• 한국광학회지
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• 제4권1호
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• pp.28-35
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• 1993

수차가 정확히 알려지지 않은 결상계에 있어서, exit pupil에 인위적인 위상의 random fluctuation을 도입하고 북스펙트럼 스펙클 영상법(bispectral speckle imaging)을 이용하므로서 수차의 효과를 극소화하여 거의 회절한계의 영상을 얻을 수 있다. Defocus, 구면수차, 코마수차, 비점수차가 각각 1파장씩 있을 때, 주어진 사용영상수(50개)에 대해서 Gaussian random phase model의 correlation length가 어느 정도일 때 최적의 결과를 얻을 수 있는지를 점 물체에 대해 컴퓨터 시뮬레이션을 시행하므로서 연구하였다. 평가기준으로서는 복원된 점물체에 대한 point spread function의 FWHM, normalized peak intensity, MTF 그리고 visual inspection을 채용하였는데, exit pupil 위에서 Fried parameter ${\Upsilon}_0$ 범위에 대한 수차의 차의 rms값 $\sigma$가 구면수차에 대해서는 0.27~0.53 파장일 때, defocus와 비점수차에 대해서는 0.24~0.36 파장일 때, 좋은 결과를 주는 것으로 나타났고, 코마수차의 경우에는 좋은 결과를 얻을 수 없었다.

• 대한기계학회논문집B
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• 제32권2호
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• pp.92-99
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• 2008

The "energy separation phenomenon" through a vortex tube has been a long-standing mechanical engineering problem whose operational principle is not yet known. In order to find the operational principle of the vortex tube, CFD analysis of the flow field in the vortex tube has been carried out. It was found that the energy separation mechanism in the vortex tube consists of basically two major thermodynamic-fluid mechanical processes. One is the isentropic expansion process at the inlet nozzle, during which the gas temperature is nearly isentropically cooled. Second process is the viscous dissipation heating due to the high level of turbulence in both flow passages toward cold gas exit as well as the hot gas exit of the vortex tube. Since the amount of such a viscous heating is different between the two passages, the gas temperature at the cold exit is much lower than that at the hot exit.

• Journal of Mechanical Science and Technology
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• 제15권2호
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• pp.239-247
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• 2001

Measured radiative heat fluxes on the furnace exit plane of a heavy duty power boiler of steam output 1650 T/h are discussed. A high-ash pulverized bituminous coal was used. Such measurements are necessary to improve heat fluxes inside a steam boiler furnace was manufactured. An extra small heat radiation sensor was placed in the water cooled head of the probe. The sensor had no direct contact with furnace gases and measured only the radiant energy. There was no exposure to convective heat transfer. With the radiometric probe, one can obtain a spherical indicatrix of radiation intensity as well as hemispherical radiative heat flux incident on any surface passing through a measuring point inside the furnace. Thus, the quantity of radiation energy, passing through the furnace exit plane, to the convective heating surfaces and the quantity of radiation energy going in the opposite direction were measured. A formula for relative radiative heat flux on the furnace exit plane has been proposed.

• 한국CDE학회논문집
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• 제6권4호
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• pp.222-228
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• 2001

In the milling operation, the burr can be generated on the intersection of cutting tool and workpiece. Due to burr formation, we expect lower efficiency in the operation and the cost increase. In order to understand the burr formation mechanism in the milling operation on the arbitrary feature, we developed an algorithm to analyse and predict the exit burr formation mechanism. Firstly, the recognition of arbitrary shaped workpiece was done through the CAD data. This data includes point information on the vertices of the workpiece. Secondly, tile CAM data regarding tool geometry, tool path, cutting speed, and material data are retrieved to simulate the actual cutting process. Thirdly, we predict the exit burr formation on the edge of workpiece based on the geometric analysis. Lastly, an algorithm implemented in the Windows environment to visualize the burr formation simulation. With this information, we can predict which portion of workpiece would have the exit burr in advance so that we call manage to find a way to minimize the edit burr formation in the actual cutting.

• International Journal of Aeronautical and Space Sciences
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• 제17권3호
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• pp.296-314
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• 2016

This paper presents experimental and computational investigations of synthetic jets with a circular exit for improving flow control performance. First, the flow feature and vortex structure of a multiple serial circular exit were numerically analyzed from the view point of flow control effect under a cross flow condition. In order to improve separation control performance, experimental and numerical studies were conducted according to several key parameters, such as hole diameter, hole gap, the number of hole, jet array, and phase difference. Experiments were carried out in a quiescent condition and a forced separated flow condition using piezoelectrically driven synthetic jets. Jet characteristics were compared by measuring velocity profiles and pressure distributions. The interaction of synthetic jets with a freestream was examined by analyzing vortical structure characteristics. For separation control performance, separated flow over an airfoil at high angles of attack was employed and the flow control performance of the proposed synthetic jet was verified by measuring aerodynamic coefficient. The circular exit with a suitable hole parameter provides stable and persistent jet vortices that do beneficially affect separation control. This demonstrates the flow control performance of circular exit array could be remarkably improved by applying a set of suitable hole parameters.

• 제어로봇시스템학회논문지
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• 제14권3호
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• pp.248-253
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• 2008

This paper presents a sensing system for smart home which can detect an location transition events such as entrance/exit of a member and identify the user in a group at the same time. The proposed system is compose of two sub-systems; a wireless sensor network system and a database server system. The wireless sensing system is designed as a star network where each of sensing modules with ultrasonic sensors and a Bluetooth RF module connect to a central receiver called Bluetooth access point. We propose a method to discriminate a user by measuring the height of the user. The differences in the height of users is a key feature for discrimination. At the same time, the each sensing module can recognize whether the user goes into or out a room by using two ultrasonic sensors. The server subsystem is a sort of data logging system which read the detected event from the access point and then write it into a database system. The database system could provide the location transition information to wide range of context-aware applications for smart home easily and conveniently. We evaluate the developed method with experiments for three subjects in a family with the installation of the developed system into a real house.

• 한국산학기술학회논문지
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• 제19권2호
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• pp.86-89
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• 2018

본 논문은 일상 생활스포츠의 일환으로 누구라도 쉽고 편하게 단거리 육상기록 측정을 할 수 있는 4레인 무선 구간기록 측정 시스템에 적용된 기술을 소개한다. 무선 육상경기 기록측정 시스템은 출발점의 스타트 버튼과 음성안내 스피커, 주자의 도착을 탐지하는 발판 스위치, 시작점과 도착점간의 지그비 통신, 구간기록을 계산하고 그 결과를 디스플레이하는 컨트롤보드 및 전광판 등으로 구성된다. 구간기록은 시작점의 스피커를 통한 레디-셋-고(총성) 음성 안내방송 시점과 결승점 발판 스위치의 주자 도착 탐지 시간의 차로 계산되며, 출발선의 지그비 통신노드는 시작스위치 탐지 시각을 자신의 내부시간을 기준으로 무선을 통하여 도착점의 통신노드로 전송하기 때문에 출발과 도착 통신노드간의 시간동기화가 구간기록 측정의 정밀도를 좌우한다. 이 논문에서 소개한 무선 구간 기록 측정 시스템은 10ms의 시간정밀도를 목표로 하고 있으며, 기존 전문 상용화시스템의 1ms의 시간정밀도와 다르게 일상 생활스포츠용으로 개발하여 비용이 상당히 저렴하며 기존의 수동 측정 방식을 사용한 경우보다 더 간편하게 기록 정보를 획득할 수 있다는 장점이 있다.

• 한국자동차공학회논문집
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• 제10권4호
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• pp.69-76
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• 2002

The aim of this study is to provide fundamental informations that make it possible to use a cool stream and a hot stream simultaneously. We changed the pressure of compressed air that flows into a tube, the inner diameter of orifice that a cold stream exits, and the mass flow rate ratio. And in each case, we measured the temperature of a cold stream and a hot stream in each exit of a tube. Also we measured the axial and the radial temperature distribution in internal spare of a tube. From the study, fellowing conclusive remarks 7an be made. First, As the number of nozzles increase, separation point move into the hot exit. Second, When we use guide vane type nozzle, the axial temperature distribution constant over the 0.75 of air mass flow rate radio. Third, When we use Spiral type nozzle, axial and radial temperature distribution in the inner space is higher than another nozzle. Fourth, Axial and radial temperature distribution in the inner space vortex-tube is determined by separation point. And separation point is moved by changing of air mass flow rate ratio. At last, A heating apparatus is possible far vortex-tube to use.

• 한국화재소방학회논문지
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• 제33권6호
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• pp.181-185
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• 2019

본 연구에서는 유도등의 광원과 경년변화에 따른 휘도성능을 분석하기 위하여 사무실, 상가, 병원, 공장 등에 설치된 유도등을 발취하여 CCFL, LED광원별 경년변화에 따른 휘도성능을 분석하였다. 이는 유도등과 같은 전기적 특성을 갖는 소방제품은 설치된 곳의 주위온도나 습도, 먼지 등이 그 성능에 변화를 줄 수 있기 때문에 설치장소별로 발취하여 그 특성을 분석하였다. 실험결과, CCFL유도등은 대형, 중형, 소형 모두 '휘도비 2'정도의 값을 나타내었다. 기술기준 규정값이 '휘도비 9이하'인 점을 감안할 때 매우 양호한 값을 나타냈으며, 경년변화에 의한 휘도비 변화도 거의 없음을 확인할 수 있었다. LED유도등은 '휘도비 5'정도의 값을 나타냈으며, 이는 표시면의 빛이 균일하지 못함을 뜻한다. 또한 경년변화에 의한 휘도비 변화는 거의 없으나, 휘도비의 값은 LED유도등보다 크게 나타났다. 이는 시각적인 측면에서는 만족스럽지 못한 결과이다. 이를 개선하기 위해서는 LED광원의 빛 분산이 필요하며 휘도비 관련 규정을 강화할 필요가 있다.

• 한국군사과학기술학회지
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• 제11권2호
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• pp.152-160
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• 2008

In the present paper, a transonic mixed-flow compressor that has relatively lower frontal area than that of centrifugal compressors is discussed, and aerodynamic design as well as performance prediction are performed. Main design constraints are compressor exit Mach number of 0.3 and flow angle of 30degrees at the design point, and maximum overall compressor diameter of 177mm, that is 7.0inch. The mass flow rate of design point and pressure ratio are 1.05kg/s and 5.2:1, respectively. The aerodynamic design results show that the transonic compressor designed with forward-swept inducer and curved diffuser can have the target performance with efficiency of 75% within the given constraints. And the compressor exit flow characteristics are discussed here.