1,721,014 research outputs found
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 sub-wavelength 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
Mixing materials in false ceilings to increase sound diffusion in education spaces
No full textAccording to the International standards on education spaces, in situ acoustic tests should achieve specific reverberation time targets. Since the match between predictive formulas and measurements increase with the sound field diffuseness, it is extremely important to pursue such condition through proper design choices. For example, false ceilings can play a key role in controlling room acoustic features; however, the use of such elements is generally considered only for absorption purposes. For this reason, the present work concerns mixing materials in false ceilings within a group of teaching spaces here taken as case studies. The alternation of materials with different acoustic impedances has been investigated through experimental acoustic measurements and numerical models in order to assess the related sound diffusion increase. The ceiling treatment here proposed proved to be an efficient and smart method to exploit diffraction effects along material discontinuities junctions. The match between early design predictive formulas and the results of the acoustic measurements enhanced the reliability of the acoustic design process and set up a potential new guideline for indoor acoustic treatments
Sistema 3D di posizionamento microfonico applicato a indagini di rumore delle macchine
No full textUn innovativo sistema di localizzazione tridimensionale della posizione è stato applicato alle misure del rumore emesso da un motore ibrido Diesel-elettrico Toyota. Il sistema di misura della posizione consente di ottenere le coordinate spaziali di una sonda intensimetrica, utilizzata per valutare in modo accurato e direzionale le emissioni sonore. In questo modo è stato possibile creare mappe, divise per bande di frequenza, delle emissioni della macchina e trovare eventuali punti critici
The coupled rooms of Odeo Cornaro (1534) as support for Renaissance musicians and soloists
Full text linkThe Odeo Cornaro in Padua (Italy) is a well-preserved XVI Century octangular music space (from Latin the ottangulo) surrounded by communicating smaller halls. Inspired by Roman classicism, the Renaissance architect
Falconetto designed such coupled volume system for the private villa of the Venetian nobleman Alvise Cornaro.
With the aim of assessing the acoustics of the Odeo by means of a contemporary approach, acoustic measurements
were performed, and the room acoustic criteria were derived from the acquired impulse responses.
Experimental results were employed to quantify the acoustic coupling effects throughout the environments and
to outline the acoustic features of the central space. Numerical models were used to assess the free path distribution
and the support given by the ottangulo to the singers’ voices. The main outcomes confirm the different
use of the spaces suggested by historical research: while the main hall was probably employed for singing
and playing instruments, the adjoining rooms were intended for erudite conversations and symposia. The symmetrical
shape and the moderate volume of the central octangular space contribute to creating a neat modal
behaviour that accentuates the sound propagation, highlighting the outstanding value of the Odeo as one of the
“loci resonantes” of the past
Acoustical comfort in university lecture halls: simulating the dynamic role of occupancy
Full text linkThe acoustic comfort in teaching environments is generally
determined through requirements concerning
reverberation time, speech intelligibility and HVAC
noise. The presence of students reduces the reverberation
time but concurrently increases the background
noise, that undermines the focus of students and the
vocal effort of teachers. A double set of measures were
acquired in two university lecture halls in unoccupied
and occupied state to investigate the consequences of
occupancy variations. Acoustic simulations allowed
to assess the dynamic effects of the occupancy detecting
the differences of speech intelligibility. Predicting
the student activity may return reliable outcomes improving
the quality of lessons
IDENTIFICAZIONE DELLA TRANSIZIONE DA CAMPO MODALE A DIFFUSO NEI PANNELLI IN XLAM
No full textLa modellazione dell’isolamento acustico di una partizione con i modelli SEA, adottati nelle ISO 12354, ha fra le ipotesi la diffusione del campo di vibrazione nell’elemento in esame. Per quanto riguarda i pannelli in XLAM, quest’ipotesi è senz’altro una delle più stringenti e non sempre verificate nelle frequenze utilizzate per la modellazione. Il presente lavoro riguarda quindi lo studio della transizione fra regime modale e regime diffuso negli elementi in XLAM attraverso il confronto fra misure sperimentali e modelli analitici
Phase change materials (PCM) for building envelope applications: A review of numerical models
No full textPhase Change Materials (PCM) present a great potential for energy efficiency gains in thermal systems, e.g. by
storing solar energy in buildings or heat loads in industrial processes. This is because a great amount of energy can be
stored per mass unit within a small temperature range. Significant applications of this peculiar characteristic of PCM regard
the effective adoption of macro-encapsulated PCM into building envelopes. Several studies on this topic tend to be limited
to a sort of “material selections” on PCM and a lack of systematic analysis has consequently emerged. In order to guarantee
an effective use coupled with economic feasibility, a deep understanding of the phase transition phenomenon is needed.
The study of PCM using computational fluid dynamics (CFD) is documented in several works, in accordance with the
current trend of CFD to become increasingly widespread. Numerical studies on solidification and melting processes use a
combination of formulations to describe the physical phenomena related to such processes, mainly the latent heat and the
velocity transition between the liquid and the solid phases. The methods used to describe the latent heat are divided in three
main groups: (i) source term methods (E-STM), (ii) temperature transforming models (E-TTM) and (iii) enthalpy methods
(E-EM). The description of the velocity transition is in turn divided in three main groups: (i) switch-off method (SOM),
(ii) source term method (STM) and (iii) variable viscosity method (VVM). In this context, the main objective of the present
paper is to review the numerical approaches used to describe solidification and melting processes
Fixed Grid Numerical Models for Solidification and Melting of Phase Change Materials (PCMs)
Full text linkPhase change materials (PCMs) are classified according to their phase change process, temperature, and composition. The utilization of PCMs lies mainly in the field of solar energy and building applications as well as in industrial processes. The main advantage of such materials is the use of latent heat, which allows the storage of a large amount of thermal energy with small temperature variation, improving the energy eciency of the system. The study of PCMs using computational fluid dynamics (CFD) is widespread and has been documented in several papers, following the tendency that CFD nowadays tends to become increasingly widespread. Numerical studies of solidification and melting processes use a combination of formulations to describe the physical phenomena related to such processes, these being mainly the latent heat and the velocity transition between the liquid and the solid phases. The methods used to describe the latent heat are divided into three main groups: source term methods (E-STM), enthalpy methods (E-EM), and temperature-transforming models (E-TTM). The description of the velocity transition is, in turn, divided into three main groups: switch-o methods (SOM), source term methods (STM), and variable viscosity methods (VVM). Since a full numerical model uses a combination of at least one of the methods for each phenomenon, several combinations are possible. The main objective of the present paper was to review the numerical approaches used to describe solidification and melting processes in fixed grid models. In the first part of the present review, we focus on the PCM classification and applications, as well as analyze the main features of solidification and melting processes in dierent container shapes and boundary conditions. Regarding numerical models adopted in phase-change processes, the review is focused on the fixed grid methods used to describe both latent heat and velocity transition between the phases. Additionally, we discuss the most common simplifications and boundary conditions used when studying solidification and melting processes, as well as the impact of such simplifications on computational cost. Afterwards, we compare the combinations of formulations used in numerical studies of solidification and melting processes, concluding that “enthalpy–porosity” is the most widespread numerical model used in PCM studies. Moreover, several combinations of formulations are barely explored. Regarding the simulation performance, we also show a new basic method that can be employed to evaluate the computing performance in transient numerical simulations
PROGETTO INVOLUCRO: TRASMISSIONE LATERALE ATTRAVERSO GIUNTI IN CLT E GIUNTI MISTI MURATURA-CLT
Full text linkIl progetto Involucro è un progetto di ricerca finanziato dalla Regione Emilia-Romagna nell’ambito del POR-FESR 2014-2020 ed ha lo scopo di ottenere un sistema di facciata ventilata ad alte prestazioni termiche ed acustiche attraverso un’indagine sperimentale in condizioni reali, provando diverse soluzioni innovative. In questo articolo verranno mostrati i primi risultati della campagna di misure di trasmissione laterale condotta sulla struttura degli edifici test realizzati per il progetto
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