• Rapid Communication in Photoscience
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• 제1권2호
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• pp.68-68
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• 2012

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1998년도 추계학술발표회요약집
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• pp.68-68
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• 1998

• 한국수자원학회논문집
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• 제40권2호
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• pp.101-112
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• 2007

본 연구에서는 댐군을 연계운영할 경우 발생하는 효과를 이수측면에서 평가할 수 있는 방법을 개발하여 한강수계 댐군 운영 실적의 평가에 적용하였다. 개발된 평가방법에서는 용수공급과 유황개선 부분에서 연계운영의 효과를 평가하기 위하여 평가지점에서 필요수량에 대한 충족률과 유황안정도를 평가지표로 사용하였다 발전 부분에서 연계운영의 효과는 댐군에 의해 생산된 총발전량을 평가지표로 사용하였다. 실제 운영실적은 공칭공급량을 공급하는 단독운영과 최적화 모형에 의한 평가지표들과 비교하여 평가되었다. 한강수계의 2001년부터 2004년까지의 실제 연계운영 실적을 단독운영과 최적화 모형의 결과와 각 연도별로 비교해 보면, 용수공급 측면에서 필요수량 충족률은 단독운영은 $94.36{\sim}99.68%$, 실제운영은 $97.16{\sim}99.90%$, 최적화 모형은 4개년 모두 100.0 %를 나타냈다. 댐 운영 방법별로 하상계수와 유황계수를 사용하여 유황안정도를 평가해 보면, 유황이 단독운영 보다 실제운영과 최적화 모형이 더 안정적인 결과를 나타냈다. 실제 총발전량을 다른 운영방법의 결과와 비교해 보면, 최적화 모형은 실제 총발전량 보다 $-3.47{\sim}6.54%$ 증가된 결과를 나타냈으며, 단독운영은 실제 총발전량 보다 $12.68{\sim}38.94%$ 감소된 결과를 나타냈다.

• 전력전자학회논문지
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• 제28권1호
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• pp.68-75
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• 2023

This paper proposes a three-phase single-stage AC-DC converter for the small wind generation system. Input power factor improvement and insulated output can be implemented with the proposed three-phase single-stage AC-DC converter under the wide power generation voltage (80-260 V_ac) and frequency (10-42 Hz) in a small wind power generation (WPG) system. The proposed converter is also capable of zero-voltage switching in the primary-side switches and zero-current switching in the secondary-side diodes by phase-shift control at a fixed switching frequency. In addition, it is possible to control a wide output voltage (V_o: 39 V_DC-60 V_DC) by varying the link voltage and improving the input power factor (PF) and the total harmonic distortion factor (THD_i). Simulation and experimental results verified the validity of the proposed converter.

• 한국광학회:학술대회논문집
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• 한국광학회 1999년도 제16회 광학 및 양자전자 학술발표회Proceedings of 16th Optics and Quantum Electronics Conference, 1999
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• pp.68-69
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• 1999

• 드라이브 ㆍ 컨트롤
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• 제11권3호
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• pp.66-68
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• 2014

• KSTLE International Journal
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• 제1권1호
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• pp.63-68
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• 2000

Angular contact ball bearings are mainly used in the spindle, which requires high speed and stiffness. The heat generation is studied by experiments and simulations using a pair of angular contact ball bearings. The temperature variation of inner and outer races and the temperature increment distribution are measured by using thermocouples for the rotational speed, preload, viscosity of lubricant. The measured values from experiments are used to estimate the heat conduction rate. The method of oil-air lubrication is used for the experiment. The amount of conduction heat transfer to the test spindle and the convection heat transfer coefficients long the spindle are computed by using inverse method with temperature increment distribution. Total heat generation rate is estimated with the heat partition rate which is calculated from temperatures of inner and outer races. In addition, the empirical factor of oil-air lubrication method for Palmgren's heat generation model is suggested. The empirical friction coefficients, which are obtained from the experiments, depend on the preload condition, and can give us more accurate estimation of the heat generation in ball bearings.

• 천문학회보
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• 제44권1호
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• pp.68.3-68.3
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• 2019

Even though the initial mass function (IMF) of the first generation of stars played important roles in reionization of the universe, subsequent star formation, and chemical enrichment of the universe, it is still very uncertain. In this study, among the several indirect ways of estimating the IMF of the population III (Pop III) stars, we make use of extremely metal-poor (EMP; [Fe/H] < -3.0) stars in the Milky Way, in order to infer the characteristic mass range of Pop III stars. As the progenitors of many of the EMP stars are known to be Pop III stars, we attempt to construct the characteristic mass range of the progenitors (e.g., Pop III stars) of the EMP stares by comparing their observed abundance pattern of various chemical elements with chemical yields from supernova models.

• 전기학회논문지
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• 제68권5호
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• pp.656-661
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• 2019

Currently, the devices to generate ion winds in air are mainly composed of corona electrodes and induction(ground) electrodes, of which the corona electrodes mainly use needles or wires as electrodes and the induction electrodes use plate electrodes of ring or mesh type. Ion winds can be effectively generated through a diverse combination of corona electrodes and induction electrodes mentioned above. However, only changing the form and structure of corona electrodes and induction electrodes has a limit in raising the speed of ion winds. This paper conducted a study on the characteristics of ion wind generation by additionally installing acceleration electrodes in addition to corona electrodes and induction electrodes to increase the speed of ion winds.

• 전기학회논문지
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• 제68권4호
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• pp.513-522
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• 2019

We calculate the benefit of distributed combined heat power generators from avoiding a transmission expansion cost by building distributed generators near electricity demand centers. We determine a transmission expansion plan by solving a mixed integer linear problem, where we modify capacities of existing transmission lines and build new transmission lines. We calculate the benefit by comparing the sum of generation and transmission expansion costs with or without distributed generators through two simulation frames. In the first frame, for the current demand, we substitute existing distributed generators for non-distributed generators and measure an additional cost to balance the generation and demand. In the second frame, for increased future demand, we compare the cost to invest only in distributed generators to the cost to invest only in non-distributed generators. As a result, we show that the distributed generators have at least 5.8 won/kWh of the benefit from avoiding the transmission expansion cost.