• Journal of Advanced Research in Ocean Engineering
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• 제1권4호
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• pp.252-267
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• 2015

Offshore structures might encounter several environmental and operating conditions during their lifetime of several decades. In order to predict the dynamic behavior of offshore structures, several simulation cases should be considered to deal with all the combinations of ocean environments and operating conditions. Because a sophisticated time-domain coupled dynamic analysis requires an extremely large amount of computational time to handle all the possible cases, an efficient preliminary process to prescreen the probability of severe environmental conditions can be helpful in downsizing the number of simulation cases and computational effort. In this study, a prescreening procedure to reduce the number of environmental conditions for dynamic analyses of offshore structures is proposed. For the efficiency of the procedure, frequency-domain theories were adopted to estimate the platform offset, using quasi-static analyses in line tension prediction. The results were validated by comparing with those of dynamic analysis coupled between platform and mooring lines, and reasonable agreement was observed. In addition, the characteristics of environmental conditions classified to be severe to the system were investigated through the application of the developed prescreening scheme to several actual environmental conditions.

• 한국안전학회지
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• 제23권5호
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• pp.97-104
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• 2008

This study was intended to evaluate the permeable performance through a change of reinforcing materials, curing condition, durability evaluation and permeability test, and to select the reinforcing material which could reduce the durability and water tightness from it, as the study for considering how the change of the outside's environment factors that the concrete structure actually contacted with impacted the concrete's durability especially the permeability by referring to such the background of the study. Accordingly, it was judged that evaluating the permeability by considering the severe environment condition where the concrete structure was placed in was more reasonable than measuring the existing permeability coefficient conducted in the sound state for the permeability evaluation of actually-used concrete structure. In this study, it also could be known that the specimen of hybrid fiber reinforced concrete which mixed the long and short steel fiber was the most effective for water tightness enhancement in severe environmental conditions.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2003년도 추계학술발표대회 요약집
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• pp.186-186
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• 2003

• Nuclear Engineering and Technology
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• 제50권5호
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• pp.683-689
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• 2018

To evaluate equipment survivability of the polymer Viton, used in sealing materials, the effects of its thermal degradation were investigated in severe accident (SA) environment in a nuclear power plant. Viton specimens were prepared and thermally degraded at different SA temperature profiles. Changes in mechanical properties at different temperature profiles in different SA states were investigated. The thermal lag analysis was performed at calculated convective heat transfer conditions to predict the exposure temperature of the polymer inside the safety-related equipment. The polymer that was thermally degraded at postaccident states exhibited the highest change in its mechanical properties, such as tensile strength and elongation.

• Corrosion Science and Technology
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• 제16권1호
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• pp.8-14
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• 2017

The corrosion behavior of a ferritic/martensitic steel T91 exposed to an aqueous solution containing chloride and sulfate ions is investigated depending on the stimulated all-volatile treatment (AVT) and under oxygenated treatment (OT) conditions. The corrosion of T91 steel under OT condition is severe, while the corrosion under AVT condition is not. The co-existence of chloride and sulfate ions has antagonistic effect on the corrosion of T91 steel in both AVT and OT conditions. Unlike to corrosion resistance in the aqueous solution, OT pretreatment provides T91 steel lower oxidation-resistance than VAT pretreatment. From scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD) analysis, the lower corrosion resistance in the aqueous solution by VAT conditions possibly is due to the formation of pits. In addition, the lower oxidation resistance of T91 steel pretreated by OT conditions is explained as follows: the cracks formed during the immersion under OT conditions accelerated peeling-off rate of the oxide film.

• 콘크리트학회논문집
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• 제25권5호
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• pp.539-546
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• 2013

1997년 시멘트 산업은 자원 재활용 목적을 위하여 산업폐기물을 시멘트 공장에서 사용하기 시작하였다. 그러나 최근, 산업폐기물의 재활용에 따른 시멘트의 환경유해성이 시멘트 공장주변의 오염과 시멘트 내 중금속 용출로 인하여 문제가 제기되고 있는 실정이다. 특히, 시멘트 내 $C^{6+}$의 존재는 중요한 문제가 되고 있으며, 시멘트 내 $C^{6+}$ 최소화를 위한 연구가 수행되고 있다. 그러나 국내에서는 중금속 용출에 관련된 연구는 대부분 시멘트 관점에서 수행되고 있는 실정이다. 시멘트는 콘크리트 재료로 사용되기 때문에 콘크리트 관점에서의 환경안전성 평가가 필요하다. 따라서 이 논문에서는 가혹한 조건에서 열화된 콘크리트의 중금속 용출평가를 실시하였다. 평가 결과 모든 변수에서 $C^{6+}$는 검출되지 않았다.

• Journal of Radiation Protection and Research
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• 제38권4호
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• pp.208-213
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• 2013

원전의 안전성분석보고서에는 운영기간중 만일의 사고에 따른 방사선안전성 확보를 위해 부지의 적합성 평가가 요구된다. 부지 적합성은 극히 보수적인 가정을 적용하여 제한구역경계에서 방사선 피폭영향을 평가하여 판단하게 된다. 이들 평가는 방사선영향평가 모델을 보수적인 기상조건 등에 적용하여 수행된다. 본 연구에서는 보수적인 평가 결과의 타당성 검증을 목적으로 확산에 양호하지 못한 악기상 조건에서 추적자확산실험을 실시하였다. 원전부지 실험에 앞서 대전시 인근 유성구 학하리 평지에서 추적자 확산실험을 실시하였다. 확산실험의 분석결과 기존의 확산조건이 좋은 경우의 실험결과와 비교할 때 크게 두 가지 큰 차이를 발견할 수 있었다. 하나는 풍속이 매우 낮고 풍향의 변화가 심해 주 풍하 방향에서 나타나는 최대 농도를 찾기 어렵다는 것이고, 다른 하나는 대기가 매우 안정하여 지상 10 m 낮은 높이에서의 방출임에도 불구하고 방출점에서 수 백 m 떨어진 지점에서 처음으로 상대적으로 높은 농도 분포가 나타나는 경우가 있다는 것이다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년 학술대회 논문집 정보 및 제어부문
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• pp.600-602
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• 2006

Some abnormal signals diagnostics and analysis through an important equivalent circuits modeling for passive elements under severe accident conditions have been performed. Unlike the design basis accidents, there are inherently some uncertainties in the instrumentation capabilities under the accident conditions. So, the circuit simulation analysis and diagnosis methods are used to assess instruments in detail when they give apparently abnormal readings as an accident alternative method. The simulations can be useful to investigate what the signal and circuit characteristics would be when similar to a variety of symptoms that can result from the environmental conditions such as high temperature, humidity, and pressure condition. In this paper, a new simulator through an analysis of the important equivalent circuits modeling under temperature accident conditions has been designed, the designed simulator is composed of the LabVIEW code as a main tool and the out-put file of the Multi-SIM code as an engine tool is exported to in-put file of the LabVIEW code. The procedure for the simulator design was divided into two design steps, of which the first step was the diagnosis method, the second step was the circuit simulator for the signal processing tool. It has three main functions which are a signal processing tool, an accident management tool, and an additional guide from the initial screen. This simulator should be possible that it could be applied a output signal analysis to some transient signal by variation of the resistance passive elements in the R-L-C equivalent circuit modeling under various degraded conditions in NPPs.

• 소성∙가공
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• 제26권6호
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• pp.365-371
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• 2017

During sling wear of a ferrous metal, a surface layer is formed. Its microstructure, constituting phases, and mechanical property are different from those of the original wearing material. Since wear occurs at the layer, it is important to characterize the layer and understand how wear rate changes with different layers. Various layers are formed depending on external wear conditions such as load, sliding speed, counterpart material, and environmental conditions. In this research, sliding wear tests of pure iron were carried out against two different counterparts (AISI 52100 bearing steel and $Al_2O_3$) in the air and in an inert Ar gas atmosphere. Pure iron was employed to exclude other effects from secondary phases in steel on the wear. Wear tests were performed at room temperature. Worn surfaces, wear debris, and cross-sections were analyzed after the test. It was found that these two different counterparts and environments produced diverse layers, resulting in significant changes in wear rate. Against the bearing steel, pure iron showed higher wear rate in an Ar atmosphere due to severe adhesion than that in the air. On the contrary, the iron showed much higher wear rate in the air against $Al_2O_3$. Different layers and wear rates were analyzed and discussed by oxidation, severe plastic deformation, and adhesion at wearing surfaces.

• 대기
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• 제26권1호
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• pp.97-109
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• 2016

Heavy rainfall (over $80mm\;hr^{-1}$) system associated with unstable atmospheric conditions occurred over the Seoul metropolitan area on 27 July 2011. To investigate the heavy rainfall system, we used three-dimensional data from Korea Local Analysis and Prediction System (KLAPS) reanalysis data and analysed the structure of the precipitation system, kinematic characteristics, thermodynamic properties, and Meteorological condition. The existence of Upper-Level Jet (ULJ) and Low-Level Jet (LLJ) are accelerated the heavy rainfall. Convective cloud developed when a strong southwesterly LLJ and strong moisture convergence occurring around the time of the heavy rainfall is consistent with the results of previous studies on such continuous production. Environmental conditions included high equivalent potential temperature of over 355 K at low levels, and low equivalent potential temperature of under 330 K at middle levels, causing vertical instability. The tip of the band shaped precipitation system was made up of line-shaped convective systems (LSCSs) that caused flooding and landslides, and the LSCSs were continuously enhanced by merging between new cells and the pre-existing cell. Difference of wind direction between low and middle levels has also been considered an important factor favouring the occurrence of precipitation systems similar to LSCSs. Development of LSCs from the wind direction difference at heights of the severe precipitation occurrence area was also identified. This study can contribute to the identification of production and development mechanisms of heavy rainfall and can be used in applied research for prediction of severe weather.