• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.1
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• pp.193-200
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• 2021

In this study, an analysis technique using static condensation is proposed for an efficient local nonlinear static analysis. The static condensation method is a model reduction method based on the degrees of freedom, and the analysis model is divided into a target part and a condensed part to be omitted. In this study, the nonlinear and linear parts were designated to the target and the omitted parts, respectively, and both the stiffness matrix and load vector corresponding to the linear part were condensed into the nonlinear part. After model condensation, the reduced model comprising the stiffness matrix and the load vector for the nonlinear part is constructed, and only this reduced model was updated through the Newton-Raphson iteration for an efficient nonlinear analysis. Finally, the efficiency and reliability of the proposed analysis technique were presented by applying it to various numerical examples.

• Journal of Energy Engineering
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• v.9 no.4
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• pp.358-365
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• 2000

본 연구에서는 수직 단일관에서의 재관수(reflux) 응축 현상에서 증기유량이 역류제한치보다 큰 경우에 발생하는 다양한 유동 패턴을 예측하고, 그 동적 특성을 해석하기 위한 모델을 개발하였다. 특히 L/D가 큰 재관수 응축기에서 발생하는 충전 방출 모드에서의 동적 특성을 예측하는 것이 목표이다. 응축기의 내부를 액체와 증기의 두 영역으로 나누어 질량, 에너지, 운동량 보존에 입각한 본 모델은, 형성된 물기둥의 진동시 갈래질 경계(bifurcation boundary)와 진동주기를 예측할 수 있다. 이 모델은 McMaster 대학에서 수행한 실험결과와 비교한 결과 양호한 예측을 했고, 튜브 직경변화 효과를 잘 묘사하였다. 이러한 단순 모델은 재관수 응축기의 설계시에 설계변수를 도출하는데 사용될 수 있고, 인위적으로 부여한 압력펄스를 이용하여 재관수 응축기의 운전영역을 개선하는데 기초로 활용될 수 있다.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.813-820
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• 2001

The Safety depressurization System(SDS) of KNGR prevents RCS from overpressurization by discharging high pressure and temperature coolant through the I-sparger into the IRWST during an accident. If IRWST water temperature rise locally, around the sparger, beyond $200_{\circ}$2000 F by the discharged coolant, unstable steam condensation can cause large pressure load on the IRWST wall. To investigate whether this condition can be avoided for the design basis event IOPOSRV(Inadvertent Opening of one Pilot Operated Safety Relief Valve), the flow and temperature distribution of water in the IRWST is calculated by using CFX 4.3 computational fluid dynamic code. According to the results, since pool water temperature does not exceeds temperature limit within 50 seconds after the opening of one POSRV, it can be assured that the integrity of IRWST wall is maintained.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.4
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• pp.47-60
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• 1999

The stability and efficiency of structural control systems depend on the accuracy of mathematical model of the system to be controlled. In this study, state equation models of a small scale test structure and an AMD(active mass damper) are obtained separately using OKID(observer/Kalman filter identification) which is a time domain system identification method. The test structure with each floor acceleration as outputs is identified for two inputs - the ground acceleration and the acceleration of the moving mass of AMD relative to the installation floor - individually and the two identified state equation models are integrated into one by model reduction method. The AMD is identified with the motor control signal as an input and the relative acceleration of the moving mass as an output, and it is shown that the identified model has large damping ratio and phase shift. The transfer functions and the time histories reconstructed from the identified models of the test model and the AMD match well with those measured from the experiment.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.4
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• pp.920-926
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• 1990

본 연구에서는 Fig.1과 같은 2상 자연순환 회로의 1차원 해석을 수행하고, 액 상의 과냉정도와 각 상 영역에서의 밸브 마찰저항이 순환유속에 미치는 영향을 살펴보 므로써 정적 불안정의 조건을 알아보는데 있다. 본 모델에서는 유한 길이를 갖는 증 발기와 응축기를 고려하였으며, 정적 불안정의 가능성을 해석적으로 보여주기 위해 간 단한 모델(point-heat-source/sink)도 함께 다루었다.

• Nuclear Engineering and Technology
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• v.16 no.4
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• pp.195-201
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• 1984

A state-of-the-art mechanistic model has been developed to accurately predict the void fraction in the subcooled boiling region having axial nonuniform heat flux. In this study, the void-dependent drift-flux parameters of the Lahey/Ohkawa model were introduced and the mass flux-dependent condensation coefficient were determined by fitting with the experimental data. This model was tested against several experimental data sets to verify its accuracy. Finally the comparison between the predicted void fraction profiles with this model and the profile-fit model for the hot assembly of Kori-Unit 1, Cycle 1 has been performed. It is conclusive that the results show the good agreement between the measured and predicted void fractions, and the profile-fit model has been found to underestimate the void fraction in the subcooled boiling region.

• Clean Technology
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• v.28 no.3
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• pp.249-257
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• 2022

The adsorption equilibria of nitrogen on a region of nanoporous carbonaceous adsorbent with local molecular orientation (LMO) were calculated by grand canonical Monte Carlo simulation at 77.16 K. Regions of LMO of identical size were arranged on a regular lattice with uniform spacing. Microporosity was predominately introduced to the model by removing successive out-of-plane domains from the regions of LMO and tilting pores were generated by tilting the basic structure units. This pore structure is a more realistic model than slit-shaped pores for studying adsorption in nanoporous carbon adsorbents. Their porosities, surface areas, and pore size distributions according to constrained nonlinear optimization were also reported. The adsorption in slit shaped pores was also reported for reference. In the slit shaped pores, a clear hysteresis loop was observed in pores of greater than 5 times the nitrogen molecule size, and in capillary condensation and reverse condensation, evaporation occurred immediately at one pressure. In the LMO pore model, three series of local condensations at the basal slip plane, armchair slip plane and interconnected channel were observed during adsorption at pore sizes greater than about 6 times the nitrogen molecular size. In the hysteresis loop, on the other hand, evaporation occurred at one or two pressures during desorption.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.2
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• pp.233-241
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• 1999

본 연구는 개별 메모리를 갖는 소결합 구조의 MIMD형 병렬컴퓨터인 트랜스퓨터시스템 하에서 구조최적화를 위한 병렬처리 과정을 보이고 시험모델에 적용하여 타당성 및 효율성을 검증한다. 전체 최적화과정의 대부분을 차지하는 해석 및 민감도 알고리즘은 영역단위의 병렬성을 갖는 부구조화에 근거하고 하드웨어 구성에 맞춰 변환 재구성한다. 각 노드간 통신은 정적응축과 설계도함수에 한정, 그 횟수를 최소화하고 그들을 동기화하므로써 개별메모리형 연산모델의 약점인 통신비용의 문제를 해소한다. PC를 호스트로 한 수치실험은 고속화 효율성 면에서 고무적인 결과를 보여주고 있으며, 이런 점에서 시스템의 확장성을 함께 고려한다면 트랜스퓨터 시스템에 기초한 병렬처리는 공학 환경의 변화와 요구에 부응하는 좋은 대안이 될 수 있다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.2
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• pp.91-97
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• 2002

Dynamic extinction of solid propellants subjected to rapid pressure drop was studied with the aid of energy equation of condensed phase and flame model in gas phase. It is found that the total residence time($\tau_\gamma$) which measures the residing time of fuel in the reaction zone may play a crucial role in determining the dynamic response of the combustuion to extinction. Residence time was modeled by various combinations of diffusion and chemocal kinetic time scale. Effect of pressure history coupled with chamber volume on the extinction response was also performed and was found that dynamic extinction is more susceptible in a confined chamber than in open geometry. And, dynamic extinction was revealed to be affected profoundly by diffysion time scale rather than chemical kinetic time scale.

• Nuclear Engineering and Technology
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• v.23 no.2
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• pp.200-209
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• 1991

A new semi-empirical average heat transfer correlation applicable for both laminar and turbulent film-wise condensation on a vertical surface has been presented. Re functional form of the present correlation is based on the representative existing correlations for laminar and turbulent film flows, whereas the numerical coefficients of the present correlation have been determined by the least squares method using experimental data obtained from the open literatures. In addition, the performance of the present as well as the seven existing correlations (four for laminar and three for turbulent film flow regimes) were evaluated for their accuracy and the range of application. The result shows that for laminar film filow regimes Zazuli's and the present correlations give the samllest values of mean error, whereas for turbulent film How regimes Kirkbride and Badger's and the present correlations produce the smallest values of mean error.