• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.129-136
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• 2001

본 논문에서는 석탄회 매립지반의 액상화 가능성을 평가하기 위해 순수 모래시료와 더불어서 모래시료와 석탄회가 혼합된 모래시료에 대한 일련의 진동삼축실험을 변형률제어 방법으로 수행하였다. 실험결과 진동하중에 의해서 시료 내에 발생하는 간극수압의 크기는 작용하는 전단변형률의 크기에 심각하게 영향을 받고, 작용하는 전단변형률이 지반의 한계전단변형률 보다 작은 경우에는 진동수가 높은 조건에서도 간극수압이 발생하지 않음을 알았다. 또한 전단변형률이 약 0.1%보다 작고 한계전단변형률에 가까운 경우에는 순수 모래시료와 비교하여 본 논문에서 조사한 석탄회 함유율 범위 (10%~30%)의 시료에서 간극수압이 더 크게 발생하였다. 반면에, 전단변형률이 큰 경우에는 순수 모래시료에서 간극수압이 크게 발생하는 추세를 보였다. 반복 전단에 따른 간극수압의 발생량은 전반적으로 석탄회 함유율이 증가할수록 커지는 경향을 보였다. 이러한 결과를 근거로 해안이나 하천에 인접한 한계지 개발에 있어서 사질토에 석탄회를 혼합 매립하여 지반을 조성하는 경우에 액상화에 대해서 불안정한 지반이 될 가능성이 있는 것으로 판단되었다.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.12
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• pp.45-56
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• 2002

A pneumatic servo system requiring a fine gap control in a photo-electric sensor which is used for a LCD array detection device is introduced. The gap controlled by the pneumatic servo system remains within around 50~80 ${\mu}{\textrm}{m}$, and the system possesses an effect to eliminate undesirable particles on the LCD plate by blowing air out. The air flow rate is initially controlled by a servo valve and expanded by a booster valve, thus the controlled air pressure contributes to maintaining an appropriate gap between the LCD plate and photo-electric sensor An air floating plate of two degrees of freedom is designed and fabricated, and a fine tilting motion control is also implemented by assigning different gap commands. The pressure control and direct gap control are proposed, and each performance is verified experimentally.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.5
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• pp.495-501
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• 2011

We present an experimental study of electrical discharge in nanoscale gaps. The discharge occurred between a cathode made of sharpened Pt-Ir wire and a gold-plated anode. Electric discharges were detected for electric potentials from 10 V to 80 V, and their gaps ranged from 50 nm to 800 nm. The spark signals indirectly showed spark phenomena such as discharges or shortages in the system. The sparks and discharges strongly depended on the electric potential (voltage) and the radius of the tips. For small gaps, the electrical discharge was random and strongly depended on the radius of the cathode tips.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1004-1008
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• 2003

Near-filed optical storage using cantilever aperture tip is a promising way fer next generation optical data storage. To enhance the speed of reading and writing data, gap between tip and media should be controlled fast and precisely within near field region. In this paper, several PZT actuators are analyzed far constructing dual servo control algorithm: coarse actuators(stact. PZT, bimorph PZI) for media surface inclination and One actuator(film PZT) for media surface roughness. Dynamic analysis of stack PZT, bimorph PZT, and film PZT are performed through the frequency response. Based on the frequency response and mathematical model, fast analog controller is designed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.5 s.110
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• pp.479-484
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• 2006

This paper presents an active control of the aperture type near-field storage head. In order to achieve a fast and accurate control, a dual servo control algorithm is applied. Based on the big difference in time constants of two actuators, they are used independently. With the combination fine and coarse actuator, the disk is rotated up to 10 rpm speed until the gap is controlled within 100 nm. From the experimental results, the feasibility and the performance of active dual servo gap control is proved.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.875-878
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• 2005

This paper presents active control of aperture type near-field storage head. In order to achieve fast and accurate control, dual servo control algorithm is applied. Based on the big difference in time constant, we seperate two actuator and control independently. With the combination of fine and coarse actuator, gap is controlled within 100nm until the disk rotates upto 10 rpm speed. From the experimental results, the feasibility and performance of active gap control is proved.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.218-223
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• 1997

유압장치의 핵심부품인 유압 제어밸브(hydraulic control valve)는 유압펌프 등에 의하여 가압된 유압유의 압력과 유량을 제어하고 유동방향을 변화시키는 주요기능을 수행한다. 특히, 대부분의 제어밸브는 스푸울(spool)과 슬리브(sleeve)를 기본구조로 채용하고 있다. 피스톤 형상인 스푸울이 슬리브내를 왕복운동하면 스푸울과 슬리브 사이의 간극(clearance)에서는 점성유체인 유압유의 윤활작용에 의하여 원주방향으로 비대칭인 유체압력이 발생한다. 이 결과로 스푸울에 측력(lateral force)이 작용하며, 조건에 따라서는 스푸울에 작용하며, 조건에 따라서는 스푸울에 작용하는 마찰력이 증대할 뿐만 아니라 스푸울과 슬리브의 내벽에 과도한 마멸(wear)을 유방시키기도 하여 제어밸브의 성능을 크게 저하시키기도 한다. 유압공학분야서는 이를 유체고착(hydraulic locking) 현상이라고 부른다. 본 논문에서는 항공기 Flap actuator의 Selector manifold에서 사용되는 스푸울 밸브의 성능에 큰 영향을 미칠 것으로 예상되는 스프울과 슬리브 사이 간극에서의 윤활특성을 이론적으로 조사하고자 한다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.6
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• pp.796-802
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• 2018

The effects of inner liquid sloshing on vessel motions are a well-known factor. It was investigated experimentally and numerically. In this regard, the study of many efforts to reduce natural phenomena of vessel motions by adopting special devices especially for roll motions. Among many devices, inserting baffles in the inner liquid tank is very common. In this study, one investigated the vessel motions with inner sloshing tanks with baffles inside. For the numerical simulation, one employed a dynamically coupled program between boundary-element-method-based vessel motion analysis program and a particle-based computational fluid dynamics program. Comparing corresponding experimental results validated the dynamically coupled program. The validated coupled program was used to simulate vessel motions, including sloshing effects with various lengths of inner baffles. The simulation results show that not only the filling ratio of inner liquid, but also the length of clearance due to baffles influenced the vessel motions. The significant point of this study was that the natural frequency of vessel motions can be maintained irrespective of the amount of filling ratio through adjustment of the clearance. In a future study, the effects of various numbers of baffles with various clearances would be conducted to percuss the possibility of vessel motion control with inner liquid sloshing effects.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.2 s.54
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• pp.81-94
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• 2007

In most experimental researches on the liquefaction phenomenon, an earthquake as a random vibration has been regraded as a sinusoidal wave or a triangular wave with an equivalent amplitude. Together with the development in the part of signal control and data acquisition, dynamic experimental equipments in the soil dynamics have also developed rapidly and further more, several real earthquakes have been simulated in the large model test such as shaking table tests and centrifuge tests. In Korea, several elementary laboratory tests to simulate the real earthquake load were performed. From these test results, it was reported that the sinusoidal wave cannot reliably reflect the soil dynamic behavior under the real earthquake motion. In this study, 4 types of dynamic motions such as the sinusoidal wave, the triangular wave, the incremental triangular wave and several real earthquake motions which were classified with shock-type and vibration-type were loaded to find something new to explain the change of the excess pore water pressure under the real earthquake load. Through the detailed investigation and comparison on all test results, it is found that the dynamic flow is generated by the soil plastic deformation and the velocity head of dynamic flow is changed the pressure head in the un-drained condition. It can be concluded that the change of the excess pore water pressure is related to the pressure head of dynamic flow. Lastly, a new hypothesis to explain such a liquefaction initiation phenomenon under the real earthquake load is also proposed and verified.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.2 s.152
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• pp.101-110
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• 2007

Recently, rudder erosion due to cavitation frequently has occurred at large high speed container carriers. Especially, in the case of a horn-type rudder, the rudder erosion is severe around a gap. The gap-flow characteristics are investigated through a computational method to understand the effects of a gap on the cavitation and rudder efficiency. A viscous flow theory utilizing a cavitation model is applied to calculate the flow around idealized 2-dimensional rudder sections in a full scale. The effects of gap clearance and flow-control projection are also investigated. From the computational results, the mass flow rate through a gap is found to be one of the important parameters to affect the cavitation and rudder efficiency.