• Title, Summary, Keyword: Friction Coefficient

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Seismic Performance Evaluation of Seismically Isolated Nuclear Power Plants Considering Various Velocity-Dependent Friction Coefficient of Friction Pendulum System (마찰진자시스템의 마찰계수 변화에 따른 면진된 원전구조물의 거동특성 비교)

  • Seok, Cheol-Geun;Song, Jong-Keol
    • Journal of the Earthquake Engineering Society of Korea
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    • v.20 no.2
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    • pp.125-134
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    • 2016
  • In order to improve seismic safety of nuclear power plant (NPP) structures in high seismicity area, seismic isolation system can be adapted. In this study, friction pendulum system (FPS) is used as the seismic isolation system. According to Coulomb's friction theory, friction coefficient is constant regardless of bearing pressure and sliding velocity. However, friction coefficient under actual situation can be changed according to bearing pressure, sliding velocity and temperature. Seismic responses of friction pendulum system with constant friction and various velocity-dependent friction are compared. The velocity-dependent friction coefficients of FPS are varied between low-and fast-velocity friction coefficients according to sliding velocity. From the results of seismic analysis of FPS with various cases of friction coefficient, it can be observed that the yield force of FPS becomes larger as the fast-velocity friction coefficient becomes larger. Also, the displacement response of FPS becomes smaller as the fast-velocity coefficient becomes larger.

Friction Model for Finite Element Analysis of Sheet Metal Forming Processes (박판 성형공정 유한요소 해석용 마찰모델)

  • Keum Y.T.;Lee B.H.
    • Transactions of Materials Processing
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    • v.13 no.6
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    • pp.528-534
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    • 2004
  • In order to find the effect of lubricant viscosity, tool geometry, forming speed, and sheet material properties on the friction in the sheet metal forming, friction tests were performed. Friction test results show that as the lubricant viscosity becomes lower, the friction coefficient is higher. When surface roughness is extremely low or high, the friction coefficient is high. The bigger die corner radii and punch speed are, the smaller is the friction coefficient. From the experimental observation, the friction model which is the mathematical expression of friction coefficient in terms of lubricant viscosity, roughness and hardness of sheet surface, punch corner radius, and punch speed is constructed. By comparing the punch load found by FEM using the proposed friction model with that obtained from the experiment in 2-D stretch forming, the validity and accuracy of the friction model are demonstrated.

Inertia and Coefficient of Friction Estimation of Electric Motor using Recursive Least-Mean-Square Method (순환 최소자승법을 이용한 전동기 관성과 마찰계수 추정)

  • Kim, Ji-Hye;Choi, Jong-Woo
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.56 no.2
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    • pp.311-316
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    • 2007
  • This paper proposes the algorithm which estimates moment of the inertia and friction coefficient of friction for high performance speed control of electric motor. The proposed algorithm finds the moment of inertia and friction coefficient of friction by observing the speed error signal generated by the speed observer and using Recursive Least-Mean-Square method(RLS). By feedbacking the estimated inertia and estimated coefficient of friction to speed controller and full order speed observer, then the errors of the inertia and coefficient of friction and speed due to the inaccurate initial value are decreased. Inertia and coefficient of friction converge to the actual value within several times of speed changing. Simulation and actual experiment results are given to demonstrate the effectiveness of the proposed parameter estimator.

FRICTION CHARACTERISTICS OF A PAPER-BASED FRICTION MATERIAL

  • Gao, H.;Barber, G.-C.;Chu, H.
    • International Journal of Automotive Technology
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    • v.3 no.4
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    • pp.171-176
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    • 2002
  • A bench test set-up is employed to simulate the friction characteristics of a paper-based friction material operating against a steel plate. Dry friction tests are run as well as tests with transmission fluids. Glazed friction material produces a negative coefficient of friction versus sliding velocity (f-v) curve for both dry friction and lubrication with transmission fluids. At low sliding speeds, the coefficient of friction when operating in transmission fluids for glazed friction materials is greater than that under dry friction. An appreciable negative f-v slope occurs at low sliding speeds for glazed friction materials when running with the transmission fluid. The friction material after running in produces a constant f-v curve under dry friction and a negative slope when lubricated with transmission fluid. At low sliding speeds, the coefficient of friction of the run-in friction material is lower than that of the glazed wet material. On the other hand, the run-in friction material has a larger friction coefficient than does the glazed friction material at higher sliding speeds.

Experimental Determination of Friction Characteristics for Advanced High Strength Steel Sheets (초고강도강판 마찰특성의 실험적 규명)

  • Kim, N.J.;Keum, Y.T.
    • Transactions of Materials Processing
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    • v.22 no.4
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    • pp.223-228
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    • 2013
  • The friction coefficients of advanced high strength steel sheets were experimentally determined. In the friction test, the pulling and holding forces acting on the sheet for various friction conditions, such as lubricant viscosity, pulling speed, blank holding pressure, sheet surface roughness, and hardness of the sheet were measured and the friction coefficient was calculated based on Coulomb's friction law. While the friction coefficient, generally, decreases as the value of friction factor increases, the factor associated with the sheet surface roughness shows U shape behavior for the friction coefficient. Furthermore, the relationship between friction coefficient and the wear volume, which was computed for the roughness of both sheet surfaces and the friction area, is linearly proportional.

Development of Wear Equation according to Friction Coefficient and Temperature using a Dual Leaf-Spring in the Sliding Test (판스프링을 사용한 마모실험에서 마찰계수와 마찰온도를 고려한 마모식의 개선)

  • Kim, Jung-Hyun
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.5 no.1
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    • pp.19-26
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    • 2006
  • The wear behavior as the hardness of the sliding elements on the dry wear has been investigated using a dual leaf-spring. The materials of the specimens are used as ten kinds along their hardness. In this study, both upper and lower specimens have been used the same materials. Using experimental data, we figured the relationship between wear coefficient and friction coefficient, and the relationship between wear coefficient and friction temperature. Also we combined friction temperature and friction coefficient instead of wear coefficient. We substituted this into wear equation of Archard. The result had been derived a newly wear equation in using dual leaf-spring wear system.

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Estimation of the Maximum Friction Coefficient of the Rough Terrain to Control the Mobile Robots (주행로봇 제어를 위한 험지의 최대마찰계수 추정)

  • Kang, Hyun-Suk;Kwak, Yoon-Keun;Choi, Hyun-Do;Jeong, Hae-Kwan;Kim, Soo-Hyun
    • Journal of Institute of Control, Robotics and Systems
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    • v.14 no.10
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    • pp.1062-1072
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    • 2008
  • When mobile robots perform the mission in the rough terrain, the traversability depended on the terrain characteristic is useful information. In the traversabilities, wheel-terrain maximum friction coefficient can indicate the index to control wheel-terrain traction force or whether mobile robots to go or not. This paper proposes estimating wheel-terrain maximum friction coefficient. The existing method to estimate the maximum friction coefficient is limited in flat terrain or relatively easy driving knowing wheel absolute velocity. But this algorithm is applicable in rough terrain where a lot of slip occurred not knowing wheel absolute velocity. This algorithm applies the tire-friction model to each wheel to express the behavior of wheel friction and classifies slip-friction characteristic into 3 major cases. In each case, the specific algorithm to estimate the maximum friction coefficient is applied. To test the proposed algorithm's feasibility, test bed(ROBHAZ-6WHEEL) simulations are performed. And then the experiment to estimate the maximum friction coefficient of the test bed is performed. To compare the estimated value with the real, we measure the real maximum friction coefficient. As a result of the experiment, the proposed algorithm has high accuracy in estimating the maximum friction coefficient.

Friction Model to Realize Self-Excited Vibration of Multi-body Systems (다물체계의 자려진동 구현을 위한 마찰 모델링)

  • Roh, Hyun-Young;Yoo, Hong-Hee
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.103-108
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    • 2007
  • This paper presents a friction model to realize self-excited vibration of multi-body systems. The friction coefficient is modeled with a spline function in most commercial codes. Even if such a function resolves the problem of discontinuity in friction force, it cannot realize self-excited vibration phenomena. Furthermore, as the relative velocity approaches zero, the friction coefficient approaches zero with the conventional model. So, slip occurs when small force is applied to the system. To avoid these problems a new friction model is proposed in this study. With the new friction model, the self-excited vibration can be realized since the friction coefficient changes with the relative velocity. Furthermore, the slip phenomena could be reduced significantly with the proposed model.

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Friction Model to Realize Self-excited Vibration of Multi-body Systems (다물체계의 자려진동 구현을 위한 마찰 모델링)

  • Roh, Hyun-Young;Yoo, Hong-Hee
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.17 no.6
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    • pp.524-530
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    • 2007
  • This paper presents a friction model to realize self-excited vibration of multi-body systems. The friction coefficient is modeled with a spline function in most commercial codes. Even if such a function resolves the problem of discontinuity in friction force, it cannot realize self-excited vibration phenomena. Furthermore, as the relative velocity approaches zero, the friction coefficient approaches zero with the conventional model. So, slip occurs when small force is applied to the system. To avoid these problems a new friction model is proposed in this study. With the new friction model, the self-excited vibration can be realized since the friction coefficient changes with the relative velocity. Furthermore, the slip phenomena could be reduced significantly with the proposed model.

Analysis of Friction Coefficient Dependent on Variation of Steel Grade and Reduction Ratio in High Temperature Rolling Process (고온압연공정에서 강종 및 감면율 변화에 따른 마찰계수 변화 분석)

  • Her, J.;Lee, H.J.;Na, D.H.;Lee, Y.
    • Transactions of Materials Processing
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    • v.18 no.5
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    • pp.410-415
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    • 2009
  • Experimental and numerical studies were performed to examine the effect of material temperature and reduction ratio on friction coefficient during hot flat rolling. We carried out a single pass pilot hot flat rolling test at the temperatures range of $900{\sim}1200^{\circ}C$ and measured the spread of deformed material while reduction ratio varied from 20% to 40%. Materials used in this study were a high carbon steel and two alloy steels. The dimension of specimen used in hot rolling experiment was $50mm{\times}50mm{\times}300mm$. We performed a series of finite element simulation of the hot rolling process to compute the friction coefficient change in terms of steel grade and reduction ratio. Results showed that temperature dependency of friction coefficient is not noteworthy but the effect of reduction ratio on friction coefficient is quite large. For high carbon steel, friction coefficient at reduction ratio of 30% is lower than that at that of 20%. Meanwhile friction coefficient at reduction ratio of 40% was one and half times large compared with that at that of 20%. The effect of steel grade on friction coefficient was significant when reduction ration was large, e.g., 40%.