• 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.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.602-605
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• 2011

본 논문에서는 마찰감쇠기가 설치된 건물이 붕괴하중을 받을 때의 에너지소산능력을 고려하여 등가감쇠비를 유도하였다. 마찰감쇠기는 주로 지진과 같은 수평하중에 대한 에너지를 소산하기위해 설치된다. 마찰감쇠기를 대각 가새형으로 설치하면 수평하중에 대한 저항력뿐 만아니라 수직하중에 대한 저항성능도 발휘된다. 건물에 설치된 마찰감쇠기는 외력의 크기에 따라 정지와 운동의 상태를 반복하여 외부 입력에너지를 소산시키기 때문에 외력과 응답관계가 비선형이다. 건물은 고유의 점성감쇠를 가지므로 마찰감쇠기가 설치된 건물은 마찰과 점성감쇠를 동시에 고려해야하므로 해석적인 정해를 구하기가 어렵다. 에너지 평형을 이용하여 등가감쇠비를 구하고 운동방정식을 등가선형화하면 쉽게 저항 성능을 파악할 수 있다. 우선 건물에 영향을 미치는 것은 감쇠이므로 감쇠의 영향력을 마찰력비, ${\gamma}_c$로 나타내었다. 둘째, 정해를 마찰력비로 표현하여 유도하고 응답특성을 파악하였다. 셋째, 에너지 균형식을 통해 등가감쇠비를 산정하였다. 마지막으로 등가감쇠비를 검증하기 위하여 등가감쇠비를 이용하여 등가선형화한 응답과 실제 마찰감쇠기를 설치하여 비선형 수치해석한 결과와 비교, 검증하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.134-134
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• 2018

반데그라프 발전기는 큰 전위차를 생성하고 입자를 가속시키기 위해 발명된 정전기 발생기이다. 현재 반데그라프 발전기는 사이클로톤의 개발 이후 입자 가속 목적으로 주로 사용되고 있지는 않지만 접촉 전하 생성, 전달, 및 축적을 가능하게 하는 전하 운반 시스템에 기반하여 간단한 구조로 직류를 발생시킬 수 있는 점은 주목할만하다. 특히, 최근 경량성, 고효율 발전 등의 장점으로 에너지 하베스팅 분야에서 많은 관심을 받고 있는 마찰전기 에너지 하베스팅 기술 분야에서는 최근, 높은 에너지 저장 효율을 위해 직류 발생이 가능한 마찰전기 에너지 발전 소자에 대한 연구들이 진행되고 있다. 그러나 전하 운반 시스템을 기반으로 한 마찰 전기 직류 발전기에 대한 연구는 거의 이루어 지지 않았으며, 보고된 몇 연구에서는 저 전류, 고 임피던스 및 저효율과 같은 반데그라프 발전기의 구조적 및 물질적 한계를 극복하지 못했다. 또한 마찰에 의해 발생하는 마모에 의한 출력 감소 또한 해결되지 못한 문제이다. 따라서 뛰어난 마찰전기 특성과 함께 우수한 내마모성을 가지는 폴리머에 기반하여 기존의 한계를 극복 한 전하 운반 시스템 기반 마찰 전기 직류 발전기를 제안한다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.54-63
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• 2022

This paper is a study on the friction damper, which is one of the seismic reinforcement devices for structures. This study developed a damper by replacing the internal friction material with ultra high molecular weight polyethylene (UHMWPE), a type of composite material. In addition, this study applied a multi-friction method in which the internal structure where frictional force is generated is laminated in several layers. To verify the performance of the developed multi-friction damper, this study performed a characteristic analysis test for the basic physical properties, wear characteristics, and disc springs of the material. As a result of the wear test, the mass reduction rate of UHMWPE was 0.003%, which showed the best performance among the friction materials based on composite materials. Regarding the disc spring, this study secured the design basic data from the finite element analysis and experimental test results. Moreover, to confirm the quality stability of the developed multi-friction damper, this study performed an seismic load test on the damping device and the friction force change according to the torque value. The quality performance test result showed a linear frictional force change according to the torque value adjustment. As a result of the seismic load test, the allowable error of the friction damper was less than 15%, which is the standard required by the design standards, so it satisfies the requirements for seismic reinforcement devices.

• Journal of the Korean Geosynthetics Society
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• v.17 no.2
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• pp.33-40
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• 2018

Characteristics of interface friction between cohesionless soils and geotechnical structure surfaces play an important role in the analysis of earth load and resistance on the structure. In general, geotechnical structures are mainly composed of either steel or concrete, and their surface roughnesses with respect to soil particle sizes influence the interface characteristics between soils and the structures. Accurate assessment of the interface friction characteristics between soils and structures is important to ensure the safety of geotechnical structures, such as mechanically stabilized earth walls reinforced with inextensible reinforcements, piles embedded into soils, retaining wall backfilled with soils. In this study, based on the database of high quality interface friction tests between frictional soils and solid surfaces from literature, equation representing peak interface friction angle is proposed. The influential factors of the peak interface friction angle are relative roughness between soil and solid surface, relative density of frictional soil, and residual (constant volume) interface friction angle. Futhermore, for the developed equation of the interface friction angle, its uncertainty was assessed statistically based on Goodness-of-fit test results.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.6
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• pp.612-619
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• 2004

Servo motor systems with ball-screw and timing-belt are widely used in NC, robot, FA and industrial applications. However, the nonlinear friction torque and damping effect in machine elements reduce the control performance. Especially tracking errors in trajectory control and very low velocity control range are serious due to the break-away friction and Stribeck effects. In this paper, a new double speed controller is proposed for compensation of the nonlinear friction torque. The proposed double speed controller has outer speed controller and inner friction torque compensator. The proposed friction torque compensator compensates the nonlinear friction torque with actual speed and speed error information. Due to the actual information for friction torque compensator without parameters and mathematical model of motor, proposed compensator is very simple structure and the stability is very high. The proposed compensator is verified by simulation and experimental results.

• Microbiology and Biotechnology Letters
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• v.14 no.5
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• pp.407-413
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• 1986

In an agitated bead reaction system, the enzymatic saccharification of uncooked starch was substantially enhanced. The enhancement mechanism was investigated front the view of the structural aspect of starch. The mechanical impact caused by the movement of the attrition-milling media resulted neither the destruction of microcrystalline structure nor the fragmentation of starch granule. instead, the most distinct phenomenon was the swelling of starch granule up to about 2.5 times, and the swelling mechanism was not similar with that caused by cooking. However, in the case of the enzyme addition in the attrition coupled reaction system, the swollen starch was easily fragmented into the large number of small particles by the synergistic action of the enzyme and milling-media. The exposed surface area of the fragmented particles plays the major role in enhancing the saccharification. The saccharification rate was quite different depending on the source of starch, the reason was discussed in terms of the granular structure of uncooked starches.

• Composites Research
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• v.13 no.1
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• pp.78-88
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• 2000

Tribological properties of fiber composite materials were measured and wear resistant hybrid structure was proposed based upon the understanding of tribological behavior of the composite materials. Unidirectional composites with glass fibers, carbon fibers, and aramid fibers were tested for tribological properties in order to propose a wear resistant hybrid structure. Hybrid composites which contain carbon and aramid fibers were prepared, the specimens were sliced by a water-jet cutter, and friction and wear properties were measured. An experimental set-up was designed and built for the friction and wear test of the composite specimens. Unidirectional fiber composite and hybrid composite specimens were tested to evaluated the tribological behavior for biomimetic applications. It is observed that the friction and wear behavior of fiber composites depends upon fiber orientation, sliding speed, and type of reinforcing fibers.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.4
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• pp.435-443
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• 2010

This study presents key parameters for the structure installed with MR controller in reducing its responses. MR controller is regarded as Bingham model of which control forces are frictional and viscous ones. The parameters are identified as friction force ratios, $R_f$ and $R_h$ which are, respectively, ratio of MR controller friction force to static restoring force for free vibration and ratio of the friction force to amplitude of harmonic force. Structure-MR controller system shows nonlinear response behavior due to friction force. Energy balance strategy is adopted to transform the behavior to linear one with equivalent damping ratio. Finally, proposed equivalent linear process is compared to the nonlinear one, which turns out to give acceptably good results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.5
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• pp.545-550
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• 2014

This study provided the analytical finite element method estimating the friction-induced noise on the complex beam structure. The frictional contact model was theoretically constructed and applied to the analytical finite element squeal model. The numerical results showed that the beam structure was excited by the mode-coupling instability of the specific system modes. Also, the direction of friction was shown to influence on the dynamic instability of the modes. Besides, the unstable modal frequencies estimated from the numerical calculation were validated by the experiment of the actual beam structure.