• Journal of Mechanical Science and Technology
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• 제19권4호
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• pp.1036-1043
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• 2005

Concentric annular heat pipes (CAHP) were fabricated and tested to investigate their thermal characteristics. The CAHPs were 25.4 mm in outer diameter and 200 mm in length. The inner surface of the heat pipes was covered with screen mesh wicks and they were connected by four bridge wicks to provide liquid return path. Three different heat pipes were fabricated to observe the effect of change in diameter ratios between 2.31 and 4.23 while using the same outer tube dimensions. The major concern of this study was the transient response as well as isothermal characteristics of the heat pipe outer surface, considering the application as uniform heating device. A better performance was achieved as the diameter ratio increased. For the thermal load of 180 W, the maximum temperature difference on the outer surface in the axial direction of CAHP was $2.3^{\circ}C$ while that of the copper block of the same outer dimension was $5.9^{\circ}C.$ The minimum thermal resistance of the CAHP was measured to be $0.004^{\circ}C/W.$ In regard to the transient response during start-up, the heat pipe showed almost no time lag to the heat source, while the copper block of the same outer dimensions exhibited about 25 min time lag.

• Nuclear Engineering and Technology
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• 제54권10호
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• pp.3732-3744
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• 2022

To investigate the effects of ocean conditions on the thermal stress and deformation caused by thermal stratification of a pressurizer surge line in a floating nuclear power plant (FNPP), the finite element simulation platform ANSYS Workbench is utilized to conduct the fluid-solid-thermal coupling transient analysis of the surge line under normal "wave-out" condition (no motion) and under ocean conditions (rolling and pitching), generating the transient response characteristics of temperature distribution, thermal stress and thermal deformation inside the surge line. By comparing the calculated results for the three motion conditions, it is found that ocean conditions can significantly improve the thermal stratification phenomenon within the surge line, but may also result in periodic oscillations in the temperature, thermal stress, and thermal deformation of the surge line. Parts of the surge line that are more susceptible to thermal fatigue damage or failure are determined. According to calculation results, the improvements are recommended for pipeline structure to reduce the effects of thermal oscillation caused by ocean conditions. The analysis method used in this study is beneficial for designing and optimizing the pipeline structure of a floating nuclear power plant, as well as for increasing its safety.

• 콘크리트학회논문집
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• 제13권3호
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• pp.268-276
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• 2001

본 논문은 고온에서의 콘크리트 재료모델을 연구하였다. 콘크리트 응력-변형률 곡선은 온도가 증가함에 따라 그 형태가 변한다. 온도에 따른 콘크리트 재료거동의 변화를 나타내기 위하여 변형된 Saenz 제안식을 이용하여 응력-변형률 관계를 표시하였다. 고온에서의 급격한 변형률의 증가현상을 설명하기 위하여, 콘크리트의 변형률 성분을 순수 열팽창 변형률, 열적크리프 변형률, 과도 변형률 및 역학적 변형률로 구분하여 나타내었다. 열적크리프 변형률은 Baily-Norton의 장기크리프 곡선 식을 수정.제안하여 1축 실험 결과를 온도, 시간 및 응력의 함수로 표현하였고, 또한 유효응력 및 유효변형률 개념을 도입하여 다차원에서도 적용할 수 있는 모델을 제시하였다. 과도 변형률을 제안하여 다공탄성 거동을 가정한 콘크리트 내에 포함된 공극 및 수분의 작용을 역학적 거동의 영향을 분석하고자 하였다. 마지막으로, 본 논문에서 제시한 고온에서의 콘크리트 재료모델을 이용한 해석결과를 실제 화재실험자료와 비교하였다.

• 한국자동차공학회논문집
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• 제14권4호
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• pp.68-76
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• 2006

The minimization of maximum DPF wall temperature and the fast Light-off during regeneration are the targets for the high durability of the DPF system and the high efficiency of regeneration. In order to predict transient thermal response of DPF, one-channel numerical modeling has been adopted. The effect of the ratio of length to diameter(L/D), cell density, the amount of soot loading on temporal thermal response and regeneration characteristics has been numerically investigated under two different running conditions: city driving mode and high speed mode. The results indicate that the maximum wall temperature of DPF increase with increasing 'L/D' in 'High speed mode'. For 'City driving mode', the maximum wall temperature decreases with increasing 'L/D' in the range of $'L/D{\geq}0.6'$. The maximum temperature decreases with increasing cell density because heat conduction and heat capacity are increased. It is also found that the effect of amount of soot loading on light-off time is negligible.

• Steel and Composite Structures
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• 제8권3호
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• pp.201-216
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• 2008

The Eurocode system provides limited information regarding the structural fire design of external steel structures. Eurocode 1 provides thermal action for external member but only in steady-state conditions. On the other hand, Eurocode 3 provides a methodology to determine heat transfer to external steelwork, but there is no distinction in cross section shapes and, in addition, the calculated temperature distribution is assumed to be uniform in the cross section. This paper presents the results of a research carried out to develop a new transient heat transfer model for external steel elements to improve the current approach of the Eurocodes. This research was carried out as part of the project EXFIRE "Development of design rules for the fire behaviour of external steel structures", funded by the European Research Programme of the Research Fund for Coal and Steel (RFCS).

• 시스템엔지니어링학술지
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• 제18권2호
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• pp.75-93
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• 2022

Machine learning (ML) data-driven meta-model is proposed as a surrogate model to reduce the excessive computational cost of the physics-based model and facilitate the real-time prediction of a nuclear power plant's transient response. To forecast the transient response three machine learning (ML) meta-models based on recurrent neural networks (RNNs); specifically, Long Short Term Memory (LSTM), Gated Recurrent Unit (GRU), and a sequence combination of Convolutional Neural Network (CNN) and LSTM are developed. The chosen accident scenario is a control element assembly withdrawal at power concurrent with the Loss Of Offsite Power (LOOP). The transient response was obtained using the best estimate thermal hydraulics code, MARS-KS, and cross-validated against the Design and control document (DCD). DAKOTA software is loosely coupled with MARS-KS code via a python interface to perform the Best Estimate Plus Uncertainty Quantification (BEPU) analysis and generate a time series database of the system response to train, test and validate the ML meta-models. Key uncertain parameters identified as required by the CASU methodology were propagated using the non-parametric Monte-Carlo (MC) random propagation and Latin Hypercube Sampling technique until a statistically significant database (181 samples) as required by Wilk's fifth order is achieved with 95% probability and 95% confidence level. The three ML RNN models were built and optimized with the help of the Talos tool and demonstrated excellent performance in forecasting the most probable NPP transient response. This research was guided by the Systems Engineering (SE) approach for the systematic and efficient planning and execution of the research.

• 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.

• Structural Engineering and Mechanics
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• 제13권6호
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• pp.695-711
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• 2002

Here, the dynamic response characteristics of thick cross-ply laminated composite cylindrical shells are studied using a higher-order displacement model. The formulation accounts for the nonlinear variation of the in-plane and transverse displacements through the thickness, and abrupt discontinuity in slope of the in-plane displacements at any interface. The effect of inplane and rotary inertia terms is included. The analysis is carried out using finite element approach. The influences of various terms in the higher-order displacement field on the free vibrations, and transient dynamic response characteristics of cylindrical composite shells subjected to thermal and mechanical loads are analyzed.

• 대한기계학회논문집B
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• 제24권7호
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• pp.994-1001
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• 2000

The dynamic behavior of a single-pressure heat recovery steam generator and turbine system for the combined cycle power plant is simulated on the basis of one-dimensional unsteady governing equations. A water level control and a turbine power control are also included in the calculation routine. Transient response of the system to the variation of gas turbine exit condition is simulated and effect of the turbine power control on the system response is examined. In addition, the effect of the treatment of inertia terms(fluid inertia and thermal inertia of heat exchanger metal) on the simulated transient response is investigated.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1572-1582
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• 2003

Hybrid rocket combustion has a manifestation of stable response to the perturbations compared to solid propellant combustion. Recently, it has revealed that the low frequency combustion instability about 10 Hz was occurred mainly due to thermal inertia of solid fuel. In this paper, the combustion response function was theoretically derived by use of ZN (Zeldovich-Novozhilov) method. The result with HTPB/LOX combination showed a quite good agreement in response function with previous works and could predict the low frequency oscillations with a peak around 10 Hz which was observed experimentally. Also, it was found that the amplification region in the frequency domain is independent of the regression rate exponent n but showed the dependence of activation energy. Moreover, the response function has shown that the hybrid combustion system was stable due to negative heat release of solid fuel for vaporization, even though the addition of energetic ingredients such as AP and Al could lead to increase heat release at the fuel surface.