• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.5
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• pp.396-403
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• 2016

Usually, large-sized buses and trucks have a very high load. In addition, frequent braking during downhill or long-distance driving, causes the conventional method using the brake friction to have a problem in safety because of brake fade and brake burst phenomenon. Auxiliary brakes dividing the braking load is essential. Hence, environment-friendly auxiliary brakes, such as contactless brake rather than the engine auxiliary brake system are needed. A study aimed at improving the energy efficiency by recharging electric energy with changing mechanical to electrical energy that occurs when braking is actively in progress. In this paper, the voltage control method is utilized to recover the electric energy generated in the electromagnetic retarder instead of the eddy current. To regenerate the braking energy into the electrical energy, the resonant L-C circuit is configured in the retarder. The voltage generated in the retarder is simply modeled as a transformer. However, retarder voltage control in this paper is simulated by modeling the induction generator because this induction generator modeling is more practical than transformer modeling. The changes in the voltage of the resonance circuit, which depends on the switch pulse duration of the control device, were analyzed. A PI controller algorithm to control this voltage is proposed. The feasibility of modeling retarder and voltage controller are shown by using MATLAB Simulink in this paper.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.59-59
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• 2009

현재 CMP분야는 광역 평탄화 반도체 소자의 집적화 및 소형화가 진행됨에 따라서 CMP 공정의 중요성은 날로 성장하고 있다. 하지만 이러한 CMP공정은 불가피하게도 scratch, pit, CMP residue와 같은 defect들을 발생시키고 있으며, 점점 선폭이 작아짐에 따라, 이러한 defect들이 반도체 수율에 미치는 영향은 심각해지고 있다. Defect들 중에 특히 scratch는 반도체에 치명적인 circuit failure를 일으키게 된다. 또한 반도체 내구성과 신뢰성을 감소시키게 되고, 누전전류를 증가시키는 등 바람직하지 못한 현상들이 생기게 된다. 본 연구에서는 scratch 와 같은 deflect들을 효율적으로 검출, 분석하고, scratch를 감소시키는데 그 목적이 있다. 본 실험을 위해 8" TEOS wafer와 commercial oxide slurry 및 friction polisher (Poli-500, G&P tech., Korea)를 사용하여 CMP 공정을 진행하였으며, CMP 공정조건은 각각 80rpm/80rpm/1psi(Platen speed/Head speed/Pressure)에서 1분 동안 연마를 한 후 scratch 발생 경향을 살펴보았다. CMP 후 wafer위에 오염되어 있는 slurry residue들을 제거하기 위해 SC-1, HF 세정을 이용하여 최적화된 post-CMP 공정기술을 제안하였다. Scratch 검출 및 분석을 위해 wafer surface analyzer (Surfscan 6200, Tencor, USA)와 optical microscope (LV100D, Nicon, Japan)를 사용하였다. CMP 공정 변수들에 따른 scratch 발생정도를 비교하였으며, scratch 발생 요인들에 따른 scratch 형태 및 발생정도를 살펴보았다. 최적화된 post-CMP 세정 조건은 메가소닉과 함께 SC-1 세정을 실시하여 slurry residue들을 제거한 후, HF 세정을 실시하여 잔여 오염물들을 제거하고 검출이 용이하도록 scratch를 확장시킬 수 있도록 제안하였으며, 100%의 particle removal efficiency (PRE)를 얻을 수 있었다. 실제 CMP 공정후 post-CMP 세정 단계별 scratch 개수를 측정한 결과, SC-1 세정 후 약 220개의 scratch가 검출되었으며, 검출되지 않았던 scratch가 HF 세정 후 확장되어 드러남에 따라 약 500개의 scratch 가 검출되었다.

• Journal of the Korean Geosynthetics Society
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• v.11 no.3
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• pp.37-42
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• 2012

The cement paste is mostly used as the filling materials of bored pile in Korea. The use of filling material based on cement paste is inefficient at field construction because it needs a lot of the charging mass. In addition, it has environmental problem according to the large amount of cement use because its strength is also larger than criterion. The excavated soil with stabilizer can be used as the filling materials when the bored pile is constructed. Therefore, this paper describes field application of solidified soil for economical efficiency and environment-friendly. The injection capacity of solidified soil is compared with cement paste's based on unconfined compressive strength test and field load test, and the appropriate of test results is evaluated by design criterion. The evaluation result shows that the capacity of excavated soil with stabilizer is similar to cement paste and the solidified soil is able to apply as filling materials of bored pile because it is satisfied with design criterion.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.21-25
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• 2016

The automotive vehicle is made through the following processes such as press shop, welding shop, paint shop, and general assembly. Among them, the most important process to determine the quality of the car body is the welding process. Generally, more than 400 pressed panels are welded to make BIW (Body In White) by using the RSW (Resistance Spot Welding) and GMAW (Gas Metal Arc Welding). Recently, as the needs of light-weight material due to the $CO_2$ emission issue and fuel efficiency, new joining technologies for aluminum, CFRP (Carbon Fiber Reinforced Plastic) and etc. are needed. Aluminum parts are assembled by the spot welding, clinching, and SPR (Self Piercing Rivet) and friction stir welding process. Structural adhesive boning is another main joining method for light-weight materials. For example, one piece aluminum shock absorber housing part is made by die casting process and is assembled with conventional steel part by SPR and adhesive bond. Another way to reduce the amount of the car body weight is to use AHSS (Advanced High Strength Steel) panel including hot stamping boron alloyed steel. As the new materials are introduced to car body joining, productivity and quality have become more critical. Productivity improvement technology and adaptive welding control are essential technology for the future manufacturing environment.

• Journal of Biosystems Engineering
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• v.26 no.3
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• pp.263-270
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• 2001

This study was conducted in order to develop wind-water heating system where frictional heat is creased between the rotor and working fluid when they are rotating in the cylindrical heat generator. The wind-water heating system is composed of rotor, stator, working fluid, motor, inverter and heat generation tank. Instead of wind turbine, we have used an electrical motor of 30㎾ to rotate the rotor in this system. Two working fluids and six levels of rotor rpm were tested to quantify heat amounts generated by the system. Generally, as motor rpm goes up heat amount increases that we have expected. At the same rpm, viscous fluid showed up better performance than the water, generating more heat by 10$\^{C}$ difference. The greatest heat amount of 31,500kJ/h was obtained when the system constantly drained out the hot water of at the flow rate of 500ℓ/h. Power consumption rate of the motor was measured by thee phase electric power meter where the largest power consumption rate was 14㎾ when motor rpm was 600 and gained heat was 31,500kJ/h, that indicated total thermal efficiency of the wind power water heating system was 62%.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.2
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• pp.82-90
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• 2011

The small precision spindle motors in the high value-added products including the visible home appliances such as DLP projector require not only the energy conversion devices but also high efficiency, low vibration and sound operation. However, the spindle motors using the conventional ball bearing and sintered porous metal bearing have following problems, respectively: the vibration by the irregularity of balls and the short motor life cycle by the ball's abrasion and higher sound noises by dry contact between shaft and sleeve. In this paper, it is proposed that the spindle motor with a fluid dynamic bearing is suitable for the motor to drive the color wheel of the DLP(digital lightening processor) in the visible home appliances. The proposed spindle motor is composed of the fluid dynamic bearing with both the radial force and the thrust force. The fluid dynamic bearing is solved by the finite element analysis of the mechanical field with the Reynolds equations. The magnetic part of spindle motor, which is a type of Brushless DC Motor, is designed by the electro-magnetic field analysis coupled with the Maxwell equation. And the load capacity and the friction loss of fluid dynamic bearing are analyzed to bearing clearance variation by the fabrication error in designed motor. The design of the proposed motor is implemented by the load torque caused by the eccentricity and the unbalance of the fluid dynamic bearing when the motors are fabricated in error. The prototype of the motor with the fluid dynamic bearing is manufactured, and experiment results show the vibration, sound, and phase current at no load and color wheel load of the motors in comparison. The high performance characteristics with the low vibration, the low acoustic noise and the optimal mechanical structure are verified by the experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.49-52
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• 2008

The plain and simple shape water front structure were designed and installed for wave protection and wave resistance. But the installation of these plain and simple structure cause deficiency of environmental affinity. Also the resonance phenomena from the reflective wave and shipwave of the harbor incident wave caused high tide and wave, consequently maintaining the tranquility of inside harbor, give difficulty for mooring the ship and loading-unloading, increase the possibility of ship collision at the quray wall and landing place To solve these problems, we develop the environmentally friendly wave dissipation block. And installation efficiency, stability of the blocks through experiment of C.E Block Joint.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.520-527
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• 1988

Liquid ejectors are widely used as marine pumps, inducer stage for the boiler feed water pump, boiler recirculating pump, cooling water recirculating pump in boiling water type nuclear reactor and a deep well pump, because of their high working confidence and simplicity. Furthermore, it requires only a modest net positive suction head for cavitation-free operation and it can be installed in remote location from mechanical power source. It is not easy to presume the friction losses, because it is complicately affected by area ratio, flowrate ratio, nozzle spacing, throat length, shape of liquid ejector and so on. Therefore, the optimization of liquid ejector design is still dependent, to a large extent, on the experimental results and empirical procedures. On the design of the liquid ejector, the area ratio and the nondimensional throat length are the most important design factors among the mentioned above. In this experiment, the effects of the area ratio and the nondimensional throat length to ejector efficiency are carried out systematically by the combination of 4 kinds of motive nozzle and 2 kinds of throat length. In this paper, the present experimental results are compared with the calculated ones by the previous computer aided design program based on one dimensional flow equation. And also, an empirical equation for the working limit of liquid ejector is reported.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.6
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• pp.1365-1373
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• 1994

A Monte-Carlo simulation model, developed to predict size distribution of air bubbles in turbulent shear flow, is applied to a laboratory-scale problem. Sensitivity to various numerical and physical parameters of the model is analyzed. Practical applicability of the model is explored through comparisons of results with experimental measurements. Bubble size increases with air-water discharge ratio and friction factor. Bubble size decreases with increasing mean flow velocity, but the total bubble surface area in the aeration region remains fairly constant. The effect on bubble size distribution of the longitudinal length increment in the simulation model is negligible. A larger radial length increment yields more small and large bubbles and fewer in between. Bubble size distribution is significantly affected by its initial distribution and the location of air injection. Collision efficiency is introduced to explain the discrepancy between collisions with and without coalescence.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.5
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• pp.427-433
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• 2017

In the case of high-strength or low thermal conductivity material milling, tool breakage occurs easily because of the high friction temperature. Therefore, the effectiveness of the coolant supply is very important for proper tool cooling. As the manually adjustable joint mechanism nozzle is generally used for coolant supply, the cooling efficiency is very low. It also has a bad influence on the workspace environment because of coolant scattering. In this study, the milling characteristics of STS316L were investigated according to the coolant spray position based on the automatic adjustable system. Tool wear and surface roughness were measured according to the coolant spray position. Through these experiments, the effectiveness of the fabricated system was explained.