• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.4
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• pp.55-61
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• 2008

One of the most recent base-isolation systems to improve the earthquake resistance of structures is the Friction Pendulum System(FPS). Simple in design but with versatile properties, the FPS has been used in some of the world s largest seismically isolated buildings, bridges and chemical tanks. FPS using PTFE(Polytetrafl-uoroethylene) based material has been developed to provide a simple and effective way for structures to achieve earthquake resistance. PTFE materials are soft, and are apt to become deformed easily after a few working cycles. In this study, magnetic force is used rather than the usual PTFE materials to improve the material shortcomings. A MF-FPS(Magnetic force-Friction Pendulum System) is proposed, and us shown to effectively protect structures against earthquakes. To demonstrate the advantages of this new system, the MF-FPS is compared with FPS as an attempt to prove its performance. A six-degree-of-freedom model is considered as a numerical example. The ground acceleration data of El Centro, Mexico and Gebze earthquakes are used as seismic excitations. The results showed that MF-FPS improved performance compared with FPS.

• Journal of the Korean Geotechnical Society
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• v.38 no.3
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• pp.5-16
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• 2022

Ground in extremely cold and hot regions can sink by various environmental factors. Ground settlement can generate the negative skin friction to pile shaft, increase the base load of pile, and cut the stability of the pile. This study proposed a member responding ground deformation which can be inserted inside the pile. The member slightly compresses according to the ground settlement to reduce the negative skin friction. As the member materials, this study considered spring and spring-dashpot. To assess the ability of the member, the present research performed model tests for piles with or without the member within settled ground. In the model tests, the base load, total shaft resistance, and horizontal earth pressure were monitored and analyzed. Experimental results show that the pile with spring member can reduce the negative skin friction under small settlement conditions whereas it acts similar to the pile without the member under large settlement conditions as the spring was no longer compressed. However, the pile with the spring-dashpot member can reduce the negative skin friction continuously upon the ground settlement as the dashpot delays the load transfer to the spring and locates friction force on the unloading path.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.159-163
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• 2001

마찰구동은 다른 구동방식에 비하여 구조가 간단하고, 기계적인 정도를 얻기 쉬우며, 백래쉬 등에 기인하는 비선형 요소인 로스트모션이 없고 관성이 작아 구동력이 작은 이점이 있다. 그 반면에 접촉부에서 미끄럼이 발생하여 큰 구동력을 얻기 어렵고 마찰저항에 의하여 마멸이 생기는 결점이 지적되고 있다. 본 연구에서는 초정밀가공기용 위치결정기구로 마찰구동기구를 사용하기 위하여 위치 결정도에 관한 설계, 구동력의 설계 및 재료의 선택에 관하 여 분석하고 시작품을 제작하여 특성을 연구하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.7166-7175
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• 2015

This paper is a study on using gas springs for reduced friction in the elevation of the large television stand. Target is applied to the operation of the elevation over 50-inch television that uses a gas spring. Gas seal lip technology is needed for development acting on the piston rod in order to obtain a reduction in friction in elevation operation. In order to acting on the gas seal lip technology, the improved friction force can be obtained through the inner diameter of gas seal lip, the design of cutting angle and the changes of material.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.30 no.3
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• pp.209-219
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• 1994

The practical application of riblet to three dimensional double model, for viscous drag reduction, was studied analytically by intergal solution to three dimensional turbulent boundary layers. The case of a V-groove riblet technique on the shear stress and boundary layer velocities were incooperated in the computation of the flow over a smooth slender ship hull. As the results the possible mechanism of turbulent drag reduction by riblets are then suggested based on detailed studies of near-wall turbulence characteristics. And a turbulent boundary layer calculation scheme based on a momentum integral method was modified for the computer program. An example of the calculation results is presented.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.11
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• pp.967-974
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• 2017

Reaction wheel shows nonlinear torque response on low-speed region due to friction. Thus precise satellite attitude control on this region is hard to achieve. Previous research tries to solve this problem, by compensating friction or applying dither command. However, due to difficulties of drag torque modeling or frequent zero wheel speed crossing, these methods are not suitable to apply on the real satellite attitude control. To solve this problem, we propose the attitude controller gain adjustment method based on the attitude error.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1995.06a
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• pp.54-64
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• 1995

대표적인 대형 베어링인 일체형 볼 베어링과 와기어 레이스형 볼 또는 로울러 베어링의 마찰 특성을 비성형 유한요소 프로그램인 MARC를 사용하여 상호간의 마찰형상에 대한 접촉응력과 마찰력 특성을 비교 해석하였다. 특히 와이어 레이스식 슬루잉 링 베어링은 우수한 마찰특성 때문에 건설기계, 하역기계, 광산기계나 탱크와 같은 국방무기 등에서 널리 사용되고 있다. 접촉면의 변형에 따른 일체형의 볼 베어링은 마찰력과 기울기면에서 와이어 레이스식 베어링에 비하여 크고, 같은 와이어 레이스식 베어링에서는 마찰력의 경우 볼 타입이 로울러 탕입에 비하여 약간 크게 나타났다. 이들의 계산결과를 종합하면 와이어 레이스식 베어링이 일체형 베어링에 비하여 마찰특성이 우수하고, 특히 와이어 레이스 베어링중에서 로울러 타입은 마찰 토오크면에서 균일하기 때문에 베어링을 사용한 제어기능 설계에서 특히 우수한 결과를 제공할 수 있다. 유한요소 해석결과는 기존의 실험결과와 잘 일치하고 있어서 슬루잉 링 베어링의 최적설계에 유한요소 해석의 유용함을 확인하였다. 또한 상부 구조물과 하부 구조물을 연결하기 위한 체결볼트의 구멍은 하중조건에 따라서 구조적 불안정성을 야기할 수 있음도 확인하였다.

• Geotechnical Engineering
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• v.14 no.1
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• pp.71-80
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• 1998

Three prestressed concrete(PC) piles were installed for research purpose at Seosan area of west sea of Korea, and also cone penetration tests (CPT) were performed near two pile locations in order to compute PC pile shaft resistance by using CPT data measured. Three common CPT prediction methods that ia, Schmertmann method, Tumay Sl Fakroo method and LCPC method in France were used to predict pile shaft resistance. The pile shaft resistance predicted by each method was compared with that obtained by full-scale loading test and pile driving analyzer to estimate reliability of each prediction method. The predicted resistances based on three CPT-based methods underestimated significantly the resistances obtained from by fullrcale loading test, performed at 25 days and 42 days text pile installtion. There were, however, good agreements of predicted shaft resistance of piles between three CPT-based methods and pile driving analyzer tested two weeks after pile installtion.

• Journal of the Korean Institute of Gas
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• v.10 no.2 s.31
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• pp.27-32
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• 2006

In this paper, the contact stress and friction force between multi-balls and rolling friction contact surfaces of two cylinders have been presented using a finite element analysis. The multi-balls for a rolling friction motion may be contacted with a reciprocating mechanism of a parallel cylinder and a misaligned cylinder in a LPG filling unit. The FEM computed results indicate that SiC ceramic and SUS 304 balls show a high contact stress and friction force on the contact spot of rolling balls. But the PEEK balls show a low contact stress and friction loss due to a high flexibility of a PEEK polymer. In this study, we may recommend SiC and SUS 304 balls for high compressive loadings between a multi-ball and a cylinder contact mechanisms and PEEK balls for a low compressive force. And the misalignment between two cylinders should be restricted for a low contact stress and friction loss, especially.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.2
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• pp.113-119
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• 2019

We have developed the multi-functioned friction measuring instrument for the previous research. In here, we improved the performance of friction measuring instrument by applying the adaptive smoothing method and analyzed the friction of plate and monitoring function of friction surface through scratch tests. We substituted lubricant steel plate to lubricant oil used for reducing the friction when fabricating steel plate because lubricant oil was regarded as one of the major causes for the environmental pollution. In particular, the functions of various plate such as galvannealed steel sheets were analyzed because friction coefficient could be changed depending on the type of organic/inorganic plate or state of coating layer. Therefore, we demonstrated that adaptive smoothing method could enhance the accuracy of measuring instrument which eliminate the noise. As a result of using the method, it showed the reduction rate 0.0417% for the friction coefficient 0.16.