• 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.

• Water for future
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• v.28 no.2
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• pp.155-168
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• 1995

The present paper discusses the traditional empirical equations of friction factor or cross-sectional mean velocity of open channel flow and suggests the new form of friction factor equation. Dimensional analysis is conducted for the possible forms of traditional empirical equations in order to satisfy the dimensional equality, and new forms of empirical equations are presented with introducing equivalent roughness height. Considering the distribution of friction factor against Reynolds number which has a similar characteristics to that of smooth turbulent flow in circular pipe, the friction factor equation of rectangular open channel flow is developed by modifying the friction factor equation of circular pipe flow for the region of smooth turbulent flow. The equations including the dimensionally-corrected empirical equations are tested against Bazin's laboratory experiments.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.850-854
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• 2009

Approximate analysis for a building installed with a friction damper is revisited to get insight of its dynamic behavior. Energy balance equation is used to have a closed analytical form solution of dynamic magnification factor (DMF) for the building with combined viscous and friction damping. It is found out that DMF is dependent on friction force ratio and resonance frequency. Linear transfer function from input external force to output building displacement is obtained by simplifying DMF equation. Root mean square of building displacement is derived under earthquake-like random excitation. Finally, design of friction damper is proposed by processing target control ratio, damping ratio factor, and friction force in sequence.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.308-312
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• 1999

Developed the model equations which calculate roll force, roll power during hot rolling in real time. The variables which mainly effect on the roll force, roll power are shape factor, reduction, roll diameter, roll velocity, strip inlet temperature, carbon content of strip and strip-roll contact friction coefficient. Among these variables roll diameter, roll velocity, inlet temperature, carbon content and friction coefficient can be excluded in interpolated model equation by introducing equation of die force(F'), power(p') of the frictionless uniform plane strain compression which can be calculated without iteration. At the case of coulomb friction coefficient of 0.3, we evaluated coefficient of polynomial equations of {{{{ { F} over {F' } }}}}, {{{{ { Pf} over {Pd }, { Pd} over {P' } }}}} from the result of finite element analysis using interpolation. It was found that the change of values of {{{{ { F} over {F' }, { P} over {P' } }}}} with the friction coefficient tend to straight line which slope depend only on shape factor. With these properties, developed model equations could be extended to other values of coulomb friction coefficient. To verify developed roll force, roll power model equation we compared the results from these model equation with the results from these model equation with the results from finite element analysis in factory process condition.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.4
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• pp.397-403
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• 1994

The seepage flow has been investigated conducting laboratory experiments mainly in order to determine the relation of seepage flow friction factor against Reynolds number. The apparatus of seepage flow measurements has the water flow almost horizontaly. Several sets of experiments were carried out, and various flow conditions were obtained in each set of flow. To cover wide range of flow conditions, used were various materials of different measurement sizes and various stages of water discharge in the seepage flow tests. Shape factor equation was developed using existing data, and based on the present laboratory data, an explicit equation was developed for the estimation of friction factor of seepage flow in the range of Reynolds number from about 1 to about 600. The same equation is expected for the flow condition of Reynolds number over 600, considering the trend of friction factor distribution.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2868-2875
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• 2015

Both the friction velocity and the friction coefficient have to be estimated to determine flow characteristic in an open channel. In spite of the importances in an open channel, the complete interpretation is highly difficult because of free water surface, the complex of cross section and the various hydraulic parameters. The researches related to the friction factor are based on empirical outcome. Therefore, the equations are difficult to be generally applied. For that reason, the new friction factor estimation equation using the entropy concept was proposed in the present study, and the data measured in rectangular and trapezoid cross sections was used to verify the accuracy of equation. The advantage of the proposed equation dose not use the energy slope term which is difficult to be measured and to be estimated in an open channel. In addition, the proposed method showed that the accurate friction factor f can be estimated on the Basis of theoretical background.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.1
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• pp.22-28
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• 2010

Approximate analysis for a building installed with a friction damper is performed to get insight of its dynamic behavior. Energy balance equation is used to have a closed analytical form solution of dynamic magnification factor(DMF). It is found out that DMF is dependent on friction force ratio and resonance frequency. Approximation of DMF and equivalent damping ratio of a friction damper is proposed with such assumption that the building with a friction damper shows harmonic steady-state response and narrow banded response behavior near resonance frequency. Linear transfer function from input external force to output building displacement is suggested from the simplified DMF equation. Root mean square of a building displacement is derived under earthquake-like random excitation. Finally, design procedure of a friction damper is proposed by finding friction force corresponding to target control ratio. Numerical analysis is carried out to verify the proposed design procedure.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.2
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• pp.73-78
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• 2010

Wave energy is dissipated mainly by friction on the seabed until the waves reach the surf zone. Many researchers have investigated the mechanism of wave friction and the bottom shear stress induced by wave motion at a certain point is now well estimated by introducing the wave friction factor related to the near bed velocity given by linear wave theory. The variation of wave energy or wave height over a long distance can be, however, estimated by an iteration process when the propagation of waves is strongly influenced by bed friction. In the present study simple semi-theoretical equation has been developed to compute the variation of wave height for the condition of wave propagation on a constant beach slope. The ratio of wave height is determined by the product of shoalng factor and wave height friction factor (frictional wave energy dissipation factor). The wave height estimated by the new equation is compared with the wave height estimated by the solution of numerical integration for the condition that the waves propagate on a constant slope.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6B
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• pp.373-378
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• 2012

In this study, a new empirical equation for the transverse dispersion coefficient has been developed based on the theoretical background in river bends. The nonlinear least-square method was applied to determine regression coefficients of the equation. The estimated dispersion coefficients derived by the new equation were compared with observed transverse dispersion coefficients acquired from natural rivers and coefficients calculated by the other existing empirical equations. From a comparison of the existing transverse dispersion equations and the new proposed equation, it appears that the behavior of the existing formula in a relative sense is very much dependent on the friction factor and the river geometry. However, the new proposed equation does not vary widely according to variation of friction factor. Also, it was revealed that the equation proposed in this study becomes an asymptotic curve as the curvature effect increases.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1782-1793
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• 2008

Republic of korea has begun operating high speed train service according as KTX service operation starts in 2004. Also, EMU whose maximum speed is over 150 kph will be starting to service with electrification and improvement of existing railroad. Moreover, metropolitan electric railways have begun an express service to increase scheduled speed. Therefore, running resistance of rolling stock becomes more important factor effects on the performance. Running resistance of rolling stock is the factor which is necessary for the performance or operation plan of rolling stock, and it's related to rolling friction, slip friction, drag force, gradient, acceleration, curvature, tunnel condition and so on. It is possible to be calculated by CFD (Computational Fluid Dynamics). However it is predicted by experimental equation from running resistance test because of the complex calculation and manifold variables. In this paper, studies about running resistance of rolling stock is introduced, and each term of experimental equation is studied through theoretical approximation. Also, running resistance of rolling stock is estimated by the result of running resistance test, and effects being related to friction, drag force, gradient is examined.