• Proceedings of the KIEE Conference
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• 1995.07b
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• pp.817-819
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• 1995

Applied by periodic Stimulating Currents in Bonhoeffer-Van der Pol(BVP) model, chaotic and periodic phenomena occured at specific conditions. The conditions of the chaotic motion in BVP comprised 0.7182< $A_{1}$ <0.792 and 1.09< $A_{1}$ <1.302 proved by the analysis of phase plane, bifurcation diagram, and lyapunov exponent. To control the chaotic motion, two methods were suggested by the first used the amplitude parameter $A_{1}$,$A_{1}={\varepsilon}((x-x_{s})-(y-y_{s}))$ and the second used the temperature parameter c, c=c$(1+ {\eta}cos{\Omega}t)$ which the values of $\eta$, ${\Omega}$ varied respectlvly, and $x_{s}$, $y_{s}$ are the periodic signal. As a result of simulating these methods, the chaotic phenomena was controlled with the periodic motion of periodisity. The feasibilities of the chaotic and the periodic phenomena were analysed by phase plane and lyapunov exponent.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1503-1512
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• 2013

In this study, we proposed an indentation evaluation method for fracture toughness using cohesive finite element simulations. First, we examined the effect of material properties (yield strain, Poisson's ratio, and elastic modulus) on crack size during Vickers indentation and then generated a regression formula that explains the relations among fracture toughness, indentation load, and crack size. We also proposed another indentation formula for fracture toughness evaluation using the contact size a and E/H (H: hardness). Finally, we examined the relation between the crack size and the indenter shapes. Based on this, we can generate from the formula obtained using the Vickers indenter a formula for an indenter of different shapes. Using the proposed method, fracture toughness is directly estimated from indentation data.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.6
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• pp.8-22
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• 1995

Three dimensional numerical study of non-evaporating and evaporating spray characteristics was performed in a quiescent and motoring condition of direct injection diesel engine. The calculation parameter was breakup model. The breakup models used were Reitz & Diwakar model and TAB model. The modified k-${\varepsilon}$ turbulence model considering the compressibility effect due to the compression and expansion of piston was used. The calculation results of the spray tip penetration and tip velocity using the TAB model showed similar trends comparing with the experimental data. Although the evaporation rate was not nearly affected with the breakup model at the higher injection pressure, in the low injection case, the evaporation rate result using the TAB model became higher than that of R&D model. The evaporation rate was increased with the injection pressure due to the vigorous interaction with the gas field.

• Polymer(Korea)
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• v.29 no.5
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• pp.468-474
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• 2005

PLGA and PCL copolymers initiated by carbitol as drug carriers were synthesized by ring-opening polymerization of L-lactide (LA), glycolide (GA), and $\varepsilon-caprolactone(\varepsilon-CL)$. Implantable wafers were simply fabricated by direct compression method after physical mixing of copolymers and bovine serum albumin-fluorescein isothiocyanate (BSA-FITC) as a model protein drug. The release amounts of BSA-FITC from wafers were determined by fluorescence intensity using the fluorescence spectrophotometer. Also, the release behavior of BSA-FITC on wafers was controlled by adding the additives such as collagen, small intestinal submucosa (SIS), poly(vinyl pyrrolidone) (PVP), and poly(thylene glycol) (PEG). The wafer prepared by PLGA and PCL exhibited slow release within $10\%$ for 30 days. But, those prepared by a variety of additives exhibited the controlled BSA release patterns with a dependence on the additive contents. furthermore, the wafers containing natural materials such as collagen and SIS showed more zero-order release profile than that with synthetic materials such as PVP and PEG. It was confirmed that the release of BSA from implantable wafers could be easily controlled by adding natural additives.

• Fire Science and Engineering
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• v.14 no.3
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• pp.6-12
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• 2000

This paper describes the smoke movement of a fire field model based on a self-developed SMEP(Smoke Movement Estimating Program) code to the simulation of fire induced flows in the two types of compartment space containing the radiation effect under smoke movement in room fire. The SMEP using PISO algorithm solves conservation equations for mass, momentum, energy and species, together with those for the modified k-$\varepsilon $ turbulence model with buoyancy term. Also it solves the radiation equation using the discrete ordinates method. The result of the calculated smoke temperature containing radiation effect has shown reasonable agreement compared with the experimental data. On the other hand, a difference of a lot was found between the temperature predicted by the SMEP with only convection effect and obtained by the experimental result. This seems to come from the radiation effect of $H_2$O and $CO_2$ gas under smoke productions. Thus, the consideration of the radiation effect under smoke in fire may be necessary in order to produce more realistic result.

• Journal of Environmental Science International
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• v.7 no.2
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• pp.223-232
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• 1998

The spatial characteristics of stratification In Deukryang Bay were studded using observed data and analytical models. From the description of the density structure and its the potential energy anomaly (PEA) from observed data along longitudinal direction (from the mouth to head of the bays, we found that the stratification Intensity could be changed strongly by density current effect during the spring-neap tidal cycle, and depth variation. To find out density current effect for the formation of the stratification In detail, we Implemented a diagnostic approach by using the modified analytical model including density current, tidal current, surface heating and wind stirring. The model allowed for the observed similarities for the whole domain in the bay and increased tidal mixing efficiency value s up to 0.006-0.007 as compared to the results without density current effect. We found that the density current effect was also an important key factor In determining the formation of the spatial distribution of stratification.

• Korean Chemical Engineering Research
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• v.45 no.6
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• pp.619-626
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• 2007

It is of special interest in our membrane separation technology due to its low energy consumption and cost, relatively simple equipment, low investment and operation cost, et al. Full scale utilization of such processes can be widely utilized to the various fields. Using the difference of permeability of gas molecules between the filter layers, it is able to separate effectually pure gases from the mixed gases. In this paper, the membranes of PDMS, ${\gamma}-radiated$ PDMS, PTFE, PTFE-X are chosen to develop the predictive model for the separation of pure gases such as oxygen, nitrogen, hydrogen, and other gases from mixed gases. By utilizing the thermodynamic gas properties($\sigma$, $\varepsilon/k$) and experimental data of gas transport characteristics for different polymer membranes, it is able to develop the predictive model equation under the influence of temperature, pressure and polymer characteristics. Predictive model developed in this research showed good agreement with experimental data of gas permeability characteristics for develop four different polymer membranes. The proposed model can also be extended to the general equation for predicting the separation of gases based on the properties of polymeric membranes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.10
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• pp.1368-1379
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• 2000

A numerical study on swirling pulverized coal combustion in an axisymmetric enclosure is carried out by applying the 2-phase weighted sum of gray gases model (WSGGM) approach with the discrete ordinate method (DOM) to model the radiative heat transfer equation. In the radiative transfer equation, the same polynomial equation and coefficients for weighting factors as those for gas are adopted for the coal/char particles as a function of partial pressure and particle temperature. The Eulerian balance equations for mass, momentum, energy, and species mass fractions are adopted with the standard and RNG k-${\varepsilon}$ turbulence model, whereas the Lagrangian approach is used for the particulate phase. The eddy-dissipation model is employed for the reaction rate for gaseous mixture, and the single-step and two-step first-order reaction model for the devolatilization process for coal. Special attention is given to establish the thermal boundary conditions on radiative transfer equation By comparing the numerical results with experimental ones, the radiation model used here is confirmed and found to provide an alternative for simulating the radiative transfer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.2
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• pp.175-184
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• 1999

A theoretical study on the turbulent round jet diffusion flame impinging on the wall was carried out to predict the characteristics and structure of Impinging jet flame and heat transfer to the wall. Finite chemistry via Arrhenius equation and eddy dissipation model was adopted as a combustion model, and the Favre averaging and $k-{\varepsilon}$ model were Introduced In the theoretical modeling. The SIMPLE algorithm was applied to the calculation. All the transport properties were considered as the variable depending on the temperature and composition. For the parametric study, the distance from nozzle to impinging wall and Reynolds number at nozzle exit were chosen 88 the major parameters. As the results of the present study, the characteristics of flow fields, the distributions of main variables and each chemical species and the flame shapes were obtained. The heat transfer rate from the flame to the wall and the effective heating area were calculated to investigate the Influences of the major parameters on the heat transfer characteristics.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.934-939
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• 2001

In computational study of the flow in piston engines and the flow through moving valves, the use of moving vertices is essential for modelling flows with moving boundaries. The positions of cell vertices in such cases must be allowed to vary with time. To simulate 3-dimensional port-valve and piston-cylinder of HIMSEN 6H21/32 engine, a commercially available code, STAR-CD, was used. Changes in mesh geometry was specified by PROSTAR commands.(i.e. the Change Grid operation in the EVENTS command module.) Control of the intake flow is expected to play an important role as designers seek to obtain better fuel spray characteristics, fuel mixing and mixture preparation, combustion performance, and emissions reductions to meet national standards. As a result of analysis, velocity fields indicate the presence of a structured flow comprised of one pair of counter-rotating vortices under the intake valve during the early induction process. These flow structures remain visible for most of the intake process. As the piston moves towards BDC, these vortices develops into a larger tumbling motion that dominates the flow structure.