A hybrid finite element approach to modeling sound radiation from circular and rectangular ducts

This is the post-print version of the Article - Copyright @ 2012 Acoustical Society of AmericaA numerical model based on a hybrid finite element method is developed that seeks to join sound pressure fields in interior and exterior regions. The hybrid method is applied to the analysis of sound radiation from open pipes, or ducts, and uses mode matching to couple a finite element discretization of the region surrounding the open end of the duct to wave based modal expansions for adjoining interior and exterior regions. The hybrid method facilitates the analysis of ducts of arbitrary but uniform cross section as well the study of conical flanges and here a modal expansion based on spherical harmonics is applied. Predictions are benchmarked against analytic solutions for the limiting cases of flanged and unflanged circular ducts and excellent agreement between the two methods is observed. Predictions are also presented for flanged and unflanged rectangular ducts, and because the hybrid method retains the sparse banded and symmetric matrices of the traditional finite element method, it is shown that predictions can be obtained within an acceptable time frame even for a three dimensional problem.This study is supported by the U.K. Engineering and Physical Sciences Research Council (EPSRC)

Indoor air quality in Michigan schools

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72796/1/j.1600-0668.2006.00459.x.pd

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LAI based trees selection for mid latitude urban developments: A microclimatic study in Cairo, Egypt

To study the leaf area index, LAI, based thermal performance in distinguishing trees for Cairo's urban developments, ENVI-met plants database was used as platform for a foliage modeling parameter, the leaf area density, LAD. Two Egyptian trees: Ficus elastica. and Peltophorum pterocarpum were simulated in 2 urban sites with one having no trees, whilst the second is having Ficus nitida trees. Trees LAD values were calculated using flat leaves' trees LAI definition to produce maximum ground solid shadow at peak time. An empirical value of 1 for LAI is applied to numerically introduce LAD values for ENVI-met. Basically, different meteorological records showed improvements for pedestrian comfort and ambient microclimate of the building using E elastica. About 40-50% interception of direct radiation, reductions in surfaces' fluxes around trees and in radiant temperature T-mrt in comparison to base cases gave preferability to E elastica. The lack of soil water prevented evapotranspiration to take place effectively and the reduced wind speeds concluded negligible air temperature differences from both base cases except slightly appeared with the F elastica. Results show that a flat leaves tree if does not validate LAI of 1, the ground shading would not fulfill about 50% direct radiation interception and this value can be used as a reference for urban trees selection. Further simulations were held to investigate LAI value of maximum direct radiation interception. Performing additional simulations, F elastica of LAI of 3 intercepted almost 84% of direct radiation and revealed implications about urban trees in practice and its actual LAI. (C) 2009 Elsevier Ltd. All rights reserved

Energetic, environmental and economic modeling of a solar-assisted residential micro-trigeneration system in a Mediterranean climate

Reducing energy consumption in buildings has become a priority for most countries. However, designing energy-efficient buildings is not a straightforward task - the increasing demand for high comfort standards, provided by conventional ‘energy-hungry’ cooling and heating devices conflicts with the need for demand reduction. Trigeneration, the simultaneous production of electricity, cooling and heating is often viewed as a means of improving energy-efficiency in large and medium sized buildings whilst still delivering thermal comfort. For hot climates, the benefit of utilising the waste heat emitted from an engine unit to power a thermally driven cooling device provides scope to utilise an otherwise wasted energy stream. However, in smaller sized residential buildings, the relatively low and intermittent energy demand coupled with high capital costs, has stifled the uptake of the technology - although the potential for substantial energy savings exists. Moreover, it is very common for home owners in hot climates to opt for other energy-saving devices such as solar water heaters (SWH), which would tend to reduce further the possible demand for space and water heating, possibly making the simultaneous use of both micro-trigeneration and SWH unfeasible. This paper compares the performance of a residential micro-trigeneration system to a hybrid micro-trigeneration/SWH system. The performance of both systems was simulated using a whole building simulation tool run at a high time resolution. The results obtained were then used to quanti fy the energetic and environmental performance of both systems; and also to assess their financial viability against the effect of varying fuel prices, electricity tariffs and a varying Feed-in Tariff (FIT). Results show that whereas the solar aided micro-trigeneration system obtains an overall higher (though marginal) energetic and environmental performance, the financial performance for the same fiscal parameters (fuel prices and electricity tariffs) deteriorates. Moreover FIT, plays an important role in the financial feasibility of the system.peer-reviewe

Gas leakage and distribution characteristics of methyl bromide and sulfuryl fluoride during fumigations in a pilot flour mill

The half-loss time (HLT) is used as an indicator to quantify gas leakage rates during methyl bromide (MB) and sulfuryl fluoride (SF) fumigations. Comparisons of HLTs between three MB and three SF fumigations were quantified in the Hal Ross pilot flour mill, Department of Grain Science and Industry, Kansas State University, USA. The sealing quality or gas tightness of the mill before each fumigation was verified by a pressurization test. Fumigant concentrations during the six fumigations were monitored continuously at 30 locations among the five mill floors during the 24 h fumigation period. A weather station on the mill roof monitored barometric pressure, wind speed and direction, temperature, and relative humidity. A data logger on each mill floor recorded temperature and relative humidity. The pressurization test showed that the relationship between airflow rate and building static pressure varied among the fumigations despite the same areas being sealed by two separate fumigation service providers due to environmental conditions not being identical among the fumigations. Concentrations of both fumigants within the mill ranged from 2 to 7 g/m³ . The observed HLTs for the MB and SF fumigations were in the range of 3.61 to 28.64 h and 9.97 to 31.65 h, respectively, and were inversely related only to wind speeds during fumigation and not any other environmental conditions recorded. In our study, the fumigant leakage rate was found to be predominantly a function of wind speed rather than inherent gas characteristics of MB and SF