• 한국음향학회지
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• 제32권5호
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• pp.369-376
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• 2013

Lowson의 음향상사식을 이용하여 시간영역에서 풍력터빈의 저주파수 소음을 예측 하였고, 관련 소음원들의 기여도를 분석하였다. 소음원으로서 날개-깃 상 평균 압력 분포를 구하기 위하여 XFOIL를 이용하였다. 이 때, 소음 예측 시 입력 값 인 유한 요소 상의 힘을 계산하기 위해 날개-깃을 여러 개의 요소로 분할하였다. 소음원을 힘 섭동항, 가속도항, 속도항으로 분리하여 주파수 기여도를 분석하였다. 끝으로, 예측 스펙트럼을 운용 중 인 풍력터빈에 대하여 측정한 저주파수 소음과 비교하였고, 그 결과 풍속 증가에 따라 힘 섭동 성분이 저주파수에서 크게 기여하는 것을 확인하였다.

• 한국자동차공학회논문집
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• 제19권2호
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• pp.26-34
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• 2011

Hybrid powertrain systems have been developed to improve the fuel efficiency of internal combustion engines. In the case of a parallel hybrid powertrain system, an engine and a motor are directly coupled. Because of the hardware configuration of the parallel hybrid system, friction and the pumping losses of internal combustion engines always exists. Such losses are the primary factors that result in the deterioration of fuel efficiency in the parallel-type hybrid powertrain system. In particular, the engine operates as a power consumption device during the fuel-cut condition. In order to improve the fuel efficiency for the parallel-type hybrid system, cylinder deactivation (CDA) technology was developed. Cylinder deactivation technology can improve fuel efficiency by reducing pumping losses during the fuel-cut driving condition. In a CDA engine, there are two operating modes: a CDA mode and an SI mode according to the vehicle operating condition. However, during the mode change from CDA to SI, a serious fluctuation of the air-fuel ratio can occur without adequate control. In this study, an air-fuel ratio control algorithm during the mode transition from CDA to SI was proposed. The control algorithm was developed based on the mean value CDA engine model. Finally, the performance of the control algorithm was validated by various engine experiments.

• Journal of Electrical Engineering and Technology
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• 제12권2호
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• pp.726-737
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• 2017

The use of energy storage systems (ESSs) has become a feasible solution to solve the wind power intermittency issue. However, the use of ESSs increases the system cost significantly. In this paper, an optimal power flow control scheme to minimize the ESS capacity is proposed by using the zero-phase delay low-pass filter which can eliminate the phase delay between the dispatch power and the wind power. In addition, the filter time constant is optimized at the beginning of each dispatching interval to ensure the fluctuation mitigation requirement imposed by the grid code with a minimal ESS capacity. And also, a short-term power dispatch control algorithm is developed suitable for the proposed power dispatch based on the zero-phase delay low-pass filter with the predetermined ESS capacity. In order to verify the effectiveness of the proposed power management approach, case studies are carried out by using a 3-MW wind turbine with real wind speed data measured on Jeju Island.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권6호
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• pp.589-601
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• 2016

The hybrid grid was adopted and numerical prediction analysis of propeller unsteady bearing force considering free surface was performed for mode and full-scale KCS hull-propeller-rudder system by employing RANS method and VOF model. In order to obtain the propeller velocity under self-propulsion point, firstly, the numerical simulation for self-propulsion test of full-scale ship is carried out. The results show that the scale effect of velocity at self-propulsion point and wake fraction is obvious. Then, the transient two-phase flow calculations are performed for model and full-scale KCS hull-propeller-rudder systems. According to the monitoring data, it is found that the propeller unsteady bearing force is fluctuating periodically over time and full-scale propeller's time-average value is smaller than model-scale's. The frequency spectrum curves are also provided after fast Fourier transform. By analyzing the frequency spectrum data, it is easy to summarize that each component of the propeller bearing force have the same fluctuation frequency and the peak in BFP is maximum. What's more, each component of full-scale bearing force's fluctuation value is bigger than model-scale's except the bending moment coefficient about the Y-axis.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권1호
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• pp.69-84
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• 2018

In order to analyze the characteristics of propeller exciting force, the hybrid grid is adopted and the numerical prediction of KCS ship model is performed for hull-propeller-rudder system by Reynolds-Averaged Navier Stokes (RANS) method and volume of fluid (VOF) model. Firstly, the numerical simulation of hydrodynamics for bare hull at oblique state is carried out. The results show that with the increasing of the drift angle, the coefficients of resistance, side force and yaw moment are constantly increasing, and the bigger the drift angle, the worse the overall uniformity of propeller disk. Then, propeller bearing force for hull-propeller-rudder system in oblique flow is calculated. It is found that the propeller thrust and torque fluctuation coefficient peak in drift angle are greater than that in straight line navigation, and the negative drift angle is greater than the positive. The fluctuation peak variation law of coefficient of side force and bending moment are different due to various causes.

• 한국수소및신에너지학회논문집
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• 제29권2호
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• pp.197-204
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• 2018

In the present study, unsteady flow analysis has been conducted to investigate the blade forces and wake flow around a hybrid street-lamp having a vertical-axis small wind turbine and a photovoltaic panel. Uniform velocities of 3, 5 and 7 m/s are applied as inlet boundary condition. Relatively large vortex shedding is formed at the wake region of the photovoltaic panel, which affects the increase of blade torque and wake flow downstream of the wind turbine. It is found that blade force has a good relation to the variation of the angle of attack with the rotation of turbine blades. Variations in the torque on the turbine blade over time create a cyclic fluctuation, which can be a source of turbine vibration and noise. Unsteady fluctuation of blade forces is also analyzed to understand the nature of the vibration of a small wind turbine over time. The detailed flow field inside the turbine blades is analyzed and discussed.

• 한국유통학회지:유통연구
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• 제11권1호
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• pp.99-124
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• 2006

본 연구는 기존의 연구들이 간과했던 점포유형, 제품유형, 가격유형을 고려하여 온라인과 오프라인 유통경로에서 가격수준과 가격편차에는 차이가 있는지를 비교하였다. 즉, 제품특성 및 점포 유형, 배송료, 적립금, 사은품 등과 같은 요인들에 따라서 소비자가 부담하는 총가격이 어떻게 달라지는지, 가격수준, 가격편차, 가격변동 빈도가 어떤 차이가 있는지에 대해서 살펴보았다. 그 결과 온라인 점포의 가격수준이 오프라인 점포보다 더 낮았고, 제품유형(대용량/소용량)에 따라서는 순수온라인 점포에서 소용량 상품의 가격수준이 더 낮았으며, 가격편차는 Hybrid 점포의 가격편차가 더 낮게 나타났다. 가격변동은 Hybrid 점포에서 가장 많이 발생했고, 총가격과 배달가격간의 가격편차는 순수온라인 점포에서 특정상품(화장품)을 제외하고는 총가격 기준의 가격편차가 더 큰 것으로 나타났다. 따라서 가격수준이나 가격편차 등을 고려해 볼 때, 온라인 유통경로가 효율적이거나, 점차 효율적으로 진행되어 가고 있다고 할 수 있었다. 그러나 계절적인 영향이 큰 상품이나, 유통 지배력이 있는 상품의 경우는 순수온라인 생포보다 Hybrid 점포가 더 가격 면에서 효율적인 유통경로로 나타났다.

• 전기학회논문지
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• 제65권6호
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• pp.962-968
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• 2016

The large scaled lead-acid battery is widely used for efficient operation of the photovoltaic system in many islands. However, lithium-ion battery is now being introduced to mitigate the fluctuation of wind power and to replace lead-acid battery. Therefore, hybrid ESS(Energy Storage system) that combines lithium-ion battery with lead-acid battery is being required because lithium-ion battery is costly in present stage. Under this circumstance, this paper presents the optimal algorithm to create composition rate of hybrid ESS by considering fixed and variable costs in order to maximize advantage of each battery. With minimization of total cost including fixed and variable costs, the optimal composition rate can be calculated based on the various scenarios such as load variation, life cycle and cost trend. From simulation results, it is confirmed that the proposed algorithms are an effective tool to produce a optimal composition rate.

• KEPCO Journal on Electric Power and Energy
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• 제2권1호
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• pp.49-54
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• 2016

현재 대부분의 도서지역에서는 태양광발전을 효율적으로 운용하기 위하여 대용량 연축전지가 많이 사용되고 있지만, 풍력발전의 도입, 축전지 교체로 인하여 리튬이온전지의 도입이 증가하고 있다. 따라서 본 논문에서는 기존에 많이 보급되어 사용되고 있는 연축전지와 리튬이온전지의 장점을 최대한 활용하기 위하여, 연축전지와 리튬이온전지용 하이브리드 ESS의 최적 운용평가를 할 수 있는 알고리즘을 제시하였다. 상기의 알고리즘을 이용하여 시뮬레이션을 수행한 결과, 각 전지의 도입비용과 운용비용이 최소화 되는 운용조건에서 최적구성비를 산출하였다. 이에 따라 본 논문에서 제안한 하이브리드 ESS의 최적구성 알고리즘에 대한 유용성을 확인하였다.

• 융합신호처리학회논문지
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• 제16권4호
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• pp.182-188
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• 2015

아날로그 AVR은 부하의 변동에 따라 전압이 비정상상태가 되었다가 다시 정상상태로 돌아가는데 걸리는 시간이 빠른 장점이 있다. 하지만 아날로그 AVR은 부하 변동에 따른 전압변동이 크다는 문제가 있다. 디지털 AVR의 전압변동률은 매우 안정적이지만, 불안정상태에서 안정한 정상상태로 회복하는데 걸리는 시간인 시정수가 아날로그 AVR에 비해 매우 길다. 따라서 부하변동이 매우 큰 상황에서 불안정한 출력성능을 나타낸다. 본 논문에서는 두 AVR의 혼합된 형태를 가지며 빠른 시정수와 안정된 전압조정 능력을 갖는 하이브리드 AVR을 제안한다. 개발된 하이브리드 AVR의 경우 부하에 따른 전압 변동이 1[%] 이내로 안정적이며, 전압 안정률도 개선되었다. 또한 아날로그 AVR 수준의 빠른 시정수를 나타내었다. 따라서 본 연구를 통해서 개발된 하이브리드 AVR은 산업현장에서 다양한 용도의 전원공급장치로 활용될 수 있다.