Seok-Weon Choi

In-Situ Diagnosis of Vapor-Compressed Chiller Performance for Energy Saving

In-situ diagnosis of chiller performance is an essential step for energy saving business. The main purpose of the in-situ diagnosis is to predict the performance of a target chiller. Many models based on thermodynamics have been proposed for the purpose. However, they have to be modified from chiller to chiller and require profound knowledge of thermodynamics and heat transfer. This study focuses on developing an easy-to-use diagnostic technique that is based on adaptive neuro-fuzzy inference system (ANFIS). The effect of sample data distribution on training the ANFIS is investigated. It is found that the data sampling over 10 days during summer results in a reliable ANFIS whose performance prediction error is within measurement errors. The reliable ANFIS makes it possible to prepare an energy audit and suggest an energy saving plan based on the diagnosed chilled water supply system.

A line rate calculation method for arbitrary directional imaging of an Earth observing satellite

For an earth observing satellite, a line rate is the number of lines which the CCD of push broom type camera scans in a second. It can be easily calculated by ground velocity divided by ground sample distance. Accurate calculation of line rate is necessary to obtain high quality image using TDI CCD. The earth observing satellite has four types of imaging missions which are strip imaging, stereo imaging, multi-point imaging, and arbitrary directional imaging. For the first three types of imaging, ground scanning direction is aligned with satellite velocity direction. Therefore, if the orbit propagation and spacecraft attitude information are available, the ground velocity and ground sample distance could be easily calculated. However, the calculation method might not be applicable to the arbitrary directional imaging. In the arbitrary directional imaging mode, the ground velocity is not fixed value which could be directly derived by orbit information. Furthermore, the ground sample distance might not be easily calculated by simple trigonometry which is possible for the other types of imaging. In this paper, we proposed a line rate calculation method for the arbitrary directional imaging. We applied spherical geometry to derive the equation of ground point which is the intersection between the line of sight vector of the camera and earth surface. The derivative of this equation for time is the ground velocity except the factor of earth rotation. By adding this equation and earth rotation factor, the true ground velocity vector could be derived. For the ground sample distance, we applied the equation of circle and ellipse for yaw angle difference. The equation of circle is used for the yaw angle representation on the plane which is orthogonal to the line of sight vector. The equation of ellipse is used for the yaw angle representation on the ground surface. We applied the proposed method to the KOMPSAT-3A (Korea Multi-Purpose Satellite 3A) mission which is the first Korean satellite with optical and infrared sensor. The satellite was launched by a Dnepr on 26 March 2015 and started normal operation on September 2015. The payload of the satellite is AEISS-A(Advanced Earth Imaging Sensor System-A) which has 0.55m GSD for panchromatic image, 2.2m GSD for multi-spectral image, and day-and-night infrared image. The main mission objective of the satellite is providing high resolution electro-optical images and infrared images for GIS application. By applying the proposed method, the line rate error was reduced to about 0.2% from 0.5% of previous method. The arbitrary directional imaging mode became a major operation mode and various application modes including due north directional imaging, pitch steering imaging, pitch step imaging are now developing. These application modes are based on technical achievement of the proposed method. In this paper, the details of line rate calculation method are described. The experimental results show the accuracy of the proposed method is less than 0.2% in average. For the application results, the mission operation of KOMPSAT-3A and arbitrary directional imaging results are described.

Range estimation of passive infrared targets through the atmosphere

Abstract. Target range estimation is traditionally based on radar and active sonar systems in modern combat systems. However, jamming signals tremendously degrade the performance of such active sensor devices. We introduce a simple target range estimation method and the fundamental limits of the proposed method based on the atmosphere propagation model. Since passive infrared (IR) sensors measure IR signals radiating from objects in different wavelengths, this method has robustness against electromagnetic jamming. The measured target radiance of each wavelength at the IR sensor depends on the emissive properties of target material and various attenuation factors (i.e., the distance between sensor and target and atmosphere environment parameters). MODTRAN is a tool that models atmospheric propagation of electromagnetic radiation. Based on the results from MODTRAN and atmosphere propagation-based modeling, the target range can be estimated. To analyze the proposed method’s performance statistically, we use maximum likelihood estimation (MLE) and evaluate the Cramer-Rao lower bound (CRLB) via the probability density function of measured radiance. We also compare CRLB and the variance of MLE using Monte-Carlo simulation.

Development and Validation of Cryopanel Cooling System Using Liquid Helium for a Satellite Test

A cooling system utilizing liquid helium to chill the cryopanel (800 mm × 700 mm dimensions) down to 4.2 K was designed, implemented, and tested to verify the role of the cryopanel as a heat sink for the payload of a spacecraft inside the large thermal vacuum chamber (effective dimensions : 8 m (Φ) × 10 m (L)) of KARI (Korea Aerospace Research Institute). Two LHe (Liquid Helium) Dewars, one for the main supply and the other for refilling, were used to supply liquid helium or cold helium gas into this cryopanel, and flow control for the target temperature of the cryopanel within requirements was done through fine adjustment of the pressure inside the LHe Dewars. The return helium gas from the cryopanel was reused as a thermal barrier to minimize the heat influx on the core liquid helium supply pipe. The test verified a cooling time of around three hours from the ambient temperature to 40 K (combined standard uncertainty of 194 mK), the capacity for maintaining the cryopanel at intermediate temperatures, and a 1 K uniformity over the entire cryopanel surface at around 40 K with 20 W cooling power. § 이 논문은 2009년도 열공학부문 춘계학술대회(2009. 5. 20-22, BEXCO) 발표논문임 † Corresponding Author, wittycho@kari.re.kr 조혁진 · 문귀원 · 서희준 · 이상훈 · 홍석종 · 최석원 214 Fig. 1 Schematic of cryopanel cooling system W @ 85 K)을 위해서, 방열판에서 일정거리만큼 떨어져 설치된 가로 약 800 mm, 세로 약 700 mm, 두께 약 7 mm의 극저온패널을 40 K이하로 냉각시키고, 극저온패널 전 표면에 대하여 1 K 이내의 균일한 온도 분포를 갖도록, 액체헬륨 Dewar를 이용해 액체헬륨을 직접 극저온패널에 공급한 뒤 외부로 배출하는 방식을 적용하였다. 냉각 시스템의 선정시, 상용의 G-M 냉동기의 콜드헤드를 이용해 열전도 링크로 시편을 연결하는 방법과 압축된 헬륨가스를 G-M 냉동기의 콜드헤드와 열교환시켜 순환시키는 방법, 액체헬륨 액화기를 이용한 방법 등이 고려되었으나, 열용량과 시편 표면의 온도분포도, 사용 빈도, 제작 기간 등을 고려하여 경제성과 효율성을 최우선으로 하여 최종 액체헬륨 Dewar를 사용하는 방법이 선택되었다. 액체헬륨 Dewar를 사용해 직접 액체헬륨을 시험대상에 공급하는 경우, 사용된 액체헬륨을 외부로 그대로 배기하여 소모하기 때문에 시험 요구 조건을 만족시키는 범위 내에서 공급 유량을 최소화하여 액체헬륨의 소비를 최소화는 것이 시스템 효율화의 가장 중요한 목표가 된다.

Evaluation of KOMPSAT-2 System in the Conducted EMC Environment

Satellite generates a complex electromagnetic noise by conducted and radiated coupling effect of the various electrical instruments. This noise may cause serious problems on the satellite system. To minimize the electromagnetic coupling effects and maintain the system safety margin, system noise reduction technique should be applied from the beginning of the system design. The KOMPSAT-2 system is evaluated by measuring the conducted noise on system electrical power leads and verifying a 6dB system safety margin under the complex noise environment with current injection. This paper describes the KOMPSAT-2 system evaluation result performed on ETB(Electrical Test Bed) and the analysed noise element, the analysed result will be reflected on FM(Flight Model) EMC test.

Theoretical and Experimental Considerations of Thermal Humidity Characteristics

Thermal humidity characteristics were considered theoretically and experimentally. A Simply well-fitted correlation of a saturated vapor pressure-temperature curve of water was introduced based on Antoine equation to make theoretical prediction of relative humidity according to temperature variation. Characteristics of dew point were also examined theoretically and its relation with temperature and humidity was evaluated. The exact mass of water vapor in a specified humidity and temperature condition was estimated to provide useful insight into the idea about how much amount of water corresponds to a specified humidity and temperature condition in a confined system. A simple but well-fitting model of dehumidification process was introduced to anticipate the trend of relative humidity level during GN2(gaseous nitrogen) purge process in a humidity chamber. Well-suitedness of this model was also verified by comparison with experimental data. The overall appearance and specification of two thermal humidity chambers were introduced which were used to perform various thermal humidity tests in order to yield useful data necessary to support validity of theoretical models.