1,720,995 research outputs found
Review of metamaterials principles and methods in ventilation ducts: 1928–2024
No full textAcoustic metamaterials (AMMs) have emerged as a promising strategy for low-frequency noise control in ventilation ducts, offering subwavelength, tunable solutions that overcome key limitations of conventional silencers, such as high pressure drop and reduced long-term performance. This review presents a structured analysis of 54 studies on AMMs for duct acoustics, with civil, mechanical, aerospace, and biomedical engineering applications. AMM unit designs are categorized by physical mechanism, including resonant cavities, acoustic membranes, Herschel–Quincke tubes, Fano-like interference structures, duct shape modifications, micro-perforated panels, and porous materials. The associated acoustic and flow-related performance parameters, such as insertion loss, transmission loss, absorption coefficient, flow velocity, temperature, pressure drop, Reynolds number, and Mach number, are systematically examined. Analytical, numerical, and experimental approaches are reviewed with attention to their respective merits and limitations, particularly in capturing multi-physical interactions between acoustics, fluid flow, and structural dynamics. Of the studies surveyed, 35 employed monophysical models, 8 used loosely coupled (monophysical parallel) methods, and only 11 adopted fully coupled multi-physical frameworks. This review highlights the need for integrated design methodologies and standardized evaluation under realistic flow conditions to advance the effective implementation of AMMs in ducted acoustic systems
Effective soundscape characterisation of an acoustic metamaterial based window: A comparison between laboratory and online methods
No full textQualitative investigation of the sound environment from human perception has lately reached wider attention through psychophysical and Soundscape descriptors; However, laboratory or in situ questionnaire can only reach a limited amount of demographic backgrounds, as, in a limited variety of cultural and geographical variation in a medium-short time, risking to bias/influence the results of the analysis. Starting from a related paper, the authors illustrated how to include human perception and psychoacoustics in evaluating an acoustic metawindow (AMW) unit effectiveness. This paper investigates the robustness of the mixed laboratory and online methodology and proves the validity of the exclusively online-based soundscape questionnaire method according to a number of headset setups. For this reason, a first Laboratory experiment with a fixed and controlled setup was followed by an Online 1 experiment, where the same participants took the same questionnaire (with a three weeks' time difference). Finally, the Online 2 experiment was used to broaden the sample background (results concerned the online method only). The setups mostly influenced the participants' responses by neutralising it (in 48% of the cases) while reporting a rate with an acceptable error (45% of Δrate = 0/5 and 39% of Δrate = 1/5). Wired headphones based rates agreed with the laboratory one consistently (36% of Δrate = 0 and overall CV = 2–25% through soundscape descriptors). Wired earphones had a similar Δrate percentage but with an overall more neutralised soundscape perception (overall CV = 1–40% compared with Laboratory rates). Wireless earphones caused the extremer Δrate (54% of Δrate = 3). Finally, natural and human noises are more detectable spontaneously, while traffic or other artificial noise are mostly recognised when directly addressed to the participants. This additional analysis gives more precise information about how efficient is the online method compared to the laboratory one. If accounted accordingly, an online-based soundscape questionnaire setup could also be viewed as a solid alternative to grasp a wider range of human perception points of view according to a broader cultural and geographical background
Broadband potential optimisation of a full scale acoustic metawindow performance
No full textNoise control and airflow in duct-like systems are among some of the most interesting applications to conjugate AMMs innovation and sustainability. Specifically applied to the built environment, they opened up a new field of research supporting indoor wellbeing, sanitised environments, and public activities. Previous research conducted by the authors has proved AMM based window to be a resourceful way to address both natural ventilation and reduce the incoming noise propagation; however, the effective spectral range did not cover lower frequencies (50-350 Hz). For this reason, in the presented paper, implementation in the AMM unit geometry was performed over a full-scale acoustic metawindow (AMW). The resonating volume has been enhanced (by 200% of the original one) and coupled with a set of lateral flanks. Numerical analysis through FEM proved that on a range of opening ratio from 3 to 33%, the TL related to the window is improved overall of the 70% on the frequency range from 50 to 350 Hz. Such results encourage the use of new AMMs ergonomic windows in place of standard ones to achieve both natural ventilation and noise attenuation from 50 to 5k Hz, being resourceful for domestic, sanitary, and public applications
The influence of thermo-hygrometric conditions on metamaterials' acoustic performance: an investigation on a 3-D printed coiled-up resonator
No full textIn the last decades, coiled-up resonators have become popular within the metamaterial research community for narrow band, low frequency resonances combined to subwavelength thickness. Such structures are particularly suited to one of the most widespread manufacturing processes, i.e. PET-based 3D printing. Acoustic performance of coiled-up resonators depends on the geometrical parameters’ variation, which is influenced by thermo-hygrometric conditions; however, the deformation itself needs to be further investigated. For this reason, the present paper evaluates the correlation between temperature, relative humidity, and the geometrical parameters’ (spiral length and hole diameter) deformations and, consequently, the acoustic performance of a 3D printed coiled-up resonator. A combined approach through analytical, numerical, and experimental measurements quantified the coefficient increasing the temperature (T = 10 – 50 °C) , and the relative humidity (RH = 20 – 50 – 80 %) of the samples. Relative humidity variations turned neglectable discrepancies on sound absorption’s peaks. On the other hand, the increase in temperature caused a frequency peaks’ shift following an exponential trend. This study can be a starting point for practical applications when the thermos-hygrometric variations are of concern
Acoustic Requalification of an Urban Evolving Site and Design of a Noise Barrier: A Case Study at the Bologna Engineering School
Full text linkThe increase in new infrastructure development has raised closer attention to the environmental noise of new expansion areas. This study investigates the urban evolution of Terracini Street's surrounding area in the Navile district, Bologna, Italy. In the last 20 years, this area has undergone various transformations, from a suburban industrial area to a new university and residential one. First, the morphologic and infrastructural characteristics of the site are established. Then, the existing regulations (acoustic, urban, and infrastructural regulations, whether local or national) are evaluated. Next, the results of environmental noise measurements are presented. Since a heavily trafficked infrastructure is very close to the occupied public area, noise limits are severely exceeded. A noise mitigation design stage follows, focusing on a novel noise barrier design. Specifically, particular attention is paid to the visual and ecological impact of the noise barrier on the area's landscape, which must be representative of the new location of the School of Engineering. The sonic crystal technique is exploited to implement an effective noise barrier (average insertion loss of 10 dB(A) in the 200 Hz-1 kHz range), allowing air ventilation and visual transparency. This case study could further evolve using other acoustic metamaterial techniques or in different application sites
Development of metacage for noise control and natural ventilation in a window system
Full text linkVentilation window is one of the critical elements in sustainable building development, although frequently, outdoor factors such as environmental noise can limit their use. It is necessary to develop windows with both natural ventilation and noise mitigation functions. Acoustic Metamaterials (AMMs) set a new trend in solving physical challenges related to sound wave control, which can find their applications in ventilation window. This study presents a design based on acoustic metacage concept to enhance the window’s natural ventilation and acoustic performance. Finite Element Method (FEM) is used to study and optimise the acoustic performance of the metacage window. The ventilation is evaluated at the same time following predefined guidelines related to the window’s opening ratio and air-flow directivity. The metacage window structure finally, reduces the noise transmission with a mean value of 30 dB within a frequency range of 350–5000 Hz and has an opening ratio of the 33% compared to the whole system surface. The front panel gives a mean high frequencies TL contribution of 17 dB (2000–5000 Hz). Additional lateral constraint and cavities increase the TL performance up to 70% on a wider lower frequency range (350–5000 Hz). Thanks to the cavities, the resonant unit cells among the acoustic metasurface (AMS) significantly suppress sound from exiting the structure in broadband frequencies and allow bigger opening on the lateral side. This significantly contributes to the natural ventilation potential of the metacage window, which in the long term, becomes equally effective to the conventional open windows
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
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