• 대한기계학회논문집B
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• 제30권12호
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• pp.1173-1180
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• 2006

This study deals with fluid flow and heat transfer around a module cooled by forced air flow generated by a piezoelectric(PZT) fan in an enclosure. The fluid flows were generated by a flexible PZT fan which deflects inside a fluid transport system of comparatively simple structure mounted on a PCB in an enclosure($270\times260\times90mm^3$). Input voltages of 30V and 40V, and a resonance frequency of 28Hz were used to vibrate the cooling fan. Input power to the module was 4W. The height in an enclosure was changed 23$\sim$43mm. The fluid flow around the module was visualized by using PIV system. The temperature distributions around a heated module were visualized by using liquid crystal film. As the height in an enclosure and the input voltage of PZT fan increased, the cooling effect of module using a PZT fan increased. We found that the flow type was T- or Y-shape and the cooling effect was increased by the wake generated by a PZT fan.

• Journal of Korean Society for Atmospheric Environment
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• 제17권E2호
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• pp.61-70
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• 2001

In recent years there have been growing interests in the potential environmental effects of global climate change. Of specific interests is the role that climate change may play in altering natural volatile organic compound.(NVOC) emissions from trees and the subsequent impact of this perturbation on air quality and ozone formation. A novel vegetation enclosure chamber method was designed and constructed of Tedlar in order to estimate more accurate and precise NVOC emission rates of either small whole plants or the branches of large trees. The enclosure chamber was initially tested in the laboratory and also successfully evaluated in the field. Overall precision for this enclosure was estimated as RSD<10%(n=9). The overall errors associated with the enclosure method in a laboratory system might be relatively small (say<$\pm$15%); however, they might be rather large(say$\pm$40%) in a field-based system. Two consecutive samples were collected on each sampling day from the two pine species during the test period. Slash pine studies showed that the absolute percentage difference between the first and second samples varied from 0.33 to 29%. The percent differences between consecutive emission for loblolly pines varied from 0.74 to 24.2%.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.216-221
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• 2001

The equivalent source method(ESM) is used for the calculation of the internal pressure field for an enclosure which can have arbitrary boundary conditions and may include internal objects which scatter the sound field. The advantage of using ESM is that it requires relatively low computing cost and is easy to model the internal diffracting objects. In the ESM modelling, some of the equivalent positions are chosen to be the same as the first order images of the source inside the enclosure, some are positioned on a spherical surface some distance outside the enclosure. The normal velocity on the surfaces of the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and the expected is minimized by adjusting the strength of the equivalent sources. This study is on the optimal equivalent source positions, the far field sources. Typically, the far field sources are evenly distributed on a surface of a virtual sphere which is centered at the enclosure with a sufficiently large radius. In this study, optimal far field source locations are searched using simulated annealing method and simulation results showed that optimally located sources gave better accuracy even with a smaller number of far field sources.

• 설비공학논문집
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• 제12권2호
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• pp.150-160
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• 2000

Turbulent natural convective flow and heat transfer in a square enclosure with horizontal partition are investigated numerically. The enclosure is composed of a lower hot and a upper cold horizontal walls and adiabatic vertical walls. Partitions carried with the upward, downward, and both control plates are attached perpendicularly to the one of the vertical insulated walls, respectively. The low Reynolds number $k-\varepsilon$ model is adopted to calculate the turbulent thermal convection. The governing equations are solved by using the finite element method with Galerkin method. The computations have been carried out by varying the length of partition, the position of control plates, and the Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height for water(Pr=4.95). When the control plates are attached at the edge of partition, the stability of oscillating flow grows wrose with the increase of Rayleigh number and the partition length. The heat transfer rate has been reducer than that of no control plate due to the restraint of control plates with the increase of Rayleigh number.

• 한국전자파학회논문지
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• 제23권5호
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• pp.652-659
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• 2012

직사각형 슬릿 개구를 갖는 금속 함체에 수직, 수평 편파를 입사하여 차폐 효과를 연구하였다. 직사각형 슬릿개구의 magnetic polarizability와 금속 함체의 공진 모드를 이론적으로 분석하였고, 이를 바탕으로 시뮬레이션 결과와 측정 결과를 비교 분석하였다. 또한, 함체 내부 프로브의 위치에 따른 차폐 효과 의존성도 분석하였다.

• 대한안전경영과학회지
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• 제24권4호
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• pp.101-107
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• 2022

To test a flameproof enclosure for the safety certificate, a reference pressure of explosion needs to be determined. However, the explosion pressure may be changed according to relative humidity of explosive gases. Therefore, the guideline on relative humidity should be recommended for measuring the explosion pressure for accurate and reproducible testings. This study examined the relationship of explosion pressure with relative humidity of hydrogen (31 vol %)-air and acetylene (14 vol %)-air mixture gases. The explosion pressures were measured by increasing the relative humidity of the gases by 10 % from dry state to 80 % in a cylindrical explosion enclosure of 2.3 L. on ambient temperature and atmospheric pressure (1 atm). The maximum explosive pressures were remained almost constant until the relative humidity reached 10 % for the hydrogen-air mixture and 20 % for the acetylene-air mixture. However, the maximum explosive pressures linearly decreased as the relative humidity increased. Based on the results of the study, it would be recommended to use 10 % relative humidity for the hydrogen-air mixture and 20 % for the acetylene-air mixture as the critical value in testing a flameproof enclosure.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1993년도 학술논문발표회 논문집 제12권 1호
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• pp.68-72
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• 1993

A method to measure the distortions of the loudspeaker at low frequencies without an anechoic chamber is proposed. This method utilizes the fact that the n-th harmonic distortion outside the enclosure is boosted by 40log n dB compared to that inside the enclosure. By compensating for the effect of standing waves occuring inside the enclosure, it is possible to predict the distortions for wide frequency ranges below the first break-up frequency of the diaphragm. The method is applicable to the intermodulation distortion as well.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 하계학술대회 논문집 A
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• pp.290-292
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• 1993

In this paper, analysis of the noise induced by rotating machines and the mode analysis of a 3-dimensional enclosure are presented. Adaptive active noise control algorithms for the multi-channel case are proposed. Computer simulations were done to show usefulness of the designed algorithm in a 3-dimensional enclosure case.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.786-789
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• 2005

An acoustic total or partial enclosure is widely used to reduce the sound pressure level propagating from a noise source. However, the performance of the acoustic enclosure is decreased by its inherent limitations such as temperature rise or acoustic pressure build up inside the enclosed acoustic field. In general, a silencer is installed to overcome these limitations, for large amount of air can be exchanged through the silencers. In this reason, a parallel baffle type duct silencer with acoustic resonators is studied to reduce the transmitted noise from a transformer. In this silencer, the high frequency components of the transmitted noise over 360Hz are effectively absorbed by the parallel baffles and the other ones, 120 and 240 Hz, are reduced due to the presence of Helmholtz resonators. Large sound attenuation is achieved by applying the sound resonating barrier to the large transformers in a substation.

• 한국전자파학회논문지
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• 제20권1호
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• pp.60-66
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• 2009

본 논문은 유전체로 막힌 개구를 갖는 함체의 차폐 효과(SE)를 계산하는 해석적 방법을 제안한다. 제안된 방법은 기존의 방법으로 해석할 수 없는 유전체로 막힌 개구를 갖는 함체의 SE 해석이 가능하다. 제안된 방법의 타당성을 검증하기 위해 기존에 제시된 방법과 상용 프로그램의 SE 해석 결과를 비교 검증하였다. 제안된 방법을 이용하여 덮개 유전체의 유전율과 두께 변화, 함체 내 관측점 위치 변화, 개구의 폭과 높이 변화에 대한 SE 변화를 계산하였다.