geometrici che governano le prestazioni acustiche del pannello
Different analysis methods for centrifugal fan noise
No full textThis work tackles the difficulties that appear with measuring- and analysis techniques for industrial centrifugal fans. In the made study we've tried to achieve data of a centrifugal fan in order to find a characterising fingerprint of the fan itself. Simply looking to the spectral information seems not to offer a detailed view of the underlying phenomenons. This due to several reasons: like the enormous impact of the generated wind and the limits of the techniques themselves. We've analysed the fan using soundpressure techniques and intensity techniques in anechoic and reverberant rooms respectively.We believe that a fingerprint requires at least both time and frequency information even if fan noise is considered stationary. The made measurements are analysed using wavelet analysis which offers a broader platform to characterise different relations between the mechanical construct and the noise. This by looking to self similarities, discontinuities, pure tones and short term evolution of the noise
Dependence of NVH Performance of Plastic Air Intake Manifolds on the Structural Design
No full textIn recent years, automotive engine manufacturers are increasingly focusing their attention on noise generated by plastic air intake manifolds (AIMs). Due to their lower density and stiffness, some deficiencies in terms of acoustical properties have been observed for plastic intake systems compared to metallic manifolds. In this framework, it seems to be very important to address not only the issue of reducing inlet noise, but also noise radiated via the coupled fluid-structure interaction.
In this work three AIMs, a baseline and two modified models, nominally having equal breathing performance, have been analyzed and compared. The modified ones presented ribs and stays for strengthening the structure. The analyses were performed with concurrent experimental and numerical validated procedures. Accelerometer data on the engine head coupling flange, inner pressure data at the inlet ports and sound intensity measurements on a surrounding grid were collected on the AIMs mounted on a dynamic flow test bench. A structural FEM approach coupled with an acoustic indirect BEM (IBEM) procedure was used to calculate the radiated sound power. Attempts were made at identifying the main noise sources by comparing the results obtained from the coupled simulations, with those achieved with other approaches: uncoupled acoustic IBEM, modal analysis (fluid and structural calculations) and coupled simulations including structural damping.
Due to their equal breathing performance, the differences calculated for the three manifolds could be ascribed to the structure-borne sound. Apart from the first few bands, the latter appeared to be significant throughout the whole examined frequency range and it showed a complex behavior (i.e. shift of resonance frequencies, stiffening the structure). Depending on the design targets (e.g. overall noise reduction, interior sound quality), the optimization of the NVH performance should be rather different and also the structural design of the component should follow different criteria
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
- …
