• International Journal of Fluid Machinery and Systems
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• 제3권2호
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• pp.113-121
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• 2010

LES(Large Eddy Simulation) with a cavitation model was performed to calculate an unsteady flow for a mixed flow pump with a closed type impeller. First, the comparison between the numerical and experimental results was done to evaluate a computational accuracy. Second, the torque acting on the blade was calculated by simulation to investigate how the cavitation caused the fluctuation of torque. The absolute pressure around the leading edge on the suction side of blade surface had positive impulsive peaks in both the numerical and experimental results. The simulation showed that those peaks were caused by the cavitaion which contracted and vanished around the leading edge. The absolute pressure was predicted by simulation with -10% error. The absolute pressure around the trailing edge on the suction side of blade surface had no impulsive peaks in both the numerical and experimental results, because the absolute pressure was 100 times higher than the saturated vapor pressure. The simulation results showed that the cavitation was generated around the throat, then contracted and finally vanished. The simulated pump had five throats and cavitation behaviors such as contraction and vanishing around five throats were different from each other. For instance, the cavitations around those five throats were not vanished at the same time. When the cavitation was contracted and finally vanished, the absolute pressure on the blade surface was increased. When the cavitation was contracted around the throat located on the pressure side of blade surface, the pressure became high on the pressure side of blade surface. It caused the 1.4 times higher impulsive peak in the torque than the averaged value. On the other hand, when the cavitation was contracted around the throat located on the suction side of blade surface, the pressure became high on the suction side of blade surface. It caused the 0.4 times lower impulsive peak in the torque than the averaged value. The cavitation around the throat caused the large fluctuation in torque acting on the blade.

• 한국산학기술학회논문지
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• 제10권2호
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• pp.248-255
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• 2009

통신시스템에서의 에러의 처리는 매우 중요한 문제로서 비터비 디코더와 같은 에러처리를 위해서 주로 절대값으로 표현하기 때문에 아날로그 절대값 회로가 자주 필요하게 된다. 이 논문에서는 절대값을 정확하게 계산할 수 있는 아날로그 절대값 회로를 제안하였다. 제안한 절대값 회로에는 부호가 반대인 두 신호들을 만든 다음, 이 신호들을 아날로그MAX회로에 인가하여 둘 중 최대값을 출력하게 하는 방법이다. 이 구조를 회로로 구현하기 위해서는 두 개의 입력 신호를 반대방향으로 차를 구하여, 크기는 같고 부호가 다른 두 개의 신호를 만든 다음 이들을 MAX회로의 입력으로 사용하는 회로를 설계하였다. 본 논문에서는 제안한 회로를 Hspice를 이용하여 시뮬레이션을 수행했으며, 그 결과를 제시하였다.

• 한국터널지하공간학회 논문집
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• 제9권3호
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• pp.229-240
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• 2007

터널 및 지하공간 시공 중 일상계측에서의 계측관리 효율성 및 고급의 내공변위 분석을 위해 3차원 광파기, 선단앵커정착형 타겟부착장치, 절대변위 계측관리 프로그램으로 구성된 3차원 절대변위 계측시스템을 구축하였다. 본 연구를 통해 3차원 절대변위 계측에 필요한 광파기의 종류와 사양을 제시하였고, 기존 타겟부착장치의 문제점을 개선한 선단앵커정착형 타겟부착장치에 대한 성능시험을 수행하여 우수한 시준거리와 측정정밀도를 확인하였다. 또한 절대변위 계측관리 프로그램에 대한 현장성능시험을 수행하여 얻어진 경향선/영향선 등 다양한 분석방법을 활용하여 막장전방의 연약대 존재 예측이 가능하였고, TSP탐사결과와 비교하여 정확성을 확인하였다.

• 산업경영시스템학회지
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• 제38권3호
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• pp.159-168
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• 2015

Aggregate Production Planning determines levels of production, human resources, inventory to maximize company's profits and fulfill customer's demands based on demand forecasts. Since performance of aggregate production planning heavily depends on accuracy of given forecasting demands, choosing an accurate forecasting method should be antecedent for achieving a good aggregate production planning. Generally, typical forecasting error metrics such as MSE (Mean Squared Error), MAD (Mean Absolute Deviation), MAPE (Mean Absolute Percentage Error), and CFE (Cumulated Forecast Error) are utilized to choose a proper forecasting method for an aggregate production planning. However, these metrics are designed only to measure a difference between real and forecast demands and they are not able to consider any results such as increasing cost or decreasing profit caused by forecasting error. Consequently, the traditional metrics fail to give enough explanation to select a good forecasting method in aggregate production planning. To overcome this limitation of typical metrics for forecasting method this study suggests a new metric, WACFE (Weighted Absolute and Cumulative Forecast Error), to evaluate forecasting methods. Basically, the WACFE is designed to consider not only forecasting errors but also costs which the errors might cause in for Aggregate Production Planning. The WACFE is a product sum of cumulative forecasting error and weight factors for backorder and inventory costs. We demonstrate the effectiveness of the proposed metric by conducting intensive experiments with demand data sets from M3-competition. Finally, we showed that the WACFE provides a higher correlation with the total cost than other metrics and, consequently, is a better performance in selection of forecasting methods for aggregate production planning.

• 한국통신학회논문지
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• 제40권1호
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• pp.165-170
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• 2015

본 논문은 3D 위치 정보를 산출하기 위한 기압고도계 및 기준국을 이용한 절대 고도 측정 정확도 향상에 관한 연구이다. GPS와 같은 위성 항법 시스템이 신뢰성이 있는 절대 고도를 제공하지 못하는 점과 기압 고도계가 변화하는 대기압의 특성상 절대 고도 정보를 제공하지 못한다는 문제점을 인식하고, 이를 개선하기 위해 새로운 기법을 제안하였다. 제안된 기법을 검증하기 위해 RTK를 활용한 기준국을 지정하고 시중에 판매하는 압력 센서 및 EVK 단말기를 활용하였으며, 실내 외에서의 사람의 이동으로 인한 고도 변화 실험과 차량을 이용한 이동 실험을 통해 검증하였다. 이 논문의 결과는 기준국을 이용하는 기존의 2D 측위 시스템을 간단히 3D 측위 시스템으로 확장할 수 있는 저가 솔루션을 제공할 수 있음을 보였다.

• 대한안전경영과학회지
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• 제20권3호
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• pp.37-46
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• 2018

According to enhancement of roles and functions of enterprises' distribution centers, recent trend of distribution centers are specialization and diversification which have generated lots of new distribution center building or expansion of the existing ones and led attention on stock transfer importance in case of distribution center relocation. This thesis is a study for how to reduce stock transfer leadtime in order to minimize business risk and how to increase inventory accuracy when stock ownership is transferred in case of distribution center relocation, and to provide inventory accuracy management methods and inventory in/out management types, detailed definition to evaluate level for inventory accuracy management and pros/cons by inventory in/out management type assuming 'the higher inventory accuracy before stock transfer, the shorter stock transfer leadtime when distribution center is relocated'. This thesis provides detailed procedure to secure an absolute stock transfer leadtime and process to confirm hugh inventory accuracy by stakeholders which should be sloved by Task Force Team for stock transfer in case of distribution center relocation.

• 한국측량학회지
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• 제30권3호
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• pp.323-332
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• 2012

항공라이다 시스템은 대상지역의 자료를 취득하기 위하여 여러번 경로 관측을 수행하게 되며, 이로 인해 취득된 데이터의 인접 경로간에 편차가 발생한다. 본 연구에서는 스트립 데이터의 비행경로간 관측값의 상대오차를 제거하고 기준 데이터에 절대보정하는 방법으로 수정된 ICP를 이용한 자동 오차보정 기법을 제안하였다. 항공라이다 데이터에 절대 자동보정을 수행하기 위하여 기존의 수치지형도에서 기준점 데이터를 추출하고, 수정된 ICP알고리즘을 적용하였다. 위의 과정을 통하여 항공라이다 데이터의 평균 점간 거리 이내로 스트립간 조정 정확도를 향상시킬 수 있었으며, 대축척 수치지형도를 이용한 절대보정 과정의 자동화 가능성을 확인하였다.

• International Journal of Computer Science & Network Security
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• 제21권2호
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• pp.77-87
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• 2021

In this study, a novel improved second order Radial Basis Function Neural Network based method with excellent scheduling capabilities is used for the dynamic prediction of short and long-term energy required applications. The effectiveness and the reliability of the algorithm are evaluated using training operations with New England-ISO database. The dynamic prediction algorithm is implemented in Matlab and the computation of mean absolute error and mean absolute percent error, and training time for the forecasted load, are determined. The results show the impact of temperature and other input parameters on the accuracy of solar Photovoltaic load forecasting. The mean absolute percent error is found to be between 1% to 3% and the training time is evaluated from 3s to 10s. The results are also compared with the previous studies, which show that this new method predicts short and long-term load better than sigmoidal neural network and bagged regression trees. The forecasted energy is found to be the nearest to the correct values as given by England ISO database, which shows that the method can be used reliably for short and long-term load forecasting of any electrical system.

• 제어로봇시스템학회논문지
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• 제20권5호
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• pp.578-583
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• 2014

Optical pick-up is a core component for data read/write operations in optical disc drives, and an optical pick-up performance evaluator is an instrument used to analyze the overall performance of an optical pick-up. Due to inevitable errors in an analog measurement circuit, resultant evaluation data is not guaranteed to be accurate. In this paper, a calibration method for an optical pick-up performance evaluator is proposed to ensure evaluation accuracy. Measured data is corrected by a 1st order correction function, and a calibration process based on least-square method is utilized to obtain correction coefficients of the correction function. The proposed calibration method is applied to experiments, and enhanced accuracy is presented with resultant evaluation data.

• 한국정보시스템학회:학술대회논문집
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• 한국정보시스템학회 2002년도 추계학술대회
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• pp.289-312
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• 2002

This study suggests the Link weight analysis approach to choose input variables and an integrated model to make more accurate bankruptcy prediction model. the Link weight analysis approach is a method to choose input variables to analyze each input node's link weight which is the absolute value of link weight between an input nodes and a hidden layer. There are the weak-linked neurons elimination method, the strong-linked neurons selection method in the link weight analysis approach. The Integrated Model is a combined type adapting Bagging method that uses the average value of the four models, the optimal weak-linked-neurons elimination method, optimal strong-linked neurons selection method, decision-making tree model, and MDA. As a result, the methods suggested in this study - the optimal strong-linked neurons selection method, the optimal weak-linked neurons elimination method, and the integrated model - show much higher accuracy than MDA and decision making tree model. Especially the integrated model shows much higher accuracy than MDA and decision making tree model and shows slightly higher accuracy than the optimal weak-linked neurons elimination method and the optimal strong-linked neurons selection method.