• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.125-131
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• 1997

The extinction of premixed flames under the influence of stretch is studied numerically. A wide range of fuel (hydrogen, ethylene, acetylene, methane, propane and methanol) and air mixtures are established in an opposed jet and their flame properties such as flame speed, flame thickness, thermal diffusivity, and stretch rate at extinction are computed. Computations are made using several chemical kinetic mechanism (Smooke, Kee et al. and Peters). The major result is that, in contrast to the various previous claims of extinction Karlovitz number varying over three orders of magnitude, it is found to be constant around two for all of the mixtures tested. That is, premixed flames are extinguished when the physical flow time decreases (due to increased stretch rate) to the point where it approximately equals the chemical reaction time. Here the relevant chemical reaction time is not the one computed using the one-dimensional flame properties as originally suggested in the formulation of Karlovitz number, but rather it is the one obtained using the stretched flame properties which fully reflect the effect of straining on the flame structure.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.1
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• pp.110-114
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• 2009

Organic field-effect transistors (OFETs) are of interest for use in widely area electronic applications. We fabricated a copper phthalocyanine (CuPc) based field-effect transistor with different substrate temperature. The CuPc FET device was made a top-contact type and the substrate temperature was room temperature and $150^{\circ}C$. The CuPc thickness was 40nm, and the channel length was $50{\mu}m$, channel width was 3mm. We observed a typical current-voltage (I-V) characteristics in CuPc FET.

• Progress in Superconductivity
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• v.13 no.2
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• pp.90-96
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• 2011

We investigated the properties of artificial pinning centers of YBCO multilayer films in which $Y_2O_3$ and ZnO nanoparticles are uniformly introduced by using the pulsed laser deposition (PLD) technique. $Y_2O_3$ and ZnO nanoparticles were deposited on top of YBCO buffer layer and the density of nanoparticles was controlled by varying the number of nanoparticle layers. YBCO superconducting layers with total thickness of 250 nm were deposited on top of $Y_2O_3$ and ZnO nanoparticles. Based on analyses of the surface morphology, the transition temperature $T_c$, and the critical current density $J_c$, we discussed the difference between the two kinds of nanoparticles as flux pinning centers.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.11
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• pp.1806-1812
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• 2016

We propose an interior permanent magnet syhchronous motor (IPMSM) with arc-shape ferrite permanent magnets (PMs) as a substitute for the rare-earth permanent magnet, and determine its optimal design through parametric study. First, we use 2D finite element analysis to analyze 4-poles and 6-slots initial model according to performance requirements and design parameters. The current angle of the maximum average torque considered in the analysis is different compared with the current angle of the minimum torque ripple. Thus, the parametric study for optimal rotor design is performed by varying the thickness and the offset radius of the PMs according to current angle. In particular, a narrow bridge is required in conventional IPMSM for reducing flux leakage; however, the increase in cogging torque in the analysis model saturates the narrow bridge (large offset radius). Therefore, we suggest an appropriate shape considering limiting conditions such as DC link voltage, average torque, torque ripple, and cogging torque taking into account performance requirements.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.2
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• pp.529-539
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• 1996

Fracture resistance(J-R) curves, which are used for elastic-plastic fracture mechanics analyses, are known to be dependent on the specimen geometry. The objective of this paper is to investigate the effect of crack tip constraint an the J-R curves in CT specimens. Fracture toughness tests on CT specimens with varying planform size were performed and test results showed that the J-R curves were increased with an increase in the planform size. Finite element analysis were also performed and the numerical results showed that this experimental phenomenon was probably due to the relaxation of crack tip constraint resulting from the stress triaxiality.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.706-711
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• 2007

Numerical studies were performed to examine the effects of notch location of impact specimens on the failure behavior of HAZ (heat affected zone) when Charpy V-notch impact test were made at a low temperature ($1^{\circ}C$). Carbon steel plate (SA-516 Gr. 70) with thickness of 25mm for pressure vessel was welded by SMAW (shielded metal-arc welding) and specimens were fabricated from the welded plate. Charpy tests were then performed with specimens having different notch positions of specimens varying from the fusion line through HAZ to base metal. A series of finite element analysis which simulates the Charpy test and crack propagation initiating at the tip of V-notch was carried out as well. The finite element analysis takes into account the irregular fusion line and non-homogenous material properties due to the notch location of the specimen in HAZ. Results reveals that the energies absorbed during impact test depend significantly on the notch location and direction of specimen. Finite element analysis also demonstrates that the notch location of specimens, to a great extent, influences the reliability and consistency of the test.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.3
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• pp.193-200
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• 2004

The Active Constrained Layer Damping(ACLD) combines the simplicity and reliability of passive damping with the low weight and high efficiency of active control to attain high damping characteristics. The proposed ACLD treatment consists of a viscoelastic damping which is sandwiched between an active piezoelectric layer and a host structure. In this manner, the smart ACLD consists of a Passive Constrained Layer Damping(PCLD) which is augmented with an active control in response to the structural vibrations. The arc type shell model is introduced to describe the interactions between the vibrating host structure, piezoelectric actuator and viscoelastic damping. The system is modeled by applying ARMAX model and changing a state-space form through the system identification method. An optimum control law for the piezo actuator is obtain by LQR(Linear Quadratic Regulator) method. The performance of the ACLD system is determined and compared with PCLD in order to demonstrate the effectiveness of the ACLD treatment. Also, the actuation capability of a piezo actuator is examined experimentally by varying thickness of viscoelastic material(VEM).

• Tribology and Lubricants
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• v.21 no.2
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• pp.53-62
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• 2005

In this study a general Galerkin FE lubrication analysis method was utilized to analyze the complex lubrication performance of a spiral groove seal having an additional inner circular groove, which was designed for a chemical process mixer operating at a low speed of the maximum 500 rpm. Equilibrium seal clearance analyses under varying outer pressure revealed that the seal maintains a certain levitation seal clearance under the outer pressure of more than about 1.5 bar, regardless of a rotating speed. Also, under the normal outer pressure of 11 bar, the axial stiffness of the seal was predicted to have a high value of more than 7.0 e + 07 N/m, regardless of a rotating speed and thereby, the seal is expected to maintain a stable thickness of lubrication film under a certain external excitation acting. A seal levitation test rig was designed and constructed. Experimental results at 500 rpm agreed well with analytical predictions and the applied lubrication analysis method was verified.

• Journal of Pharmaceutical Investigation
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• v.25 no.1
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• pp.47-54
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• 1995

Transdermal patch formulations of estradiol to treat post-menopausal symptoms and prevent osteoporosis in women were developed and evaluated for the permeation characteristics through the excised hairless mouse abdorminal skin and the uterotropic effect on the ovariectomized rabbits. The design of patch formulations was optimized by varying several formulation parameters, such as type of enhancers, amount of enhancers, amount of drug loading and coating thickness. Compared to a commercially available transdermal product, several patch formulations showed the similar skin permeation profiles (following zero-order kinetics), but their skin permeation rates were lasted for the longer period (a week). In one-week uterotropic efficacy test in the ovariectimized rabbits, the selected patch formulations showed the positive effect in atrophy of the urogenital epithelium. The mean values of uterus weight in rabbits after application of patches containing estradiol were much higher than those in control group (containing no drug).

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.199-205
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• 1998

Butt fusions were practiced with butt fusion in the various conditions of fusion temperatures, pressure and time, and the tests of tesile strength, breaking water pressure and fusion features were also practiced so that the reliability of the butt fusion and the fittets fusion condition may be closely examined. And the width, height and thickness of the beads were also closely measured. The fittest fusion result was achieved in the condition of the temperature of $210^{\circ}C$, heating time hight pressure of 14 seconds on the pressure of $1.5kg/cm^2$, heating time hight pressure of 100 seconds and pressure buid-up time of 11 seconds. And in case of the temperature of $250^{\circ}C$, the fittest fusion result was showed in the condition of the heating time hight pressure of 3 seconds on the pressure of 1.0$kg/cm^2$, the heating time low pressure variable of 100 seconds. heating time hight pressure of 14 seconds and the heating maintenance of around 60 seconds. The result of breaking water pressure test of a test piece fusion in the fittest fusion condition was that the fusion condition of the PE pipe showed a good stability and hight reliance. Through this test, it is proved that the temperature of fusion PE pipes can be increased to $250^{\circ}C$ from $210^{\circ}C$. And it can be expected that the above fusion method greatly helps to reduce the fusion time.