• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2257-2265
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• 1996

In the cold rolling mill, it is very important that a constrained static flow stress of rolled strip and rolling force calculation model be exactly considered to improve an prediction accuracy for rolling forces. Therefore, in this study, the values of the constrained static flow stress are used by deriving the regression equation which is a function of rolling conditions(FDT, CT) and chemical compositions(C, Si, Mn), previously applied by making the tables of yield strength for hot coils with size. And with the consideration that an elastic deformation part of an rolled strip appears at the entry and delivery side of the contacting area between the work roll and rolled strip is calculated. By applying these methods, the more accurate prediction for rolling force is obtained. As a results, the deviation of thickness is significantly reduced in the rolling direction.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.765-768
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• 2009

In this work, we prepared the activated multi-walled carbon nanotubes (Acti-MWNTs) with well developed physical surface structures, high specific surface area, and higher adsorption capacity by a physical activation process, in order to enhance the hydrogen storage capacity. The Acti-MWNTs' changes in the crystalline phase and in their lattice distortions were characterized by X-ray diffraction (XRD). The textural properties of the Acti-MWNTs were investigated by a nitrogen adsorption isotherms by Brunauer-Emmett-Teller (BET) equation and Harvath-Kawazoe (H-K) calculation, respectively. The hydrogen storage capacity of the Acti-MWNTs was investigated by BEL-HP at 298 K/100 bar. The hydrogen storage capacity of the Acti-MWNTs was improved with the physical activation, resulted from the formation of new hydrogen-favorable sites on the Acti-MWNT surfaces. In conclusion, the physical activation was one of the effective method to enhance the hydrogen storage capacity of the MWNTs.

• Geomechanics and Engineering
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• v.14 no.5
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• pp.439-451
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• 2018

The stress path characteristics of surrounding rock in the formation of gob were analysed and the unloading was solved. Taking Chengchao Iron Mine as the engineering background, the model for analysing the instability of deep gob was established based on the mechanism of stress relief in deep mining. The energy evolution law was investigated by introducing the local energy release rate index (LERR), and the energy criterion of instability of surrounding rock was established based on the cusp catastrophe theory. The results showed that the evolution equation of the local energy release energy of the surrounding rock was quartic function with one unknown and the release rate increased gradually during the mining. The calculation results showed that the gob was stable. The LERR per unit volume of the bottom structure was relatively smaller, which mean the stability was better. The LERR distribution showed that there was main energy release in the horizontal direction and energy concentration in the vertical direction which meet the characteristics of deep mining. In summary, this model could effectively calculate the stability of surrounding rock in the formation of gob. The LERR could reflect the dynamic process of energy release, transfer and dissipation which provided an important reference for the study of the stability of deep mined out area.

• Steel and Composite Structures
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• v.17 no.3
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• pp.287-303
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• 2014

8 steel reinforced concrete (SRC) columns with the encased steel ratio of 13.12% and 15.04% respectively were tested under the test axial load ratio of 0.33-0.80 and the low-frequency cyclic lateral loading. The cross sectional area of composite columns was $500mm{\times}500mm$. The mechanical properties, failure modes and deformabilities were studied. All the specimens produced flexure failure subject to combined axial force, bending moment and shear. Force-displacement hysteretic curves, strain curves of encased steels and rebars were obtained. The interaction behavior of encased steel and concrete were verified. The hysteretic curves of columns were plump in shapes. Hysteresis loops were almost coincident under the same levels of lateral loading, and bearing capacities did not change much, which indicated that the columns had good energy-dissipation performance and seismic capacity. Based on the equilibrium equation, the suggested practical calculation method could accurately predict the flexural strength of SRC columns with cross-shaped section encased steel. The obtained M-N curves of SRC columns can be used as references for further studies.

• Korean Journal of Optics and Photonics
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• v.4 no.1
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• pp.101-107
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• 1993

We carried out the useful theoretical calculation for the optimum design of a 1.48 ${\mu}m$ diode laser pumped E$r^{3+}$ doped fiber amplifier. The model we established is based on the rate equations of three level laser system and the overlap integral between fundamental mode L$P_{01}$ and E$r^{3+}$ doped area. We determined several fiber parameters (N.A., V value, fiber length, E$r^{3+}$ concentration, cutoff wavelength etc.) for the optimum design of a high optical gain. We found that our theoretical results are very useful to the design of E$r^{3+}$ doped fiber used in EDFA.

• Journal of Korea Water Resources Association
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• v.32 no.4
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• pp.427-435
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• 1999

The Clark unit hydrograph is a three parameter synthetic unit hydrograph procedure that can be used in flood hydrology. The present work is an attempt to estimate parameters of the Clark model in ungaged basin by means of relationships that provides for the hydrologic similarity. The time area concentration curve was determined by analytic method and the Clark model was generalized by being made dimensionless form. Calculation of the concentration time was made with the formula fractal concept used, and the storage coefficient was estimated by the empirical and regional equation. Evaluation on Dongok basin was performed to prove the validity of the proposed model. The derived hydrograph predicted the observed hydrograph fairly well.

• Water for future
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• v.29 no.4
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• pp.199-208
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• 1996

The multiple flow direction algorithm to calculate the spatial variation of the saturation tendency, i.e. topographic index, is integrated into the Geogrphic Information System, GRASS. A procedure is suggested to consider the effect of a tile system on calculating the topographic index. A small agricultural subwatershed (3.4$\textrm{km}^2$) is used for this study. The impact of a tile system on the groundwater table can be effectively considered by the Laplace's equation to the DEM. The analysis shows that a tile system has a high degree of saturation compared to the case without tile drainage, and the predicted riparian area is well fitted to the actual watershed condition. A procedure is suggested to consider the effect of tile system on calculating the topographic index.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.803-810
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• 2007

An analytical method capable of predicting various stress-strain responses in axially loaded concrete confined with FRP (fiber reinforced polymers) composites in a rational manner is presented. Its underlying idea is that the volumetric expansion due to progressive microcracking in mechanically loaded concrete is an important measure of the extent of damage in the material microstructure, and can be utilized to estimate the load-carrying capacity of concrete by considering the corresponding accumulated damage. Following from this, an elastic modulus expressed as a function of area strain and concrete porosity, the energy-balance equation relating the dilating concrete to the confining device interactively, the varying confining pressure, and an incremental calculation algorithm are included in the solution procedure. The proposed method enables the evaluation of lateral strains consecutively according to the related mechanical model and the energy-balance equation, rather than using an empirically derived equation for Poisson's ratio or dilation rate as in other analytical methods. Several existing analytical methods that can predict the overall response were also examined and discussed, particularly focusing on the way of considering the volumetric expansion. The results predicted by the proposed and Samaan's bilinear equation models correlated with observed results with a reasonable degree, however it can be judged that the latter is not capable of predicting the response of lateral strains correctly due to incorporating the initial Poisson's ratio and the final converged dilation rate only. Further, the proposed method seems to have greater benefits in other applications by the use of the fundamental principles of mechanics.

• Journal of the Korean Society of Food Science and Nutrition
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• v.34 no.2
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• pp.196-201
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• 2005

The aim of this study was to confirm the validity of predictive equations for the calculation of basal energy expenditure (BEE). One hundred twenty female college students were participated in this study. The resting energy expenditure (REE) was measured by indirect calorimetry for 30 minutes following an 12 hour overnight fasting. Among the available equations for predict BEE, Harris-Benedict, WHO/FAO/UNU and Cunningham methods were selected. Body composition was estimated by bioelectrical impedance analysis (BIA) for the equation of predicted BEE. The mean of measured REE was 1257.2$\pm$147.9 kcal/day, while the predicted value by Harris-Benedict, WHO/FAO/UNU and Cunningham were 1373.3$\pm$45.4 kcal/day, 1290.0$\pm$61.7 kcal/day and 1187.6$\pm$49.2 kcal/day, respectively. The Cunningham equation was more closed to measured values than Harris-Benedict and WHO/FAO/UNU equation by the correlation coefficient. Comparing Pearson's correlation coefficients, fat-free mass (FFM), body surface area (BSA) and body weight were higher than others such as height, body mass index (BMI), fat and fat%. The FFM's correlation coefficient was the highest as 0.74. Thus, the conclusion of this study suggested that the main determinant of BEE was FFM, and we derived a prediction equation as follows: BEE=-569.86+48.27 (FFM).

• Tribology and Lubricants
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• v.31 no.6
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• pp.302-307
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• 2015

The use of turbocharger in internal combustion engines has increased as it is a key components for improving system efficiency without increasing engine size. Because of increasing demand, many studies have evaluated rotordynamic performance so as to increase rotation speed. This paper presents a linear and nonlinear analysis model for a turbocharger rotor supported by a floating ring bearing. We constructed rotor model by using the finite element method and approximated bearings as being infinitely short. In the linear model, we considered fluid film force as stiffness and damping element. In nonlinear analysis, calculation of the fluid film force involved solving the time dependent Reynolds equation. We verified the developed model by comparing the results to those of previous research. The analysis results show that there are four unstable modes, which are rigid body modes combining ring and rotor motion. As the rotating speed increases, the logarithmic decrement shows that certain unstable modes goes into the stable area or the stable mode goes into the unstable area. These unstable modes appear as sub-synchronous vibrations in nonlinear analysis. In nonlinear analysis frequency jump phenomenon demonstrated in several experimental studies appears. The analysis results also showed that frequency jump phenomenon occurs when the vibration mode changes and the sequence of unstable mode matches the linear analysis result. However, the natural frequency predicted using linear analysis differs from those obtained using nonlinear analysis.