• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.119-124
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• 1999

Quantitative evaluation of the tribological conditions at the tool-workpiece interface in metal forming is usually accomplished by the ring-compressinon. test This paper describes an experimental investigation into shear friction factor under cold and hot forming conditions according to materials and lubricants using the ring compression test. Six different materials and five different lubricants were applied in the experiments. calibration curves with the friction coefficient were obtained using FEM analysis and verified by the verified by the experimental results. The influence of materials and lubricants level on friction are discussed. In the ring compression test the shear friction factor has a different from steels and aluminum water base graphite lubricants on cold working conditions and hot working conditions.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.814-820
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• 2000

This papers investigates the combined effects of parameters such as die surface finish, die directionality of stoning, contact pressure and draw speed on the resulting friction factor. Also, this study show the correlation between the NN(Neural Network) and DOE (Design of Experiments) to reduce the number of experiments without the loss of the effects of parameter upon friction factor. The experiments were run in random order with at least three replicates. It was found that the directional stoning orthogonal to the pulling direction is lower friction than directional stoning parallel to the pulling direction using FCD55 die and SPCEN

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.587-592
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• 1999

The combined effects of radius ratio and roughness pitch ratio on the turbulent fluid flow characteristics of the fully developed flow in the annullar tubes with rib-roughened core walls were determined for Reynolds number ranging from 12,000 to 66,000. To understand the underlying physical phenomena responsible for friction factor enhancement, measurements of velocity profiles and zero shear stress and maximum velocity positions were combined to propose the friction factor correlation. Friction factors were found to be a function of the roughness pitch ratio and radius ratio.

• International Journal of Air-Conditioning and Refrigeration
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• v.16 no.2
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• pp.70-76
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• 2008

The effects of the inclined perforated baffles on the distributions of the local heat transfer coefficients and friction factors for air flows in a rectangular channel were determined for Reynolds numbers from 23,000 to 57,000. Four different types of the baffle are used. The inclined baffles have the width of 19.8cm, the square diamond type hole having one side length of 2.55cm, and the inclination angle of $5^{\circ}$, whereas the corresponding channel width-to-height ratio was 4.95. Results show that the heat transfer and friction factor depend significantly on the number of baffle holes and Reynolds number. The friction factor decreases with increasing Reynolds number and the number of holes on the baffle, and the heat transfer performance of baffle type II (3 hole baffle) has the best value.

• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.445-449
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• 2009

With the recent increase in the demand for the net-shape forming, numerical simulations are being commonly adopted to increase the efficiency and effectiveness of design of bulk metal forming processes. Proper consideration of tribological problems at the contact interface between the tool and workpiece is crucial in such simulations. In other words, lubrication and friction play important roles in metal forming by influencing the metal flow, forming load and die wear. In order to quantitatively estimate such friction condition or lubricant characteristic, the constant shear friction model is widely used for bulk deformation analyses. For this, new friction testing method based on the forward or backward extrusion process is proposed to predict the shear friction factor in this work. In this method, the tube-shaped punch pressurizes the workpiece so that the heights at the center and outer of punch (or mandrel) become different according to the friction condition. That is, the height at the center of punch is higher than that at the outer of the punch when the friction condition at the contact interface is severe. From this founding, the proposed friction testing method can be applied to effectively evaluate the friction condition in bulk metal forming processes.

• Transactions of Materials Processing
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• v.12 no.8
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• pp.693-701
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• 2003

In this paper, the influence of frictional conditions on the backward impact extrusion of aluminum battery casing with large aspect ratio has been investigated. In the simulation, MSC.Superforge, a package based on the finite volume method, is used for the extrusion analysis. The formability and earing problem during the production have been evaluated by studying the sensitivity to frictional effects. During the sensitivity analysis, the friction factor was varied from 0.02 to 0.24. As the friction factor is increased, the forming height of the narrow edge is decreased, and the forming height of the wide edge is increased. When the friction factor becomes 0.2, the earing problem does not occur The experimental results show a good agreement with analytical results.

• Journal of Mechanical Science and Technology
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• v.15 no.9
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• pp.1217-1225
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• 2001

The governing equations are derived for the analysis of a stepped labyrinth gas seal generally used in high performance compressors, gas turbines, and steam turbines. The bulk-flow is assumed for a single cavity control volume set up in a stepped labyrinth cavity and the flow is assumed to be completely turbulent in the circumferential direction. The Moodys wall-friction-factor model is used for the calculation of wall shear stresses in the single cavity control volume. For the reaction force developed by the stepped labyrinth gas seal, linearized zeroth-order and first-order perturbation equations are developed for small motion about a centered position. Integration of the resultant first-order pressure distribution along and around the seal defines the rotordynamic coefficients of the stepped labyrinth gas seal. The resulting leakage and rotordynamic characteristics of the stepped labyrinth gas seal are presented and compared with Scharrers theoretical analysis using Blasius wall-friction-factor model. The present analysis shows a good qualitative agreement of leakage characteristics with Scharrers analysis, but underpredicts by about 20%. For the rotordynamic coefficients, the present analysis generally yields smaller predictied values compared with Scharrers analysis.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.532-537
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• 1998

Friction factor and two-phase flow frictional multiplier for a CANFLEX bundle are newly developed and presented in this paper. CANFLEX as a 43-element fuel bundle has been developed jointly by AECL/KAERI to provide greater operational flexibility for CANDU reactor operators and designers. Friction factor and two-phase flow frictional multiplier have been developed by using the experimental data of pressure drops obtained from two series of Freon-l34a (R-134a) CHF tests with a string of simulated CANFLEX bundles in a single phase and a two-phase flow conditions. The friction factor for a CANFLRX bundle is found to be about 20 % higher than that of Blasius for a smooth circular pipe. The pressure drop predicted by using the new correlations of friction factor and two-phase frictional multiplier are well agreed with the experimental pressure drop data of CANFLEX bundle within ${\pm}\;5\;%$ error.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.3
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• pp.348-357
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• 1998

The flow characteristics inside U-bend tube of the laminated plate heat exchanger were numerically investigated. The behavior of fluid flow, and the variations of the faulty area and friction factor are examined according to the distance between the span and the wall and the diameter of the round attacked to the end of span. The results show that the diameter(d) of the round attached to the span is mainly associated with the smooth circulation of fluid flow rather than the size of faulty area and the friction factor. As the distance($\ell$) between the span and the wall decreases, the faulty area decreases, however the friction factor dramatically increases. It is also found that one can obtain a good result in the view of the flow characteristics and pressure drop at d=7.5mm and $\ell$=30.5mm.