• 전기학회논문지
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• 제68권1호
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• pp.61-68
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• 2019

Only the power is converted from AC to DC, in accordance with IEC 60587 based test method, in order to develop the LSR(Liquid Silicone Rubber) insulator material for HVDC, the experiment of Inclined Plate Tracking and Erosion Resistance was conducted. A contaminant (2.5 mS/cm: ammonium chloride) was applied at a rate of 0.3 ml/min and a voltage of ${\pm}3.5kV$, and was evaluated on the basis of 60 mA/2s. The samples were prepared by dispersing LSR/Nano silica_25wt% Composites in LSR. The erosion phenomena of surface discharge and tracking due to DC polarity and negative polarity were measured by image, leakage current maximum and thermal camera. The thermal imaging camera measured the surface temperature generated by the joule heat of the leakage current due to the drying discharge and the conductive current. After the measurement, the tracking and erosion mechanisms were evaluated for erosion weight, erosion depth and erosion length. Positive and negative polarity of LSR/Nano Silica_25wt% composite Tracking and erosion results show that positive polarity is more severe than negative polarity.

• 대한건축학회논문집:구조계
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• 제35권5호
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• pp.133-143
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• 2019

Various problems regarding the wet floor method such as its complicated process and waste of thermal storage have been raised, but the usage of dry floor recommended for long-life housing has declined due to lack of confidence on the performance of dry floor. The purpose of this study is to secure the credibility of dry floor. Under this purpose, this study considered precedent studies and established directions to secure the performance of long-life housing infill, and thus, 9 performance items (Impact sound, Smoothness, thermal comfort, sensation hardness while walking, falling safety, impact resistance, local compression load, local strength and strain at heating) were drawn. In addition, the experiment was carried out for 5 performances except for legal performance, some dry floor performances and whole spatial performance. As a result, an appropriate result from all performances except was obtained. The performance of dry floor was verified for each item from these results and it is expected to use such results as basic data on dry floor in the future.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1518-1527
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• 2023

A method was proposed for in-situ evaluating the thickness and resistivity of the oxide/hydroxide film formed on the surface of aluminum alloy exposed to sump water formed in the containment after a loss-of-coolant accident. The evaluation entailed fitting a model for the film impedance, which has film thickness and other variables describing the resistivity profile of the film along its thickness direction as fitting parameters, to the practically measured electrochemical impedance data. The obtained resistivity profiles implied that the films formed at pHs_25℃ 7, 8, 9, 10, and 11 all had a duplex structure; compared to the outer layer in contact with the solution, the inner layer of the film had a much higher resistivity and was inferred to be denser and provide most of the protectiveness of the film. Both the thickness and the total resistance of the film decreased with the increasing solution pH_25℃, suggesting that the films formed in more alkaline solutions had less protectiveness against corrosion, consistent with the increasing aluminum alloy corrosion rates previously identified.

• 한국건축시공학회지
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• 제19권6호
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• pp.539-547
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• 2019

최근 국제사회는 지구온난화 방지를 위한 기후변화협약을 체결하고 건축물의 냉방 및 난방 에너지로 공급하는 화석연료 사용을 줄이고자 신축 또는 기존건물에 대한 녹색건축인증(G-SEED) 및 에너지효율등급, 건축물 에너지절약 설계기준 등을 일정조건 이상인 건축물에 의무적으로 적용하고 있다. 건물에 공급하는 에너지 공급을 줄이고 보온성을 향상시키는 건축자재로 단열재가 사용되고 있으며 신축건축물의 에너지절약 설계기준을 만족하는 건물외피 구성 재료 중 총 열 저항성의 90% 이상을 차지하고 있다. 그러나 기존건축물에 시공된 단열재의 경시변화에 대한 명확한 자료가 부족하여 건축물의 에너지성능 판단기준인 단위면적당 1차에너지 소요량 산정에 대한 의문점을 갖게 되었다, 이에 20년 이상 된 노후 건축물의 리모델링 현장에서 단열재(압출법,비드법)를 직접 채취하여 단열재성능을 비교·평가하였다. 실험결과, 압출법(XPS)은 생산초기 품질기준인 KS M 3808보다 열전도율은 48%, 압축강도는 36%가 저하되어 본래의 성능을 발휘하지 못함을 알 수 있었고, 비드법(EPS)의 경우 단열재 두께가 50mm인 경우 열전도율과 압축강도, 굴곡파괴하중 등이 생산초기 품질기준을 유지함을 알 수 있었다. 따라서 비드법의 경우 단열재 두께를 고려하여 현재의 단위면적당 1차 에너지소 요량을 기존대로 산정하고, 압출법의 경우는 단위면적당 1차 에너지소요량 산정시 보정계수를 적용해야 할 것으로 판단된다.

• Computers and Concrete
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• 제13권3호
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• pp.325-342
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• 2014

The use of lightweight aggregate (LWA) instead of ordinary aggregate may make lightweight aggregate concrete, which possesses many advantages such as lightweight, lower thermal conductivity, and better fire and seismic resistance. Recently the developments of LWA have been focused on using industrial wastes as raw materials to reduce the use of limited natural resources. In view of this, the intent of this study was to apply Taguchi optimization technique in determining process condition for producing synthetic LWA by incorporating waste thin film transition liquid crystal displays (TFT-LCD) glass powder with reservoir sediments. In the study the waste TFT-LCD glass cullet was used as an additive. It was incorporated with reservoir sediments to produce LWA. Taguchi method with an orthogonal array L16(45) and five controllable 4-level factors (i.e., cullet content, preheat temperature, preheat time, sintering temperature, and sintering time) was adopted. Then, in order to optimize the selected parameters, the analysis of variance method was used to explore the effects of the experimental factors on the performances (particle density, water absorption, bloating ratio, and loss of ignition) of the produced LWA. The results showed that it is possible to produce high performance LWA by incorporating waste TFT-LCD glass cullet with reservoir sediments. Moreover, Taguchi method is a promising approach for optimizing process condition of synthetic LWA using recycled glass cullet and reservoir sediments and it significantly reduces the number of tests.

• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1304-1310
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• 2021

Two-phase flow, especially gas-liquid two-phase flow, has a wide application in industrial field. The diagnosis of two-phase flow parameters, which directly determine the flow and heat transfer characteristics, plays an important role in providing the design reference and ensuring the security of online operation of two-phase flow system. Computer tomography (CT) is a good way to diagnose such parameters with imaging method. This paper has proposed a novel image reconstruction method for thermal neutron CT of two-phase flow with improved simulated annealing (ISA) algorithm, which makes full use of the prior information of two-phase flow and the advantage of stochastic searching algorithm. The reconstruction results demonstrate that its reconstruction accuracy is much higher than that of the reconstruction algorithm based on weighted total difference minimization with soft-threshold filtering (WTDM-STF). The proposed method can also be applied to other types of two-phase flow CT modalities (such as X(𝛄)-ray, capacitance, resistance and ultrasound).

• 한국초전도ㆍ저온공학회논문지
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• 제25권1호
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• pp.16-20
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• 2023

The International Electrotechnical Commission (IEC) 61788-26:2020 provides guidelines for measuring the critical current of Rare-earth barium copper oxide (REBCO) tapes using two methods: linear ramp and step-hold methods. The critical current measurement criterion, 1 or 0.1 μV/cm of electric field from IEC 61788-26 has been normally applied to REBCO coils or magnets. No-insulation (NI) winding technique has many advantages in aspects of electrical and thermal stability and mechanical integrity. However, the leak current from the NI REBCO coil can cause distortion in critical current measurement due to the characteristic resistance which causes the radial current flow paths. In this paper, we simulated the NI REBCO coil by applying both linear ramp and step-hold methods based on a simplified equivalent circuit model. Using the circuit analysis, we analyzed and evaluated both methods. By using the equivalent circuit model, we can evaluate the critical current of the NI REBCO coil, resulting in an estimation error within 0.1%. We also evaluate the accuracy of critical current measurement using both the linear ramp and step-hold methods. The accuracy of the linear ramp method is influenced by the inductive voltage, whereas the accuracy of the step-hold method depends on the duration of the hold-time. An adequate hold time, typically 5 to 10 times the time constant (τ), makes the step-hold method more accurate than the linear ramp method.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2010년도 춘계학술발표대회 초록집
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• pp.57-57
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• 2010

For thin panel welded structure, the various welding distortions were found due to the low resistance against welding deformation. Especially, buckling distortion induced in the thin panel welded structure produce severe problems related to cost in production stage and safety in service life. So, many researches including mechanical and thermal tensioning method for preventing the occurrence of buckling distortion in the production stage have been performed. The purpose of this study is to identify the behavior of longitudinal residual stress at the SA butt weldment with thin plate of 6mm thickness under tension load by 3 dimensional FEA. For it, mesh design for 3D FEA was constructed with 20 nodes brick element for butt weldment and 8 nodes shell element for base metal. According to FEA results, the longitudinal compressive strain inducing tensile residual stress at the butt weldment decreased. It was because the compressive thermal strain in way of weldment was reduced by tension load. The control effect of residual stress increased with an increase in tension load. So, if the amount of tension load applied to the weldment exceeds 1.5 times of longitudinal shrinkage force, the amount of longitudinal residual stress decreased below the critical value inducing the buckling distortion at the SA butt weldment. Its validity was verified by experiment.

• 한국화재소방학회논문지
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• 제30권5호
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• pp.54-59
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• 2016

구조재료 중에서 강재는 불연성 재료이지만 열전도가 높고, 온도상승에 의하여 강성의 저하가 높은 편이다. 일반적으로 강재의 항복강도 및 탄성계수는 $350^{\circ}C$에서 70%, $600^{\circ}C$에서 50% 이하로 감소하기 때문에 고온에서의 철골구조의 재하능력은 급격히 감소하게 된다. 통상 내화구조로 인정받기 위해서는 공인기관으로부터의 품질시험을 거쳐야 한다. 하지만, 실물내화실험은 공간과 시간의 제약, 고비용의 문제점을 안고 있으므로, 본 연구에서는 ABAQUS 프로그램의 유한요소법을 이용한 열해석을 수행하여 압축을 받는 H-형강기둥의 내화실험과의 비교로 해석모델의 신뢰성을 입증하고, 실물실험의 보완책으로의 가능성을 제시한다.

• 한국재료학회지
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• 제9권12호
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• pp.1205-1210
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• 1999

분무건조법으로 용사용 원적외선 세라믹/알루미늄 복합분말을 제조하여 플라즈마 용사법으로 알루미늄 모재에 용사한 후, 미세구조, 결정상, 열충격저항성 그리고 분광복사율을 조사하였다. 분무건조된 복합분말의 입형은 구형으로 34~105${\mu}m $. 영역에서 높은 복사율을 보였다. 그러나 알루미늄 첨가량이 증가할수록 원적외선 방사특성은 감소하였다. 결과적으로 용사법으로 원적외선 방사특성의 큰 손실 없이 방사체를 제조하기 위해서는 20~30%wt%Al를 첨가하여 복합분말을 제조하는 것이 가장 효율적이라고 판단된다.