• 대한토목학회논문집
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• 제9권2호
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• pp.115-123
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• 1989

종래의 탄성 고체법을 이용하여 말뚝의 부마찰력을 산정하는 전산프로그램을 개발하였다. 그리고 한계 상대 변위 개념을 도입하여 이 전산프로그램의 수정을 시도하였다. 끝으로 한계 상대변위로서 말뚝과 흙사이의 미끄러짐 발생 여부를 결정하고 모아-쿨롱의 파괴 방정식을 이용하여 부마찰력을 산정하는 단순 전이함수법을 개발하였다. 이 세가지 방법에 의한 결과는 모두 현장 측정치와 잘 일치하였다. 그러나, 이들이 원심력을 이용한 모형실험 결과를 예측할 때에는 각기 다른 결과를 나타내었다. 종합적으로 보면, 이 논문에서 제안한 단순전이 함수법이 말뚝 부마찰력 산정시 그 결과의 정확성과 계산상의 효율성들을 고려할 때 가장 능률적이라고 판단된다.

• 센서학회지
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• 제28권6호
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• pp.371-376
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• 2019

We have developed an acoustic resonance inspection system to inspect the welding defects in the mechanical parts fabricated using friction stir welding method. The inspection system was consisted of a DAQ board, a microphone sensor, an impact hammer, and controlled by a PC software. The system was developed to collect and analyze the sound signal generated by hitting the sample with an impact hammer to determine whether it is defective. In this study, 100% welded good samples were compared with 95%, 90%, and 85% welded samples, respectively. The variation of the completeness in welding did not affect the visual appearance in the samples. As a result of analyzing the natural frequencies of the good samples, the five natural frequency peaks were identified. In the case of the defective samples, the frequency change was observed. The welding failure detection time was fast enough to be only 0.7 seconds. Employing our welding defect inspection system to the actual industrial field will maximize the efficiency of quality inspection and thus improve the productivity.

• 한국경영과학회지
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• 제12권1호
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• pp.157-157
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• 1987

Hydro-electric power generation from multi-purpose dams has been playing important roles in the electric power supply network in Korea. Although the total share of hydro power in national electricity supply now becomes very small, the peak-shaving and frequency control capability of hydro power helps the power company enormously in maintaining the quality of power. But since the company that builds and operates the multi-purpose dams in Korea has to sell all the electricity produced to the monopolistic utility, there have been various problems in justifying the investment, designing pricing mechanism, and controlling operations of the power plants. In addition, economic evaluation of the hydro power has been distorted by a variety of reasons and hence it has been very difficult to encourage effective development and utilization of national water resources. To make the problem worse, both parties are public companies with X-inefficiency problems. Thus, changing environment requires to reengineer the system that governs hydro power generation. We address the problems of Korean hydro-electric power generation system in four areas: the investment justification process, the operations decison right of the hydro power plants, the pricing of the purchased-power, and the negotiation of contract revision. Then we propose improvement directions of new hydro-electric power system in view of static and dynamic efficiency, X-inefficiency and equity.

• 로봇학회논문지
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• 제12권2호
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• pp.116-123
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• 2017

Wearable robots are receiving great attention from the public, as well as researchers, because its motivation is to improve the quality of lives of people. Above all, complete paraplegic patients due to spinal cord injury (SCI) might be the most adequate target users of the wearable robots, because they definitely need physical assistance due to the complete loss of muscular strength and sensory functions. Furthermore, the medical care of complete paraplegics by using the wearable robots have significantly reduced the mortality rate and improved the life expectancy. The requirements of the wearable robot for complete paraplegics are actuation torque, locomotion speed, wearing sensation, robust gait stability, safety, and practicality (i.e., size, volume, weight, and energy efficiency). A WalkON Suit is the wearable robot that has satisfied the requirements of the wearable robot for complete paraplegics and participated in the powered exoskeleton race of Cybathlon 2016. In this paper, configuration of the WalkON Suit, human-machine interface, gait pattern, control algorithm, and evaluation results are introduced.

• Journal of Electrical Engineering and Technology
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• 제3권1호
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• pp.52-59
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• 2008

This paper describes the secant method for solving the economic dispatch (ED) problem with generator constraints and transmission losses. The ED problem is an important optimization problem in the economic operation of a power system. The proposed algorithm involves selection of minimum and maximum incremental costs (lambda values) and then the evaluation of optimal lambda at required power demand is done by secant method. The proposed algorithm has been tested on a power system having 6, 15, and 40 generating units. Studies have been made on the proposed method to solve the ED problem by taking 120 and 200 units with generator constraints. Simulation results of the proposed approach were compared in terms of solution quality, convergence characteristics, and computation efficiency with conventional methods such as lambda iterative method, heuristic methods such as genetic algorithm, and meta-heuristic methods like particle swarm optimization. It is observed from different case studies that the proposed method provides qualitative solutions with less computational time compared to various methods available in the literature.

• Industrial Engineering and Management Systems
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• 제6권1호
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• pp.11-21
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• 2007

The PDCA (Plan, Do, Check and Act) cycle is often used in the field of quality management. Recently, business environments have become more competitive, and the due time of products has shortened. In a short production run process, to increase efficiency of management, the necessity for distinguishing the PDCA design that starts with PLAN and the CAPD design that starts with CHECK has been clarified. Starting from Duncan (1956), there have been a number of papers dealing with the economic design of control charts from the viewpoint of production run. Some authors (Gibra, 1971; Ladany and Bedi, 1976; etc.) have studied the economic design for finite-length runs; other authors (Crowder, 1992; Del Castillo and Montgomery, 1996; etc.) have studied the economic design for short runs. However, neither the PDCA nor the CAPD design of control charts has been considered. In this paper, both the PDCA and CAPD designs of the $\bar{\x}$ chart are defined based on Del Castillo and Montgomery's design (1996), and their mathematical formulations are shown. Then from an economic viewpoint, the optimal values of the sample size per each sampling, control limits width, and the sampling interval of the two designs are studied. Finally, by numerically analyzing the relations between the key parameters and the total expected cost per unit time, the comparisons between the two designs are considered in detail.

• 경영과학
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• 제12권1호
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• pp.157-173
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• 1995

Hydro-electric power generation from multi-purpose dams has been playing important roles in the electric power supply network in Korea. Although the total share of hydro power in national electricity supply now becomes very small, the peak-shaving and frequency control capability of hydro power helps the power company enormously in maintaining the quality of power. But since the company that builds and operates the multi-purpose dams in Korea has to sell all the electricity produced to the monopolistic utility, there have been various problems in justifying the investment, designing pricing mechanism, and controlling operations of the power plants. In addition, economic evaluation of the hydro power has been distorted by a variety of reasons and hence it has been very difficult to encourage effective development and utilization of national water resources. To make the problem worse, both parties are public companies with X-inefficiency problems. Thus, changing environment requires to reengineer the system that governs hydro power generation. We address the problems of Korean hydro-electric power generation system in four areas: the investment justification process, the operations decison right of the hydro power plants, the pricing of the purchased-power, and the negotiation of contract revision. Then we propose improvement directions of new hydro-electric power system in view of static and dynamic efficiency, X-inefficiency and equity.

• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2006년도 추계학술발표회
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• pp.245-251
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• 2006

본 연구는 ANP법을 이용하여 수색구조선의 우선 배치순위를 평가하였다. 이러한 평가를 위해서 본 연구에서는 퍼지추론 및 계층분석법을 이용하여 인명피해, 선박피해, 환경오염피해에 대해 위험성을 평가하였다. 또한 DEA 법 및 리커트 척도법을 이용하여 수색구조선의 정량적, 정성적 운영효율성을 평가하였다. 마지막으로는 위험성 평가와 운영효율성 평가를 ANP법을 이용하여 종합 평가치를 산출하였다. 그 결 과 MP, YS RCC/RSC 구역이 수색구조선의 우선 배치순위가 비교적 높은 것으로 나타났다.

• 한국농공학회논문집
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• 제54권4호
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• pp.1-8
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• 2012

This study is to assess the reduction of non-point source pollution loads for rice straw surface covering of upland crop cultivation at a watershed scale. For Byulmi-cheon watershed ($1.21km^2$) located in the upstream of Gyeongancheon, the HSPF (Hydrological Simulation Program-Fortran), a physically based distributed hydrological model was applied. Before evaluation, the model was calibrated and validated using 9 rainfall events. The Nash-Sutcliffe model efficiency (NSE) for streamflow was 0.62~0.78 and the NSE for water quality (Sediment, T-N, and T-P) were 0.68, 0.60, and 0.58 respectively. From the field experiment of 16 rainfall events, the rice straw covering reduced surface runoff average 10 % compared to normal surface condition. By handling infiltration parameter (INFILT) in the model, the value of 16.0 mm/hr was found to reduce about 10 % reduction of surface runoff. For this condition, the reduction effect of Sediment, T-N, and T-P loads were 87.2, 28.5, and 85.1 % respectively. The rice straw surface covering was effective for removing surface runoff dependent loads such as Sediment and T-P.

• 한국농공학회논문집
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• 제53권6호
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• pp.17-22
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• 2011

Biomass gasification provides synthesis gas or syngas that can be used for internal combustion engines as fuel or chemical synthesis as feedstock. Among different types of gasifiers, downdraft gasifier can produce relatively clean syngas with lower tar contents. In this study, a downdraft gasifier was fabricated with 150 mm of hearth diameter to gasify woodchip that is commercially available in this country. After drying woodchip to about 20 %, gasification experiments were conducted measuring temperature, pressure, air and gas flow rates. The volumetric concentrations of CO, $H_2$, $CO_2$, $CH_4$ were 10.7~14.5, 16.5~21.4, 12.5~16.6, and 2.3~2.9, respectively. They were overall within the ranges of the results that the previous studies showed. However, CO concentration was relatively lower and H2 was slightly higher than those from other studies. It seemed that water gas shift reaction was occurred due to the moisture in the fuel woodchip. Additional drying process coupled with syngas cooling would be required to improve the overall efficiency and syngas quality.