• 설비공학논문집
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• 제13권12호
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• pp.1184-1195
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• 2001

Analysis of fluid flow in rectangular ducts has been conducted since it has a wide application. The purpose is to provide experimental data for the comparison with computational results. Velocity distributions inside a rectangular duct with $90^{\circ}$ mitered elbow are measured by 5W laser doppler velocity meter for Reynolds numbers of 4,049, 8,104, and 12,186. Flow rates obtained by the integration of measured velocity profile at three cross-sections, which are inlet, middle section after the elbow, and outlet, have errors less than 0.9% among them. Turbulent fluctuation components in two directions are found to have almost similar magnitude each other at a certain location due to the isotropic characteristic of turbulence.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.1035-1037
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• 2001

This paper presents an improved hys- teresis current control method for three-phase PWM power inverters using 3-level comparator. Hysteresis current controller using 3-level comparator has an advantage of constant switching frequency compared with conventional hysteresis current controller. However, this method has disadvantage that the longer sampling period, the larger current error because the switching is performed without considering current error magnitude of each phase. The proposed method improves the control performance by selecting the optimum switching pattern in which the magnitudes of current errors are considered introducing space vector concept. Simulation results using Matlab/Simulink show that the proposed control method reduces current error keeping the merit of previous hysteresis current control method.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2002년도 ICCAS
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• pp.80.4-80
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• 2002

Performance of the previously proposed 2D-image reconstruction method for soft tissues in x-ray computed tomography is evaluated thoroughly through numerical experiments with 4 assumed absorption rates of different symmetries under practical conditions, and the following special features are made clear: It is quite precise, especially at points where the object taking larger values; about two orders less magnitude errors than the conventional most precise method when no noise existing, without any 1D- or 2D-interpolation. In spite of its high sensitivity to the noises, it is even more precise by about 8dB than the latter, to relative pojection data noise power of 5%.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 A
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• pp.276-279
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• 2004

The purpose of this paper is to describe and demonstrate how a utility-connectable inverter for photovoltaic or fuel-cell applications can be well modeled using PSCAD/EMTDC. In this paper, a single-phase IGBT inverter using SPWM is modeled. Simple voltage magnitude and phase controls are implemented using PSCAD's Pl controller, PLL, and a 'user defined' component called Modulo (found in their extensive collection of example circuits). The circuit model also takes advantage of PSCAD's interpolated firing pulse option, which provides improved simulation results by preventing errors from being introduced when switches fire between time simulation steps. Additionally, SCAD's Online Frequency Scanner for FFT is utilized for a demonstration of PSCAD's frequency-domain analysis capabilities.

• 한국통신학회논문지
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• 제21권5호
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• pp.1109-1122
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• 1996

Generally, moving images contain the various components in motions, which reange from a static object and background to a fast moving object. To extract the accurate motion parameters, we must consider the various motions. That requires a wide search egion in motion estimation. The wide search, however, causes a high computational complexity. If we have a few knowledge about the motion direction and magnitude before motion estimation, we can determine the search location and search window size using the already-known information about the motion. In this paper, we present a local adaptive motion estimation approach that predicts a block motion based on spatio-temporal neighborhood blocks and adaptively defines the search location and search window size. This paper presents a technique for reducing computational complexity, while having high accuracy in motion estimation. The proposed algorithm is introduced the forward and backward projection techniques. The search windeo size for a block is adaptively determined by previous motion vectors and prediction errors. Simulations show significant improvements in the qualities of the motion compensated images and in the reduction of the computational complexity.

• 대한전기학회논문지
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• 제39권2호
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• pp.199-209
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• 1990

In this paper, a multivariable robust controller for a boiler-burbine system is designed by using a modified LQG/LTR method. From the known nonlinear dynamic model, a linearized model is obtained with the saturations at both input magnitude and input varying rate. The modeling error is analyzed at various operation points. A new dynamics augmentation method in the LQG/LTR method is suggested which can be applied to LQG/LTR method to reject the input and output disturbances and to follow reference inputs under modeling errors. The good performance of the designed controller is shown by simulations in various conditions.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 하계학술대회 논문집 A
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• pp.316-318
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• 1993

In order to estimation the optimum PID parameter of the turbine speed controller, the response cure of the object plant was compared with the reference pattern and then the magnitude peak value error and peak time error was calculated. With the calculated errors as input into the Fuzzy inference Method was introduced to propose the tuning method for each parameter. And the computer simulation was performed with the above Fuzzy inference method in which the Chunju hydro power plant turbine governor system was used as a model. This Study also aims to develop the exclusive tuner for govenor using industrial computer.

• 대한전자공학회논문지SD
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• 제40권5호
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• pp.354-360
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• 2003

연속된 데이터를 위한 새로운 롬 압축 방식이 제한 되었다. 이 롬 압축 방식은 새롭게 제안된 두 롬 압축 알고리즘들을 기반으로 한다. 하나는 영역 선택 롬 압축 알고리즘이다. 이 방식은 크기와 주소로 여러 영역들로 나눈 후 데이터를 포함하는 영역들만을 선택적으로 저장하는 방식이다. 다른 하나는 양자화 롬과 오차 롬 압축 알고리즘이다. 이 방식은 양자화된 데이터와 양자화에 의한 오차를 나누어 저장하는 방식이다. 이 두 알고리즘을 사용하면 다양한 연속된 데이터들에 대하여 40∼60%의 롬 크기의 감소를 얻을 수 있다.

• 한국산림과학회지
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• 제88권3호
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• pp.285-291
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• 1999

미국(美國) 남부(南部) 지역(地域)의 주요(主要) 경제(經濟) 조림수종(造林樹種)인 테에다소나무(Pinus taeda L.)와 엘리오티소나무(Pinus elliottii Engelm.) 조림지(造林地)에 대한 지위지수식(地位指數式)을 개발(開發)하였으며, 지위지수(地位指數)의 값들에 대한 오차(誤差)의 크기를 규명(糾明)하기 위하여 영구적(永久的)으로 설치(設置)된 plot으로부터 측정(測定)된 data sets을 이용(利用)하였다. 분석(分析)에 이용(利用)된 자료(資料)는 3년(年)을 측정주기(測定週期)(measurement cycle)로 하여 측정(測定)하였으며, 각각(各各)의 누적(累積) 측정(測定) 주기(週期) 자료(資料)와 이들 모두를 종합(綜合)한 자료(資料)를 이용(利用)하였다. 최종적(最終的)인 지위지수(地位指數) 예측식(豫測式)의 유도(誘導)는 모든 측정(測定) 자료(資料)를 종합(綜合)하여 Chapman-Richards의 생장함수식(生長函數式)을 사용(使用)하였으며, 이를 기초(基礎)로 하여 두 수종(樹種)의 동형(同形)(anamorphic) 지위지수(地位指數) 곡선(曲線)을 작성(作成)하였다. 임령(林令)의 변화추이(變化推移)에 따른 지위지수(地位指數)값에 대한 오차(誤差)의 크기를 규명(糾明)하기 위하여, 최종적(最終的) 측정주기(測定週期)의 누적(累積) 자료(資料)를 이용(利用)한 지위지수(地位指數) 예측치(豫測直)와 각각(各各)의 주기별(週期別) 누적(累積) 자료(資料)를 이용(利用)한 지위지수(地位指數) 예측치(豫測直) 간의 차이(差異)에 대한 절대(絶對) 평균치(平均値)를 사용(使用)하였다. 그 결과(結果), 지위지수(地位指數)의 값들은 임령(林令)이 5년(年) 이하(以下)에서 예측(豫測)되었을 경우(境遇), 두 수종(樹種) 모두 절대치(絶對値)의 평균(平均) 오차(誤差) 약(約) 5 meter 정도로 크게 나타났다. 따라서 임령(林令)이 5년(年) 이하(以下)인 유령(幼令) 임분(林分)에 대한 지위지수(地位指數) 값의 예측치(豫測直)들은 많은 오차(誤差)를 내포(內包)하고 있는 것으로 판단(判斷)다.

• Journal of Astronomy and Space Sciences
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• 제39권4호
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• pp.159-167
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• 2022

Because of the small number of spacecraft available in the Earth's magnetosphere at any given time, it is not possible to obtain direct measurements of the fundamental quantities, such as the magnetic field and plasma density, with a spatial coverage necessary for studying, global magnetospheric phenomena. In such cases, empirical as well as physics-based models are proven to be extremely valuable. This requires not only having high fidelity and high accuracy models, but also knowing the weakness and strength of such models. In this study, we assess the accuracy of the widely used Tsyganenko magnetic field models, T96, T01, and T04, by comparing the calculated magnetic field with the ones measured in-situ by the GOES satellites during geomagnetically disturbed times. We first set the baseline accuracy of the models from a data-model comparison during the intervals of geomagnetically quiet times. During quiet times, we find that all three models exhibit a systematic error of about 10% in the magnetic field magnitude, while the error in the field vector direction is on average less than 1%. We then assess the model accuracy by a data-model comparison during twelve geomagnetic storm events. We find that the errors in both the magnitude and the direction are well maintained at the quiet-time level throughout the storm phase, except during the main phase of the storms in which the largest error can reach 15% on average, and exceed well over 70% in the worst case. Interestingly, the largest error occurs not at the Dst minimum but 2-3 hours before the minimum. Finally, the T96 model has consistently underperformed compared to the other models, likely due to the lack of computation for the effects of ring current. However, the T96 and T01 models are accurate enough for most of the time except for highly disturbed periods.