• Journal of the Korea Convergence Society
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• v.7 no.6
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• pp.13-21
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• 2016

In this paper we are trying to explain the effect of temperature on polymer membrane exchange water electrolysis (PEMWE) and polymer membrane exchange fuel cell (PEMFC) simultaneously. A comprehensive studying approach is proposed and applied to a 50Watt PEM fuel cell system in the laboratory. The monitoring process is carried out through wireless LoRa node and gateway network concept. In this experiment, temperature sensor measure the temperature level of electrolyzer, fuel cell stack and $H_2$ storage tank and transmitted the measured value of data to the management control unit (MCU) through the individual node and gateway of each PEMWE and PEMFC. In MCU we can monitor the temperature and its effect on the performance of the fuel cell system and control it to keep the lower heating value to increase the efficiency of the fuel cell system. And we also proposed a mathematical model and operation algorithm for PEMWE and PEMFC. In this model, PEMWE gives higher efficiency at lower heating level where as PEMFC gives higher efficiency at higher heating value. In order to increase the performance of the fuel cell system, we are going to monitor, communicate and control the temperature and pressure of PEMWE and PEMFC by installing these systems in a building of university which is located in the southern part of Korea.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.167-167
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• 2017

스마트팜 내부의 3차원 공간의 온도, 습도, 기압, 공기질 분석을 통한 돈사 미세 조절 기술에 대한 연구가 진행 중이다. 해당 특성 중에서 기압을 제외한 환경인자들은 돈사 내의 구조 특성상 위치별로, 시간별로 매우 상이한 변이의 형태를 보인다. 일정 시점을 기준으로 계측 지점 이외의 지점에 대한 환경인자들을 공간적으로 추정하는 기술은 대표적으로 컴퓨터 분석 기술에 의존하고 있다. 시간 복잡도가 매우 높은 CFD(Computer Fluid Dynamics) 방식은 정밀도 측면에서 유리하나, 상응하는 제어 기술/하드웨어 등의 부재로 모델링 결과의 활용도가 낮다고 볼 수 있다. 본 연구에서는 CFD를 수행하는 과정에 있어 실질적으로 유효한 단위로 공간 분해능을 낮추고, 동등한 크기의 세부 공간에 대한 모델링을 병렬적으로 수행하기 위한 방안을 연구하였다. 실험적으로 돈사 환경을 3차원으로 구성하기 위하여, 공기 흡입구, 배출구, 기둥, 덕트 요소를 포함시켰다. 실내 공간을 1차적으로 가로, 세로, 높이방향으로 $3{\times}3{\times}3$ 균등 분배한 후 3차원 행렬로 분할하였다. 각 분할된 행렬에 대한 연산 수행을 위하여 현재까지 대중에 공개된 SBC(Single Board Computer) 중 가장 높은 연산 수행 능력이 있는 Odroid-XU4(Hardkernel, AnYang, Korea) 16식을 병렬 클러스터링 기술로 연동하였다. 하나의 AP당 8개의 코어가 내장되어 있으므로, 총 128개의 코어를 이용하여 동시에 128개의 3D 정방행렬 연산이 가능하도록 구성하였다. 모델링을 위한 수학적 모델로는 실험적으로 Steady turbulent model (Newtonian coefficient)을 이용하였다. 클러스터링을 이용한 병렬 처리의 특성상 균등한 정보량을 동시에 배분해야 하므로 108 ($27{\times}4$)개의 코어를 이용하여 1차적으로 나뉜 공간을 다시 4등분하여 동시에 $12{\times}12{\times}12$에 해당하는 공간 분해능에 대한 처리를 동시에 수행할 수 있도록 하였다. 2단계에 걸쳐 분할한 공간 세그먼트에 대한 클러스터링 연산 수행 결과 초당 15회 정도의 연산을 수행할 수 있었으며, 시간 분해능을 100으로 설정한 경우 약 5초가 수행되었다. 선행적으로 수행하였던 CFD 모델링 (OpenFOAM)과 비교하였을 때 상대적으로 정밀도가 낮은 3차원 모델링 결과를 얻을 수 있었다. 모델링에 소요되는 시간을 비약적으로 경감 시킨 장점을 살려 적정한 공간 분할 기법과 추가로 발생하는 다수의 바운더리 조건을 근사적으로 추정할 수 있는 데이터 마이닝 기술이 보완되어야 할 것이다.

• Economic and Environmental Geology
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• v.36 no.3
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• pp.243-255
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• 2003

The mathematical models for GIS-based spatial data integration have been developed for geological applications such as mineral potential mapping or landslide susceptibility analysis. Among various models, the effectiveness of fuzzy logic based integration of multiple sets of geological data is investigated and discussed. Unlike a traditional target-driven fuzzy integration approach, we propose a data-driven approach that is derived from statistical relationships between the integration target and related spatial geological data. The proposed approach consists of four analytical steps; data representation, fuzzy combination, defuzzification and validation. For data representation, the fuzzy membership functions based on the likelihood ratio functions are proposed. To integrate them, the fuzzy inference network is designed that can combine a variety of different fuzzy operators. Defuzzification is carried out to effectively visualize the relative possibility levels from the integrated results. Finally, a validation approach based on the spatial partitioning of integration targets is proposed to quantitatively compare various fuzzy integration maps and obtain a meaningful interpretation with respect to future events. The effectiveness and some suggestions of the schemes proposed here are illustrated by describing a case study for landslide susceptibility analysis. The case study demonstrates that the proposed schemes can effectively identify areas that are susceptible to landslides and ${\gamma}$ operator shows the better prediction power than the results using max and min operators from the validation procedure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.5
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• pp.355-361
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• 2020

Among these satellites, low - orbit small satellites with military characteristics require multi - target observation, and demand for high-resolution photographs and images is increasing. Fast maneuverability is the most important factor for high-resolution images and multi - target observations. However, in the case of a small satellites, it is possible to perform the attitude maneuver if it has high speed, but the residual vibration occurs when the attitude maneuver is completed and the next attitude maneuver is completed. In this study, to verify the vibration characteristics of the plate generated after attitude maneuver, an experimental fixture for simulating the attitude maneuver was fabricated and tested. In addition, Eddy Current Damper (ECD) using Eddy Current Brake system (ECB) is proposed as a passive damping method using permanent magnet to reduce vibration. A mathematical model was established to apply ECD and it was experimentally implemented according to the magnetic flux density and the air gap of the permanent magnet. One plate of four solar panels (plate) was specified, the residual vibration reduction performance after the test was verified experimentally.

• Journal of Preventive Medicine and Public Health
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• v.43 no.2
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• pp.109-116
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• 2010

Objectives: The pandemic of novel influenza A (H1N1) virus has required decision-makers to act in the face of the substantial uncertainties. In this study, we evaluated the potential impact of the pandemic response strategies in the Republic of Korea using a mathematical model. Methods: We developed a deterministic model of a pandemic (H1N1) 2009 in a structured population using the demographic data from the Korean population and the epidemiological feature of the pandemic (H1N1) 2009. To estimate the parameter values for the deterministic model, we used the available data from the previous studies on pandemic influenza. The pandemic response strategies of the Republic of Korea for novel influenza A (H1N1) virus such as school closure, mass vaccination (70% of population in 30 days), and a policy for anti-viral drug (treatment or prophylaxis) were applied to the deterministic model. Results: The effect of two-week school closure on the attack rate was low regardless of the timing of the intervention. The earlier vaccination showed the effect of greater delays in reaching the peak of outbreaks. When it was no vaccination, vaccination at initiation of outbreak, vaccination 90 days after the initiation of outbreak and vaccination at the epidemic peak point, the total number of clinical cases for 400 days were 20.8 million, 4.4 million, 4.7 million and 12.6 million, respectively. The pandemic response strategies of the Republic of Korea delayed the peak of outbreaks (about 40 days) and decreased the number of cumulative clinical cases (8 million). Conclusions: Rapid vaccination was the most important factor to control the spread of pandemic influenza, and the response strategies of the Republic of Korea were shown to delay the spread of pandemic influenza in this deterministic model.

• Korea journal of population studies
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• v.29 no.2
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• pp.27-51
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• 2006

In this paper, I have tested various kinds of methods for mortality projection and chose Lee-Carter method for projection of Korean mortality by age and sex. I reviewed the trends of life tables and life expectancies by age and sex from 2005 to 2050 projected by Lee-Carter method and found that the method was very applicable for Korean mortality projection. The differences between reported and estimated data for the period of 1971-2003 were small enough for both sexes and for all of the age groups. The projected life expectancies in 2051 were 82.73 years for males and 89.41 for females, and the differences decreased from 7.06 years in 2005 to 6.68 years. Because of the limitation of Korean infant mortality rate, I adopted the Japanese estimated IMR in 2050 as Korean object level in 2051. When the time series of IMR become long enough, we can use Korean IMR directly for the mortality projection. In addition, if we can estimate the changes of the main cause of death correctly in future, the mortality projection will be more correct and reliable. This will be available when we can produce a long series of life tables by cause of deaths.

• The Journal of the Korea Contents Association
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• v.14 no.11
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• pp.450-466
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• 2014

This study compared and analyzed body composition, physical fitness, and physical self-concept between gifted students in mathematics and science attending Korea Science Academy (KSA) and non-gifted students attending traditional high schools. The KSA students were 117 males who entered the school in 2009. As a control group, a total of 117 non-gifted students were randomly selected from 5 cities. The results of covariate analysis taken 2 year interval, pretest (2009) and posttest (2010), indicated that gifted students were significantly taller (p<.05) than non-gifted students, and were lower in BMI (p<.05) and PBF (p<.001). There was no significant difference in physical fitness between gifted and non-gifted students. But non-gifted students have a significantly higher self-concept in physical appearance (p<.05) and physical strength (p<.05). The internal/external frame of reference model and the Big Fish Little Pond Effect (BFLPE) theory were supported. Especially, gifted students were significantly higher (p<.01) in endurance self-concept than non-gifted students. We have discussion this result as the future research subject whether it come from the characteristics of the gifted's tenacity at high level tasks.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.9
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• pp.925-932
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• 2014

If a rotor possesses a high gyroscopic coupling or the running speed is high, the dynamical changes in the rotor become prominent. When active magnetic bearings are used to support such rotors, it is necessary for the bearing controller to take these dynamical changes into consideration. Independent-axis controllers, which are the most commonly used, modulate the bearing force solely based on the sensor output of the same axis. However, this type of controller has difficulties in overcoming the dynamical changes. On the other hand, mixed-axis controllers transform the sensor output into components corresponding to the vibrational modes. A separate controller can then be designed for each vibrational mode. In this way, the controller can be designed based on the dynamics of the rotor. In this paper, we describe a design process for a mixed-axis controller that uses a detailed mathematical model of the system. The performance of the controller is evaluated based on the ISO sensitivity requirements and unbalance response, while considering the change in the system dynamics due to the running speed.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.1
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• pp.65-78
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• 2007

The pollutants (Rn, CH, CO, HS, radioactive gas from radiolysis) were generated from the process of construction and operation of underground repository, and after disposal of low-intermediate radioactive waste inside there must be controlled by a ventilation system to distribute them in area where enough air is supported. Therefore, a suitable technical approach is needed especially at an underground repository that is equipped with many entry tunnels, storage tunnels, exhaust-blowing tunnels, and vertical shafts in complicated network form. For the technical approach of such a ventilation system, WIPP (Waste Isolation Pilot Plant) in U. S and SFR (Slutforvar for Reaktorafall) low-intermediate radioactive waste repository in Sweden were selected as the models, for calculating the required air quantity, organizing a ventilation network considering cross section, length, surface roughness of the air passage, and describing a calculation of resistance of each circuit. Based on these procedures, a best suited ventilation system was completed with designing proper capacity of fans and operating plan of vertical shafts. As a result of comparing the two repositories based on the geometry dimensions and ventilation facility equipment operation, more parallel circuit as in WIPP, brought decrease in resistance for entire system leading to reduce of operating costs, and the larger cross-sectional area of the SFR, the greater the percentage of disposal capacity. Accordingly, the mixture of parallel circuit of WIPP repository for reducing resistance and SFR repository formation for enlargement of disposal capacity would be the most rational and efficient ventilation system.

• Journal of Energy Engineering
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• v.22 no.2
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• pp.175-183
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• 2013

For the optimal design of the vehicle electric system, it is important to have a reliable modeling tool to predict the dynamic behavior of the automotive battery. In this work, a one-dimensional modeling was carried-out to predict the dynamic behaviors of a 12-V automotive lead-acid battery. The model accounted for electrochemical kinetics and ionic mass transfer in a battery cell. In order to validate the modeling, modeling results were compared with the experiment data of the dynamic behaviors of the lead-acid batteries of two different capacities that were mounted on the automobiles manufactured by Hyundai Motor Company. The discharge behaviors were measured with various discharge rates of C/3, C/5, C/10, C/20 and combination. And dynamic behaviors of charge and discharge were measured. The voltage curves from the experiment and simulation were in good agreement. Based on the modeling, the distributions of the electrical potentials of the solid and solution phases, and the current density within the electrodes could be predicted as a function of charge and discharge time.