핵비등이탈 현상 재구성을 위한 조건부 적대적 생성 신경망 활용

나웅진(UngJin Na),최문희(Moonhee Choi),이석용(SeockYong Lee),박세현(SeHyeon Park),조항진(HangJin Jo) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.11

Understanding the nuances of the departure from nucleate boiling (DNB) is paramount for ensuring the safety and functionality of high thermal flux systems. The DNB, characterized by a sudden drop in heat transfer, remains a challenge to pinpoint due to its intricate nature. Many techniques aim to decode these complexities, but obtaining detailed data often demands excessive resources. This study presents a novel approach using conditional generative adversarial networks (cGANs) to reinterpret thermal data during DNB. We utilize paired images: total reflection visualizations and infrared thermometry from flow boiling experiments. Our method not only reveals links between phase interface dynamics and thermal patterns but also streamlines traditionally labor-intensive experimental setups related to infrared imaging.

수중부재의 파력산정에 관한 고찰

오재택,나웅진,O, Jae-Taek,Na, Ung-Jin 한국해안해양공학회 2011 해안과 해양 Vol.4 No.1

FRP로 보강된 콘크리트 부재의 압축응력-변형률 예측을 위한 뉴로퍼지모델의 적용

박태원(Tae-Won Park),나웅진(Ungjin Na),권성준(Sungjun Kwon) 한국콘크리트학회 2010 콘크리트학회논문집 Vol.22 No.1

PCHE (Printed Circuit Heat Exchanger)를 이용한 고온에서의 열 회복을 고려한 2단계 열화학적 수소 생산 방식의 효율 및 경제성 분석

이석용(SeockYong Lee),나웅진(Woongjin Na),이수원(Suwon Lee),정성균(Sungkun Jung),조항진(Hangjin Jo) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11

A two-step thermochemical method, which is in the spotlight for its simplicity and ease of scale-up among various hydrogen production methods, was studied. In order to practically consider heat recuperation in high temperature, which has been pointed out as a problem of the method, the efficiency and economic feasibility of the two-step thermochemical method were evaluated considering changing effectiveness of PCHE depending on condition. Based on the in-house code, calculations were carried out for Ceria in two-step separated type reactor. Change in the thermal to hydrogen efficiency was calculated depending on temperature, oxygen partial pressure, effectiveness. The optimized volume and differential pressure were calculated in consideration of economic feasibility. Based on the results, portion of cost for production using Ceria was investigated and further research direction for future commercialization were suggested.

차세대 원자로와 마이크로 웨이브를 이용한 2단계 열 화학적 물 분해 방식의 경제성 분석

이석용(SeockYong Lee),나웅진(UngJin Na),조항진(HangJin Jo) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11

The climate emergency emerges as a global problem. The transition from the existing carbon economy to a hydrogen economy is emerging to solve the problem. This study focuses on the two-step thermochemical water splitting method suitable for large-scale green hydrogen production, which is essential for the upcoming hydrogen economy. Economic assessment is conducted considering a High-temperature gas-cooled reactor as the primary heat source in consideration of that microwave could induce a significant change in the electrical conductivity of metal oxide at a low-temperature range. Ceria or (FeMgCoNi)Ox is selected as a catalyst. The change of LCOH (Levelized cost of hydrogen) according to microwave power and operating conditions was quantitatively evaluated. The system with an advanced nuclear power plant showed a better performance in that an advanced nuclear power plant has stable and continuous operating compared with a solar power system. The results opened up the possibility of commercialization of the two-step thermochemical water-splitting method.

차세대 원자로와 마이크로 웨이브를 이용한 2단계 열 화학적 물 분해 방식의 경제성 분석

이석용(SeockYong Lee),나웅진(UngJin Na),조항진(HangJin Jo) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11

The climate emergency emerges as a global problem. The transition from the existing carbon economy to a hydrogen economy is emerging to solve the problem. This study focuses on the two-step thermochemical water splitting method suitable for large-scale green hydrogen production, which is essential for the upcoming hydrogen economy. Economic assessment is conducted considering a High-temperature gas-cooled reactor as the primary heat source in consideration of that microwave could induce a significant change in the electrical conductivity of metal oxide at a low-temperature range. Ceria or (FeMgCoNi)Ox is selected as a catalyst. The change of LCOH (Levelized cost of hydrogen) according to microwave power and operating conditions was quantitatively evaluated. The system with an advanced nuclear power plant showed a better performance in that an advanced nuclear power plant has stable and continuous operating compared with a solar power system. The results opened up the possibility of commercialization of the two-step thermochemical water-splitting method.

염화물을 혼합한 OPC 모르타르의 전자기 특성에 대한 연구

권성준(Kwon Seung-Jun),나웅진(Na Ung-Jin),M. Q. Feng 대한토목학회 2008 대한토목학회논문집 A Vol.28 No.4A

Recently, the evaluation technique using NDT (Nondestructive Technique: NDT) is widely utilized because it makes little damage on RC (Reinforced Concrete: RC) structures. The techniques using electromagnetic properties (EM properties) are also attempted for the evaluation of the performance of concrete which is nonmetallic. For the economic manufacturing of concrete material, sea-sand is often used as aggregate, however, chloride ion in concrete has direct effects on steel corrosion and EM properties. In this study, OPC mortar specimens with 5 different chloride amount (0.0, 0.6, 1.2, 2.4, and 3.6 ㎏/㎥) and 3 different water-cement ratios (45%, 55%, and 65%) are prepared in order to investigate the EM properties corresponding to concrete properties. The EM properties of conductivity and dielectric constant are measured in the frequency range over 0.2~20 ㎓. To facilitate the comparison of EM properties with chloride content, average values are taken respectively for the conductivity and dielectric constant measured over the 5~20 ㎓ frequency range. According to the results of this experiment, dielectric constant and conductivity are increased with lower W/C ratio and larger amount of chloride content. 최근들어 구조물에 직접적인 손상을 주지 않는 비파괴평가를 통한 콘크리트 구조물의 성능평가에 대한 연구가 다양하게 진행되고 있으며, 특히 비자성체인 시멘트계 재료의 특성을 이용하여, 전자기 특성을 콘크리트에 적용하려는 연구가 시도되고 있다. 경제적인 콘크리트 생산을 위하여 해사가 잔골재로서 많이 사용되는 현실을 감안할 때, 철근의 부식에 직접적으로 관여하는 콘크리트 내부 염화물이 콘크리트의 재료적 특성에 미치는 영향 또한 중요한 연구과제 중의 하나이며, 본 연구에서는 이와 연계한 전자기 특성 변화를 중점적으로 살펴보고자 한다. 본 연구에서는 5가지의 다른 염화물 함유량(0.0, 0.6, 1.2, 2.4, 3.6 ㎏/㎥)이 포함된 보통포틀랜트시멘트(Ordinary Portland Cement : OPC) 모르타르를 이용하여 유전상수를 측정하고 그 변화를 분석하였다. 각 시편은 3가지 물-시멘트비(45%, 55%, 65%)를 가지도록 하였으며, 0.2~20 ㎓의 영역에서 유전상수(dielectric constant)와 전도율(conductivity)이 측정되었다. 전자기 특성과 염화물량의 변화를 용이하도록 하기 위하여, 5~20 ㎓ 영역에서의 전도율 및 유전상수의 평균값이 사용되었다. 각각의 전자기 특성들은 물-시멘트비가 낮을수록 높게 평가되었으며, 염화물량의 증가에 따라 측정값이 증가하였다.

시멘트 모르타르의 수분변화에 따른 평균화된 전자기 특성에 대한 실험적 연구

권성준(Seung-Jun Kwon),Maria, Q. Feng,나웅진(Ung-Jin Na) 한국콘크리트학회 2009 콘크리트학회논문집 Vol.21 No.2

경사식 방파제의 피복재 침식피해 표준화

김승우(Kim Seung-Woo),서경덕(Suh Kyung-Duck),나웅진(Na Ungjin) 대한토목학회 2010 대한토목학회 학술대회 Vol.2010 No.10

확률론적 해석을 통한 염해에 노출된 균열부 콘크리트 구조물의 내구수명 평가

권성준(Kwon Seung-Jun),박상순(Park Sang-Soon),나웅진(Na Ung-Jin) 대한토목학회 2007 대한토목학회논문집 A Vol.27 No.6A

콘크리트 구조물의 균열은 건조수축 및 수화열과 같은 초기재령 거동으로 인해 시공중 피할수 없이 발생할 수 있다. 이러한 균열은 열화인자 유입의 주된 경로가 되고 있으며, 특히 염해에 노출된 콘크리트 구조물에서 발생한 균열은 철근부식의 큰 원인이 되고 있다. 일반적으로 염화물 거동의 평가는 Fick의 확산법칙에 근거한 결정론적인 방법이 수행되고 있는데 최근들어, 재료 및 설계단계에서의 다양한 변동성을 고려하기 위해 확률론적인 연구가 시도되고 있다. 본 연구에서는 실태조사를 통하여 8년, 11년 경과된 해상 콘크리트 구조물의 건전부 및 균열부 확산계수를 도출하였으며, 몬테카를로 시뮬레이션과 Fick의 확산법칙을 통하여 내구적 파괴확률 및 내구수명을 분석하였다. 이를 위하여 피복두께와 시간의존적 확산계수를 확률변수로 설정하고, 도출된 균열부 확산계수를 적용하여 내구적 파괴확률을 분석하였다. 몬테카를로 시뮬레이션을 이용한 해석을 수행한 결과, 균열부 콘크리트에서의 내구적 파괴확률은 균열폭의 증가에 따라 크게 증가하였으며, 이에따라 내구수명이 크게 감소함을 알 수 있었다. 한편 현재 국내 시방서에서 제시하고 있는 균열영향인자를 고려한 확산계수는 허용균열폭을 고려하고 있는데, 허용균열폭이 큰 균열부 콘크리트 부재에서는 실태조사에 비해 낮은 염화물 확산계수를 예측하게 된다. 낮게 예측된 염화물 확산계수로부터 염화물 거동이 실태조사에 비하여 낮게 평가할 수 있으므로 광범위한 실태조사를 통한 균열부 확산계수의 도출이 필요함을 알 수 있다. Cracks in early-age due to hydration heat and drying shrinkage may occur unavoidably. These can be the main routes for deteriorating agents and also can be one of the major reasons of steel corrosion in concrete structures exposed to chloride attack. Generally, deterministic method using Fick's 2nd Law is utilized for durability design, however, stochastic method is recently attempted for consideration of variable characteristics in material and construction. In this study, apparent diffusion coefficients in sound and cracked concrete structures, exposed to chloride attack with 8 and 11 years used, are derived through field investigation and service life is predicted by utilizing Monte Carlo Simulation (MCS) and Fick's 2nd law, respectively. For the purpose, random variables such as critical chloride amount, cover depth, and time-dependent diffusion coefficient are established and probability of durability failure is calculated using the derived diffusion in cracked concrete. Utilizing MCS in cracked concrete, the probability of durability failure is evaluated to be rapidly increased with growing crack width and accordingly, service life is also decreased. In Domestic Specification, allowable crack width is considered in crack effect on diffusion. However, if a concrete member is designed with increased allowable crack width, relatively more reduced diffusion coefficient may be obtained than that from the field investigation. The chloride behavior also may be underestimated due to the reduced diffusion coefficient so that derivation of relationship between crack width and chloride diffusion through extensive field investigation is necessary for durability design of concrete structures permitting allowable crack width under chloride attack.