• 제어로봇시스템학회:학술대회논문집
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• 1991.10b
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• pp.1639-1645
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• 1991

Because of the important role LD converters play in the production of high quality steel, various dynamic models have been attempted in the past by many researchers not only to understand the complex chemical reactions that take place in the converter process but also to assist the converter operation itself using computers. And yet no single dynamic model was found to be completely satisfactory because of the complexity involved with the process. The process indeed involves dynamic energy and mass balances at high temperatures accompanied by complex chemical reactions and transport phenomena in the molten state. In the present study, a mathematical model describing the dynamic behavior of LD converter process has been developed. The dynamic model describes the time behavior of the temperature and the concentrations of chemical species in the hot metal bath and slag. The analysis was greatly facilitated by dividing the entire process into three zones according to the physical boundaries and reaction mechanisms. These three zones were hot metal (zone 1), slag (zone 2) and emulsion (zone 3) zones. The removal rate of Si, C, Mn and P and the rate of Fe oxidation in the hot metal bath, and the change of composition in the slag were obtained as functions of time, operating conditions and kinetic parameters. The temperature behavior in the metal bath and the slag was also obtained by considering the heat transfer between the mixing and the slag zones and the heat generated from chemical reactions involving oxygen blowing. To identify the unknown parameters in the equations and simulate the dynamic model, Hooke and Jeeves parttern search and Runge-Kutta integration algorithm were used. By testing and fitting the model with the data obtained from the operation of POSCO #2 steelmaking plant, the dynamic model was able to predict the characteristics of the main components in the LD converter. It was possible to predict the optimum CO gas recovery by computer simulation

• Journal of Korea Water Resources Association
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• v.33 no.5
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• pp.551-559
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• 2000

In order to diagnose the water environment and assess the water quality restoration, long term trend of water environment has been surveyed at 3-R stations from 1994 to 1999 in Lake Shihwa. Annual mean values of $COD_{Mn}$, Chlorophyll a, total nitrogen, total phosphorus and Secchi depth are ranged in 5.2-15.1 mg/L, 7.3-14R.1 jlg/L, 1.50-4.84 mgN/L, 0.055-0.281 mgP/L and 0.5 -1.4 m, respectively, during the study periods. Carson's trophic state indeies were varied from mesotrophy in 1994 and 1995, hyper-eutrophy in 1996 and 1997, to meso eutrophy in 199R and 1999. After dike construction, water quality were rapidly deteriorated by allochthonous and autochthonous loading of high nutrients and organic carbon. Eutrophication phenomena were characterized by massive phytoplankton blooms and high concentration of COD. However, after onset of restoration program, lake water quality was rapidly restored to the level of just after sea-dike construction. The diversion of waste water inflowing from the Panwol and the Sihwa industrial districts which was started from March, 1997 has contributed to improve water quality in the surface layer. And the tidal mixing (sea water inflowing) through the continuous gate operation was the most effective measure to the whole lake restoration.ration.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.120-125
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• 2002

In the preceding tests using the KSR-III Sub.(I) engines, it was observed that the heat resistant capability of the engines was not enough for the mission. So Sub.(I) Mod. engines were designed and tested. The Sub.(I) Mod. engines have three major design parameters - the arrangement of main injectors, the impinging angle of main injectors and thermal barrier coating. More than twenty experiments were carried on to evaluate engine performance and heat resistance capability with respect to design parameters. In this study, the test results are introduced. Analysing the result of Sub.(I) engine tests, it is found that decreasing the impinging angle, adopting the H-type arrangement(rather than radial type arrangement) and adopting the thermal barrier coating can increase heat resistance capacity substantially. Also, engine performance evaluation is conducted using specific impulse and characteristic velocity parameter. The results show that the performance variation is small(about 5%) and the performance is better in the case of radial arrangement. It is suspected that these phenomena are caused by the change of flame structure atomization mixing characteristic of sprays and the distortion of recirculation zone. Also from the low frequency instability point of view, it is observed that reducing the impinging angle and adopting the H type arrangement can increase the instability characteristics.

• Korean journal of food and cookery science
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• v.20 no.6 s.84
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• pp.598-606
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• 2004

The application of Dongchimi liquid to Naengmyon broth to improve its eating quality was scientifically explored by reviewing the quality of the product properties. Primarily, the optimum fermentation conditions for Dongchimi from which the liquid portion was extracted were pursued and the optimum mixing ratio sought on the basis of the product physicochemical properties. The liquid portions, periodically extracted from Dongchimi at intervals of two or five days, during fermentation at $10^{\circ}C$, were added to Naengmyon broth. The treatments were prepared at three levels namely, basic broth only ('A') and with ratios of Dongchimi liquid to basic broth of 3:7 (v/v, 'B') and 5:5 (vfv, 'C'). As a typical phenomenon of kimchi fermentation, a gradual decrease in the pH with increasing total acidity was observed as the fermentation of the Dongchimi progressed. At $10^{\circ}C$, the optimum ripening was obtained from day 8, and continued until day 15, when the pH was maintained at about 3.8 to 4.0. The total vitamin C and reducing sugar contents increased until the 13th-day of fermentation, but then decreased thereafter. The turbidity and solid content of the Dongchimi liquid increased with progression of the fermentation. With respect to the color values, the lightness (L) decreased, with increases in the redness (a), yellowness (b) and total color difference $({\Delta}E)$ during fermentation. Most of these observed phenomena for the Naengmyon broth substituted with $30\%$ (Treatment 'A') and $50\%$ (Treatment 'B') Dongchimi liquid, with different storage periods, confirmed the previous fermentation patterns of Dongchimi. A decrease in the pH with increasing total acidity, as well as gradual increases in the total vitamin C and reducing sugars (glucose and fructose) up to the 13th-day of fermentation were accompanied by subsequent declining patterns. The turbidity and solid content of the mixed broth also increased with increasing Dongchimi liquid fermentation period. With respect to the color of the mixed broth, the lightness was decreased, while the redness, yellowness and total color difference increased with increasing Dongchimi liquid fermentation period. It was also proven that the addition of slightly over-ripened Dongchimi liquid to the Naengmyon broth was more preferable.

• Korean journal of food and cookery science
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• v.21 no.1 s.85
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• pp.1-11
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• 2005

The application of Dongchimi liquid into Naengmyon broth for the improved eating quality of Naengmyon was scientifically explored by reviewing the quality properties of the product. Primarily, the optimum fermentation conditions for Dongchimi from which the liquid portion was extracted were pursued and the optimum mixing ratio was sought on the basis of sensory and microbiological properties of the product. The liquid portions which had been periodically extracted from Dongchimi at intervals of two or five days during fermentation at $10^{\circ}C$ were added to Naengmyon broth. The treatments were prepared with three levels, namely, basic broth only('A') and the ratios of 3:7(v/v, 'B') and 5:5(v/v, 'C') of Dongchimi liquid and basic broth, respectively. According to assessments of Dongchimi liquid on taste and intensity based on sensory analyses, the organoleptic factors such as color, smell, sour taste, carbonated taste, and overall acceptability were given higher values from day 11 to day 17 in all items. As for the assessment of Dongchimi liquid on intensity, color, sour odor, moldy odor, and carbonated taste have shown the increasing scores during with high intensities while those for clearness has stayed low. Most of the phenomena observed from the Naengmyon broth substituted with $30\%$ (Treatment 'A') and $50\%$ (Treatment 'B') of Dongchimi liquids with different storage periods ensued much of the previous fermentation pattern of Dongchimi itself. Organoleptic assessment on taste and its intensity showed that better(the best) scores could be obtained at between day 16$\~$25(17) and 13$\~$20(15) for Treatments A and B, respectively. The intensity scores of taste for color, smell, carbonated taste, sour taste, and mouthfeel were increased while those for clearness, palatability, and meaty ones were decreased with lapse of fermentation. The numbers of total cell and lactic acid bacterial counts of Dongchimi has increased until day 13 and then decreased in the later stages. Total cell count and lactic acid bacterial counts of Naengmyon broth also increased until the 13th day and then they began to decrease. It was also proven that slightly over-ripened Dongchimi liquid was more preferable for adding into Naengmyon broth. Granting the optimum ripening period of Dongchimi liquid itself to be 13 days, both Treatment A and Treatment B were evenly favored using Dongchimi liquids slightly over-ripened at days 13 to 17. However, Treatment A was more favored than Treatment B when Dongchimi liquid over-ripened for 20 to 26 days was used.

• Polymer(Korea)
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• v.30 no.1
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• pp.85-89
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• 2006

The effect of vapor grown carbon fiber (VGCF) contents on electrical and rheological properties of VGCF filled polyphenylene sulfide (PPS) composites prepared through melt mixing using a twin screw exruder was studied. This method was proved to be quite effective to produce good dispersion of VGCF in the matrix even for highly filled PPS. From the dependence of the electrical conductivity on VGCF content, the percolation phenomena began to occur above $10\;wt\%$. While there is only a marginal increase of viscosity for 1 and $5\;wt\%$ VGCF filled PPS, the composites containing $10\;wt\%$. While VGCF showed abrupt increase in viscosity as well as flattening of frequency vs modulus curve, indicating a transition from a liquid-like to a solid-like behavior due to the creation of VGCF network. This result agrees well to the fact that the network formation in the composite can be composite by rheological property dependence on filler content as well as by electrical conductivity measurement.

• Nuclear Engineering and Technology
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• v.14 no.4
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• pp.186-195
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• 1982

The steam line break accident for Kori Unit 1 is analyzed by a code SYSRAN which calculates nuclear power and heat flux using the point kinetics equation and the lumped-parameter model and calculates system transient using the mass and energy balance equation with the assumption of uniform reactor coolant system pressure. The 1.4 f $t^2$ steam line break accident is analyzed at EOL (End of Life), hot shutdown condition in which case the accident would be most severe. The steam discharge rate is assumed to follow the Moody critical flow model. The results reveal the peak heat flux of 38% of nominal full power value at 60 second after the accident initiates, which is higher than the FSAR result of 26%. Trends for the transient are in good agreement with FSAR results. A sensitivity study shows that this accident is most sensitive to the moderator density coefficient and the lower plenum mixing factor. The DNBR calculation under the assumption of $F_{{\Delta}H}$=3.66, which is used in the FSAR with all the control and the shutdown assemblies inserted except one B bank assembly and of Fz=1.55 shows that minimum DNBR reaches 1.62 at 60 second, indicating that the fuel failure is not anticipated to occur. The point kinetics equation, the lumped-parameter model and the system transient model which uses the mass and energy balance equation are verified to be effective to follow the system transient phenomena of the nuclear power plants.lear power plants.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.1
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• pp.39-50
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• 2003

This study aims to figure out water quality impacts due to sudden disturbances of sediments during dike construction in land reclamation for the northern part of the Siwhaho Lake where heavily deteriorated settlements from upstream loadings are outstanding. We exploit a 3-D water quality model CE-QUAL-ICM combined with a hydrodynamic model TIDE3D. Simulations are done accounting water-sediment interaction in a 4-$\sigma$ layers. Long-term simulation for 1-year shows that bottom layers around the disturbance location are only affected and marks very high concentration. Complete vertical mixing appears at least 5km apart to downward due to complex effects of geometry, bathymetry and river inflows. It should be addressed that existing condition of the Siwhaho Lake stands for high concentration of COD and TP in winter and spring due to relatively high incoming loadings, however the effect of sediment disturbances yields reverse phenomena, i.e., impacts of dike construction arise greatly in summer and fall. Refined grid system consisting of 150m${\times}$150m rectangular grid, which is doubled system compared to previous study (Suh et al.,2002), gives affordable results by reducing flux differences through a cell especially in front of gate.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.1-10
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• 2020

The application of multiphase flows is increasingly being applied to analyze phenomena such as single phase flows where the fluid boundary changes continuously over time or the problem of mixing a liquid phase and a gas phase. In particular, multiphase flow models that take into account incompressible Newtonian fluids for liquid and gas are often applied to solve the problems of the free water surface such as wave fields. In general, multi-phase flow models require time-based the surface tracking of each fluid's phase boundary, which determines the accuracy of the final calculation of the model. This study evaluates the advection performance of representative VOF-type boundary tracking techniques applied to various CFD numerical codes. The effectiveness of the FCT method to control the numerical flux to minimize the numerical diffusion in the conventional VOF-type boundary tracking method and advection calculation was mainly evaluated. In addition, the possibility of tracking performance of free surface using CIP method (Yabe and Aoki, 1991) was also investigated. Numerical results show that the FCT-VOF method introducing an anti-diffusive flux to precent excessive diffusion is superior to other methods under the confined conditions in this study. The results from this study are expected to be used as an important basic data in selecting free surface tracking techniques applied to various numerical codes.

• Journal of the Korean Society of Food Science and Nutrition
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• v.33 no.5
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• pp.880-887
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• 2004

This study was carried out to examine the effect of added Doenjang on wheat flour dough and gluten rheological properties using Micro-extensigraph method and correlation between factors relating with Doenjang or dough rheology and bread Quality. There were big differences in pretense activity and free amino acid contents among seven commercial Doenjangs. The addition of Doenjang to wheat flour dough required increased mixing time for gluten development. Dry gluten content increased significantly with addition of less than 5.0% of Doenjang powder. As the amount of Doenjang powder increased, dough peak force decreased and extensibility increased up to a certain level an then decreased, producing the weak dough. This phenomena was seen more obviously in wet gluten than wheat flour dough. Especially, the Doeniang having high pretense activity and high cystein content, caused highly extensible weak dough resulting in bread with high loaf volume and tender texture at the levels of 2.5% added Doenjang. Increase of dry gluten content and extensibility of wheat flour dough or wet gluten positively correlated (r=0.76, 0.91, 0.93), with loaf volume and negatively with hardness values, respectively. Therefore, it was concluded that improvement of bread quality with Doenjang resulted from increase of gluten content and dough extensibility.