• Journal of Welding and Joining
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• v.15 no.6
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• pp.85-95
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• 1997

This study is to investigate the optimum conditions of Nd:YAG laser beam welding for Zircaloy-4 end cap closure by optical fiber transmission. Laser welding parameters which affect the penetration depth and bead width were experimentally examined using the various beam radius by the beam quality analyzer, joint geometries of end cap and the laser parameters which mean pulse width, repetition rate and pulse energy. Also, an optimum welding speed and the effect of assistant gas with varying the flow rate of He were investigated. We found that the laser average power for the end cap welding will be 230W and rotation speed must not exceed 8 RPM, the best position of focus using optical fiber with 600.mu.m will be 2 to 3mm below the surface of the material.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.612-612
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• 2013

The band-gap opening in graphene is a key factor in developing graphene-based field effect transistors. Although graphene is a gapless semimetal, a band-gap opens when graphene is formed into a graphene nanoribbon (GNR). Moreover, the band-gap energy can be manipulated by the width of the GNR. In this study, we propose a site-specific synthesis of a width-tailored GNR directly onto an insulating substrate. Predeposition of a diamond-like carbon nanotemplate onto a SiO2/Si wafer via focused ion beam-assisted chemical vapor deposition is first utilized for growth of the GNR. These results may present a feasible route for growing a width-tailored GNR onto a specific region of an insulating substrate.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.145.2-145.2
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• 2013

The band-gap opening in graphene is a key factor in developing graphene-based field effect transistors. Although graphene is a gapless semimetal, a band-gap opens when graphene is formed into a graphene nanoribbon (GNR). Moreover, the band-gap energy can be manipulated by the width of the GNR. In this study, we propose a site-specific synthesis of a width-tailored GNR directly onto an insulating substrate. Predeposition of a diamond-like carbon nanotemplate onto a SiO2/Si wafer via focused ion beam-assisted chemical vapor deposition is first utilized for growth of the GNR. These results may present a feasible route for growing a width-tailored GNR onto a specific region of an insulating substrate.

• Journal of Power Electronics
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• v.19 no.3
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• pp.702-713
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• 2019

Multilevel Inverters (MLIs) are widely used in medium voltage applications due to their various advantages. In addition, there are numerous types of MLIs for such applications. However, the diode-less 3-level (3L) T-type Neutral Point Clamped (NPC) MLI is the most advantageous due to its low conduction losses and high potential efficiency. The power circuit of a 3L T-type NPC is derived by the conventional two level inverter by a slight modification. In order to explore the MLI performance for various Pulse Width Modulation (PWM) schemes, this paper examines the operation of a 3L (five level line to line) T-type NPC MLI for various types of Multi-Carriers Pulse Width Modulation (MCPWM) schemes. These PWM schemes are compared in terms of their voltage profile, total harmonic distortion (THD) and conduction losses. In addition, a 3L T-type NPC MLI is also compared with the conventional NPC in terms of number of switches, clamping diodes, main diodes and capacitors. Moreover, the capacitor-balancing problem is also investigated using the Neutral Point Fluctuation (NPF) method with all of the MCPWM schemes. A 1kW 3L T-type NPC MLI is simulated in MATLAB/Simulink and implemented experimentally and its performance is tested with a 1HP induction motor. The results indicate that the 3L T-type NPC MLI has better performance than conventional NPC MLIs.

• Proceedings of the Korean Nuclear Society Conference
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• 2004.05a
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• pp.150.1-150.1
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• 2004

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.399-409
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• 2017

This study numerically investigates the characteristics of the velocity field including the average flow velocity, longshore current and turbulent kinetic energy acting as the main external forces of the salient formed behind the permeable submerged breakwaters. Shoreline response is also predicted by the longshore-induced flux. In this paper, a three-dimensional numerical wave tank based on the OLAFOAM, CFD open source code, is utilized to simulate the velocity field around permeable submerged breakwaters under the formation condition of salient. The characteristics of the velocity field around permeable submerged breakwaters with respect to the gap width between breakwaters and the installing position away from the shoreline under a range of regular waves for different wave height are evaluated. The numerical results revealed that as the gap width between breakwaters increases, the longshore currents become stronger. Furthermore, as the gap width becomes narrower, the point where flow converges moves from the center of the breakwater to the head part. As a result, it is possible to understand the formation of the salient formed behind the submerged breakwaters. In addition, it was found that the longshore currents caused by the gap width between breakwaters and the installation position away from the shoreline are closely related to the turbulent kinetic energy.

• Journal of Advanced Navigation Technology
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• v.20 no.4
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• pp.265-274
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• 2016

In this study, the system was composed of the booster chopper and the power converter, which is a pulse width modulation (PWM) voltage inverter using a hybrid power generation system solar cell energy and wind force, Furthermore, in order to compensate the PWM voltage type inverter was linked with the general commercial power source, and through a normal operation of energy storage system (ESS), the system operated the LED Taxi Light by Wavelength according to Meteorological Changes at the airport in an efficient manner. The performance of the system was compared with the solar cell characteristics specification. In addition, for phase synchronization with the PWM voltage type inverter, the grid voltage was detected so as to operate the grid voltage and inverter output in the same phase and to connect the surplus electric power with the system. Finally, by developing a control circuit at the same time from which an excellent dynamic characteristics can be obtained through applying to the airport runway taxi light, it was concluded that a variety of taxi light can be pursued.

• Earthquakes and Structures
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• v.18 no.2
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• pp.215-222
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• 2020

In this paper, slit steel rubber bearing is presented as an innovative seismic isolator device. In this type of isolator, slit steel damper is an energy dissipation device. Its advantages in comparison with that of the lead rubber bearing are its simplicity in manufacturing process and replacement of its yielding parts. Also, slit steel rubber bearing has the same ability to dissipate energy with smaller value of displacement. Using finite element method in ABAQUS software, a parametric study is done on the performance of this bearing. Three different kinds of isolator with three different values of strut width, 9, 12 and 15 mm, three values of thickness, 4, 6 and 8 mm and two steel types with different yield stress are assessed. Effects of these parameters on the performance characteristics of slit steel rubber bearing are studied. It is shown that by decreasing the thickness and strut width and by selecting the material with lower yield stress, values of effective stiffness, energy dissipation capacity and lateral force in the isolator reduce but equivalent viscous damping is not affected significantly. Thus, by choosing appropriate values for thickness, strut width and slit steel damper yield stress, an isolator with the desired behavior can be achieved. Finally, the performance of an 8-storey frame with the proposed isolator is compared with the same frame equipped with LRB. Results show that SSRB is successful in base shear reduction of structure in a different way from LRB.

• Asian-Australasian Journal of Animal Sciences
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• v.3 no.2
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• pp.125-133
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• 1990

The effect of dietary protein-energy restriction (PER) on the growth of long bone were examined in sheep during growing period and then following a cycle of reproduction. Three months-old female sheep were offered protein-energy restricted feed for 6 months (growing period), thereafter changed to normal nutritional conditions for 8 months (reproduction period). A half of animals in each group took pregnancy, parturition and lactation. The nutritional restriction reduced the growth in bone diameter more than that in bone length. Compensatory growth resulting from the removal of the nutritional restraint strongly occurred in bone diameter, especially the bone cortical width, as compared to bone longitudinal growth. A cycle of reproduction severely decreased the growth in the bone cortical width relative to that in the bone width, and little effect was found on the growth in bone length and bone mass. The depression of bone development by pregnancy and lactation tended to exhibit severer in animals having received normal nutrition than in those having received PER. Bone mineral density was not affected by the nutritional restriction. A cycle of reproduction had an adverse effect on the mineral density between in animals having received normal nutrition and in those having received PER.

• Journal of IKEEE
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• v.23 no.4
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• pp.1140-1149
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• 2019

In general, there are various pulse width modulation(PWM) methods simply using the offset voltage injection in voltage source converter(VSC). In accordance with the AC side voltage synthesis method with the offset voltage, DC side voltage utilization factor in VSC is changed. Also, this can apply equally to the MMC system. In other words, if the DC side capacity of the high voltage DC(HVDC) transmission system is determined, the maximum reactive power which can be supplied to the AC side can be changed according to the applied output voltage synthesis method with the offset voltage. In this paper, the leg energy pulsation in MMC system according to the AC side output voltage synthesis method with offset voltage which several representative PWM are applied to are mathematically analyzed and compared with each other. Finally, the above results are verified by simulation emulating the 400MVA full-scale MMC system to determine the consistency of the mathematical analysis.