• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.914-917
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• 2001

Single-shot laser damage of thin Cr films on glass substrates has been studied to understand the cracking and peeling-off mechanism. A numerical model is developed for the calculation of transient heat transfer and thermal stresses in Cr films during excimer laser irradiation and cooling, the transient temperature, and the stress-strain fields are analyzed by using a three-dimensional finite-element model of heat flow. According to the numerical analysis for the experimentally determined cracking and peeling-off conditions, cracking is found to be the result of the tensile brittle fracture due to the excessive thermal stresses formed during the cooling process, while peeling-off is found to be the combined result of films bulging from the softened glass surface at higher temperature and the tensile brittle fracture during the cooling process.

• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1731-1735
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• 2021

The operation of the nuclear reactor requires accurate and fast methods and techniques for analysing its kinetics. These techniques become even more important when the MOX-fuel is used due to the lower value of delayed neutron fraction 𝛽 for ²³⁹Pu. Based on a Birth-and-Death process review, the mathematical model of thermal reactor core has been proposed different from existing ones. The analytical method for thermal point-reactor parameters evaluation is described within this work. The proposed method is applied for analysis of the unsteady transient processes taking place in a thermal reactor at its start-up or shutdown power change, as well as during small accidental power variation from the rated value. Theoretical determination of MASURCA reactor core reactivity through the analysis of experimental data on neutron time spectra was made.

• 한국압력기기공학회 논문집
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• 제14권2호
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• pp.77-87
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• 2018

In the case of high-energy line breaks in nuclear power plants, supersonic steam jet is formed due to the rapid depressurization. The steam jet can cause impingement load on the adjacent structures, piping systems and components. In order to secure the design integrity of the nuclear power plant, it is necessary to evaluate the load characteristics of the steam jet generated by high-energy pipe rupture. In the design process of nuclear power plant, jet impingement load evaluation was usually performed based on ANSI/ANS 58.2. However, U.S. NRC recently pointed out that ANSI/ANS 58.2 oversimplifies the jet behavior and that some assumptions are non-conservative. In addition, it is recommended that dynamic analysis techniques should be applied to consider transient load characteristics. Therefore, it is necessary to establish an evaluation methodology that can analyze the dynamic load characteristics of steam jet ejected when high energy pipe breaks. This research group has developed and validated the CFD analysis methodology to evaluate the transient behavior of supersonic impinging jet in the previous study. In this study, numerical study on the transient load characteristics of supersonic steam jet impingement was carried out and amplitude and frequency analysis of transient jet load was performed.

• 한국수소및신에너지학회논문집
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• 제15권3호
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• pp.175-186
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• 2004

In this paper, we developed the dynamic model of a fuel cell system suitable for controller design and system operation. The transient phenomena captured in the model include the flow characteristics and inertia dynamics of the compressor, the intake manifold filling dynamics, oxygen partial pressures and membrane humidity on the fuel cell voltage. In the simulations, we paid attention to the transient behavior of stack voltage and compressor pressure, stoichiometric ratio. Simulation results are presented to demonstrate the model capability. For load current following, stack voltage dynamic characteristics are plotted to understand the Electro-chemistry involved with the fuel cell system. Compressor pressure and stoichiometric ratio are strongly coupled, and independent parameters may interfere with each other, dynamic response, undershoot and overshoot.

• 대한전자공학회논문지
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• 제18권2호
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• pp.27-35
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• 1981

본 연구에서는 비정질 갈코게나이트박막의 스위칭과도 특성을 분석하기 위해 공체전하중를 모델에 의한 수식적 이론과 그 이론의 타부성에 따른 실험을 연하였다. 이론과 실험에 대한 분석적인 관찰을 실온에서 비정용 잘코게나이드박막에 전압펄스를 인가할 때 생기는 스위칭과도 특성에 대해 비교하였다. 결과로는 전자스위칭 특성에 대한 단순한 이론적 모델의 형태로 설명할 수 있다. 캐리어의 주입은 스위칭 특성을 유발시키기에 필요하며 주입된 캐리어들은 공간전하제한전류(SCLC)로서 전류 흐름에 기여한다. 그러므로 제안된 전하제어 스위칭 특성은 2중 주입 공간 전하중첩 모델로 해석할 수 있다.

• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3196-3206
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• 2021

For the Korean design of the PCCS (passive containment cooling system) in an innovative PWR, the overall thermal resistance around a condenser tube is dominated by the heat transfer coefficient of steam condensation on the exterior surface. It has been reported, however, that the calculated heat transfer coefficients by thermal-hydraulic system codes were much lower than measured data in separate effect tests. In this study, a new empirical model of steam condensation in the presence of a noncondensable gas was implemented into the MARS-KS 1.4 code to replace the conventional Colburn-Hougen model. The selected correlation had been developed from condensation test data obtained at the JERICHO (JNU Experimental Rig for Investigation of Condensation Heat transfer On tube) facility, and considered the effect of the Grashof number for naturally circulating gas mixture and the curvature of the condenser tube. The modified MARS-KS code was applied to simulate the transient response of the containment equipped with the PCCS to the large-break loss-of-coolant accident. The heat removal performances of the PCCS and corresponding evolution of the containment pressure were compared to those calculated via the original model. Various thermal-hydraulic parameters associated with the natural circulation operation through the heat transport circuit were also investigated.

• 한국통신학회논문지
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• 제28권11B호
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• pp.999-1006
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• 2003

본 논문에서는 Mobile IPv6 망에서 Smooth 핸드오프가 패킷의 전송에 끼치는 영향을 분석한다. 분석결과 핸드오프는 단말의 관점에서 불안정구간(UTP), 묵음구간(UTP), 핸드오프구간(HTP)으로 구분됨을 보인다. 또한 정확한 구간의 값을 구하기 위해 큐잉 모델을 제시한다. 수치해석의 결과 불안정구간, 묵음구간, 핸드오프구간은 핸드오프 되는 패킷의 큐잉 지연과 패킷이 전송되는 링크의 대역폭에 영향을 받음을 보인다. 한편, 핸드오프의 수행기간이 길어지면 핸드오프로 인한 응용의 피해는 증가한다. 우선순위 스케줄링 기법을 이용하면 기존의 IP망에서 최선형 서비스를 위한 FIFO 스케줄링 방식보다 더 짧은 과도기간을 가짐을 확인한다.

• 한국전산유체공학회지
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• 제20권3호
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• pp.87-93
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• 2015

In this study, a numerical analysis was performed to simulate the thermal-hydraulic response of the secondary side of a steam generator(SG) model equipped with an orifice-type SG outlet flow restrictor to a main steam line break(MSLB) at a pressurized water reactor(PWR) plant. The SG analysis model includes the SG upper steam space and the part of the main steam pipe between the SG outlet and the broken pipe end. By comparing the numerical calculation results for the present SG model to those obtained for a simple SG model having no flow restrictor, the effects of the flow restrictor on the thermal-hydraulic response of SG to the MSLB were investigated.

• 제어로봇시스템학회논문지
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• 제15권12호
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• pp.1175-1183
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• 2009

In photovoltaic(PV) generator systems, DC-DC converters are significantly considered for control system performance in power quality point of view. This paper presents a novel adaptive control method for DC-DC converters applied in PV generator systems. First, we derive a state-space average model of the converter system and then propose a reset control methodology to enhance transient response performance for time-varying PV systems. For estimating parameters of a reset control, a gradient descent optimization is utilized and an adjustment rule of them are derived respectively. An objective of the optimization is that characteristic equation of an augmented system model which is formed with an converter system model and an reset control is to trace a predefined polynomial given as a reference characteristic model. Next, we accomplish stability analysis by means of a well-known Lyapunov theory for nonlinear converter systems including time-varying voltage excitation from a PV generator. Numerical simulation demonstrates reliability of our control methodology and its superiority by comparison to a traditional control strategy.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1651-1664
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• 2023

It is very difficult to capture the multi-dimensional phenomena such as asymmetric flow and temperature distributions with the one-dimensional (1D) model, obviously, due to its inherent limitation. In order to overcome such a limitation of the 1D representation, many state-of-the-art system codes have equipped a three-dimensional (3D) component for multi-dimensional analysis capability. In this study, a standard multi-dimensional analysis model of APR1400 (Advanced Power Reactor 1400) has been developed using TRACE (TRAC/RELAP Advanced Computational Engine). The entire reactor pressure vessel (RPV) of APR1400 has been modeled using a single 3D component. The fuels in the reactor core have been described with detailed and coarse representations, respectively, to figure out the impact of the fuel description. Using both 3D RPV models, a comparative analysis has been performed postulating a double-ended guillotine break at a cold leg. Based on the results of comparative analysis, it is revealed that both models show no significant difference in general plant behavior and the model with coarse fuel model could be used for faster transient analysis without reactor kinetics coupling. The analysis indicates that the asymmetric temperature and flow distributions are captured during the transient, and such nonuniform distributions contribute to asymmetric quenching behaviors during blowdown and reflood phases. Such asymmetries are directly connected to the figure of merits in the LBLOCA analysis. Therefore, it is recommended to employ a multi-dimensional RPV model with a detailed fuel description for a realistic safety analysis with the consideration of the spatial configuration of the reactor core.