• Proceedings of the KIPE Conference
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• 2007.11a
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• pp.212-214
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• 2007

Regenerative energy which is generated during brake periods of DC traction might cause malfunction or destruction of rectifier or any other power conversion devices caused the increment of DC line voltage. Regenerative energy storage system using super-capacitor is one of the method to control the DC line voltage safely. And super-capacitor is very important device as energy storage device. Therefore, In this paper, we designed the regenerative energy storage system using super-capacitor and propose the method about predicting the lifetime of super-capacitor established in storage system. According to the this research, we can estimate the proper replacement moment for the existed super-capacitor due to the safety of the system. And improve the reliability of regenerative energy storage system using super-capacitor.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1380-1397
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• 2018

The synchronous reluctance motor (SynRM) servo-drive system has highly nonlinear uncertainties owing to a convex construction effect. It is difficult for the linear control method to achieve good performance for the SynRM drive system. The nonlinear backstepping control system using upper bound with switching function is proposed to inhibit uncertainty action for controlling the SynRM drive system. However, this method uses a large upper bound with a switching function, which results in a large chattering. In order to reduce this chattering, a nonlinear backstepping control system using an adaptive law is proposed to estimate the lumped uncertainty. Since this method uses an adaptive law, it cannot achiever satisfactory performance. Therefore, a nonlinear backstepping control system using a reformed recurrent Hermite polynomial neural network with an adaptive law and an error estimated law is proposed to estimate the lumped uncertainty and to compensate the estimated error in order to enhance the robustness of the SynRM drive system. Further, the reformed recurrent Hermite polynomial neural network with two learning rates is derived according to an increment type Lyapunov function to speed-up the parameter convergence. Finally, some experimental results and a comparative analysis are presented to verify that the proposed control system has better control performance for controlling SynRM drive systems.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.1
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• pp.79-84
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• 2009

In order to increase the capacity of the superconducting fault current limiter(SFCL), the current and voltage grades of the SFCL must be increased. As a method for the increase of the current and voltage grades of the SFCL, we compared the various characteristics between the flux-lock type SFCL "With three superconducting units connected in series and the transformer type SFCL using the transformer with three secondary circuits. One of three superconducting units had not quenched in the flux-lock type SFCL. Therefore, the unbalanced power burden happened because of the voltage difference generated by unbalanced quenching between the superconducting units. In the meantime, the three superconducting units were all quenched in the transformer type SFCL using the transformer, and the voltage difference generated between the superconducting units was decreased. Therefore, the difference of critical characteristics was complemented by distribution of fault current in accordance with the turn's ratio between primary and secondary windings. The unbalanced power burden of the superconducting units was reduced due to flux-share between the superconducting units in the transformer. In conclusion, the capacity increment of the SFCL using a transformer was easier due to equal distribution of voltages generated by simultaneous quench of the superconducting units. We think that the characteristics is improved more because of the decrease of saturation in the iron core if the secondary winding is increased in the SFCL using the transformer.

• Laser Solutions
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• v.17 no.4
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• pp.1-6
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• 2014

Femtosecond laser induced shock generation in water and vitreous humor of enucleated porcine eyeball was investigated. When focusing the femtosecond laser into the liquid mediums, the acoustic waves with a frequency of about 15.6kHz could be observed by using wide-band microphone. The amplitude of the acoustic signals from water has attained a maximum under a laser power of about 5mW. Further increment of the power results in a decrement of the acoustic signals due to nonlinear optical process including filamentation of laser beam. We have further investigated the effect of femtosecond laser induced acoustic waves by applying the laser pulse into enucleated porcine eyeball. The comparative studies on both healthy and diseased eyeballs led us propose that the femtosecond laser pulses could be utilized as a novel tools for treatment of partially detached retina layers from their choroid structures.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.39-42
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• 2008

In the case of the general helicopter among rotorcraft, length of the rotor blade for thrust-generation is longer than that of fuselage and tail rotor is required in order to compensate moment of the fuselage. For those reasons, enough space for take-off and landing should be secured and an accessibility for building is low. Also, the accidents caused by tail rotor occur frequently. However, the case of counter-rotating has merits that tail rotor is unnecessary as well as length of the rotor blade can be shortened but has a weakness that the weight of body is increased. In the present study, aerodynamic force measurement on single rotor system equipped with NACA0012 airfoil, which has aspect ratio of 6 and chord length of 35.5 mm, was carried out. And measurement was conducted with blade which has a half size of the former blade by using single motor counter-rotating. Aerodynamic force measurement was acquired by using 6-component balances and coefficients of thrust and power were derived along the pitch angle varying from 0$^{\circ}$ to 90$^{\circ}$ with the increment of 10$^{\circ}$. Those aerodynamic force data will be utilized for the design and production of brand-new counter-rotating rotor blade system which has same thrust with single blade system and provides a good accessibility to building by reducing its blade length.

• Journal of Power System Engineering
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• v.18 no.3
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• pp.42-50
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• 2014

The main object of this study is to investigate the collection characteristics of wet-type multi-layered and multi-staged porous plate system experimentally. The experiment is carried out to analyze the characteristics of pressure drop and collection efficiency for the present system with the experimental parameters such as water spray, inlet velocity, stage number and inlet particle concentration, etc. In results, for the present system of wet-type, the pressure drop represents 158 $mmH_2O$ higher 3% than that in dry-type at 5 stage and $v_{in}$=3.53 m/s. In case of 5 stage, $v_{in}$=3.53 m/s and water spray 250 ml/min, the collection efficiency of the present system becomes significantly higher as 99.7% comparing to that of the conventional wet-type scrubber. Additionally, for 5 stage and 250 ml/min, $SO_2$ removal efficiencies decrease with the increment of inlet velocity representing 75.0, 62.5, 50.0%, at $v_{in}$=2.12, 2.82, 3.53 m/s, respectively.

• Progress in Superconductivity
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• v.12 no.1
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• pp.12-16
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• 2010

We have measured the trapped field of YBCO bulk with different configuration by applying the magnetic field of $Nb_3Sn$ superconducting magnet. Initially the circular type of YBCO bulk superconductor was prepared and then hole, parallel to the c-axis and located at the center of bulk was mechanically drilled. The YBCO bulk with hole was filled with resin. Typical size of hole in YBCO bulk was 10 mm in diameter. Trapped field characteristics were compared with different specimen conditions. Our preliminary result indicates the increment rate of trapped field, 0.232 kG, measured on the YBCO without hole was much higher than that, 0.011 kG, measured on YBCO with hole.

• Journal of the Korean Society of Visualization
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• v.13 no.1
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• pp.15-20
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• 2015

Sensitivity studies of blade angle and twisted angle are numerically investigated to optimize the Savonius blade. As blade angle increases, the contact area between blade and wind decreases, showing the suppression of the vortex generation near blade. Compared to the blade angle of 0 degree, the blade angle of 20 degree shows about 2.6% increment of power efficiency. Based on the blade angle of 20 degree, sensitivity studies of the twisted angle are performed. The result indicates that the adjustment of the twisted angle causes the torque of blade to increase. Optimized blade can suppress the formation of the vortex structure in rear region. Also, wind flows without disturbance of vortex when passing through the optimized blade. The 1kw vertical wind turbine system with optimized blade can generate 4442.2kWh per year and have 53% capacity factor.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.9 s.102
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• pp.1077-1083
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• 2005

Electro-Active Paper (EAPap) is one of attractive electro-active polymer (EAP) materials for artificial muscles due to its many advantages such as light weight, biologically degradable, low cost, large displacement output, low actuation voltage and low power consumption. However, drawbacks of EAPap actuators include low force output and humidity dependence. To enhance the performance of EAPap, conductive polymer (PPy) and SWNT/conductive polymer (PANI) are coated on EAPap PPy as conductive polymer is coated on cellulose EAPap by means of electrochemical deposition. Two different dopants are used in PPy through conducting polymer processing. SWNTS are mixed with PANI in emeraldine base along with different dopants. The compound materials are coated on cellulose EAPap using spin coating system. The performance of PPy/EAPap and SWNT/PANI/EAPap are evaluated in terms of bending displacement, blocked force, and the effects of dopants, humidity, coaling time, voltage and frequency are investigated. Comparing with EAPap actuators, SWNT/PANI/EAPap actuators show $200\%$ improvement of bending displacement and $300\%$ increment of blocked force.

• Laser Solutions
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• v.18 no.4
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• pp.17-22
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• 2015

In this paper, ablation rate of $Al_2O_3$ ceramics by femtosecond laser fluence is derived with experimental method. The automatic three axis linear stage makes laser optics to move with high spatial resolution. With 10 times objective lens, minimal pattern width of $Al_2O_3$ is measured in the focal plane. Ablated surface area is shown as linear tendency increasing number of machining times with various laser power conditions. Machining times is most sensitive condition to control $Al_2O_3$ pattern width. Also, the linear increment of pattern width with laser power change is investigated. In high machining speed, the ablation volume rate is more linear with fluence because pulse overlap is minimized in this condition. Thermal effect to surrounding medium can be minimized and clean laser process without melting zone is possible in high machining speed. Ablation volume rate decelerates as increasing machining times and multiple machining times should be considered to achieve proper ablation width and depth.