• Nuclear Engineering and Technology
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• v.16 no.2
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• pp.47-57
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• 1984

Mathematically-rigorous time-volume averaged conservation equations were simplified to established the differential equations of THERMIT-6S, which is a two-fluid 3-D code. The difference equations of THERMIT-6S were obtained by discretizing the proceeding set of differential equations. The spatial discretization is characterized by a first-order spatial scheme, donor cell method, and staggered mesh layout. For time discretization, a first order semi-implicit scheme treats implictly sonic terms and terms relating to local transport phenomena and explicitly convective terms. The results were linearized by the Newton-Raphson method. In order to construct the reduced pressure equation, the linearized equations were manipulated so that all variables are coupled between mesh cells through only the pressure variable. By simulating numerically the OPERA-15 experiment, it was found that THERMIT-6S is a very powerful code in predicting reactor behavior after sodium boiling including flow coastdown, reversal flow and flow oscillation.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.185.1-185.1
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• 2010

원격탐사(remote sensing)란 관측 대상과의 접촉 없이 멀리서 정보를 얻어내는 기술을 말한다. 기상관측분야에는 이미 소다(SODAR) 장비가 폭넓게 사용되거 왔으나 최근 풍력자원평가(wind resource assessment)를 위한 풍황측정에 SODAR와 더불어 라이다(LIDAR)가 적극적으로 활용되기 시작하고 있다. 참고로 SODAR(SOnic Detection And Ranging)는 수직 및 동서 남북 방향으로 음파를 발생시키고 대기유동에 의해 산란 반사된 에코를 수신하여 진동수 변화와 반사에코 강도를 측정하여 각 방향의 에코자료를 벡터 합성함으로써 풍향 및 풍속을 산출하는 원리이다. 반면 LIDAR(Light Detection And Ranging)는 비교적 최근에 풍황측정 용도로 개발된 레이저 탐지에 바탕을 둔 원거리 센서로, 공기입자(먼지, 수증기, 구름, 안개, 오염물질 등)에 의해 산란된 레이저 발산의 도플러 쉬프트(Doppler shift)를 이용하여 풍향 및 풍속을 측정하는 원격탐사 장비이다. 풍력자원평가 측면에서 라이다는 그 정확도가 IEC61400-12에 의거한 풍황탑(met-mast) 측정자료 다수와의 비교검증 실측평가(Albers et al., 2009)를 통하여 입증된 바 있다. 한편 한국에너지기술연구원에서 운용 중인 라이다 시스템은 그림 1의 우측 그림과 같이 1초에 $360^{\circ}$를 스캔하여 50지점에서 반사되는 레이저를 스펙트럼으로 측정하되 설정된 관측높이에서 풍속은 샘플링 부피(sampling volume)의 평균값으로 정의된다. 그런데 샘플링 부피는 설정된 관측높이로부터 상하 12.5m, 총 25m의 높이구간에서 관측한 스펙트럼의 평균값을 그 중앙지점에서의 풍속으로 환산하는 알고리듬(algorithm)을 채택하고 있다. 따라서 비선형적으로 변화하는 풍속연직분포 관측 시 풍속환산 알고리듬에 의한 측정오차가 개입될 가능성이 존재하는 것이다. 이에 본 연구에서는 라이다에 의한 풍속연직분포 측정 시 샘플링 부피의 구간 평균화 과정에서 발생하는 불확도(uncertainty)를 정량적으로 분석함으로써 라이다에 의한 풍속연직분포 관측의 불확도를 정량평가하고자 한다.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.75-81
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• 2007

Percentage that aggregate of materials that concrete composed about $70{\sim}80%$ of whole volume, therefore influence that quality of aggregate gets in concrete characteristics are very important. Schmidt hammer and ultra-sonic velocity method are commonly used for crushed sand concrete compressive strength test in a construction field. At present, various equations for prediction of strength are present, which have been used in a construction field. The purpose of this study is to evaluate the correlation between prediction strength by present equations and destructive strength to test specimen, and find out which is a suitable equation for the construction site, a strength test was carried out destructive test by means of core sampling and traditional test. The experimental parameters were concrete age, curing condition, and strength level. It is demonstrated that the correlation behavior of crushed sand concrete strength in this study good due to the perform analysis of correlation between core, destructive strength and non-destructive strength.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1167-1173
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• 2013

This study aimed to calculate the CFFs (critical flow functions) of a sonic nozzle bank with a 12-nozzle package within 1 s. Toward this end, the Helmholtz free energy of natural gas was formulated by using the AGA8-dc equation of state in a form without integral terms, and thereafter, thermodynamic properties such as the enthalpy, entropy, speed of sound, and heat capacity, which are used in CFF calculation, were derived in analytical form. As a result, the calculation time of CFFs was improved from 6.7 s in a previous study to 0.6 s per 12-nozzle package and kept almost constant regardless of the number of components in natural gas. Furthermore, it was confirmed that the calculated CFF values were in agreement with the results of a CFF international comparison test carried out under ISO management in 1998-1999.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.12
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• pp.996-1001
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• 2005

Recently, with the development of service robots and with the new concept of ubiquitous world, the position estimation of mobile objects has been raised to an important problem. As pre-liminary research results, some of the localization schemes are introduced, which provide the relative location of the moving objects subjected to accumulated errors. To implement a real time localization system, a new absolute position estimation method for a mobile robot in indoor environment is proposed in this paper. Design and implementation of the localization system comes from the usage of active beacon systems (based upon RFID technology). The active beacon system is composed of an RFID receiver and an ultra-sonic transmitter: 1. The RFID receiver gets the synchronization signal from the mobile robot and 2. The ultra-sonic transmitter sends out the traveling signal to be used for measuring the distance. Position of a mobile robot in a three dimensional space can be calculated basically from the distance information from. Three beacons and the absolute position information of the beacons themselves. In some case, the mobile robot can get the ultrasonic signals from only one or two beacons, because of the obstacles located along the moving path. Therefore, in this paper, as one of our dedicated contribution, the position estimation scheme with less than three sensors has been developed. Also, the extended Kalman filter algorithm is applied for the improvement of position estimation accuracy of the mobile robot.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.10
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• pp.1897-1904
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• 2006

Home service robot must recognize and build map for indoor and components of the house such as furniture and chair etc. The previous researcher has developed a indoor map building system by using CCD camera and ultra sonic sensor. %no stems have some problem in such a way that (1) a distun resolution can be changed according to the number of pixel when we use a CCD camera system, (2) a measured distance can be decreased when it transmitted to the rubber because of being absorbed the sound energy. This paper represents an intelligent sensor controller of module has been developed by using optic PSD(Position Sensitive Detector) sensor any at a low price. To deduce the switching noise from beam power module and diffused reflection noise, we proposed a heuristic soft filter. The performance of the developed system was compared with ultra sonic sensor system by detecting the indoor wall environment. Some experiments were illustrated for the validity of the developed system.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.159.1-159.1
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• 2011

Partial oxidation reformer was fabricated and operated using commercial transportation fuels. Fuel injector and heating coil were used for fuel atomization and startup, respectively. The reformer was designed to produce syngas for $150{\sim}200W_e$ class solid oxide fuel cell. The reformer was operated in the $O_2$/C range between 0.6 and 0.8 while the capacity was fixed at $150W_e$. The temperature range in catalyst bed was between $500^{\circ}C$ and $900^{\circ}C$. Only 83% fuel was converted to $H_2$, CO, $CO_2$ and $CH_4$ at the operating conditions. The lowest temperature increase to $700^{\circ}C$ when the reformer was operated at $200W_e$, Although the temperature profiles was improved, fuel conversion was 88%. On the other hand, fuel was completely converted when micro-reactor operated at the same condition. This difference maybe due to aromatic compounds formation at homogeneous region. In addition, a significant amount of coke deposition was observed at vent line. Homogeneous reaction depends on the degree of mixing. For this purpose, two fluid nozzle and Ultra sonic injector were compared to investigate the effect of atomization. Sauter mean diameter(SMD) of Ultra sonic injector was lower than two-fluid nozzle at test condition. However, conversion efficiency and fuel conversion were not improved by using two-fluid nozzle. these results imply that the temperature of homogeneous reaction region should be controlled to prevent coke formation.

• The Journal of Engineering Geology
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• v.27 no.3
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• pp.323-330
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• 2017

For the formation identification, surface geological survey, drill core analysis, core description and well log analysis are widely used. Among them well log analysis is a popular method with drill core analysis, since it measures continuously physical properties at in-situ. In this study we calculated Thomsen anisotropic parameters (${\varepsilon},\;{\delta},\;{\eta}$) after applying Backus averaging method to the P wave velocity, S wave velocity, and density logs. The well log data application of Blackfoot, Canada, shows the formation could be divided by 12 layers. This shows that Thomsen anisotropic parameters for identifying formation using anisotropic parameters is useful if there is no natural gamma log that is widely used for the formation identification.

• The Journal of Korea Robotics Society
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• v.2 no.1
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• pp.40-47
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• 2007

Recently, with the development of service robots and with the new concept of ubiquitous world, the position estimation of mobile objects has been raised to an important problem. As pre-liminary research results, some of the localization schemes are introduced, which provide the absolute location of the moving objects subjected to large errors. To implement a precise and convenient localization system, a new absolute position estimation method for a mobile robot in indoor environment is proposed in this paper. Design and implementation of the localization system comes from the usage of active beacon systems (based upon RFID technology). The active beacon system is composed of an RFID receiver and an ultra-sonic transmitter: 1. The RFID receiver gets the synchronization signal from the mobile robot and 2. The ultra-sonic transmitter sends out the traveling signal to be used for measuring the distance. Position of a mobile robot in a three dimensional space can be calculated basically from the distance information from three beacons and the absolute position information of the beacons themselves. Since it is not easy to install the beacons at a specific position precisely, there exists a large localization error and the installation time takes long. To overcome these problems, and provide a precise and convenient localization system, a new auto calibration algorithm is developed in this paper. Also the extended Kalman filter has been adopted for improving the localization accuracy during the mobile robot navigation. The localization accuracy improvement through the proposed auto calibration algorithm and the extended Kalman filter has been demonstrated by the real experiments.

• Journal of the Korean Wood Science and Technology
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• v.46 no.1
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• pp.93-99
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• 2018

It is necessary to review the non-destructive indexes in order to estimate the bending strength performance of the domestic larch lumber. In this study, MOEs (modulus of elastic) the larch lumber (cross-section $89{\times}120mm$) were evaluated through non-destructive methods such as the ultra-sonic method, longitudinal vibration method, and non-destructive bending method. The non-destructive measurement method which best represented the static MOE was determined and applied as the MOR(modulus of rupture) estimation index. The MOE that was measured through the longitudinal vibration method showed the highest correlation with the static MOE. The MOR was highly related to the static MOE. Therefore, the non-destruction MOE measured through the longitudinal vibration method was used to estimate the MOR of the lumber.