1,720,992 research outputs found
Design and performance of a ThermoAcoustic Electric Generator powered by waste-heat based on linear and nonlinear modelling
Full text linkThis article presents the design, numerical modeling, and performance evaluation of a multistage ThermoAcoustic Electric Generator (TAEG), aimed at converting thermal energy from internal combustion engine exhaust gases into electricity. The proposed TAEG adopts a double-stage looped resonator configuration, using helium as the working fluid, with an internal static pressure limited to 20 bar for safety reasons. Gas-to-gas hot heat exchangers were specifically designed to recover waste heat at approximately 530 K. Due to practical constraints, commercial audio speakers were employed as acoustic-to-electric transducers, despite their lower impedance compared to ideal linear alternators. Initial linear thermoacoustic simulations conducted using DeltaEC software optimized geometric and operational parameters, predicting an electrical power output around 300 W (150 W per stage) with a resistive load of 10 Omega. However, recognizing the inherent limitations of linear modeling, particularly the omission of nonlinear thermo-fluid dynamics, a computational fluid dynamics (CFD) analysis was conducted using OpenFOAM. The CFD model integrated novel nonlinear porous media formulations tailored for oscillatory flow conditions within the thermoacoustic core. Comparisons between a purely linear DeltaEC and OpenFOAM results revealed excellent qualitative agreement but quantitative differences, primarily due to minor losses caused by abrupt geometric discontinuities, and conical segments. A second DeltaEC model including all minor losses based on the steadystate approximation reveals that dissipation were overestimated compared to the CFD model. Therefore, a third DeltaEC model was built by calibrating minor losses based on CFD data. The findings emphasize the critical role of accurately modeling nonlinear effects to reliably predict TAEG performance and the limitation of the local pressure drop coefficients based on steady-state analysis
INFLUENZA SUGLI INDICI DI VALUTAZIONE DEI REQUISITI ACUSTICI PASSIVI IN SITU DELLA MISURA DEL TEMPO DI RIVERBERAZIONE
No full textA diversi anni dall’entrata in vigore del DPCM 5\12\97 si verificano sempre più casi di contenzioso fra venditore ed acquirente, talvolta basate su risultati differenti ottenuti in situ, nelle misure fatte eseguire dalle parti in causa. Il presente lavoro valuta come la misura del tempo di riverberazione in opera, eseguita in uno stesso ambiente, con l’utilizzo delle metodologie di misura basate sul rumore interrotto o sul rumore impulsivo, incida sugli indici di valutazione dei requisiti acustici passivi a seconda della tipologia di sorgenti utilizzate
Heating and cooling loads with electrochromic glazing in Mediterranean climate
No full textThe energy consumption necessary to maintain thermal comfort in buildings remains a significant and partially unjustified part, accounting for about 30–40% of the total energy consumption. Despite the increasingly pressing regulations in the energy sector (EPBD recast), the quality of the internal environment remains one of the critical parameters on which to pay more attention in view of a consistent evaluation of the Nzeb building. The windowed components are often designed with thermal insulation performances higher than the minimum requirements but still they lack in design of the incident solar radiation control, which is a particularly delicate topic for indoor comfort and more generally for a higher energy efficiency in buildings. If we think of the numerous variables of influence (typology, orientation, geographical location, etc.), the possibilities to associate energy saving, lighting control and users’ comfort are inevitably entrusted to dynamic systems integrated into the glass. In this paper authors present the results related to the experimental characterization of two identical test rooms with different typologies of windows. One room is furnished with a traditional high thermal performance glass and the other, with an electrochromic glass suitably controlled by remote. The operative temperature measured in both test rooms have been utilized to verify the simulation model developed to assess the energy saving achievable in a Mediterranean climate, taking properly into account the hourly variations of the climate and the actions on the shading regulation systems
An adaptive nonlinear autoregressive ANN model for high time resolution traffic noise predictions. Experimental results for a port city waterfront
Full text linkIn this research study an adaptive recurrent artificial nonlinear neural network identification model has been developed and experimentally tested for dynamically predicting the traffic noise level Leq,1′ with a time refine ment of 1 min. The model has been successfully applied in three selected positions, representative of the waterfront in a Mediterranean port city. Several maritime cities are exposed to a wide range of road traffic fluctuations that negatively impact liveability in the area concerned. Large volumes of road traffic periodically access the port, dynamically affecting the acoustic scenario in neighbouring areas, especially in seaside towns during the tourist season. A signalized intersection, a roundabout, and a wide entrance to a vehicular underpass have been analyzed in the course of two characteristic periods, during which traffic ranged widely from normal to peak yearly intensity. Detailed traffic data for 15 road lanes and noise sequence regressors have been considered as input data sources. This exploratory investigation reveals a good predictive performance of the
model developed, the prediction error of Leq,1′ falling prevalently within the range ±0.5 dB. The experimental profile of Leq,1′ is well reflected by the simulated sequence, and the auto and cross correlation functions confirm how well the identified neural model is able to explain the functional dependence underlying the experimental observations
ASSESSMENT AND COMPARISON AMONG PREDICTION METHODS FOR THE LOW FREQUENCY NOISE PRODUCED BY WIND TURBINES: APPLICATION TO A CASE STUDY
No full textThe present energy scenario leads to an acceleration in the development of the exploitation of renewable sources. Latest regulations impose higher and higher percentage shares of energy from renewable sources. The current technological advancement stresses the wind energy as an energy source endowed of a special reliability. The technology to take advantage of such a source is based on large size wind turbines, with a rated power of about 3 MW.
Among the main environmental problems that have to be faced in planning a new wind farm, the acoustic impact stands out. It consists of noise engendered by wind turbines with a special effect of noise emitted at the low frequency spectrum. Recently Denmark has produced a new regulation which calls for specific procedures for the assessment of noise at low frequencies.
Purpose of the present work is to take stock of the procedures currently employed in the predictive study of the low frequency noise produced by wind turbines. The analysis was carried out by applying the expounded procedures to a real case situated in Sardinia. It concerns a wind farm formed with 21 large size turbines, where a comparison between the results obtained by applying the procedures of ISO 9613 and those provided for by the Danish regulation is shown
An Adaptive Neural Network model for thermal characterization of building components
Full text linkBuilding materials are usually characterized in stationary or almost-stationary conditions and mono dimensional heat flow regime. The existing standards (such as ISO 9869 or EN ISO 6946, EN 12664, EN 12667, ISO 8302 etc), require experiments carried out in steady-state conditions, with a very fine control of the measuring parameters with the aim to apply a simple and reproducible procedure for the determination of thermal properties. However, the thermodynamic conditions that lead to a steady-state operating mode and mono dimensional flow are very difficult to obtain (in real conditions) or very expensive and time consuming (in climate chambers). In this paper the authors present the development of a method for thermal characterization of building components, inferring the steady-state conditions, when only measures in transient conditions are available. The method, based on an adaptive linear neural network (ALNN) model also could be have the potentialities to determine the thermal diffusivity from a significant transient behavior ad hoc imposed. The study targets multilayered walls homogeneous and the results are compared with the experimental data measured by a climate chamber that operate according to the standard EN 12667 (c) 2017The Authors. Published by Elsevier Ltd
Neutral Point Clamped Non-Isolated Three Phase Grid-Integrated PV Inverter Topologies for Leakage Current Reduction
No full textThis study analyses neutral point clamped-based non-isolated grid-connected inverter topologies. Transformerless inverters are widely used because of their higher efficiency, lower cost, and compatibility with grid integration. The main drawback of the non-isolation inverter is maintaining the Common Mode Voltage (CMV), eliminating the Leakage Current (LC) and galvanic isolation during the grid fault condition. Galvanic isolation and elimination of leakage current in non-isolated inverter topologies mainly depend on inverter configuration and pulse width modulation techniques used in the inverter topologies. Many single-phase non-isolated inverter topologies are configured and analysed based on these issues. However, only a few studies have been conducted on three-phase non-isolated inverter configurations. Hence, this paper examines different three-phase non-isolated inverter topologies based on neutral point clamping with modified discontinuous pulse width modulation technique on CMV, LC reduction, current total harmonic distortion, conduction losses and efficiency of the inverter structures. Simulations are carried out in MATLAB/Simulink for proposed inverter topologies, and experimental analysis has been done for validation
An Adaptive Neural Network model for thermal characterization of building components
Full text linkBuilding materials are usually characterized in stationary or almost-stationary conditions and mono dimensional heat flow regime. The existing standards (such as ISO 9869 or EN ISO 6946, EN 12664, EN 12667, ISO 8302 etc), require experiments carried out in steady-state conditions, with a very fine control of the measuring parameters with the aim to apply a simple and reproducible procedure for the determination of thermal properties. However, the thermodynamic conditions that lead to a steady-state operating mode and mono dimensional flow are very difficult to obtain (in real conditions) or very expensive and time consuming (in climate chambers). In this paper the authors present the development of a method for thermal characterization of building components, inferring the steady-state conditions, when only measures in transient conditions are available. The method, based on an adaptive linear neural network (ALNN) model also could be have the potentialities to determine the thermal diffusivity from a significant transient behavior ad hoc imposed. The study targets multilayered walls homogeneous and the results are compared with the experimental data measured by a climate chamber that operate according to the standard EN 12667
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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