• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.5
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• pp.47-57
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• 2012

A modified ignition and growth(I&G) model which is necessary to simulate the combustion phenomena of energetic materials and an analytical model determining the unknown parameters of the reaction rate equation are proposed. The modified I&G model sustains important physical implications with overcoming some problems of previous rate equations. This rate model consists of ignition term which represents the formation of the hotspot due to void collapse and growth term which means the shock to detonation transition phenomena. Also, the theoretical model is used to investigate the combustion characteristics of certain energetic materials before running Hydrocode by pre-determination of unknown parameter, $b,\;G,\;x,\;I$. The analytical model provides efficient and highly accurate results rather than previous method which simulated the unconfined-rate-stick via the numerical means.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.331-341
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• 2012

A modified Ignition and Growth(I&G) model which is necessary to simulate the combustion phenomena of energetic materials and an analytical model determining the unknown parameters of the reaction rate equation are proposed. The modified I&G model sustains important physical implications with overcoming some problems of previous rate equations. This rate model consist of Ignition term which represent the formation of the hotspot due to void collapse and Growth term which means the shock to detonation transition phenomena. Also, the theoretical model is used to investigate the combustion characteristics of certain energetic materials before running Hydrocode by pre-determination of unknown parameter, b, G, x, I. The analytical model provides efficient and highly accurate results rather than previous method which simulated the unconfined-rate-stick via the numerical means.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.890-898
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• 2001

4H-SiC(silicon carbide) MESFET large signal model was studied using modified Materka-Kacprzak large signal MESFET model. 4H-SiC MESFET device simulation have been conducted by Silvaco\`s 2D device simulator, ATLAS. The result is modeled using modified Materka large signal model. simulation and modeling results are -8 V pinch off voltage, under V$\_$GS/=0 V, V$\_$DS/=25 V conditions, I$\_$DSS/=270 mA/mm, G$\_$m/=52.8 ms/mm were obtained. Through the power simulation 2 GHz, at the bias of V$\_$GS/-4 V md V$\_$DS/=25 V, 10 dB Gain, 34 dBm (1dB compression point)output porter, 7.6 W/mm power density, 37% PAE(power added efficiency) were obtained.7.6 W/mm power density, 37% PAE(power added efficiency) were obtained.d.

• Proceedings of the IEEK Conference
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• 2001.06b
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• pp.229-232
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• 2001

4H-SIC(silicon carbide) MESFET large signal model was studied using modified Materka-Kacprzak large signal MESFET model. 4H-SiC MESFET device simulation have been conducted by Silvaco's 2D device simulator, ATLAS. The result is modeled using modified Materka large signal model. simulation and modeling results are -8V pinch off voltage, under $V_{GS=0V}$, $V_{DS=25V}$ conditions, $I_{DSS=270㎃}$mm, $G_{m=45㎳}$mm were obtained. Through the power simulation 2GHz, at the bias of $V_{GS=-4V}$ and $V_{DS=25V}$, 10dB Gain, 34dBm(1dB compression point)output power, 7.6W/mm power density, 37% PAE(power added efficiency) were obtained.d.d.d.

• Journal of the Korean Society of Clothing and Textiles
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• v.38 no.3
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• pp.347-354
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• 2014

The color appearance of a yarn-dyed woven fabric depends on the color of the yarn as well as on the weave structure. Predicting the final color appearance or formulating the recipe is a difficult task, considering the interference of colored yarns and structure variations. In a modern fabric design process, the intended color appearance is attained through a digital color methodology based on numerous color data and color mixing recipes (i.e., color prediction models, accumulated in CAD systems). For successful color reproduction, accurate color prediction models should be devised and equipped for the systems. In this study, the final colors of yarn-dyed woven fabrics were predicted using six geometric-color mixing models (i.e., simple K/S model, log K/S model, D-G model, S-N model, modified S-N model, and W-O model). The color differences between the measured and the predicted colors were calculated to evaluate the accuracy of various color models used for different weave structures. The log K/S model, D-G model, and W-O model were found to be more accurate in color prediction of the woven fabrics used. Among these three models, the W-O model was found to be the best one as it gave the least color difference between the measured and the predicted colors.

• Journal of the Korean Chemical Society
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• v.55 no.6
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• pp.1024-1029
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• 2011

PVA/silica hybrid xerogels were synthesized by sonohydrolysis of a mixture of 2-way catalyzed TEOS and water solution of PVA. PVA was successfully removed from the xerogels through calcination and its removal was confirmed through TGA analysis of the calcined gel. Microstructure of the gels was studied through SEM, XRD and FTIR. Nitrogen sorption studies were conducted to find out surface area of different samples. It was found out that the samples having PVA removed through calcinations have higher surface area (411.64 $m^2$/g) than the samples (353.544 $m^2$/g) synthesized without any PVA. Adsorption properties of these xerogels synthesized by using different ratios of components were studied by taking Rhodamine G6 as a model adsorbate. The experiments were conducted at room temperature ($25^{\circ}C$). UV visible spectroscopy was used to measure the concentration of the dye before and after adsorption. The adsorption data of Rhodamine G6 on PVA modified silica is described by the Freundlich's adsorption model.

• Imaging Science in Dentistry
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• v.42 no.3
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• pp.163-167
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• 2012

Purpose: ANSI/ADA has established standards for adequate radiopacity. This study was aimed to assess the changes in radiopacity of composite resins according to various tube-target distances and exposure times. Materials and Methods: Five 1-mm thick samples of Filtek P60 and Clearfil composite resins were prepared and exposed with six tube-target distance/exposure time setups (i.e., 40 cm, 0.2 seconds; 30 cm, 0.2 seconds; 30 cm, 0.16 seconds, 30 cm, 0.12 seconds; 15 cm, 0.2 seconds; 15 cm, 0.12 seconds) performing at 70 kVp and 7 mA along with a 12-step aluminum stepwedge (1 mm incremental steps) using a PSP digital sensor. Thereafter, the radiopacities measured with Digora for Windows software 2.5 were converted to absorbencies (i.e., A=-log (1-G/255)), where A is the absorbency and G is the measured gray scale). Furthermore, the linear regression model of aluminum thickness and absorbency was developed and used to convert the radiopacity of dental materials to the equivalent aluminum thickness. In addition, all calculations were compared with those obtained from a modified 3-step stepwedge (i.e., using data for the 2nd, 5th, and 8th steps). Results: The radiopacities of the composite resins differed significantly with various setups (p<0.001) and between the materials (p<0.001). The best predicted model was obtained for the 30 cm 0.2 seconds setup ($R^2$=0.999). Data from the reduced modified stepwedge was remarkable and comparable with the 12-step stepwedge. Conclusion: Within the limits of the present study, our findings support that various setups might influence the radiopacity of dental materials on digital radiographs.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1993.04a
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• pp.183-190
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• 1993

The seismic response of the reactor structures depends on the dynamic charact-eristics of the structures and the input earthquake loadings. The stuctural integ-rity of the reactor internal components can be verified by the dynamic response analyses to implement the effects of the design loadings like earthquakes. The sensitivity analyses of the dynamic characteristics for the analytical model of reactor structures considering the possible variations of the stiffnesses of the CSB upper flange and the snubber were performed to improve the dynamic characteri-stics of the structures against seismic loading. And to enhance the structural design margin of the reactor internal components the nonlinear time history analyses were attempted for the modified analytical model, and the results were compared between the reference model and the modified ones.

• Journal of Biosystems Engineering
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• v.37 no.4
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• pp.233-244
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• 2012

Purpose: The kinetic evaluation was performed for swine manure (SM) degradation and biogas generation. Methods: The SM was anaerobically digested using batch digesters at feed to inoculum ratio (F/I) of 1.0 under mesophilic conditions ($36.5^{\circ}C$). The specific gas yield was expressed in terms of gram total chemical oxygen demand (mL/g TCOD added) and gram volatile solids added (mL/g VS added) and their effectiveness was discussed. The biogas and methane production were predicted using first order kinetic model and the modified Gompertz model. The critical hydraulic retention time for biomass washout was determined using Chen and Hashimoto model. Results: The biogas and methane yield from SM was 346 and 274 mL/ TCOD added, respectively after 100 days of digestion. The average methane content in the biogas produced from SM was 79% and $H_2S$ concentration was in the range of 3000-4108 ppm. It took around 32-47 days for 80-90% of biogas recovery and the TCOD removal from SM was calculated to be 85%. When the specific biogas and methane yield from SM (with very high TVFA concentration) was expressed in terms of oven dried volatile solids (VS) basis, the gas yield was found to be over estimated. The difference in the measured and predicted gas yield was in the range of 1.2-1.5% when using first order kinetic model and 0.1% when using modified Gompertz model. The effective time for biogas production ($T_{Ef}$) from SM was calculated to be in the range of 30-45 days and the critical hydraulic retention time ($HRT_{Critical}$) for biomass wash out was found to be 9.5 days. Conclusions: The modified Gompertz model could be better in predicting biogas and methane production from SM. The HRT greater than 10 days is recommended for continuous digesters using SM as feedstock.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.1
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• pp.87-100
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• 1997

The ability of turbulence model to accurately describe the complex characteristics of the flow field and the fuel spray is of great importance in the optimum design of diesel engine. The numerical simulations of the flow field and the spray characteristics within the combustion chamber of direct injection model entgine are performed to examine the applicability of turbulence model. The turbulence models used are the RNG $\varepsilon$ model and the modified $\varepsilon$ model which included the compressibility effect due to the compression/expansion of the charges. In this study, the predicted results in the quiescent condition of direct injection model engine show reasonable trends comparing with the experimental data of spray characteristics, i. e., spray tip penetration, spray tip velocity. The results of eddy viscosity obtained using the $\varepsilon$ model in the spray region is significantly larger than that obtained using the RNG $\varepsilon$ model. The application of the RNG model seems to have some potential for the simulations of the spray characteristics, e. g., spray tip penetration, spray tip velocity, droplets distribution over the $\varepsilon$ model.