• Journal of Mechanical Science and Technology
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• v.18 no.1
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• pp.153-166
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• 2004

This paper presents a comparative study of a fully coupled, upwind, compressible Navier-Stokes code with three two-equation models and the Baldwin-Lomax algebraic model in predicting transonic/supersonic flow. The k-$\varepsilon$ turbulence model of Abe performed well in predicting the pressure distributions and the velocity profiles near the flow separation over the axisymmetric bump, even though there were some discrepancies with the experimental data in the shear-stress distributions. Additionally, it is noted that this model has y$\^$*/ in damping functions instead of y$\^$＋/. The turbulence model of Abe and Wilcox showed better agreements in skin friction coefficient distribution with the experimental data than the other models did for a supersonic compression ramp problem. Wilcox's model seems to be more reliable than the other models in terms of numerical stability. The two-equation models revealed that the redevelopment of the boundary layer was somewhat slow downstream of the reattachment portion.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.3 s.18
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• pp.165-173
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• 2004

Matching inviscid and boundary layer methods are developed for analysis of hypersonic flow with thick boundary layer. The new equations match all the boundary layer properties with a variation in the inviscid solution near the edge, except for the normal velocity. Computational comparison are peformed for incompressible and compressible flows over a flat plate. Results from the present method are compared with Wavier-Stokes solutions. The present results are in good agreement with Wavier-Stokes solutions. They show that the new technique can provide improved predictions of heating rates and skin friction predictions for preliminary design of vehicles where shear layers and entropy layer swallowing are importantfor for preliminary design.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.12
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• pp.1663-1673
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• 2002

In the present paper, flow and heat transfer characteristics of confined impinging slot jets have been numerically investigated using a SIMPLE-based segregated SUPG finite element method. For laminar jets, it is shown that the skin friction coefficient obtained from the present SUPG formulation approaches the grid-independent Galerkin solution inducing negligible false diffusion in the flow field when a moderate number of grid points are used. For turbulent jets, the k-$\omega$turbulence model is adopted. The streamwise mean velocity and the heat transfer coefficient respectively agree very well with existing experimental data within limited ranges of parameters.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.222-231
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• 1996

Temperature distribution on the flank face in orthogonal turning with cutting tool of high speed steel is studied by using a finite element method and experiments. Experiments are carried out to verify the validity of the temperature measurement by using a thermoelectric couple junciton imbedded in a cutting tool of high speed steel. Good agreement is obtained between the analytical results and the experimental ones for the temperature distributions on flank face of cutting tool with igh speed steel. The analytical results show that the temperature on the top flank face of a tool is higher because of the difference of the friction velocity on each face of the tool.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1542-1547
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• 2003

Air entrainment can become a significant problem in a web handling process. The development of air film between a web and an idle roller can cause a reduction of traction and traction coefficient, by which a slip is occurrred. Computational and experimental study was carried out to describe the slippage of an idle roller for given operating conditions, tension and web velocity. An extended mathematical model to find out a slip condition was developed by using the models of air film height, dynamic traction coefficient, and torque balance of a rotational roller. And by using the extended model, a mechanism to define the slippage between the roller and the moving web was suggested. The results of simulation and experiment showed that the extended dynamic model could properly characterize the rotational motion of the idle roller by considering dynamic traction coefficient. By examining the rotational motion of the idle roller with web dynamics(speed), the mechanism to define al slip condition between the roller and the web was found to be effective.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.358-359
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• 2005

Chemical mechanical polishing(CMP) process depends on a variety of variables. Especially, surface roughness of pad plays a key role in material removal in CMP in terms of transportation ability of pores and real contact area. The surface roughness is deteriorated with polishing time by applied pressure and relative velocity. In this reason, diamond conditioner has been used to maintain the roughness on the pad. The authors try to investigate the correlation between pad roughness and frictional behavior by comparing ex-situ conditioning with in-situ conditioning.

• Transactions of The Korea Fluid Power Systems Society
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• v.5 no.1
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• pp.1-5
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• 2008

Pneumatic driving systems have hard non-linear characteristic and large friction force compared with driving power. Hence, it cannot be robust against parameter uncertainties, modelling error, disturbance and noise. In this study, we apply a mixed $H_2/H_{\infty}$ control to the generalized plant for a pneumatic driving apparatus system including parameter uncertainty and disturbance. In order to design the $H_2/H_{\infty}$ controller, we use the LMI technique. To evaluate control performance and robust stability of the designed controller, we compare it with a conventional controller such as PVA(Position-Velocity-Acceleration state controller) using the simulation results. As a result, it can be known that designed controller shows better robust stability than the conventional controller.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.32-38
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• 2006

A premixed flame propagating in a tube suffers strong variation in its shape and structure depending on boundary conditions. The effects of thermal boundary conditions and flow fields on flame propagation are numerically investigated. Navier-Stokes equations and species equations are solved with a one-step irreversible global reaction model of methane-air mixture. Finite volume method using an adaptive grid method is applied to investigate the flame structure. In the case of an adiabatic wall, friction force on the wall significantly affected the flame structure while in the case of an isothermal wall, local quenching near the wall dominated flame shapes and propagation. In both cases, variations of flow fields occurred not only in the near field of the flame but also within the flame itself, which affected propagation velocities. This study provides an overview of the characteristics of flames in small tubes at a steady state.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.144-149
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• 1996

In this paper, the clamping type forging of helical gears has been investigated. Clamping type forging is an operation in which the product is constrained to extrude sideways through an orifice in the container wall. Punch is cylindrical shaped. The punch compresses a cylindrical billet placed in a die insert. As a consequence the material flows in a direction perpendicular to that of punch movement. The forging has been analysed by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, an involute curve has been introduced to represent tooth profile of the gear. Numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth, helix angle, friction factor and initial height of billet on the forging of helical gears.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.4
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• pp.151-157
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• 2003

A new type of precision actuator is developed using piezoelectric bimorphs. This type of actuator is applicable for the flat surface or in-pipe system and can make forward and backward motion. Two bimorphs are linked serially and two different phased voltages are applied to each bimorph. Therefore, The end of the bimorph makes ellipsoidal motion. The device moves by the friction force between the rubber attached at the bimorph end and the inner surface of the pipe. As the results, the driving range of the device is about 0~18Hz and the device guarantees very high linearity at low frequency, 0~1 Hz. The maximum velocity of the device is about 6mm/s at 10Hz. The developed mechanism is very simple and use piezoelectric bimorph. So, it is possible to miniaturize and educe the power consumption.