• Nuclear Engineering and Technology
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• v.49 no.7
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• pp.1369-1378
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• 2017

The present paper reports the development of a computational code based on the Adaptive Group of Ink Drop Spread (AGIDS) for reconstruction of the neutron noise sources in reactor cores. AGIDS algorithm was developed as a fuzzy inference system based on the active learning method. The main idea of the active learning method is to break a multiple input-single output system into a single input-single output system. This leads to the ability to simulate a large system with high accuracy. In the present study, vibrating absorber-type neutron noise source in an International Atomic Energy Agency-two dimensional reactor core is considered in neutron noise calculation. The neutron noise distribution in the detectors was calculated using the Galerkin finite element method. Linear approximation of the shape function in each triangle element was used in the Galerkin finite element method. Both the real and imaginary parts of the calculated neutron distribution of the detectors were considered input data in the developed computational code based on AGIDS. The output of the computational code is the strength, frequency, and position (X and Y coordinates) of the neutron noise sources. The calculated fraction of variance unexplained error for output parameters including strength, frequency, and X and Y coordinates of the considered neutron noise sources were $0.002682{\sharp}/cm^3s$, 0.002682 Hz, and 0.004254 cm and 0.006140 cm, respectively.

• Proceedings of the KIEE Conference
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• 1997.07f
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• pp.2033-2036
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• 1997

In this paper, we proposed a novel current-fed DC-DC converter with multi-output. It has two winding reactor in series with the input source of the converter. By using the 2nd winding recycling the energy stored in the reactor to the input, the double-outputs DC-DC converter can be created, which makes it a good choice for a multi-output power supply with more outputs and has savings in cost and space. The steady state and dynamic characteristics of the converter are analyzed in detail by using the state space averaging method. It is found that the maximum value of $V_{o2}$ exists in the 2nd output and also during the MOSFET off period, the energy stored in the magnetizing inductance is reset through auxiliary winding $N_3$, so the duty cycle is restricted to 50%. Theoretical and experimental results were taken from the converter rated at switching frequency 50kHz. input voltage 50V. output voltage 5V. 12V and output power 65W. As a result, both results were well consistent. Therefore, it is varified the validity of the proposed converter in this paper.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1819-1830
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• 1991

The problems associated with noise/energy source identification using multiple input/single output model in linear systems are investigated. Partial coherence function is formulated for the model introducing a virtual force and extraneous noises into the conventional two input/single output system. The analytical results show that the partial coherence function in two input/single output linear system is the function of noise/signal ratios when multiple inputs are mutually coherent and extraneous noises exist. Parametric studies for ordinary and partial coherence functions are carried out to demonstrate the effects of noise/signal ratios for these functions.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.66 no.4
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• pp.236-241
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• 2017

This paper presents a single-phase grid connected voltage-ed inverter with a power decoupling circuit. In the single-phase grid connected voltage-ed inverter, it is well known that a power pulsation with twice the grid frequency is contained in the input power. In a conventional voltage type inverter, electrolytic capacitors with large capacitance have been used in order to smooth the DC voltage. However, lifetime of those capacitors is shortened by the power pulsation with twice grid frequency. The authors have been studied a active power decoupling(APD) method that reduce the pulsating power on the input DC bus line, this enables to transfer the ripple energy appeared on the input DC capacitors into the energy in a small film capacitor on the additional circuit. Hence, extension of the lifetime of the inverter can be expected because the small film capacitor substitutes for the large electrolytic capacitors. Finally, simulation and experimental results are discussed.

• Environmental Engineering Research
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• v.17 no.1
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• pp.27-34
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• 2012

This paper deals with the evaluation of environmental impact of rail and road transport in South Korea. A framework of energy input-output analysis is employed to estimate the total energy consumption and $CO_2$ emission in acquiring and using a life cycle of passenger and freight transport activity. The reliability of $CO_2$ emission based on uncertainty values is assessed by means of a Monte Carlo simulation. The results show that on a passenger-kilometers basis, passenger roads have life cycle emissions about 1.5 times those of rail, while that ratio is ten times greater when the scope of evaluation regards the tailpipe. In the case of freight transport, on a million ton-kilometers basis, the value for road mode is estimated to be about three times compared to those of rail mode. The results also show that the main contribution of $CO_2$ emission for road transport is the operation stage, accounting for 70%; however, the main contribution for rail transport is the construction and supply chain stage, accounting for over 50% emission.

• Journal of Welding and Joining
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• v.31 no.6
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• pp.8-16
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• 2013

As the energy consumption increases rapidly, power generation needs the high energy efficiency continuously. To achieve the high efficiency of power generation, the materials used have to endure the higher temperature and pressure. The 9-12%Cr steels possess good mechanical properties, corrosion resistance, and creep strength in high temperature due to high Cr contents. Therefore, the 9-12%Cr steels are widely used for the high-temperature components in power plants. Even though the steels usually have a fully martensitic microstructure, they are susceptible to the formation of ${\delta}$-ferrite specifically during the welding process. The formation of ${\delta}$-ferrite has several detrimental effects on creep, ductility and toughness. Therefore, it is necessary to avoid its formation. As the volume fraction of ${\delta}$-ferrite is less than 2% in microstructure, it has the isolated island morphology and causes no significant degradation on mechanical properties. For ${\delta}$-ferrite above 2%, it has a polygonal shape affecting the detrimental influence on the mechanical properties. The formation of ${\delta}$-ferrite is affected by two factors: a chemical composition and a welding heat input. The most effective ways to get a fully martensite microstructure are to reduce the chromium equivalent less than 13.5, to keep the difference between the chromium and nickel equivalent less than 8, and to reduce the welding heat input.

• Nuclear Engineering and Technology
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• v.52 no.5
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• pp.1022-1028
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• 2020

One of the possible options for spent-fuel management in Korea is pyroprocessing, which is a process for electrochemical recycling of spent nuclear fuel. Nuclear material accountancy is considered to be a safeguards measure of fundamental importance, for the purposes of which, the amount of nuclear material in the input and output materials should be measured as accurately as possible by means of chemical analysis and/or non-destructive assay. In the present study, a neutron measurement system based on the fast-neutron energy multiplication (FNEM) and passive neutron albedo reactivity (PNAR) techniques was designed for nuclear material accountancy of a spent-fuel assembly (i.e., the input accountancy of a pyroprocessing facility). Various parameters including inter-detector distance, source-to-detector distance, neutron-reflector material, the structure of a cadmium sleeve around the close detectors, and an air cavity in the moderator were investigated by MCNP6 Monte Carlo simulations in order to maximize its performance. Then, the detector responses with the optimized geometry were estimated for the fresh-fuel assemblies with different ²³⁵U enrichments and a spent-fuel assembly. It was found that the measurement technique investigated here has the potential to measure changes in neutron multiplication and, in turn, amount of fissile material.

• Journal of the Korean earth science society
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• v.32 no.2
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• pp.190-199
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• 2011

A photovoltaic energy map that included a topography effect on the Korean peninsula was developed using the Gangneung-Wonju National University (GWNU) solar radiation model. The satellites data (MODIS, OMI and MTSAT-1R) and output data from the Regional Data Assimilation Prediction System (RDAPS) model by the Korea Meteorological Administration (KMA) were used as input data for the GWNU model. Photovoltaic energy distributions were calculated by applying high resolution Digital Elevation Model (DEM) to the topography effect. The distributions of monthly accumulated solar energy indicated that differences caused by the topography effect are more important in winter than in summer because of the dependency on the solar altitude angle. The topography effect on photovoltaic energy is two times larger with 1 km resolution than with 4 km resolution. Therefore, an accurate calculation of the solar energy on the surface requires high-resolution topological data as well as high quality input data.

• Journal of IKEEE
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• v.21 no.1
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• pp.66-69
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• 2017

In recent year, energy harvesting technologies from the ambient environments such as light, motion, wireless waves, and temperature again a lot of attraction form research community [1-5] due to its efficient solution in order to substitute for conventional power delivery methods, especially in wearable together with on-body applications. The drawbacks of battery-powered characteristic used in commodity applications lead to self-powered, long-lifetime circuit design. Thermoelectric generator, a solid-state sensor, is useful compared to the harvesting devices in order to enable self-sustained low-power applications. TEG based on the Seebeck effect is utilized to transfer thermal energy which is available with a temperature gradient into useful electrical energy. Depending on the temperature difference between two sides, amount of output power will be proportionally delivered. In this work, we illustrated a low-input voltage energy harvesting circuit applied discontinuous conduction mode (DCM) method for getting an adequate amount of energy from thermoelectric generator (TEG) for a specific wearable application. With a small temperature gradient harvested from human skin, the input voltage from the transducer is as low as 60mV, the proposed circuit, fabricated in a $0.6{\mu}m$ CMOS process, is capable of generating a regulated output voltage of 4.2V with an output power reaching to $40{\mu}W$. The proposed circuit is useful for powering energy to battery-less systems, such as wearable application devices.

• Journal of the Korean Solar Energy Society
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• v.35 no.3
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• pp.65-71
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• 2015

A solar thermal simulator is suitable for indoor experiments of solar receivers and reactors when solar insolation and weather conditions are not favorable. Moreover, due to the easy control of electric power input, the solar thermal simulator allows the adjustment of power input incident on solar receivers and reactors and thus the implementation of accurate experiments. We manufactured a solar simulator, which is comprised of three sets of a xenon lamp and an elliptical reflector. In order to serve as a test facility, optical characterization of the solar simulator via radiation heat flux measurement is a critical prerequisite. We applied the flux mapping method to measuring the heat flux distribution of the three lamps. We presented the measurement results in terms of the heat flux distribution, the peak heat flux, the power distribution, the maximum power, and the efficiency for electric power conversion into radiation power. Characterization results show that our solar simulator provides the peak heat flux of $3,019kW/m^2$, the maximum power of 16.9 kW, and the conversion efficiency of 45%, additionally with a 10% operation margin for output increase.