• 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.

• Fashion & Textile Research Journal
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• v.2 no.5
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• pp.443-449
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• 2000

An investigation of the relative velocity of friction surface for the newly developed cone drum twister texturing mechanism is reported. The cone drum twister is one of the outer surface contacting friction-twisting devices in false-twist texturing. In this cone drum twister, a filament yam passes over the surface of the cone drum that rotates by passing the yarn without a special driving device. This research is theoretically composed of the analysis of the false twisting mechanism. The equations were derived by using the conical angle of the cone drum, projected wrapping angle, and yarn helix angle. Theoretical values of the relative velocity of friction surface were calculated and discussed. It is shown that, as the projected wrapping angle increased, the relative velocity of friction surface decreased. But as the conical angle increased the relative velocity of friction surface also increased.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.4
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• pp.440-446
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• 1999

This study is mainly concerned with the friction and wear properties for the specimens of crank shaft which are made of ductile cast iron. The friction and wear tests were carried out for the nor-malized ductile cast iron specimens and their properties were compared with each other at reheat-ing temperatures(550^{\circC,\; 600^{\circ}C,\; 650^{\circ}$) and in dry condition at different friction velocity(0.94 m/s 1.88m/s 2.83m/s) range. After austenized at $910^{\circ}C$ it is observed that the higher the reheating temperature is the hardness becomes decrease which is supposedly attributed to the fact that the amount of pearlite austenite matrix is rduced by reheating after normalizing and that as the reheating temperature goes up the pearlite generated is less and the interval between the pearlites were widened at last to make pearlite globular. At the low velocity the friction coefficient increase in the beginning and gets stabilized as the sliding distance increases. As the friction velocity grows the friction coefficient decreases suppos-edly since the abrasive wear is heavier at low velocity than at the high velocity as the friction tem-perature at low velocity is lower than at high velocity.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.1045-1049
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• 1996

For the precision positioning and tracking control, the proper friction compensation is essential. The friction causes steady state error. The friction compensation based on the velocity and the controlling input or the desired velocity provides limited performance if the compensation value is fixed. In this paper, a friction compensation scheme using a fuzzy logic is proposed. The friction compensation amount is adjusted depending on the velocity and controlling input. The proposed fuzzy friction compensator with a pole-assignment controller is implemented in a linear positioning system. To illustrate the effectiveness of this scheme, computer simulations and experiments are carried out for the cases of no friction compensation, the proposed fuzzy friction compensation, and another friction compensation scheme based on velocity and control input, and the results are compared with each other.

• The Journal of the Korea Contents Association
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• v.16 no.4
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• pp.614-623
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• 2016

Grid(pipe network) design is an important element of Smart Water Grid, which essential to estimate hydraulic parameters such as the pressure, friction factor, friction velocity, head loss and energy slope. Especially, friction velocity in a grid is an important factor in conjunction with energy gradient, friction coefficient, pressure and head loss. However, accurate estimation friction head loss, friction velocity and friction factor are very difficult. The empirical friction factor is still estimated by using theory and equation which were developed one hundred years ago. Therefore, in this paper, new equation from maximum velocity and friction velocity is developed by using integration relationship between Darcy-Weisbach's friction head loss equation and Schlichting equation and regression analysis. To prove the developed equation, smooth pipe data areis used. Proposed equation shows high accuracy compared to observed data. Study results are expected to be used in stability improvements and design in a grid.

• The Journal of the Korea Contents Association
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• v.15 no.2
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• pp.499-506
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• 2015

The friction velocity is a quantity with the dimensions of velocity defined by the friction stress and density of a wall surface at near wall of flow condition. Also, the friction velocity is the hydraulic parameter describing shear force at the bottom flow. Moreover, it is a very important factor in designing open channel and essential to determine the mixing coefficient in the main flow direction. The estimation of the friction velocity are such as methods using channel slope, linear law of the mean velocity at viscous sub-layer and direct measurement of wall shear stress, etc. In the present study, we propose a friction velocity equation that has been optimized by combining the concept of entropy, which is used in stochastic method, and to verify the proposed equation, the experimental data measured by Song was used. The R squared for friction velocities between proposed equation and friction velocity formula analyzed 0.999 to 1.000 in a very good agreement with each equation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.3
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• pp.427-435
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• 1997

Conditional sampling techniques are utilized to investigate the relation between the wall skin-friction and stream wise velocity fluctuations in a turbulent boundary layer. Conditionally averaged results using a peak detection and the VITA (variable-interval time-averaging) technique show that a high skin friction is associated with high frequency components of the wall skin-friction fluctuations. The conditionally averaged wall skin-friction fluctuations obtained by using the VITA technique have a positively-skewed characteristics compared with the conditionally averaged stream wise velocity fluctuations. It is confirmed that there exists a phase shift between the wall skin-friction and stream wise velocity fluctuations, which was also found from the long-time averaged space-time correlations. The amount of phase shift between the wall skin-friction and stream wise velocity fluctuations is the same as that from the long-time averaged space-time correlations and does not change despite the variation of the detection threshold.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.261-261
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• 2000

This paper analyzes the characteristics of pre-sliding friction of an X-Y table of CNC machining center at velocity reversal, and presents a simple and effective method of friction compensation based on this characteristics. At velocity reversal, a large position tracking error occurs because of the discontinuous change of friction. The relationship between the occurrence time of maximum position tracking error and the acceleration at zero velocity is analyzed by using the spring-like friction model. Furthermore, the experimental observation verifies this relation. From this, the state transition tine from pre-sliding regime into sliding regime can be predicted. Using the predicted transition time, the friction can be effectively compensated and table experimental results show its effectiveness.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.1
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• pp.28-34
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• 2014

This study provides the numerical finite-element method(FEM) estimating the friction noise induced by the negative slope in the friction-velocity curve. The friction noise due to the friction-velocity curve is experimentally investigated through the pin-on-disk setup. The measured squeal frequency is estimated by FEM. The friction curve is measured by the friction test, then it is applied to the complex eigenvalue analysis. The results shows that the experimental squeal frequency can be determined by the FEM analysis. Also, it is emphasized that the negative friction-velocity slope is essential in generating friction noise in the pin-on-disc system.

• Water Engineering Research
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• v.3 no.2
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• pp.135-142
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• 2002

This study investigates the effects of sediment on the flow characteristics such as velocity distribution, friction velocity, turbulent intensities, Reynolds stress, etc. Particle tracking velocimetry (PTY) is used to measure the vertical flow field. Results show that flow over the high bed-load concentration region has larger values of mean velocity and friction velocity and smaller values of turbulence intensities, compared to those for flow over the low bed-load concentration region.