• 물과 미래
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• 제29권4호
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• pp.223-231
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• 1996

보다 효율적인 관로운영에 필수적인 통수능 변화 및 영향인자 산정을 위하여 국내 도송수강관에 대하여 124개의 Hazen Williams및 Darcy-Weisbach 마찰계수를 실측, 분석하였다. 그 결과 국내 도송수강관은 국외의 마찰계수 변화형태와 유사한 경향을 보이며 관경이 클수록 (Diameter>1100mm) 통수능은 관령에 많은 영향을 받으나 관경이 작을수록 관경과 관령에 동시에 영향을 받는다는 사실을 알았다. 또한 Hazen Williams의 C 값은 외국에 비해 약 5-10 정도 작은 것으로 나타났으며, 조도높이의 성장률은 약 0.41 mm/년으로 관의 통수능이 외국에 비해 빨리 저하한다는 사실이 밝혀져 그 원인 파악 및 통수능 산정기준을 재 검토해야 할 것으로 판단되었다. For the most efficient operation of water mains, 124 head losses in domestic water supply steel mains were measured to provide the values of friction coefficient and the variable affecting the deterioration rate of Hazen Williams' and Darcy-Weisbach's friction coefficient. The experimental results show that pipe age is governing the friction coefficient of large mains (Diameter > 1100 mm). On the other hands, pipe age and pipe diameter are affecting the variation of carrying capacity for small mains (Diameter < 1100 mm). The friction coefficient of water mains in foreign countries is higher than that in Korea by about 5 to 10 in Hazen Williams' C value. The growing rate of roughness height of domestic water main is about 0.41 mm/year which is higher than the average of United States of America. So further study is required to find out what causes the serious deterioration rate.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2001년도 추계학술대회 논문집
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• pp.125-130
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• 2001

It is vary importance that stopping distance for the freight train and need to design parameter of the brake force and friction coefficient. Acoording to the brake force between shoe and wheel less than the adhesion between wheel and rail. Because of vary difference between empty and weight car of 0∼500kN, this solution was made to application for variable loaded brake system. When the V=110km/h. the emergency stopping distance of freight train is about 700m, so this study was considered on the two condition, one of the increse brake force and to be different of the increse friction coefficient on the brake shoe. It was useful increse friction coefficient. Result of study, analyze effect of the brake shoe on the brake force of the freight car and high friction coefficient were proposed. To do this, ${\mu}$=0.155${\pm}$10% when S=600m on the V=110km/h of the train, 2 groove of friction surface on the temperature distribution were considered.

• Smart Structures and Systems
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• 제6권8호
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• pp.953-974
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• 2010

The performance of variable dampers for seismic protection of the benchmark highway bridge (phase I) under six real earthquake ground motions is presented. A simplified lumped mass finite-element model of the 91/5 highway bridge in Southern California is used for the investigation. A variable damper, developed from magnetorheological (MR) damper is used as a semi-active control device and its effectiveness with friction force schemes is investigated. A velocity-dependent damping model of variable damper is used. The effects of friction damping of the variable damper on the seismic response of the bridge are examined by taking different values of friction force, step-coefficient and transitional velocity of the damper. The seismic responses with variable dampers are compared with the corresponding uncontrolled case, and controlled by alternate sample control strategies. The results of investigation clearly indicate that the base shear, base moment and mid-span displacement are substantially reduced. In particular, the reduction in the bearing displacement is quite significant. The friction and the two-step friction force schemes of variable damper are found to be quite effective in reducing the peak response quantities of the bridge to a level similar to or better than that of the sample passive, semi-active and active controllers.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2021년도 학술발표회
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• pp.63-63
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• 2021

Bed shear stress is important variable in river flow analysis. The bed shear stress has an effects on bed erosion, sediment transport, and mean flow characteristics. Quadratic formula to estimate bed shear stress is widely used, 𝜏=𝜌c_fu|u| in which friction coefficient, c_f, needs to be assigned to numerical models. The aim of this study is to estimate Chezy coefficient using bathymetry data measured by ADCP. Bed form geometry variables will be estimated form bed profile, then Chezy coefficient will be determined using estimated bed form geometry variables in order to set friction coefficient to numerical model. From the probability density function obtained from the bathymetry data, Chezy coefficient will be randomly generated since Chezy coefficient is not uniform over the space and it does not depend on spatial variables such as water depth and distance from river bank. Numerical test will be performed to find to demonstrate randomly extracted Chezy coefficient is appropriate. The result of this study is valuable in that the friction coefficient is estimated in consideration of the bed profile, and as a result, uncertainty of the friction coefficient can be reduced.

• 한국안전학회지
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• 제34권5호
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• pp.139-143
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• 2019

In this study, we tried to derive the most severe scenario and its critical speed by 1-D collision simulation with a variable formation vehicle in order to prepare for the change of demand in Seoul Metropolitan Subway Line 3, which is operated by fixed arrangement. After establishing various collision scenario conditions, the friction coefficient between the wheel and the rail was evaluated as 0.3, which is considered to be severe. As a result of analysis according to all scenarios, the most severe scenario conditions were confirmed by comparing rubber shock absorber performance and vehicle collision deceleration. In addition, a typical wheel-rail friction coefficient was derived through accident cases, and the analysis was performed again and compared. Finally, the criterion of the critical speed in the condition of the friction coefficient of the normal wheel - rail condition was confirmed.

• 한국자동차공학회논문집
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• 제6권6호
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• pp.226-233
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• 1998

In this paper, an experimental study was performed to investigate the speed ratio-torque-thrust characteristics for metal belt CVT. It is observed from the experimental results that nondimensional secondary thrust force follows with the existing theoretical formula with ${\mu}$=0.09~0.12 depending on the torque and the speed ratio. In order to represent these characteristics, an effective friction coefficient was introduced. Also, the slip characteristics between the belt and the pulley were investigated experimentally and traction coefficients at gross slip were obtained for various speed ratios. Using the traction coefficients and the effective friction coefficients, an improved formula for the secondary thrust force was suggested assuming that thrust force is the summation of the thrust of pseudo inactive arc and the thrust of pseudo active arc. The effective friction coefficient and the improved formula for the speed ratio-torque-thrust relationship suggested in this work can be used to obtain the appropriate secondary thrust.

• Tribology and Lubricants
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• 제11권3호
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• pp.48-53
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• 1995

In this paper, the friction characteristics of contact region between vane tip and camring is studied using a modeled experimental device. The contact region is under the influence of variable loads with the amplitude of hundreds of Newton and frequency of tens of Hz. The condition of lubrication between vane and disk is modeled after the actual condition between vane and camring. The coefficient of friction is obtained by measuring the frictional forces in the contact region between camring and vane. The friction characteristics of the actual oil hydraulic vane pump is estimated on the basis of coefficient of friction. The analysis of frictional characteristics shows us that the lubrication condition of vane tip is that of transition regime between hydrodynamic lubrication and mixed lubrication.

• Structural Engineering and Mechanics
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• 제34권1호
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• pp.61-84
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• 2010

Presented in this paper is the behaviour of asymmetric building isolated by the double variable frequency pendulum isolator (DVFPI). The DVFPI is an adoption of single variable frequency pendulum isolator (VFPI). The geometry and coefficient of friction of top and bottom sliding surfaces can be unequal. The governing equations of motion of the building-isolation system are derived and solved in incremental form. The analysis duly considers the interaction of frictional forces in the two principal directions developed at each sliding surface of the DVFPI. In order to investigate the behaviour of the base isolation using the DVFPI, the coupled lateral-torsional response is obtained under different parametric variations for a set of six far-fault earthquake ground motions and criterion to optimize its performance is proposed. Further, influences of the initial time period, coefficient of friction and frequency variation factors at the two sliding surfaces are investigated. The numerical results of the extensive parametric study help in understanding the torsional behaviour of the structure isolated with the double sliding surfaces as in the DVFPI. It is found that the performance of the DVFPI can be optimized by designing the top sliding surface initially softer and smoother relative to the bottom one.

• 대한기계학회논문집
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• 제7권1호
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• pp.64-72
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• 1983

A method of numerical analysis is proposed for the pure stretch forming of A1 sheet by hemi-spherical punch. The analysis is performed by Woo's general method under the condition of variable friction and plastic yielding is based on the new anisotropic yield function proposed by Hill. A comparison of the calculated results with experiment shows good agreement for various lubrication when the initial values of the coefficient of coulomb friction at pole are less than 0.4.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제18권3호
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• pp.245-256
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• 2014

This work is focused on the boundary layer and heat transfer characteristics of hydromagnetic flow over a stretching sheet with variable thickness. Steady, two dimensional, nonlinear, laminar flow of an incompressible, viscous and electrically conducting fluid over a stretching sheet with variable thickness and power law velocity in the presence of variable magnetic field and variable temperature is considered. Governing equations of the problem are converted into ordinary differential equations utilizing similarity transformations. The resulting non-linear differential equations are solved numerically by utilizing Nachtsheim-Swigert shooting iterative scheme for satisfaction of asymptotic boundary conditions along with fourth order Runge-Kutta integration method. Numerical computations are carried out for various values of the physical parameters and the effects over the velocity and temperature are analyzed. Numerical values of dimensionless skin friction coefficient and non-dimensional rate of heat transfer are also obtained.