• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.99-102
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• 2007

NUFLEX is a general purpose program for the analysis 3D thermo/fluid flow and pre/post processor in a complex geometry. NUFLEX is composed various physical models, such as phase change(solidification/melting) and spray, MHD(Magneto Hydraulic Dynamics) models. It is possible to simulate of continuous cast iron process and spray droplet breakup/collision phenomenon. For the verification of these models, compared with the experimental data and commercial CFD code's results. The results show good agreements with experimental and comercial CFD codes's results.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.92-95
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• 2011

In manufacturing optical fibers, the process starts with the glass fiber drawing from the heated and softened silica preform in the furnace, and the freshly drawn glass fiber is still at high temperature when it leaves the glass fiber drawing furnace. It is necessary to cool down the glass fiber to the ambient temperature before it then enters the fiber coating applicator, since the hot glass fiber is known to cause several technical difficulties in achieving high quality fiber coating. As the fiber drawing speed keeps increasing, a current manufacturing of optical fibers requires a dedicated cooling unit with helium gas injection. A series of three-dimensional flow and heat transfer computations are carried out to investigate the effectiveness of fiber cooling in the fiber cooling unit. The glass fiber cooling unit is simplified into the long cylindrical enclosure at which the hot glass fiber passes through at high speed, and the helium is being supplied through several injection slots of rectangular shape along the cooling unit. This study presents and discusses the effects of helium injection rates on the glass fiber cooling rates.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.2
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• pp.19-25
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• 2004

The linear analysis for the balance of linear momentum of a structure is relatively easy to perform, but the error becomes large when the structure experiences large deformation. Therefore, the material and geometric nonlinearity need to be considered for the precise calculations in that case. The plastic flow of a ductile steel-like metal mainly transforms its dissipated mechanical energy into heat, which transfers under the first and second law of thermodynamics. This heat increases the temperature of the material and the strength of the material decreases accordingly, which affects mechanical behavior of the given structure. This paper presents a finite-strain thermo-elasto-plastic steel model. This model can handle large deformation and thermal load simultaneously, which is common during earthquake periods. Two 3-dimensional finite element analyses verify this formulation.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.2
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• pp.45-52
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• 2011

To improve fire-resistance of a high strength concrete against spalling under elevated temperature, fibers can be mixed to provide flow paths of evaporated water to the surface of concrete when heated. In this study, the experiment of a column under fire and mechanical loads is conducted and the material model for predicting temperature of reinforcement steel bar and mechanical behavior of fiber-mixed high strength concrete is suggested. The material model in previous studies is modified by incorporating physical behavior of internal concrete and thermal characteristics of concrete at the elevated temperature. Thermo-mechanical analysis of the fiber-mixed high strength concrete column is conducted using the calibrated material model. The performance of the proposed material model is confirmed by comparing thermo-mechanical analysis results with the experiment of a column under fire and mechanical loads.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.9
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• pp.907-915
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• 2008

The computational fluid dynamic analysis has been conducted for the thermo-chemical flow field in an arcjet thruster with mono-propellant Hydrazine (N2H4) as a working fluid. The Reynolds Averaged Navier-Stokes (RANS) equations are modified to analyze compressible flows with the thermal radiation and electric field. the Maxwell equation, which is loosely coupled with the fluid dynamic equations through the Ohm heating and Lorentz forces, is adopted to analyze the electric field induced by the electric arc. The chemical reactions of Hydrazine were assumed to be infinitely fast due to the high temperature field inside the arcjet thruster. The chemical and the thermal radiation models for the nitrogen-hydrogen mixture and optical thick media respectively, were incorporated with the fluid dynamic equations. The results show that performance indices of the arcjet thruster with 1kW arc heating are improved by amount of 180% in thrust and 200% in specific impulse more than frozen flow. In addition thermo-physical process inside the arcjet thruster is understood from the flow field results.

• Korean Chemical Engineering Research
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• v.52 no.2
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• pp.233-239
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• 2014

The slagging which generated from ash deposition on furnace wall and tube in boiler reduces the heat transfer efficiency and damages to safety of boiler. The slag flow behavior in boiler is affected by melting temperature which is related to ash compositions. In this study, the behavior of slag is researched by using ash fusibility test, called TMA (Thermo-Mechanical Analysis). The technique measures the percentage shrinkage as the function of temperature, T25%, T50%, T75%, T90%. These temperatures indicate different stages of melting. Then, the effect of ash chemical compositions measured from XRF (X-ray Fluorescence Spectrometer) to ash fusion temperatures is discussed. Among the chemical compositions, refractory and fluxing influence on ash fusibility is described. High levels of refractory component and limited amount of fluxing components ($Fe_2O_3$, $K_2O$, CaO) increase overall melting temperatures. High $SiO_2/Al_2O_3$ ratio decrease high melting temperatures (T75%, T90%). Meanwhile, the presence of reasonable levels of fluxing components reduces overall melting temperature. A presence of fluxing component such as $K_2O$ and CaO is found to decrease the T25% values significantly. From this research, it is possible to make a reasonable explanation and prediction of ash fusion characteristic from analysis of TMA results and ash chemical compositions.

• Tunnel and Underground Space
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• v.16 no.1 s.60
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• pp.38-49
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• 2006

LNG storage in lined rock cavern demands various techniques concerned with rock mechanics, thermo-mechanics and hydrogeology in design, construction and maintenance stage. LNG pilot cavern was constructed in Daejeon in order to verify these techniques. In this paper, evaluation of drainage system and ice ring formation was studied by numerical simulation. By Modflow analysis in the viewpoint of aquifer and Seep/W analysis in the viewpoint of flow system, it was verified that the drainage system in the pilot cavern was efficiently operated. Since ice ring formation can be simulated by interactive relation between heat transfer and water flow, coupled analysis of those was performed. In this analysis, the position of ice ring was presumed and it was demonstrated that the formation is affected by velocity and direction of groundwater flow.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.335-338
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• 2009

The process of charging an oxidizer in the liquid propellant rocket can divide into the cooling of the oxidizer tank, the high flow charge, the small flow charge, and the replenishment charge for the correction of temperature. The oxidizer of the Naro(KSLV-I) first stage uses the liquid oxygen. And the flow rate and the temperature specification corresponding to each charge mode are presented for the requirement. The flow throttling valve and heat exchanger are installed in the oxidizer filling system in order to satisfy this kind of the flow rate and temperature requirement specification. In this research, by using the Flowmaster which is a commercial one-dimension thermo-fluidic analysis program, one dimensional flow system analyses was performed to predict the exact flow rate at each specific mode. Also, the flow rate correction sensitivity of the flow control valves was analytically determined to satisfy the flow condition refinement at each mode within the limited certification test.

• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.613-624
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• 2013

Multi-dimensional two-phase phenomena occur in many industrial applications, particularly in a nuclear reactor during steady operation or a transient period. Appropriate modeling of complicated behavior induced by a multi-dimensional flow is important for the reactor safety analysis results. SPACE, a safety analysis code for thermal hydraulic systems which is currently being developed, was designed to have the capacity of multi-dimensional two-phase thermo-dynamic phenomena induced in the various phases of a nuclear system. To validate the performance of SPACE, a two-dimensional two-phase flow test was performed with slab geometry of the test section having a scale of $1.43m{\times}1.43m{\times}0.11m$. The test section has three inlet and three outlet nozzles on the bottom and top gap walls, respectively, and two outlet nozzles installed directly on the surface of the slab. Various kinds of two-dimensional air/water flows were simulated by selecting combinations of the inlet and outlet nozzles. In this study, two-dimensional two-phase void fraction profiles were quantified by measuring the local gap impedance at 225 points. The flow conditions cover various flow regimes by controlling the flow rate at the inlet boundary. For each selected inlet and outlet nozzle combination, the water flow rate ranged from 2 to 20 kg/s, and the air flow rate ranged from 2.0 to 20 g/s, which corresponds to 0.4 to 4 m/s and 0.2 to 2.3 m/s of the superficial liquid and gas velocities based on the inlet port area, respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.973-976
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• 1997

Process behavior in metal cutting results from the chip formation process which is not easily observable and measurable during machining. By means of the finite element method chip formation in orthogonal metal cutting is modeled. The reciprocal interaction between mechanical and thermal loads is taken into consideration by involving the thermo-viscoplastic flow behavior of workpiece material. Local and temporal distributions of stress and temperature in the cutting zone are calculated depending on the cutting parameters. The calculated cutting forces and temperatures are compared with the experimental results obtarned from orthogonal cutting of steel AISl 4140. The model can be applied in process design for selection of appropriate tool-workpiece combination and optimum cutting conditions in term of mechanical and thermal loads.