• Journal of the Korean Society for Precision Engineering
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• v.24 no.8 s.197
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• pp.41-49
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• 2007

In this paper, we proposed a new ultrasonic distance measurement system with high accuracy and long range. To improve accuracy and enlarge range, the time of flight of ultrasonic is calculated by the period detecting method. In the proposed ultrasonic distance measurement system, the ultrasonic transmitter and receiver are separated but synchronized by RF(Radio frequency) module. The experiment has been implemented from short distance 1m to maximum available distance 30m. And the period detecting method is compared with the conventional threshold level method. Experimental results show the accuracy and range of the distance measurement are improved by this period detecting method.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.11
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• pp.1578-1583
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• 2012

There are 3 systems in incentive-based normal load management in Korea; day or hour-ahead, week-ahead, months-ahead. These are originally similar in their operational implementation, but differ in their pre-notification period. Therefore the incentive of these systems should be different according to prenotification period. This is the key problem in implementing these load managements. Customers participating in these load managements feel their economic differences, depending on the risk by prenotification dates. The shorter prenotification period, the more risk take the customers. This paper proposes the method of incentive variation in prenotification difference, by using the theory of financial yield curve, which is used in analysing short and long duration bond interesting rates and is reflecting risk premium in their period.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.6
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• pp.33-39
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• 1998

This paper is related to economic design of tool-resetting period in NC machining. In NC lathe machining, the mean and variance of components dimension fluctuate in slow time and we should reset tool program to compensate the variation from the fluctuation. In this paper. we propose the procedure determining the optimal resetting period based on the total expected operating cost which consists of resetting cost and the quality cost related to dimension variation. As a case study, using experimental data about dimension changes of a lathe machining, we obtain the regression equations of mean and variance of the dimension fluctuation, total expected operating cost, and optimal resetting period.

• Transactions of the Korean hydrogen and new energy society
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• v.13 no.3
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• pp.233-241
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• 2002

To achieve hydrogen power system with high performance and stable operation, the COVimep of hydrogen fueled engine with direct injection was evaluated with the change of engine speed, injection timing, air-fuel equivalence ratio and spark timing. And the cause of cycle variation was analyzed by using coefficient of variation in combustion period defined in this study. the results showed that the cycle variation of hydrogen fueled engine is mainly dependent on the early combustion period.

• International Journal of Reliability and Applications
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• v.18 no.1
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• pp.9-20
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• 2017

In this paper, we consider a renewable repair-replacement warranty strategy with age-dependent minimal repair service and propose an optimal maintenance model during post-warranty period. Such model implements the repair time limit under warranty and follows with a certain form of system maintenance strategy when the warranty expires. The expected cost rate is investigated per unit time during the life period of the system as for the standard for optimality. Based on the cost design defined for each failure of the system, the expected cost rate is derived during the life period of the system, considering that a renewable minimal repair-replacement warranty strategy with the repair time limit is provided to the customer under warranty. When the warranty is finished, the maintenance of the system is the customer's responsibility. The life period of the system is defined and the expected cost rate is developed from the viewpoint of the customer's perspective. We obtain the optimal maintenance strategy during the maintenance period by minimizing such a cost rate after a warranty expires. Numerical examples using field data are shown to exemplify the application of the methodologies proposed in this paper.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1999.10c
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• pp.689-694
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• 1999

This study estimated average yearly watershed pollutant loading by using SWMM(Storm Water Management Model) which is one of the nonpoint source quality models. Two sites were measured discharge and water quality at dry period and wet period. The rainfall data is used from 1989 to 1998 . During a decade, the average year watershed pollutant loading, which is SS, BOD5 , TN, TP, were 2.39E+06kg, 0.92E +05kg, 2.53E+05kg, 2.66E+04kg respectively. During dry period, SS, BOD5 TN, TP loadings were 1.89E+05kg, 1.7E+05kg, 1.04E+05kg, 1.11E+04kg, and during wet period 1.89E+05kg, 1.17E+05kg, 1.04E+05kg, 1.11E+04kg respectively so wet period loading are more than dry day loadings.

• Publications of The Korean Astronomical Society
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• v.22 no.4
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• pp.141-149
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• 2007

Preliminary time-series observations for short-period variability survey (SPVS) were carried out using a 155mm refractor and a $2k{\times}3k$ CCD camera at Bohyunsan Optical Astronomy Observatory. We found 21 new variable stars in the $90'{\times}60'$ test field region : 9 eclipsing binary stars, $5{\delta}$ Scuti type stars, a ${\gamma}$ Doradus type star, and 6 long period variables. The observing field center is R.A. $05^h\;00^m\;00^s$, DEC. $50^{\circ}\;00'\;00"$ (J2000.0). The period and amplitude ranges for the short-period variables, i.e., ${\delta}$ Scuti stars, were 0.052day - 0.107day and 0.012mag - 0.064mag, respectively.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.32 no.4
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• pp.161-168
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• 2009

The most generalized form of the triadic operating policy for an M/G/1 queueing model is developed. It consists of three simple N, T and D operating policies and has a peculiar structure possessing concepts of dyadic policies. Using the concept of the pseudo probability density function of the busy period, its expected busy period for the controllable M/G/1 queueing model is derived. Since the obtained result is the most generalized form the triadic polity, the expected busy periods for all known dyadic policies are recovered as special cases from it.

• IE interfaces
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• v.16 no.1
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• pp.27-33
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• 2003

The maintenance cost in K Steelworks has been continuously increased in proportion to the production cost. However, there seems to be a possibility of reducing cost through the optimization of maintenance actions. The failure types of the equipment in steelworks ate various with different failure cost. Thus the failure rate and cost of each type of failures should be considered simultaneously when the optimum maintenance period is to be determined. It is considered that the equipment undergoes periodic replacement and a specified number of incomplete preventive maintenance actions are performed during a replacement period. Assuming that the time to failure follows a Weibull distribution, the parameters of the failure rate are estimated using the maximum likelihood estimation. The optimal replacement period is determined to minimize the average cost per unit time. As the result of analysis it is suggested that the existing maintenance period for a hot-rolling equipment can be extended significantly.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.11
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• pp.498-504
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• 2006

This paper describes the simple payback period analysis of small co-generation system based on the existing apartment and building data. First, We investigate apartment and building data more than $2000[m^2]$ using Ministry of Construction & Transportation's computer system. And then we calculate the latent amount of small co-generation system considering gas company and CHP. Second, we classify the latent amount of small co-generation system into office, hospital, hotel, department store, complex building and apartment. Finally, we perform the simple payback period analysis for small co-generation system. The results show the simple payback period of small co-generation system is less then 10 years.