• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제25회 KOSCI SYMPOSIUM 논문집
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• pp.173-184
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• 2002

In order to evaluate the devolatilization models of pulverized coal, various devolatilization models are examined for the numerical analysis of Drop Tube Furnace.The results of analysis are compared with the experimental results. A numerical study was conducted to explore the sensitivities of the predictions to variation of the model parameters. It helps to elucidate the source of the discrepancies. Three different wall temperature conditions of the DTF, 1100, 1300 and $1500^{\circ}C$ were considered in this analysis. Two fuels are U.S.A. Alaska coal and Australia Drayton coal. The results of analysis with constant rate model, single kinetic rate model and two competing rate modes well presented fast volatile matter release in the early devolatilization. However, in the latter devolatilization they did not coincide with experimental results which presented tardy volatile matter release on account of pyrolysis of high molecular substance. On the other hand, the results of analysis with DAEM(Distribute Activation Energy Model) coincided with experiment al results in overall devolatilization.

• International Journal of Aerospace System Engineering
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• 제6권2호
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• pp.11-16
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• 2019

A system analysis program has been developed for a gas generator cycle liquid rocket engine of 30 ton class. Numerical models have been proposed for a combustor, a turbopump, a gas generator and pressure drop through a regenerative cooling system. Numerical algorithm has been validated by comparing with the published data of MC-1. The major source of error is not the numerical algorithm but the imperfect performance models of subsystems. So the precision of the program can be improved by revising the performance models using experimental data. The sea level specific impulse and vacuum specific impulse have been demonstrated for a 30 ton class gas generator engine. The optimal condition of combustor pressure and mixture ratio for specific impulse which is a typical characteristic of a gas generator cycle engine has been illustrated.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1992년도 봄 학술발표회 논문집
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• pp.74-79
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• 1992

The confinement of concrete from splitting bond failure is studied with the experiments and finite element models. The cracks in the test beam-end specimens containing various covers show a typical splitting failure with a dominant fracture surface. The finite element model includes representation of the splitting cracking using Hillerborg's fictitious crack model. The increase in bond strength from addition of covers are consistant for both test bars and numerical models. The numerical solution agrees well with results and also with the test results and also with the empirical equations. The splitting crack in the numerical models generally matches the crack surface observed in the laboratory. The confinement of concrete from splitting is one of the governing factors in the ultimate bond force.

• 천문학논총
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• 제30권2호
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• pp.473-474
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• 2015

Halo merger trees are the essential backbone of semi-analytic models for galaxy formation and evolution. Srisawat et al. (2013) show that different tree building algorithms can build different halo merger histories from a numerical simulation for structure formation. In order to understand the differences induced by various tree building algorithms, we investigate the impact of halo merger trees on a semi-analytic model. We find that galaxy properties in our models show differences between trees when using a common parameter set. The models independently calibrated for each tree can reduce the discrepancies between global galaxy properties at z=0. Conversely, with regard to the evolutionary features of galaxies, the calibration slightly increases the differences between trees. Therefore, halo merger trees extracted from a common numerical simulation using different, but reliable, algorithms can result in different galaxy properties in the semi-analytic model. Considering the uncertainties in baryonic physics governing galaxy formation and evolution, however, these differences may not necessarily be significant.

• Structural Engineering and Mechanics
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• 제12권6호
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• pp.615-632
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• 2001

Ductility of open piled wharves under reversed cyclic loads has been investigated. Experimental testing of five wharf models having a scale of about 1:4 was conducted under the application of horizontal reversed cyclic loading. The experiments were designed to focus on the horizontal ultimate load, ductility and failure mode of the considered wharf models. Nonlinear numerical analyses using the finite element method were also performed on numerical models representing the experimentally tested wharves. The results of the experimental tests showed that open piled wharves possessed favourable ductile behaviour and that their load bearing capacity did not depreciate until a ductility factor of 3 to 4 was reached. The numerical analysis showed that the relative rotation that took place at the joints between the steel piles and the R.C. beam was responsible for a considerable portion of the total horizontal deformation of the wharves. Therefore, it was concluded that introducing the joint stiffness in calculating the deformations of open piled wharves was important to achieve reasonable accuracy.

• 한국소음진동공학회논문집
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• 제18권11호
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• pp.1111-1117
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• 2008

During the dynamic analysis of a system, the Coulomb friction law is emploved to calculate the friction force. Since the static friction coefficient is only employed during the zero relative velocity, it is impractical to employ the coefficient during the dynamic analysis. To calculate the static friction force, therefore, some friction models have been developed. In this study, the integration stability and the accuracy of the models are investigated with some numerical examples. The effect of time step size during the numerical integration is also investigated. The numerical study shows that the friction model employed for most commercial codes is not as good as the one proposed in this study.

• 국제강구조저널
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• 제18권4호
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• pp.1219-1241
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• 2018

This study aims towards the improvement of a reinforced concrete rigid-frame bridge in an effort to reduce the construction and maintenance costs, and achieve an improved seismic performance. Correspondingly, a new structural rigid connection is proposed for H-shaped steel girders and reinforcing bars at the corner of the rigid-frame structure. Both experiments and numerical analyses were performed. Prototype models were constructed and subjected to static loading tests to reveal their load-carrying capacity and failure mode. Numerical models were then developed using finite elements to evaluate the experimental results. Analyses elicited good agreement between simulation and experimental data and validated the numerical models. Moreover, the validity of the proposed rigid connection was confirmed, and the failure behavior was clarified. Finally, a full-size model of the reinforced concrete rigid-frame bridge with H-shaped steel girders was constructed and subjected to destructive loading tests to evaluate structural integrity of the proposed rigid connection.

• Advances in concrete construction
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• 제13권5호
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• pp.361-365
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• 2022

The objective of this study is to simulate the two-phase flow in pipes with various two-fluid models and determinate the shear stress. A hyperbolic shear deformation theory is used for modelling of the pipe. Two-fluid models are solved by using the conservative shock capturing method. Energy relations are used for deriving the motion equations. When the initial conditions of problem satisfied the Kelvin Helmholtz instability conditions, the free-pressure two-fluid model could accurately predict discontinuities in the solution field. A numerical solution is applied for computing the shear stress. The two-pressure two-fluid model produces more numerical diffusion compared to the free-pressure two-fluid and single-pressure two-fluid models. Results show that with increasing the two-phase percent, the shear stress is reduced.

• 한국방재안전학회논문집
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• 제16권4호
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• pp.33-43
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• 2023

장마와 같이 장기간에 내리는 강우나 단기간에 많은 양의 강우가 내리는 집중호우의 영향으로 산사태, 토석류와 같은 산지재해가 발생한다. 산사태와 토석류는 인적, 물적 피해를 야기하므로 이를 예방하기 위한 다양한 대책의 적용과 연구가 수행되고 있다. 토석류 재해 연구 중 토석류 수치모형은 비교적 간단하게 연구지역에 대한 위험도를 분석할 수 있다. 다만 경험에 의한 방정식이 적용되어 모형마다 다른 결과를 나타내고 입력변수도 모델마다 차이가 있어 수치모형의 검증은 필수적이다. 본 연구에서는 토석류 수치모형을 이용하여 토석류의 피해를 저감하기 위한 시설인 사방댐과 종단구조물인 계간수로를 반영하여 이에 따른 저감효과를 비교·분석하였다.

• 대기
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• 제24권3호
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• pp.419-432
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• 2014

An assessment of typhoon intensity predictability of numerical models was conducted to develop the typhoon intensity forecast guidance comparing with the RSMC-Tokyo best track data. Root mean square error, box plot analysis and time series of wind speed comparison were performed to evaluate the each model error level. One of noticeable fact is that all models have a trend of error increase as typhoon becomes stronger and the Global Forecast System showed the best performance among the models. In the detailed analysis in two typhoon cases [Danas (1324) and Haiyan (1330)], GFS showed good performance in maximum wind speed and intensity trend in the best track, however it could not simulate well the rapid intensity increasing period. On the other hand, ECMWF and Hurricane-WRF overestimated the typhoon intensity but simulated track trend well.