• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2454-2462
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• 1994

The effects of thermal stratification on the flow of a stratified fluid past a heated circular cylinder were examined in a wind tunnel. Turbulent intensities, rms values of temperature and turbulent convective heat flux distributions in the heated cylinder wake with and without thermal stratification were measured by using a hot-wire and cold-wire combination probe. A phase averaging method was also used to estimated coherent motion in the near wake. It is found that the vertical turbulent motion in the stably stratified flow case dissipates faster than that of the neutral case, i.e., vertical growth of vortical structure is suppressed under the strongly stratified condition. The coherent motion of temperature makes a large contribution like velocity coherent motion. However, the coherent motions of temperature fluctuation become very different with the change of experimental conditions, though the velocity coherent motions are quite similar in all experimental conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.4
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• pp.353-359
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• 2009

Wire-woven Bulk Kagome (WBK) is a new truss type cellular metal fabricated by systematic assembling of helical wires in six directions. In this work, the experiments of mechanical behaviors of WBK cored sandwich panels subjected to bending load were performed and the results were compared with those by the corresponding analytic solutions. And also, finite element simulations were performed to validate the optimal design according to the analytic solutions. It is found the sandwich panel with WBK core performed excellently in terms of energy absorption and deformation stability after the peak point as well as the load capacity.

• Interaction and multiscale mechanics
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• v.3 no.3
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• pp.257-266
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• 2010

A novel resonance based proximity DC current sensor is proposed. The sensor consists of a piezo sensed and actuated cantilever beam with a permanent magnet mounted at its free end. When the sensor is placed in proximity to a wire carrying DC current, resonant frequency of the beam changes with change in current. This change in resonant frequency is used to determine the current through the wire. The structure is simulated in micro and meso scale using COMSOL Multi physics software and the sensor is found to be linear with good sensitivity.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.2
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• pp.1-9
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• 1997

For the reduction of parasitic inductance and matching of bonding wire in the package of microwave devices, we propose multiple bonding wires buried in a dielectric material of FR-4 composite. This structure is analyzed using the method of moments (MoM) and compared with the common bondwires and ribbon interconnections. The FR-4 composite is modelled by the cole-cole model which can consider the loss and the variation of the permittivity in a frequency. At 20 GHz, the parasitic reactance is reduced by 90%, 80%, 60% compared to those of a single bonding wire in air, double bonding wires in air and ribbon interconnection in air, respectively. Also, the new bondwire shows very good matching of 60.ohm characteristic impedance and has 15dB, 10dB, 5dB improvement of the return loss and 2.5dB, 0.7dB, 0.2dB improvement of the insertion loss compared to the common interconnections. This technique can minimize the parasitic effect of bondwires in microwave device packaging.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.6
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• pp.120-127
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• 2000

This study is concerned with evaluating the effects of acoustic excitation on the development of two stream mixing layer generated by split plate. The ratios of two velocities U1 and U2 either side of the splitter plate were such that $U_1/U_2$=1.0 (uniform flow) or $U_1/U_2$<1.0(shear flow). The mixing layers were disturbed acoustically through the edge of split plate. Quantitative data were obtained with hot-wire anemometry. Flow visualization with smoke-wire was also employed for qualitative study. the results show that the large scale structures of mixing layers are strongly affected by excitation frequency and amplitude in both uniform and shear flows. The maximum streamwise and vertical turbulent intensities of the excited flow fields are apt to be decreased as compared with those of without excitation. The flow characteristics of uniform flow are more influenced by acoustic excitation than those of shear flow.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.845-850
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• 2003

Unsteady nature of a tip leakage vortex in an axial flow fan operating at a design and off-design operating conditions has been investigated by measuring the velocity fluctuation in a blade passage with a rotating hotwire probe sensor. Two hot-wire probe sensors rotating with the fan rotor were also introduced to obtain the cross-correlation coefficient between the two sensors located in the vortical flow as well as the fluctuating velocity. The results show that the vortical flow structure near the rotor tip can be clearly observed at the quasi-orthogonal planes to a tip leakage vortex. The leakage vortex is enlarged as the flow rate is decreased, thus resulting in the high blockage to main flow. The spectral peaks due to the fluctuating velocity near the rotor tip are mainly observed in the reverse flow region at higher flow rates than the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition.

• Journal of the Speleological Society of Korea
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• no.76
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• pp.1-13
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• 2006

Electrophoretic deposition (EPD) of alcohol YBCO suspensions on the Ag wire electrode is studied. Poly(ethylene glycol) was coordinated to a structure formed by the EPD process with YBCO particles. The suspension is characterized in terms of zeta potential and conductivity. The d.c electric fields of 200-300 V/cm are applied for 1-10 min. The optimal condition for the EPD allows modifying the properties and microstructure of the deposited films. Superconducting coatings with nanometer-sized pores and a preferred orientation along the c-axis were prepared from the result with chemically modified precursor solution. In contrast, YBCO coatings of submicrometer-sized pores and randomly orientated grains were prepared from the solution without PEG.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.151-158
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• 1999

In this study, we developed the simulation program of an overhead catenary-pantograph system, The overhead catenary is modeled with point mass and the pantograph is replaced with 3 d. o. f. model which is composed of mass, spring and damper. Using the developed program, we analyzed the static structure of the overhead catenary and the dynamic characteristics of an overhead catenary-pantograph system such as uplift displacement of contact wire and contact force. we compared the analysis results with the results of GASENDO software developed at RTRI in Japan. The behaviors of uplift displacement of contact wire and contact force were similar with the results of GASENDO software.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.293-295
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• 2003

KEPCO's high voltage distribution power line laid under the ground near to the J-booster pumping station that supply water for living. Lightening rod equipment does not installed at the J-booster pumping station because KEPCO's over head ground wire for protection functions as a lightening rod equipment. In this study, it is concerned whether KEPCO's over head ground wire for protect the distribution power line affect to the J-booster pumping station which is installed for reduce the damage from the direct and indirect lightening. If KEPCO's protection area does not affect to the J-pumping station, it is plan to examine the construction method of lightening rod protection angle and lightening rod equipment and to suggest the optimum protection plan using the surrounding structure based on the suitability of protection area.

• International Journal of Control, Automation, and Systems
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• v.6 no.1
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• pp.126-134
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• 2008

As many systems depend on electronics, concern for fault tolerance is growing rapidly. For example, a car with its steering controlled by electronics and no mechanical linkage from steering wheel to front tires (steer-by-wire) should be fault tolerant because a failure can come without any warning and its effect is devastating. In order to make system fault tolerant, there has been a body of research mainly from aerospace field. This paper presents the structure of predictive hybrid redundancy that can remove most erroneous values. In addition, several numerical simulation results are given where the predictive hybrid redundancy outperforms wellknown average and median voters.