• 대한산업공학회지
• /
• 제14권2호
• /
• pp.11-23
• /
• 1988

A periodic review inventory model for deteriorating items in which time is treated as a discrete variable is developed. The model is developed under deterministic but time dependent demands and instantaneous delivery. Deterioration is assumed to be a constant fraction of the on hand inventory and partial returns are allowed for the deteriorated items. The solution procedures for obtaining the optimal order quantities which maximize the total profit in the scheduling period are presented for the cases of back orders and lost sales. Finally, when the additional orders are allowed, an efficient solution algorithm determining the initial and additional order quantities and additional ordering time is developed. Some numerical examples are also presented to illustrate the results.

• International Journal of Automotive Technology
• /
• 제6권2호
• /
• pp.79-85
• /
• 2005

This work is to investigate the surface heat flux and combustion characteristics of premixed propane mixture in a constant volume chamber. The experiment of heat flux and combustion characteristics of premixed propane mixture are performed with various equivalence ratio and initial pressure conditions. Based on the experimental results, it is found that the maximum instantaneous temperature is increased with the increase of initial pressure in the chamber. There are significant differences in the burning velocity of premixed propane mixture at different measuring points in the constant volume combustion chamber. A]so, the trends of temperature difference at each measuring points are similar to the burning velocity in the combustion chamber. It is concluded that the total heat loss during the combustion period is affected by the equivalence ratio and the initial condition of fuel-air mixture.

• 전기학회논문지
• /
• 제56권8호
• /
• pp.1498-1502
• /
• 2007

There have been many different definitions of energy functions as the second statistics of a signal. In this paper, using the higher order differential energy function, we propose an algorithm separating the amplitude and frequency components in a discrete sinusoidal signal. The proposed amplitude and frequency estimation methods have less computational requirement than the existing methods. It also shows large computational advantage over the root mean square (RMS) calculation of a signal. The proposed methods can be used in the detection of abnormal events in signals on the power line. Computer simulations show that proposed frequency estimation method can detect the presence of voltage increase or decrease for a short period of time. Also, the proposed estimation methods have been compared with existing methods in terms of estimation error variance.

• 전력전자학회논문지
• /
• 제24권5호
• /
• pp.356-364
• /
• 2019

In this study, major problems, such as licensing problems due to civil complaints, deterioration of facility period, and damage of modules, are exposed to many problems in domestic businesses. Particularly, the photovoltaic (PV) modules applied to early PV systems have been repaired and replaced over the past two decades, and a new module-based aging detection method is needed to expand the maintenance market and stabilize and repair power supplies. PV modules in a PV system use a string that is configured in series to generate high voltage. However, even if only one module of the solar modules connected in series ages, the power generation efficiency of the aged string is reduced. Therefore, we propose a topology that can measure the instantaneous PV characteristic curve to determine the aging module in the solar string and the aging judgment algorithm using the measured PV characteristic curve.

• 천문학회지
• /
• 제56권1호
• /
• pp.125-135
• /
• 2023

Here, we investigated the observed sunspot areas with respect to latitudes using the Hilbert transform technique. Conventional study of the cyclic patterns of sunspots is based on the Lomb-Scargle periodogram, which only obtains the amplitude information. In comparison, our approach characterizes the amplitude as well as the phase of solar activity. We demonstrated the solar North-South asymmetry in the instantaneous amplitude by analyzing daily sunspot data set spanning from the solar cycles 11 to 24. Our findings confirm that the northern hemisphere is dominant in the solar cycles 14, 15, 16, 18, and 20. Unlike the amplitude, the North-South asymmetry in the period of solar activity could not be established. We have also found that the standard deviation as a measure of fluctuation in the phase derivative is minimum in the latitude band 10° < l < 20°, and the fluctuations obtained for latitudes above 30° are considerable.

• 한국수산과학회지
• /
• 제21권1호
• /
• pp.35-41
• /
• 1988

진해만내의 진동 고현 연안에서 진주 담치의 효율적인 종묘생산 기술 개발을 위하여 부유유생의 출현시각와 각 유생 단계별 생존율을 조사한 결과는 다음과 같다. 1. 진주 담치의 산란성기는 4월 중순경 이었다. 2. D형 유생으로부터 umbo형 유생까지는 11-13 일이 소요되었으며 umbo형 유생에서 성숙 유생까지는 10-13일이 소요 되었다. 그리고 D형 유생에서부터 채묘의 대상이 되는 성숙 유생까지는 23-25일이 소요되었다. 3. D형 유생에서 umbo형 유생으로 성장할 때까지의 평균 존재율은 $21.04\%$, umbo형 유생에서 성숙 유생까지는 $16.89\%$였고, D형유생의 $3.55\%$ 만이 성숙 유생으로 생존하였다. 4. 진해만산 진주 담치의 채묘적기는 5월 중순경이라고 판단된다.

• 한국수산과학회지
• /
• 제18권5호
• /
• pp.471-476
• /
• 1985

우리나라 굴 양식의 중심해역인 한산만에서 효율적인 채묘예보를 기하기 위한 방안으로써, 이 수역에 발생한 굴 부유유생을 대상으로 하여 각 유생의 발육단계별 출현상황과 생존율을 조사하였다. 1984년 6월 13일 부터 10월 16일까지의 조사기간 중 크기가 약 $72{\times}61{\mu}m$의 D 형 유생은 7월 16일과 9월 20일에 각각 출현 Peak가 있었으며, $189{\times}217{\mu}m$의 umbo 형 유생은 7월 21일과 9월 25일에, $303{\times}308{\mu}m$의 성숙유생은 7월 28일과 9월 30일에 각각 Peak가 있었다. D형유생에서 umbo 형 유생으로 되는데는 약 5일이 걸렸으며, 순간사망률은 0.24, 일간생존율은 0.78, 일간사망률은 0.22, 평균생존율은 약 $29.38\%$였다. umbo형유생에서 성숙유생으로 되는데는 $5{\sim}7$일 소요되었으며, 순간사망률은 0.15, 일간생존율은 0.86, 일간사망률은 0.14, 평균생존율은 약 $38.54\%$였다. D형유생의 발생에서 채묘의 대상이 되는 성숙유생으로 되는데는 $10{\sim}12$일 걸렀으며, 이 기간중의 평균생존율은 약 $11.32\%$였다.

• 한국식품과학회지
• /
• 제20권1호
• /
• pp.13-18
• /
• 1988

1% 희석 쌀전분 용액의 노화 특성을 호화후 $5^{\circ}C$에서 저장하면서 고찰하였다. 저장기간이 증가함에 따라 노화도도 증가하였는데 그 증가하는 정도는 노화 초기에 가장 현저한 반면 노화가 진행됨에 따라 감소하였다. 추정 전분의 노화특성을 Avrami식으로 해석하여 노화기작을 살펴본 결과 Avrami지수, 속도상수, 시간상수는 각각 0.96, 0.21 $days^{-1}$, 4.77 days 였다. 이때 Avrami지수가 단위치(n=1)에 접근하므로 희석 쌀전분 용액은 즉각적인 핵형성에 이은 간상구조의 생성에 의하여 노화가 진행됨을 알 수 있었다. 주사 전자 현미경에 의하여 노화과정을 관찰한결과 노화기간이 경과함에 따라 생전분과는 다른 형태의 3차원 결정구조가 형성됨을 알 수 있었다.

• Journal of Power Electronics
• /
• 제16권4호
• /
• pp.1598-1611
• /
• 2016

In some special occasions with strict size requirements, such as mine hoists, improving the design accuracy of the forced-air cooling systems of NPC three-level inverters is a key technology for improving the power density and decreasing the volume. First, a fast power-loss calculation method was brought. Its calculation principle introduced in detail, and the computation formulas were deduced. Secondly, the average and dynamic power losses of a 1MW mine hoist acting as the research target were analyzed, and a forced-air cooling system model based on a series of theoretical analyses was designed with the average power loss as a heat source. The simulation analyses proves the accuracy and effectiveness of this cooling system during the unit lifting period. Finally, according to an analysis of the periodic working condition, the maximum power-loss range of a NPC three-level inverter under multi cycle operation was obtained and its dynamic power loss was taken into the optimized cooling system model as a heat source to solve the power device damage caused by instantaneous heat accumulation. The effectiveness and feasibility of the optimization design based on the dynamic power loss calculation of the maximum power-loss range was proved by simulation and experimental results.

• 조명전기설비학회논문지
• /
• 제14권3호
• /
• pp.43-48
• /
• 2000

본 연구에서는 VHDL로 설계한 CPLD 제어기를 이용하여 3상 다이오드 정류기 입력전류에 포함된 고조파성분을 저감시켰다. 3상 다이오드는 매 순간 3상중에서 가장 높은 장에서 가장 낮은 장으로 전류가 흐르게 되므로 나머지 한 장의 전류가 불연속적이 된다. 개발된 CPID 제어기는 다어오드로 도통되지 않는 상의 전류를 부가적으로 설치한 스위치를 통하여 흐르게 하여 전류가 연속으로 도통되게 한다. CPLD 제어기는 기존의 디지털 프로세서를 이용한 제어기에 비해 고속의 처리능력과 소형화획 장점 등을 가점을 확인하였다. 시뮬레이션과 실험결과로 제안된 제어기의 성능을 검증하였다.