• 한국태양에너지학회 논문집
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• 제33권1호
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• pp.66-72
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• 2013

In this study, the thermal conductive characteristics and basic properties of the nine commercial products of bentonite grouts were studied. Six of the nine products for ground heat exchanger systems are imported and others for civil engineering are domestic. The thermal conductivities of all bentonite products are nearly similar among products. The free swell indexes, viscosities and filter losses of the ground heat exchanger grouts are lower than those of the civil engineering ones. These characteristics seem to increase of the fluidity to fill the bentonite slurry to bore-hall perfectly, rather than to prevent underground water penetration. Thus, the mixtures of bentonites and sands are recommended for high thermal conduction grouts.

• Journal of Power Electronics
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• 제11권3호
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• pp.256-263
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• 2011

This paper utilizes free oscillation and energy injection principles to generate and control the high frequency current in the primary track of a contactless power transfer system. Here the primary power inverter maintains natural resonance while ensuring near constant current magnitude in the primary track as required for multiple independent loads. Such energy injection controllers exhibit low switching frequency and achieve ZCS (Zero Current Switching) by detecting the high frequency current, thus the switching stress, power losses and EMI of the inverter are low. An example full bridge topology is investigated for a contactless power transfer system with multiple pickups. Theoretical analysis, simulation and experimental results show that the proposed system has a fast and smooth start-up transient response. The output track current is fully controllable with a sufficiently good waveform for contactless power transfer applications.

• 대한금속재료학회지
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• 제46권9호
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• pp.572-576
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• 2008

Elastostatic compression tests were carried out on amorphous alloys to evaluate their energy absorption capability during homogeneous deformation at room temperature. Experiments demonstrated that a compressive stress below the global yield imposed on amorphous alloys for extended periods causes homogeneous plastic strain associated with the irreversible structural disordering. During the disordering process, free volume was created, dissipating the externally applied strain energy and the rate of creation was found to converge to a saturated value. We evaluated the capability of energy absorption of amorphous alloys during homogeneous deformation using recent theories on the evolution of the structural state.

• 한국해양환경ㆍ에너지학회지
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• 제8권3호
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• pp.116-121
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• 2005

본 연구에서는 자유표면을 갖는 대규모의 환경유동의 해를 구하는데 있어 비정수압의 효과를 고려하는 새로운 계산 기법을 제시하였다. Sigma 좌표계에서 시간은 전진차분으로, 공간은 중간차분 및 풍상차분을 혼합하여 2단계 해법을 도입하였다. 계산기법의 타당성과 유효성을 검증하기 위하여, 자유표면을 갖는 정상유동과 비정상유동에 대한 전형적인 예를 설정하여 정수압 계산과 비정수압 계산을 수행하고 이들을 비교하였다. 계산결과 복잡한 해저지형을 갖는 자유표면 유동에 있어, 지정수압효과가 무시할 수 없는 유동영역이 존재함이 입증되었으며, MAC기법과 같은 3차원 유체동역학적 기법을 적용하기에는 비경제적인 문제에 대해 본 계산기법이 매우 유효하게 적용될 수 있다는 가능성이 입증되었다.

• 한국식품영양학회지
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• 제29권6호
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• pp.829-834
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• 2016

Free radicals originate due to the radiolysis of cytoplasmic water with low "Linear Energy Transfer" (LET) radiations. Naringenin (Ng) is a natural antioxidative compound found in citrus fruits. This study revealed that Naringenin (Ng) reduced the radiation damage of critical organs by scavenging oxidative free radicals. In the study, Ng was orally administrated to rats daily for 7 consecutive days, prior to whole body exposure to gamma-rays. The scavenging efficacy was evaluated biochemically by measuring the concentration of cytotoxic byproducts and the activity of enzymes relevant to oxidative free radicals, after extracting the organs from the exposed rat. We observed increased levels of malondialdehyde (MDA) concentration, and decrease in the activities of superoxide dismutase (SOD) and catalase (CAT) in the exposed control group. However, pretreatment with Ng significantly reduced the MDA concentration, and increased the activities of SOD and CAT, as compared to the control group, due to the free radical scavenging by Ng. The results indicate that Ng administration prior to irradiation could protect critical organs from radiation damage.

• International Journal of Fluid Machinery and Systems
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• 제8권1호
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• pp.23-35
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• 2015

This paper presents the rotordynamic performance measurement of oil-free turbocharger (TC) supported on gas foil bearings (GFBs) for 2 liter class diesel vehicles and comparison to floating ring bearings (FRBs). Oil-free TC was designed and developed via the rotordynamic analyses using dynamic force coefficients from GFB analyses. The rotordynamics and performance of the oil-free TC was measured up to 85 krpm while being driven by a diesel vehicle engine, and compared to a commercial oil-lubricated TC supported on FRBs. The test results showed that the GFBs increased the rotor speed by ~ 20% at engine speeds of 1,500 rpm and 1,750 rpm, yielding the reduction of turbine input energy by more than 400 W. Incidentally, an external shock test on the oil-free TC casing was conducted at the rotor speed of 60 krpm, and showed a good capability of vibration damping due to the well-known dry friction mechanism of the GFBs.

• 전기학회논문지
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• 제65권5호
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• pp.760-768
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• 2016

Recently, as one of the policies for carbon free operation method of independent power system replacing diesel generator with renewable energy such as wind power and photovoltaic(PV) system has been presented. Therefore, this paper proposes an operation algorithm and modeling of independent power system by considering CVCF(constant voltage constant frequency) ESS(energy storage system) for constant frequency and voltage, LC(load control) ESS for demand and supply balancing and SVC(static var compensator) for reactive power compensation. From the simulation results based on the various operation scenario, it is confirmed that proposed operation algorithm and modeling may contribute stable operation and carbon free in independent power system.

• 천문학회보
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• 제44권2호
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• pp.71.3-71.3
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• 2019

Previously we developed a method of coronal force-free field construction using vector potentials. In this method, the boundary normal component of the vector potential should be adjusted at every iteration step to implement the boundary normal current density, which is provided by observations. The method was a variational method in the sense that the excessive kinetic energy is removed from the system at every iteration step. The boundary condition imposing the normal current density, however, is not compatible with the variational procedure seeking for the minimum energy state, which is employed by most force-free field solvers currently being used. To resolve this problem, we have developed a totally new method of force-free field construction. Our new method uses a unique magnetic field description using two scalar functions. Our procedure is non-variational and can impose the boundary normal current density exactly. We have tested the new force-free solver for standard Low & Lou fields and Titov-Demoulin flux ropes. Our code excels others in both examples, especially in Titov-Demoulin flux ropes, for which most codes available now yield poor results. Application to a real active region will also be presented.

• 한국자기학회지
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• 제21권5호
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• pp.163-166
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• 2011

기계적 자유도(mechanical degrees of freedom)를 가지는 free-standing 박막의 전계 방출 특성을 연구하였다. Free-standing 박막에서의 전계 방출 효과를 보다 정확히 해석하기 위하여 기계적 자유도(mechanical degrees of freedom)를 고려한 Fowler-Nordheim 전계 방출 식을 유도하였다. 새롭게 유도된 Fowler-Nordheim 식은 실험값과 매우 잘 일치한다. 이러한 free-standing 박막에서의 전계 방출 효과를 이용하여 이온화된 생체 분자의 충돌로 인해 발생된 free-standing 박막의 고주파 기계적 진동을 탐지함으로써 단백질 질량 분석기의 디텍터로 활용될 수 있음을 보였다.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.51-59
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• 2018

Despite the advantages of energy arbitrage using energy storage systems (ESSs), the high cost of ESSs has not attracted storage owners for the arbitrage. However, as the costs of ESS have decreased and the price volatility of the electricity market has increased, many studies have been conducted on energy arbitrage using ESSs. In this study, the existing two-period model is modified in consideration of the ESS cost and risk-free contracts. Optimal investment strategies that maximize the sum of external effects caused by price changes and arbitrage profits are formulated by market participants. The optimal amounts of ESS investment for three types of investors in three different market structures are determined with game theory, and strategies in the form of the mixed-complementarity problem are solved by using the PATH solver of GAMS. Results show that when all market participants can participate in investment simultaneously, only customers invest in ESSs, which means that customers can obtain market power by operating their ESSs. Attracting other types of ESS investors, such as merchant storage owners and producers, to mitigate market power can be achieved by increasing risk-free contracts.