1,720,963 research outputs found
“Studio teorico-sperimentale delle proprietà acustiche di pannelli fonoassorbenti trasparenti microforati
No full textNella correzione acustica degli ambienti confinati si può verificare l'esigenza di co-niugare buone prestazioni di fonoassorbimento con altre proprietà di carattere estetico o funzionale, quali trasparenza alla luce, durabilità nel tempo, resistenza strutturale.
Una possibile soluzione si può ottenere con tecniche di microperforazione di lastre di materiale plastico trasparente, evitando quindi il ricorso a materiali porosi. Dal punto di vista acustico, i pannelli microforati si comportano come array di risonatori, caratte-rizzati, in virtù del piccolo diametro dei fori, da buone prestazioni anche in assenza di materiali fonoassorbenti nell’intercapedine: ciò è dovuto alle elevate dissipazioni visco-se e termiche che si realizzano nello strato limite all’interno dei fori.
Le prestazioni fonoassorbenti dei pannelli microforati sono note, sia a livello teorico che sperimentale, da vari decenni [1]. Applicazioni integrate di pannelli trasparenti mi-croforati sono state proposte più di recente, sia in ambiente confinato [2], sia in barriere antirumore per infrastrutture di trasporto [3]. Oggi sono commercialmente disponibili rivestimenti di pareti, in alternativa ai tradizionali materiali porosi, realizzati con pan-nelli e membrane microforati. Tali soluzioni, in virtù degli spessori richiesti per ottenere prestazioni fonoassorbenti elevate (inferiori ad 1 mm), richiedono strutture portanti e hanno scarsa resistenza strutturale. Inoltre, le dimensioni (diametri dell'ordine di 0,1 mm) e il numero dei fori richiesti richiedono processi di foratura relativamente com-plessi e costosi.
Nel lavoro si sono studiate, sia a livello sperimentale sia numericamente, soluzioni fonoassorbenti per ambienti confinati, ricorrendo all’impiego di configurazioni a più lastre, in grado di coniugare buone proprietà di resistenza strutturale (spessori di 1-2 mm) e semplicità di foratura (fori di diametro non inferiore ad 1 mm)
Sistema per il recupero energetico dal processo di rigassificazione del gas naturale liquefatto mediante espansione diretta
No full textOptimization of in situ noise barrier intrinsic characteristics measurements
No full textNoise barriers intrinsic characteristics evaluation is fairly complicated if one aims at simulating barrier operating conditions. One of the most successful methods consists of in situ impulse response measurement, in particular by means of MLS signals combined with cross-correlation techniques. This has been adopted by a new CEN Technical Specification. Anyway, such a method has shown limitations and drawbacks.
The aim of the research is first of all to investigate the influence of various parameters, such as source characteristics, measurement apparatus geometry and signal processing technique, on the final results of the measurements. Correlation has been found between errors due to subtraction technique, used to isolate the reflected component, and differences observed in subsequent measures. Particular attention is also paid to barrier materials and shape; reflection coefficient measurements on low- as well as on high-absorptive barriers were performed. Finally, method repeatability and reproducibility were taken into account
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
Sviluppo di un Materiale Innovativo da Granuli di Pneumatici Usati per Applicazioni Acustiche
No full textIl lavoro si pone l’obiettivo di studiare una possibile forma di valorizzazione dei pneumatici fuori uso, favorendo il recupero di materia.
Oggetto del presente lavoro è infatti lo studio di nuovi materiali fonoisolanti, prodotti con granuli di pneumatici usati (in seguito abbreviati con “PG”); si sono in particolare investigate le proprietà acustiche e meccaniche di questi materiali, al fine di valutare le effettive prestazioni raggiungibili.
L’interesse per questo tipo di materiali è dimostrato in letteratura da numerosi Autori, unitamente alla fattibilità tecnica di validi processi industriali per questi materiali, e alla loro commerciabilità
Transmission Loss Measurement of Consolidated Granular Media (L)
No full textThe normal incidence transmission loss of a new class of sustainable acoustic materials, i.e.
consolidated granular media, has been measured to determine their sound insulating performance.
Tests performed on different samples in a standing wave tube suggest that the traditional method
employing an anechoic termination assumption can yield serious errors because its accuracy
depends significantly on the properties of both the termination and the tested sample. Since it is not
possible to implement a perfect anechoic termination over a wide frequency range, a well-developed
alternative approach has been adopted. A simple theoretical analysis has been carried out to compare
these two methods. It has been shown that the two-load method, based on two sets of measurements
with different boundary conditions at the tube termination, can give more reliable and predictable
results. Greater discrepancies have been observed in the case of the anechoic termination method
applied to samples with higher values of flow resistivity. Results of the two-load method match well
with predictions based on a simple model for acoustic transmission through a porous plate
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
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