• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.307-307
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• 2022

최근 기후변화와 댐 상류 토지이용 변화 등과 같은 다양한 원인에 의해 댐 유입량의 변동성이 증가하면서 댐 관리 및 운영조작 의사 결정에 어려움이 발생하고 있다. 따라서 이러한 댐 유입량의 변동 특성을 반영하여 댐 유입량을 정확하고 효율적으로 예측할 수 있는 방안이 필요한 실정이다. 머신러닝 기술이 발전하면서 Auto-ML(Automated Machine Learning)이 다양한 분야에서 활용되고 있다. Auto-ML은 데이터 전처리, 최적 알고리즘 선택, 하이퍼파라미터 튜닝, 모델 학습 및 평가 등의 모든 과정을 자동화하는 기술이다. 그러나 아직까지 수문 분야에서 댐 유입량을 예측하기 위한 모델을 개발하는데 있어서 Auto-ML을 활용한 사례는 부족하고, 특히 댐 유입량의 예측 정확성을 확보하기 위해 High-inflow and low-inflow 의 변동 특성을 고려한 하이브리드 결합 방식을 통해 Auto-ML 기반 앙상블 모델을 개발하고 평가한 연구는 없다. 본 연구에서는 Auto-ML의 패키지 중 Auto-sklearn을 통해 홍수기, 비홍수기 유입량 변동 특성을 반영한 하이브리드 앙상블 댐 유입량 예측 모델을 개발하였다. 소양강댐을 대상으로 적용한 결과, 하이브리드 Auto-sklearn 앙상블 모델의 댐 유입량 예측 성능은 R² 0.868, RMSE 66.23 m³/s, MAE 16.45 m³/s로 단일 Auto-sklearn을 통해 구축 된 앙상블 모델보다 전반적으로 우수한 것으로 나타났다. 특히 FDC (Flow Duration Curve)의 저수기, 갈수기 구간에서 두 모델의 유입량 예측 경향은 큰 차이를 보였으며, 하이브리드 Auto-sklearn 모델의 예측 값이 관측 값과 더욱 유사한 것으로 나타났다. 이는 홍수기, 비홍수기 구간에 대한 앙상블 모델이 독립적으로 구축되는 과정에서 각 모델에 대한 하이퍼파라미터가 최적화되었기 때문이라 판단된다. 향후 본 연구의 방법론은 보다 정확한 댐 유입량 예측 자료를 생성하기 위한 방안 수립뿐만 아니라 다양한 분야의 불균형한 데이터셋을 이용한 앙상블 모델을 구축하는데도 유용하게 활용될 수 있을 것으로 사료된다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.9
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• pp.774-783
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• 2012

A simple, accurate, secure, long-lasting, and portable hybrid positioning system is proposed and designed in this paper. It consists of a lighting LED that generates visible light data corresponding to position information of a target and a Zigbee wireless network communication module with low power, security, and service area expansion characteristics. Under an indoor environment where there is 23.62m distance between an observer and the target, the presented hybrid positioning system is tested and is verified with the functions of Zigbee three hop wireless networking and visible light communication (VLC) scheme. The test results are analyzed and discussed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.7
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• pp.649-656
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• 2002

This paper addresses the phase noise analysis of high-speed DH-PLL(Digital Hybrid Phase-Locked Loops) frequency synthesizer. Because of the additional quantization noise of D/A converter in DH-PLL, the phase noise of DH-PLL is increased than the conventional PLL. Three kinds of noise sources such as reference input, D/A converter, and VCO(Voltage Controlled Oscillator) are considered to analyze the phase noise. It largely depends on the closed loop bandwidth and frequency synthesis division ratio(N) so that we can decide the optimal closed loop bandwidth to minimize the phase noise of DH-PLL. It is shown that the simulation results closely match with the results of analytical approach.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.474-478
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• 2010

Hybrid rocket combustion experiments using liquefying diaphragm made by blended liquefying fuel with 10 wt% of LDPE were performed. Results of experiments were compared to the those of pure paraffin. In case of using liquefying diaphragm, regression rate of rear fuel grain, characteristic velocity and specific impulse highly increased due to the induced turbulent intensity and heat transfer. The serious combustion instability was not observed in analysis of combustion instability. These results can imply that the liquefying diaphragm is efficient to improve low combustion efficiency in hybrid rocket using liquefying fuel.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.11a
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• pp.288-289
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• 2012

최근 데이터 저장을 위한 고속 입출력에서 병목현상을 해결하기 위해 다양한 SSD(Solid State Drive) 관련 연구가 많이 수행되고 있다. 대표적인 것으로 비휘발성 메모리인 플래시와 차세대 반도체 메모리인 SCM(Storage Class Memory) SSD가 있고, 휘발성 메모리인 DRAM기반의 SSD가 있다. 플래시 또는 SCM 메모리기반 저장장치는 하드 디스크기반 저장장치에 비해 읽기 속도가 빠르며, 내구성이 강하다는 장점으로 새로운 저장장치 시스템의 저장매체로 부각되고 있으나, 단위 저장 공간 당 높은 가격으로 인해 저장장치 시스템에 적용하기 에는 많은 문제점이 있다. 최근에는 이러한 문제를 해결하기 위해 고용량의 하드디스크와 SSD를 RAID 또는 단일 저장장치 매체로 구성하는 하이브리드 저장장치에 관한 연구와 제품이 출시되고 있다. 본 논문에서는 이러한 하이브리드 저장 매체 어레이를 저장장치 시스템으로 구성하기 위한 볼륨구성과 해당 서버에 볼륨 제공 서비스를 수행하기 위한 하이브리드 저장장치 시스템 설계 방법에 대해 설명한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.6
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• pp.2618-2623
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• 2013

A hybrid model is proposed to easily predict the effective thermal conductivity of composites with aligned- and coated-short fibers, whose aspect ratio is not constant. The thermal conductivities of coated fillers are computed by using the generalized self-consistent model, resulting in that composites are simply simulated by the matrix with the equivalent short fibers. Finally, the thermal conductivity of the composites is predicted using the modified Eshelby model. The predicted results by the representative models and hybrid model are compared for the composite with aligned- and coated-short fibers of single aspect ratio. It is demonstrated that the hybrid model can be applied to the composite with aligned- and short-fibers of aspect ratios, 2 and 10, without any difficulties.

• The KIPS Transactions:PartD
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• v.15D no.1
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• pp.31-40
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• 2008

We generally use lower-dimensional transformations to convert high-dimensional sequences into low-dimensional points in similar sequence matching. These traditional transformations, however, show different characteristics in indexing performance by the type of time-series data. It means that the selection of lower-dimensional transformations makes a significant influence on the indexing performance in similar sequence matching. To solve this problem, in this paper we propose a hybrid approach that integrates multiple transformations and uses them in a single multidimensional index. We first propose a new notion of hybrid lower-dimensional transformation that exploits different lower-dimensional transformations for a sequence. We next define the hybrid distance to compute the distance between the transformed sequences. We then formally prove that the hybrid approach performs the similar sequence matching correctly. We also present the index building and the similar sequence matching algorithms that use the hybrid approach. Experimental results for various time-series data sets show that our hybrid approach outperforms the single transformation-based approach. These results indicate that the hybrid approach can be widely used for various time-series data with different characteristics.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.8
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• pp.582-594
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• 2016

Most studies on hybrid buses are on large-sized buses and not mid-sized low-floor buses. This study uses MATLAB simulation to evaluate the fuel efficiency of such buses powered by diesel. Based on the results, a hybrid electric vehicle system is recommended for the best combination of power and gear ratio. A parallel hybrid system was selected for the hybridization, which transmits front and rear wheel power independently. The necessary power to satisfy the target performance was calculated, and the applicable capacity area was designed. Dynamic programing was used to create and optimize a component sizing algorithm, which was used to scale the capacity of each component of the power source to satisfy the design criteria. The fuel efficiency rate, optimum power source capacity, and gear ratio can be improved by converting a conventional bus into a parallel hybrid bus.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.5
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• pp.11-24
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• 2011

A real-time hybrid test of a 3 story-3 bay reinforced concrete frame which is divided into numerical and physical substructure models under uniaxial earthquake excitation was run using a fixed iteration implicit HHT time integration method. The first story inner non-ductile column was selected as the physical substructure model, and uniaxial earthquake excitation was applied to the numerical model until the specimen failed due to severe damage. A finite-element analysis program, Mercury, was newly developed and optimized for a real-time hybrid test. The drift ratio based on the top horizontal displacement of the physical substructure model was compared with the result of a numerical simulation by OpenSees and the result of a shaking table test. The experiment in this paper is one of the most complex real-time hybrid tests, and the description of the hardware, algorithm and models is presented in detail. If there is an improvement in the numerical model, the evaluation of the tangent stiffness matrix of the physical substructure model in the finite element analysis program and better software to reduce the computational time of the element state determination for the force-based beam-column element, then the comparison with the results of the real-time hybrid test and the shaking table test deserves to make a recommendation. In addition, for the goal of a "Numerical simulation of the complex structures under dynamic loading", the real time hybrid test has enough merit as an alternative to dynamic experiments of large and complex structures.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.38 no.1
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• pp.1-13
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• 2001

Due to the friction characteristics of cylinders and the rail of a passenger car, in the elevator actuated with hydraulic systems, there exist dead zones, which can not be controlled by a PID controller. To overcome the drawbacks, in this paper, we first try a hybrid controller which switches between a fuzzy logic controller and a PID controller. However, because the hybrid control scheme uses only a single type controller, except the switched layer, the high control performance can not be achieved. To solve this problem, we propose a new type fuzzy hybrid control scheme, which outputs of the output mixer arc controlled by a fuzzy logic. The hydraulic elevator system controlled by inverters has more then one switched layers due to the highly nonlinear characteristics. The proposed fuzzy hybrid control scheme achieves improved control performances by using both controllers with weighted outputs depend on the system status, to achieve improved control performances. The effectiveness of the proposed control scheme arc shown by simulation results, which the proposed fuzzy hybrid control method yields good control performance not only in the zero crossing speed region but also in the overall control region including steady-state region.