• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 춘계학술대회 논문집
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• pp.771-774
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• 2000

RP techniques have inherent disadvantages caused by their working principles: stair-stepped surface of parts due to layer-by-layer stacking of layers, low build speed caused by line-by-line solidification to finish one layer, and post processing to improve surface finish, etc. The objective of this study is to propose a new RP technique, variable deposition manufacturing (VDM), which can make up for the disadvantages of the existing RP techniques, and to develop an apparatus to implement the technique. The proposed process can greatly reduce the building time and improve the surface finish of parts generated. The experiments are carried out to obtain the range of temperature of molten material to maintain its fluidity and to investigate the effect of gas cooling on the preservation of the slopes. Based on the results, some simple shapes such as a line-shape. an S-shape, and a circle-shape were fabricated from Ethylene Vinyl Acetatecopolymer (EVA). In order to examine the applicability of VDM to more general shapes, a tensile specimen and a yo-yo shape were manufactured by the proposed RP method using EVA material as the first trial approach. The present basic study has shown the possibility of a practicable utilization of the proposed VDM process to prototyping of a general three-dimensional shape.

• Journal of Welding and Joining
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• 제32권5호
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• pp.21-25
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• 2014

Oil and gas fields were left unexploited which deemed too deep and sour. New developing markets are emerging in this part and pipe manufacturers need demanding requirements in the combination of sour service requirements with heavier wall thickness required to cope with increasing water depths. Whilst, the strength and fracture toughness needed to meet the strict requirements In order to deliver the optimum sour properties in the final pipe, attention needs to be paid to each stage throughout the process from steel making. The main key during steel making is strengthening, securing mechanical properties and suppression of center segregation by adding proper chemical elements and controlling water cooling and plate rolling. Additionally in welding, it is required to prevent HAZ softening by high heat input during welding of heavy thick pipes and hydrogen assisted cracking in high strength steels with hard phases. In this paper, we introduce markets of sour resistant linepipe steels and in response to this, have a look in the development trend of sour resistant linepipe steels and its sour characteristics in welded joints.

• 한국주거학회논문집
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• 제26권5호
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• pp.79-87
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• 2015

This study explored low-income households' experiences and perception of home energy cost burdens and determinants of the perceived home energy cost burdens. Between March and July 2014, a questionnaire survey was administered in Cheongju, South Korea. Among the 434 useable responses collected, responses from 218 households with monthly income less than 2,500,000 Korean Won (KRW) were compared with those of 216 households with higher incomes. The main findings are as follows. In the past three years, more than 10 percent of low-income households had had their electricity cut off; 5.7 percent had had their city gas cut off. To pay for their home energy expenses, nearly 70 percent of the low-income households had had to limit their heating, cooling or spending for other necessities; 38.3 percent had to borrow money. Low-income households reported more problems paying for home energy than higher-income households did. Households with more negative evaluation of rainwater leak, no one staying at home all day, monthly income less than 1,500,000 KRW and householders in their 40s and 50s tended to perceive a heavier home energy cost burden. Finally, the most popular support programs were fuel assistance and discounts on energy bills.

• 한국초전도ㆍ저온공학회논문지
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• 제15권4호
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• pp.6-9
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• 2013

Korea Superconducting Tokamak Advanced Research (KSTAR) has a helium refrigeration system (HRS) with the cooling capacity of 9 kW at 4.5 K. Main cold components are composed of 300 tons of superconducting (SC) magnets, main cryostat thermal shields, and SC current feeder system. The HRS comprises six gas storage tanks, a liquid nitrogen tank, the room temperature compression sector, the cold box (C/B), the 1st stage helium distribution box (DB#1), the PLC base local control system interconnected to central control tower and so on. Between HRS and cold components, there's another distribution box (DB#2) nearby the KSTAR device. The entire KSTAR device was constructed in 2007 and has been operated since 2008. This paper will present the maintenance result of the KSTAR HRS during the campaign and discuss the operation record and maintenance history of the KSTAR HRS.

• Transactions on Electrical and Electronic Materials
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• 제18권6호
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• pp.311-315
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• 2017

The perovskite system $(Ba^{2+}{_{1-x}}La^{3+}{_x})Fe^{3+}{_{1-t}}Fe^{4+}{_t}O_{3-y}$ (y = (1 - x --t)/2) having a composition of x = 0.0, 0.1, 0.2, and 0.3 showedean increase in $Fe^{4+}$ mole ratios with an increase in oxygen partial pressure ($N_2{\rightarrow}air{\rightarrow}O_2$), and with an increasefin s, the $Fe^{3+}$ quantity decreased and oxygen content (3-y value) increased. For each N sampls heat-treated in $N_2$ gas, a considerable weight gain, i.e.g a steadynincrease if oxygen content, was observed in the TGA data on the cooling process. The conductivity values at a constant temperature were in the order of $N_2$$O_2$; the respective log ${\sigma}$ values (${\Omega}^{-1}{\cdot}cm^{-1}$) at 323 K of the BL0 sample were -5.75 (BL0-N), -3.39 (BL0-A), and -0.53 (BL0-O). The mixed valencies of $Fe^{3+}$ and $Fe^{4+}$ ions in each sample were also confirmed by both the oxidation curve above 350 mV and the cathodic reduction curve below 200 mV from cyclic voltammetry.

• 조명전기설비학회논문지
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• 제23권7호
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• pp.57-66
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• 2009

Microturbines system (MTS) are currently being deployed as small scale on-site distributed generators for microgrids and smart grids. In order to fully exploit DG potentialities, advanced integrated controls that include power electronics facilities, communication technologies and advanced modeling are required. Significant expectations are posed on gas microturbines that can be easily installed in large commercial and public buildings. Modeling, control, simulation of microturbine generator based distributed generation system in smart grid application of buildings for both grid-connected and islanding conditions are presented. It also incorporates modeling and simulation of MT with a speed control system of the MT-permanent magnet synchronous generator to keep the speed constant with load variation. Model and simulations are performed using MATLAB, Simulink and SimPowerSystem software package. The model is built from the dynamics of each part with their interconnections. This simplified model is a useful tool for studying the various operational aspects of MT and is also applicable with building cooling, heating and power (BCHP) systems

• Journal of Advanced Marine Engineering and Technology
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• 제22권6호
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• pp.792-799
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• 1998

Further improvement of existing $H_{2}O/LiBr$ absorption refrigeration machine is absolutely neces-sary to promote the utilization of gas-cooling system Among various methods to improve the per-formance of the absorption refrigeration machine this research has focused on the use of a new working fluid that has better properties than the existing $H_{2}O/LiBr$ working fluid. In the series of the research, $H_{2}O/LiBr+HO{(CH_{2})}_{3}OH$ system was selected as the most promisable candidate. The absorption refrigeration machine is water-cooled double-effect, $H_{2}O/LiBr+HO{(CH_{2})}_{3}OH$ sys-tem with series flow type. In this study we found out the characteristic of new working solution through the cycle simulation and compared the result with that of LiBr solution to evaluate. Theoptimum designs and operating conditions were determined based on the operating constraints and the coefficient of performance. Results demonstrate that new working fluid subsrantially increases COP by as much as 10% and has a wider working range with 8% higher crystallization limits compared to the conventional $H_{2}O/LiBr$.

• 한국주조공학회지
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• 제24권2호
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• pp.94-100
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• 2004

Gas porosity which is a common defect in aluminum alloy casting, is also thought to be severer in aluminum alloy castings produced by lost foam process due to the pyrolysis of the polystyrene foam pattern during pouring. Fundamental experiments were carried out to evaluate the effect of process variables such as the melt treatment, the cooling rate and pouring temperature on the density and mechanical properties in A356.2 castings with simple bar shape. The density of grain refined specimen was slightly lower than that of degassed one, but was higher than that of no treated one and that of shot ball packed specimen was higher than the other specimens. The tensile strength and elongation were in the ranges of $200{\sim}230MPa$ and $0.5{\sim}1.5%$ respectively. The density and hardness of lost foam cast specimens decreased with increase in pouring temperature.

• Journal of Biosystems Engineering
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• 제25권2호
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• pp.107-114
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• 2000

Low temperature storage method is to increase the value of agricultural products by reducing quality loss and regulate consignment time by controlling respiration rates of agricultural products. Respiration rate of agricultural products depends on several factors such as temperature, moisture, gas composition and a microbe inside the storage room. Temperature is the most important factor among these, which affects respiration rate and causes low or high temperature damage. Fuzzy logic was used to control the temperature of a storage room ,which uses information of uncertain facts and mathematical model for room temperature control . Room temperature was controlled better by using fuzzy logic control method rather than on-off control method. Refrigerant flow rates and temperature deviations were measured for on-off system using TEV(temperature expansion valve) and for fuzzy system using EEV(Electrical Expansion Valve) . Temperature of the Storage room was lowered faster by using fuzzy system than on -off system. Temperature deviation was -0.6~+0.9$^{\circ}C$ for on-off system and $\pm$0.2$^{\circ}C$ for fuzzy system developed. Temperature deviation and variation of temperature deviation were used as inout parameters for fuzzy system. The most suitable input and output value were found by experiment. Cooling rate of the storage room decreased while temperature deviation increased for the sampling time of 20 sec.

• Journal of Welding and Joining
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• 제25권3호
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• pp.78-84
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• 2007

Laser Material Processing has been replaced the conventional machining systems - cutting, drilling, welding and surface modification and so on. Especially, LTH(Laser Transformation Hardening) process is one branch of the laser surface modification process. Conventionally, some techniques like a gas carburizing and nitriding as well as induction and torch heating have been used to harden the carbon steels. But these methods not only request post-machining resulted from a deformation but also have complex processing procedures. Besides, LTH process has some merits as : 1. It is easy to control the case depth because of output(laser power) adjustability. 2. It is able to harden the localized and complicated a.ea and minimize a deformation due to a unique property of a localized heat source. 3. An additional cooling medium is not required due to self quenching. 4. A prominent hardening results can be obtained. This study is related to the surface hardening of the rod-shaped carbon steel applied to the lathe based complex processing mechanism, a basic behavior of surface hardening, hardness distribution and structural characteristics in the hardened zone.