• 대한기계학회논문집
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• 제12권2호
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• pp.373-380
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• 1988

본 연구의 목적은 음장의 입자속도가 기류의 평균속도와 비슷한 크기인 경우에 원통으로부터 열전달의 동특성과 한 사이클의 평균값인 평균열전달이 음장에 의하여 어떠한 영향을 받는가를 구하기 위한 것이다.

• 대한조선학회논문집
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• 제43권3호
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• pp.322-330
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• 2006

Numerical calculations are carried out for flow past a circular cylinder forced oscillating normal to the free-stream flow at a fixed Reynolds number equal to 185. The cylinder oscillation frequency ranged from 0.8 to 1.2 of the natural vortex-shedding frequency, and the oscillation amplitude extended up to 20% of the cylinder diameter. IBM (Immersed Boundary Method) with direct momentum forcing was adopted to handle both of a stationary and an oscillating cylinder Present results such as time histories of drag and lift coefficients for both stationary and oscillating cases are in good agreement with previous numerical and experimental results. The instantaneous wake patterns of oscillating cylinder with different oscillating frequency ratios showed the synchronized wakes pattern in the lock-in region and vortex switching phenomenon at higher frequency ratio than the critical frequency ratio.

• Journal of Advanced Marine Engineering and Technology
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• 제33권2호
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• pp.259-266
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• 2009

An experimental study was conducted to investigate the effects of forcing amplitude on the flow structure near the nozzle exit of forced jet diffusion flames. The jet was excited up to the blowout occurrence by a considerable large amplitude with a periodic velocity fluctuation at the tube resonating frequency. In the attached flame regime, we disclosed the very interesting result newly that adding of a moderate forcing amplitude caused the jet flame to become longer in spite of being forced. Particular attention is focused on the turnabout mechanism of vortex roll-up around the elongated flame, which has not been reported previously, and on the inner coherent structure of the forced jet in the attached flame regime. From the velocity and flow visualization results, it was ascertained that the surrounding air due to the occurrence of negative velocity parts was suck into the fuel nozzle. To aid in understanding the rotating phenomenon of coherent structure, we present a schematic diagram of the turnabout mechanism of vortex roll-up. The mechanism of vortex turnabout phenomenon can be easily understood by considering the positive and negative velocity amplitudes about the instantaneous velocity of the forcing flow, as shown in this diagram.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.603-605
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• 1996

The SLIM used in the conveyance system has been generally developed the controller based on the slip frequency control and the VVVF method to obtain the quick response for the position control signal. This paper deals with the trust control of the SLIM by vector control with Bang-Bang condition. Also, the control system is composed of the PI controller for soft start of the SLIM and the q-axis current controller for correction in phase with Space Vector for reducing the harmonic pulsation in low speed. The processing for vector control and robust dynamic breaking control is carried out by MC80196KC micro processor and IGBT module. The proposed scheme is verified through the computer simulation and experiments for the 10KW SLIM.

• 한국식품과학회지
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• 제20권1호
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• pp.13-18
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• 1988

1% 희석 쌀전분 용액의 노화 특성을 호화후 $5^{\circ}C$에서 저장하면서 고찰하였다. 저장기간이 증가함에 따라 노화도도 증가하였는데 그 증가하는 정도는 노화 초기에 가장 현저한 반면 노화가 진행됨에 따라 감소하였다. 추정 전분의 노화특성을 Avrami식으로 해석하여 노화기작을 살펴본 결과 Avrami지수, 속도상수, 시간상수는 각각 0.96, 0.21 $days^{-1}$, 4.77 days 였다. 이때 Avrami지수가 단위치(n=1)에 접근하므로 희석 쌀전분 용액은 즉각적인 핵형성에 이은 간상구조의 생성에 의하여 노화가 진행됨을 알 수 있었다. 주사 전자 현미경에 의하여 노화과정을 관찰한결과 노화기간이 경과함에 따라 생전분과는 다른 형태의 3차원 결정구조가 형성됨을 알 수 있었다.

• 한국통신학회논문지
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• 제17권3호
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• pp.268-276
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• 1992

본 논문에서는 전파감측(감시 및 측정)이나 유니버셜 복조기의 개발을 위한 기초 연구로써, 미지의 디지털 변조 신호 식별에 대하여 논의한다. 제안한 식별 방법은 시간 영역의 파라미터를 이용하는 방안으로 먼저 포락선, 순시 주파수, 차위상 정보를 기본특징으로 추출한다. 추출된 기본특징은 식별을 위해 2개의 2차원 비선형 식별 공간으로 사상되며 입력 신호의 식별은 1차 선형식별함수를 이용해 이루어진다. 본 논문에서 제안한 방법의 타당성을 검증하기 위하여 가우스성 잡음 환경하에서 ASK-2, ASK-4, BPSK, QPSK, 8PSK, FSK, QAM 신호를 대상으로 특징추출과 식별과정을 모의실험한다.

• 전기학회논문지
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• 제62권10호
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• pp.1487-1493
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• 2013

A new simple control method for active power filter, which can realize the complete compensation of harmonics is proposed. In the proposed scheme, a model-based digital current control strategy is presented. The proposed control system is designed and implemented in a form referred to as internal model control structure. This method provides a convenient way for parameterizing the controller in term of the nominal system model, including time-delays. As a result, the resulting controller parameters are directly set based on the power circuit parameters, which make tuning of the controllers straightforward task. In the proposed control algorithm, overshoots and oscillations due to the computation time delay is prevented by explicit incorporating of the delay in the controller transfer function. In addition, a new compensating current reference generator employing resonance model implemented by a DSP(Digital Signal Processor) is introduced. Resonance model has an infinite gain at resonant frequency, and it exhibits a band-pass filter. Consequently, the difference between the instantaneous load current and the output of this model is the current reference signal for the harmonic compensation.

• Journal of Electrical Engineering and Technology
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• 제3권1호
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• pp.79-87
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• 2008

This paper proposes the design and implementation of a direct torque controlled induction motor drive system. The method is based on control of decoupling between amplitude and angle of reference stator flux for determining reference stator voltage vector in generating PWM output voltage for induction motors. The objective is to reduce electromagnetic torque ripple and stator flux droop which result in a decrease in current distortion in steady state condition. In addition, the proposed technique provides simplicity of a control system. The direct torque control is based on the relationship between instantaneous slip angular frequency and rotor angular frequency in adjustment of the reference stator flux angle. The amplitude of the reference stator flux is always kept constant at rated value. Experimental results are illustrated in this paper confirming the capability of the proposed system in regards to such issues as torque and stator flux response, stator phase current distortion both in dynamic and steady state with load variation, and low speed operation.

• Wind and Structures
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• 제5권2_3_4호
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• pp.337-346
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• 2002

Wind tunnel pressure measurements and numerical simulations based on the Reynolds Stress Model (RSM) are compared with full and model scale data in the flow area of impingement, separation and wake for $60^{\circ}$ and $90^{\circ}$ wind azimuth angles. The phase averaged fluctuating pressures simulated by the RSM model are combined with modelling of the small scale, random pressure field to produce the total, instantaneous pressures. Time averaged, rsm and peak pressure coefficients are consequently calculated. This numerical approach predicts slightly better the pressure field on the roof of the TTU (Texas Tech University) building when compared to the wind tunnel experimental results. However, it shows a deviation from both experimental data sets in the impingement and wake regions. The limitations of the RSM model in resolving the intermittent flow field associated with the corner vortex formation are discussed. Also, correlations between the largest roof suctions and the corner vortex "switching phenomena" are observed. It is inferred that the intermittency and short duration of this vortex switching might be related to both the wind tunnel and numerical simulation under-prediction of the peak roof suctions for oblique wind directions.

• 정보처리학회논문지D
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• 제11D권7호
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• pp.1491-1498
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• 2004

성공적인 프로젝트 계획은 활용 가능한 일정과 더불어 프로젝트를 완수하는데 요구되는 인력을 얼마나 정확히 추정하느냐에 달려있다. 새로운 또는 보다 나은 모델 개발에 많은 연구가 이루어졌지만 현존하는 소프트웨어 인력 추정 모델들은 소프트웨어 생명주기 전반에 걸쳐 투입되는 총 개발인력 또는 시간에 따른 단위시간당 개발인력 분포만을 제공하고 있다. 본 논문은 시간의 함수가 아닌 발견된 결함 수에 따라 시험단계에 투입되는 인력과 시험단계의 시험과정과 디버깅과정에 투입되는 인력을 추정하는 모델들을 제시하였다. 시험과 디버깅 과정에서 발견되는 결함에 기반한 투입 인력의 다항식 모델을 제안한다. 제안된 모델들은 5종의 다른 소프트웨어 프로젝트들에 적용되어 결정계수와 MMRE를 통해 모델의 적합성을 검증하였다.