• 한국전산구조공학회논문집
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• 제29권2호
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• pp.131-140
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• 2016

최근 강풍으로 인한 옥외광고물의 파손 및 추락으로 인해 불특정 다수에게 인적 및 물적 피해를 야기하고 있다. 옥외광고물은 사유시설과 공공시설물의 성격을 모두 갖기 때문에 옥외광물로 인한 피해를 저감하는 것은 개인의 노력뿐 아니라 제도 및 규정을 통해서도 이루어져야한다. 이러한 피해는 강풍에 취약한 옥외광고물의 내풍설계 기준의 미비가 가장 큰 요인으로 인식되고 있어 본 연구에서는 옥외광고물의 내풍설계 표준을 제시하였다. 이를 위해 풍속에 영향을 주는 옥외광고물 설치위치의 주변 풍환경이나 높이, 설치위치 등 풍속과 관련한 요소를 반영하였으며, 건축구조기준 2015(안)의 기본풍속도와 풍속보정 절차에 의한 풍하중 산정 과정을 제시하였다. 이 과정에서 공학적 판단이 요구되는 옥외광고물 설치위치 주변의 지표 조도구분 및 지형계수 평가에 대해 정략적으로 적용할 수 있는 기준을 제시하였다. 또한 비전문가 관점에서 적용하기 용이하도록 가능한 단순화된 정량화 절차를 제시하였다.

• Wind and Structures
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• 제19권1호
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• pp.15-33
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• 2014

This paper describes partial turbulence simulation and validation of the aerodynamic pressures on building models for an open-jet small-scale 12-Fan Wall of Wind (WOW) facility against their counterparts in a boundary-layer wind tunnel. The wind characteristics pertained to the Atmospheric Boundary Layer (ABL) mean wind speed profile and turbulent fluctuations simulated in the facility. Both in the wind tunnel and the small-scale 12-Fan WOW these wind characteristics were produced by using spires and roughness elements. It is emphasized in the paper that proper spectral density parameterization is required to simulate turbulent fluctuations correctly. Partial turbulence considering only high frequency part of the turbulent fluctuations spectrum was simulated in the small-scale 12-Fan WOW. For the validation of aerodynamic pressures a series of tests were conducted in both wind tunnel and the small-scale 12-fan WOW facilities on low-rise buildings including two gable roof and two hip roof buildings with two different slopes. Testing was performed to investigate the mean and peak pressure coefficients at various locations on the roofs including near the corners, edges, ridge and hip lines. The pressure coefficients comparisons showed that open-jet testing facility flows with partial simulations of ABL spectrum are capable of inducing pressures on low-rise buildings that reasonably agree with their boundary-layer wind tunnel counterparts.

• 대한기계학회논문집B
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• 제35권10호
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• pp.1075-1081
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• 2011

이중벽관 증기발생기에서 전열관의 내관과 외관 사이의 틈새에 채워진 헬륨가스의 압력변동으로 전열관의 파손을 감지하는 방법이 개발되고 있다. 이 현상을 모사하기 위해 압력으로 밀착된 두 평판사이의 미세한 틈새에서의 누설률을 측정하여 실험식을 개발하였다. 이 실험식에서는 틈새의 간격과 유동마찰계수가 표면조도에 의해 상호 결합된 형태로 기술되는데, 간단한 평판접촉 모델을 사용하여 유동마찰계수 식을 분리하였다. 이 실험식과 균열에서의 누설률 예측에 사용되고 있는 기존의 유동마찰계수 관련 실험식들을 상호 비교하였다. 레이놀즈 수의 적용범위가 상이함에도 불구하고 개발한 실험식이 0.1~0.35 에서는 레이놀즈 수가 높은 경우에 적용되는 실험식들과 유사한 값을 보였다.

• 한국재료학회지
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• 제12권11호
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• pp.865-869
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• 2002

We investigated the reaction stability of titanium, cobalt and their bilayer films with side-wall spacer materials of SiO$_2$ for the salicide process. We prepared Ti 350 $\AA$, Co 150 $\AA$, Co 150 $\AA$/Ti 100 $\AA$ and Ti 100 $\AA$/Co 150 $\AA$ films on 1000 $\AA$-thick thermally grown SiO$_2$ substrates, respectively. Then the samples were rapid thermal annealed at the temperatures of $500^{\circ}C$, $600^{\circ}C$, and $700^{\circ}C$ for 20 seconds. We characterized the sheet resistance of the metallic layers with a four-point probe, surface roughness with scanning probe microscope, residual phases with an Auger depth profilometer, phase identification with a X-ray diffractometer, and cross-sectional microstructure evolution with a transmission electron microscope, respectively. We report that Ti reacted with silicon dioxide spacers above $700^{\circ}C$, Co agglomerated at $600^{\circ}C$, and Co/Ti, Ti/Co formed CoTi compound requiring a special wet process.

• 한국전산유체공학회지
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• 제21권2호
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• pp.40-46
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• 2016

In the paper, a study on the analysis of fouling effect of the venturi flowmeter is described. In the research flow field solutions about the venturi flowmeter with fouling are obtained and then the effects on fouling states by inserting a ring into the throat of venturi flowmeter are studied. As the result shows, it is found that the inserted ring reduces the fouling effect due to the flow separation occurring at the ring. Consequently, a venturi flowmeter with ring shows smaller pressure loss differences than the original configuration with no ring on fouling state. This research suggests an efficient and economic method of inserting a ring to reduce the pressure loss effects due to fouling.

• Wind and Structures
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• 제11권5호
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• pp.413-426
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• 2008

A wind tunnel study has been carried out to determine the influence of spacing between buildings on wind characteristics above rural and suburban type of terrain. Experiments were performed for two types of buildings, three-floor family houses and five-floor apartment buildings. The atmospheric boundary layer (ABL) models were generated by means of the Counihan method using a castellated barrier wall, vortex generators and a fetch of roughness elements. A hot wire anemometry system was applied for measurement of mean velocity and velocity fluctuations. The mean velocity profiles are in good agreement with the power law for exponent values from ${\alpha}=0.15$ to ${\alpha}=0.24$, which is acceptable for the representation of the rural and suburban ABL, respectively. Effects of the spacing density among buildings on wind characteristics range from the ground up to $0.6{\delta}$. As the spacing becomes smaller, the mean flow is slowed down, whilst, simultaneously, the turbulence intensity and absolute values of the Reynolds stress increase due to the increased friction between the surface and the air flow. This results in a higher ventilation efficiency as the increased retardation of horizontal flow simultaneously accompanies an intensified vertical transfer of momentum.

• 한국분말재료학회지
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• 제20권4호
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• pp.308-312
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• 2013

In this paper, we describe experiment results using a vibration assisted hybrid femtosecond laser (${\lambda}$:795 nm) ultra-precision machining system. The hybrid system we have developed is possible that optical focal point of the femtosecond laser constantly and frequently within the range of PZT(piezoactuator) vibrator working distance. Using the hybrid system, We have experimented on brass and studied about differences of result of hole aspect ratio compare to general experiment setup of femtosecond laser system. Aspect ratio of a micro hole on brass is increased as 54% with 100 Hz vibration frequency and surface roughness of the side wall also improved compare to non-vibration.

• 한국농공학회논문집
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• 제56권1호
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• pp.81-88
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• 2014

Accurate wind data is essential for predicting airborne spread of virus. OpenFOAM was used for computational fluid dynamics (CFD) simulation procedure which is under GNU GPL (General Public License). Using complex terrain, DEM (Digital Elevation Map) that was prepared from GIS information covering a research site is converted to a three dimensional surface mesh that is composed by quad and full hexahedral space meshes. Around this surface mesh, an extended computational domain volume was designed. Atmospheric flow boundary conditions were used at inlet and roughness height and was considered at terrain by using rough wall function. Two different wind conditions that was relatively stable during certain periods were compared in 3 different locations for validating the accuracy of the CFD computed solution. The result shows about 10 % of difference between the calculated result and measured data. This procedure can simulate a prediction of time-series data for airborne virus spread that can be used to make a web-based forecasting system of airborne virus spread.

• 펄프종이기술
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• 제30권1호
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• pp.7-17
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• 1998

With the advent of CLSM in the end of 1980s, it has been applied to the field of pulp and paper science in various ways. This study showed the potentials of CLSM In analyzing a change of pulp fiber and paper properties before and after mechanical treatment. In particular, a quantification of internal fibrillation has been done using cross-sectional images of fibers and image analysis technique, then evaluated the effects of fiber wall delamination on fiber and paper properties. It showed that the delaminated fibers were closely associated to development of the interfiber bonding in a fiber network. The CLSM made it possible to investigate a density profile along the sheet thickness, which was created by some papermaking processes like pressing, drying and calendering. Through the attempt to observe the forming procedure of a fiber network during handsheet making, the CLSM images showed that the pressing stage was considered greatly to contribute to generation of interfiber bonding with removing a free water and partly a bound water between fibers. In addition, the CLSM could be used to illustrate not only a surface profile of paper showing the extent of smoothness or roughness, but also a density profile in a B-direction of the network. Finally it became evident that the CLSM could be used as an excellent tool to predict development in fiber and paper properties before and after mechanical treatment during papermaking processes.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.20-23
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• 2001

Plasma Display Panel(PDP) is a type of flat panel display utilizing the light emission produced by gas discharge. Barrier Ribs of PDP separating each sub-pixel prevents optical and electrical crosstalks from adjacent sub-pixels. The mold for forming the barrier ribs has been newly researched to overcome the disadvantages of conventional manufacturing processes such as screen printing, sand-blasting and photosensitive glass methods. The mold for PDP barrier ribs have stripes of micro grooves transferring glass-material wall. In this paper, Stripes of grooves of which width 48${\mu}{\textrm}{m}$, depth 124$\mu\textrm{m}$ , pitch 274$\mu\textrm{m}$ was acquired by machining of single crystal silicon with dicing saw blade. Maximum roughness of the bottom of the grooves was 59.6nm Ra in grooving Si. Barrier ribs were formed with silicone rubber mold, which is transferred from grooved Si forming hard mold. Silicone rubber mold has the elasticity, which enable to accommodate the waveness of lower glass plate of PDP. The methods assisted by the microwave and UV was adopted for reducing the forming time of glass paste.