• Journal of computational fluids engineering
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• v.19 no.4
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• pp.37-44
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• 2014

A detailed satellite panel thermal model composed of more than thousands nodes can not be directly integrated into a spacecraft thermal model due to its node size and the limitation of commercial satellite thermal analysis programs. For the integration of the panel into the satellite thermal model, a reduced thermal model having proper accuracy is required. A thermal model reduction method was developed and validated by using a geostationary satellite panel. The temperature differences of main components between the detailed and the reduced thermal model were less than $1^{\circ}C$ in steady state analysis. Also, the dynamic responses of the detailed and the reduced thermal model show very similar trends. Thus, the developed reduction method can be applicable to actual satellite thermal design and analysis with resonable accuracy and convenience.

• Tunnel and Underground Space
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• v.24 no.3
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• pp.201-211
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• 2014

In the present study, the thermal performance of multiple rock caverns for large-scale thermal energy storage (TES) was numerically investigated for different separation distances between the caverns through heat transfer analysis using a computational fluid dynamics code, FLUENT. The thermal performance of multiple caverns was assessed in terms of the thermal stratification within the caverns and the heat loss to the surroundings, and the heating characteristics of the rock around the caverns were investigated. The results of numerical simulation showed that there was little difference in thermal performance between multiple TES caverns with different separation distances when the surrounding rock was less heated and it reached thermal steady-state, which represent the thermal states of the surrounding rock at the early and long-term operational stages of the TES caverns, respectively. However, as the separation distance decreased, the rock between the caverns reached thermal steady-state more quickly, and thus the heat loss from the caverns tended to converge rapidly to the value of heat loss occurred under thermal steady-state conditions in the surrounding rock. This result implies that the operating cost of heating the surrounding rock (i.e., rock heating) can be reduced with a reduction in the separation distance between multiple caverns, and suggests that the separation distance should be determined by considering the operating cost of rock heating as well as the construction cost of the caverns.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.9
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• pp.1700-1710
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• 1992

The boundary element method is applied to determine thermal stress intensity factors for a cusp crack in transient state. In the steady temperature field, numerical values of thermal stress intensity factors for a Grifith crack and a symmetric lip cusp crack in a finite body are in good agreement within .+-. 5% with the previous solutions. In transient state, the numerical values of thermal stress intensity factors for the Griffith crack are also in good agreement with the pervious solutions. In both steady and transient states, those for the symmetric lip cusp crack with the crack surface insulated or fixed to the constant temperature are calculates for various effective crack lengths, configuration parameters and uniform heat flow angles. The variations of the thermal boundary conditions of the crack surface have a effect on stress intensity factors. The signs on the values of thermal stress intensity factors can be changed in time variation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.11
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• pp.951-956
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• 2014

Steady-state thermal analysis was performed on a thermal equivalent circuit to determine the heat generation during operation of an interior permanent magnet synchronous motor (IPMSM). New machines must be compact and light and produce high torque density under extreme environmental conditions. Thermal analysis of an IPMSM is particularly important because excessive heat generated from the core and magnet reduces the IPMSM's output and has adverse effects on the durability. Therefore, steady-state thermal analysis of an IPMSM was performed for changes in the design variables using a thermal equivalent circuit. The changed variables were the axis length and thickness of the housing. The results of this method were compared with those of the finite element method to verify the accuracy and reliability.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.9
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• pp.1219-1226
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• 2000

An efficient method is developed for plunger thermal cycle analysis in repeated forming process of the TV glass. The plunger undergoes temperature fluctuation during a cycle due to the repeated contact and separation from the glass, which attains a cyclic steady state having same temperature history at every cycle. Straightforward analysis of this problem brings about more than 80 cycles to get reasonable solution, and yet hard to setup stopping criteria due to extremely slow convergence. An exponential fitting method is proposed to overcome the difficulty, which finds exponential function to best approximate temperature values of 3 consecutive cycles, and new cycle is restarted with the fitted value at infinite time. Numerical implementation shows that it reduces the number of cycles dramatically to only 6-18 cycles to reach convergence within 10 accuracy. A system for the analysis is constructed, in which the thermal analysis is performed by commercial software ANSYS, and the fitting of the result is done by IMSL library. From the parametric studies, one reveals some important facts that although the plunger cooling or the glass thickness is increased, its counter part in contact is not much affected, duo to the low thermal conductance of the glass.

• Journal of computational fluids engineering
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• v.17 no.4
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• pp.41-48
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• 2012

A numerical analysis of thermal stratification in the upper plenum of the MONJU fast breeder reactor was performed. Calculations were performed for a 1/6 simplified model of the MONJU reactor using the commercial code, CFX-13. To better resolve the geometrically complex upper core structure of the MONJU reactor, the porous media approach was adopted for the simulation. First, a steady state solution was obtained and the transient solutions were then obtained for the turbine trip test conducted in December 1995. The time dependent inlet conditions for the mass flow rate and temperature were provided by JAEA. Good agreement with the experimental data was observed for steady state solution. The numerical solution of the transient analysis shows the formation of thermal stratification within the upper plenum of the reactor vessel during the turbine trip test. The temporal variations of temperature were predicted accurately by the present method in the initial rapid coastdown period (~300 seconds). However, transient numerical solutions show a faster thermal mixing than that observed in the experiment after the initial coastdown period. A nearly homogenization of the temperature field in the upper plenum is predicted after about 900 seconds, which is a much shorter-term thermal stratification than the experimental data indicates. This discrepancy is due to the shortcoming of the turbulence models available in the CFX-13 code for a natural convection flow with thermal stratification.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.82-84
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• 2008

This paper presents the modeling and power quality analysis of Jeju island power system connected with wind farm, and thermal power plant. It is for indicating the influence of wind farm operation in steady and transient state in Jeju island power system during the HVDC system overhaul period. For the computer simulation, three kinds of main item are modeled, which are 67[MW] wind farm, thermal power plant and Jeju power load. To analyze the influence of the wind power generation to the Jeju power system, two kinds of simulations are carried out by using the PSCAD/EMTDC program. One is the steady state operation under the variable speed wind, and the other is the transient state operation when all of wind farms in Jeju island are disconnected from the Jeju power grid instantaneously on the rated power output. With the comparison of these results, it is useful for analyzing the power quality of Jeju power system versus wind power generation.

• Nuclear Engineering and Technology
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• v.30 no.1
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• pp.17-25
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• 1998

Transport of carbon and boron impurity ions parallel to magnetic field lines in the tokamak SOL (scrape-off layer) is numerically investigated for a one-dimensional steady state. The spatial distributions of density and velocity of the impurity ions in a steady state are calculated by finite difference method for a single-fluid model. The calculated results show that among forces acting on SOL particles thermal force produced tv plasma temperature gradient is a principal force determining the feature of impurity distribution profiles in the tokamak edge. However, strong collisional friction forces appearing dominant in front of the diverter plate restrain impurity ion flows due to temperature gradients from moving toward the midplane. Consequently, the stagnation point develops in the impurity flow by these two forces near the diverter region, in which ion flows change their directions. Impurity ions turn out to be accumulated at the stagnation points, where peaked profiles of highly-ionized state ions are relatively predominant over those of low-ionized state ions.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.192-198
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• 2000

Three dimensional thermal cycle analysis of the plunger is carried out in repeated forming process of the TV glass, which is continued work of two dimensional analysis where an efficient method has been proposed. The plunger undergoes temperature fluctuation during a cycle due to the repeated contact and separation from the glass, which attains a cyclic steady state having same temperature history at every cycle. Straightforward analysis of this problem brings about more than 90 cycles to get reasonable solution. An exponential function fitting method is proposed, which finds exponential function to best approximate temperature values of 3 consecutive cycles, and new cycle is restarted with the fitted value at infinite time. Number of cases are analyzed using the proposed method and compared to the result of straightforward repetition, from which one finds that the method always reaches nearly convergent solution within $9{\sim}12$ cycles, but turns around afterwards without further convergence. Two step use is found most efficient, in which the exponential fitting is carried out fer the first 12 cycles, followed by simple repetition, which shows fast convergence expending only 6 additional cycles to get the accuracy within 2 error. This reduces the computation cycle remarkably from 90 to 18, which is 80% reduction. From the parametric studies, one reveals that the overall thermal behavior of the plunger in terms of cooling parameters and time is similar to that of 2 dimensional analysis.

• Journal of Power System Engineering
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• v.10 no.4
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• pp.25-30
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• 2006

This paper represents the numerical analysis in unsteady state on the variation of diameter and environmental velocity of carbon heating source. In general heating system, the oil and sheath heater is widely used, but these systems have many problems. So, the heating source with carbon ingredient has been researched in many country about manufacture, thermal and electrical properties. In this research, the carbon heating source was studied through numerical analysis on several conditions of unsteady state, heat generation, diameter and environmental velocity. The temperature distributions at steady state are appeared as a non-proportional linear pattern with variations of environmental velocity due to the Nesselt number with convective heat flux is proportioned to 0.805 of Reynolds number. As the radius is increasing, the temperature distributions is appeared the minus tilt because of the environmental condition is cooling by constant temperature. So, the correlation equation between temperature at steady state and environmental velocity was obtained.