• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.6
• /
• pp.1541-1546
• /
• 1993

To extend the widely used Gibson and Launder's second order closure model to the low-Reynolds-number region near a wall, modifications have been made for velocity pressure-gradient interaction and dissipation terms in the stress equations, and also for the dissipation rate equation. From the computation of fully developed plane channel flow, it is found that the results with present model agree well with the data of direct numerical simulation in the predictions of stress components. And, the computed mean velocity profile coincides with the universal velocity law.

• Proceedings of the KIEE Conference
• /
• 1990.07a
• /
• pp.286-288
• /
• 1990

This paper reports the characteristics of sparkover discharge in flowing air ranging from 0[m/s] to 30 [m/s] under the needle-needle gap. Flowing air duct of this investigation is circular tube. The important results obtained form this study are as follows. 1. the ratio of sparkover voltage to the Reynolds number decreases with increasing the Reynolds number. 2. The duration time of sparkover(t) decreases with increasing the Reynolds number. 3. the empirical equation obtained form this experiment is [ %]${\frac{Vs}{Re}}$ = A + $B{\varepsilon}^{C.Re}$ where A = 10.2 b = 125 c = -4.66 ${\times}$ $10^{-5}$

• 제어로봇시스템학회:학술대회논문집
• /
• 2004.08a
• /
• pp.990-994
• /
• 2004

This paper presents a method to predict the transient characteristic of the air lubricated slider head in a hard disk drive by using optimization technique. The time dependent modified Reynolds equation based on the molecular slip flow approximation equations was used to describe the fluid flow within the air bearing and the implicit finite difference scheme is applied to calculate the pressure distribution under the slider head. The exhaustive search combined with the Broyden-Fletcher-Goldfarb-Shanno method were employed to obtain optimum design variables which are taper angle, rail width and taper length in order to keep the forces and moments acting on the slider head in dynamic equilibrium. The results show that the optimal head slider of the magnetic head has good stability characteristic that can reach the steady state within 0.5 microsecond.

• Journal of computational fluids engineering
• /
• v.4 no.3
• /
• pp.12-20
• /
• 1999

The computations of the flowfield and pollutant dispersion over a flat plate and the Russian hills of various slopes are described. The Gaussian plume and the puff model have been used to calculate concentration of pollutant. The Reynolds-averaged unsteady incompressible Navier-Stokes equation with low Reynolds κ-ε model has been used to calculate the flowfield. The flow data of a flat plate and the Russian hills from Navier-Stokes equation solutions has been used as the input data for the puff model. The computational results of flowfield agree well with experimental results of both a flat plate and Russian hills. The concentration prediction by the Gaussian plume model and the Gaussian puff model also agrees flirty well with experiments.

• Tribology and Lubricants
• /
• v.21 no.6
• /
• pp.283-288
• /
• 2005

This paper presents the theoretical model and analysis results to investigate the effect of Coulomb damping in the sub-structure of a foil bearing. Vertical and horizontal deflection of a bump is restricted by friction of the bump. Equivalent viscous damping of the bump foil is derived from the Coulomb friction. Dynamic equation of the bump is constituted by stiffness and damping terms. The air film is modeled by the compressible Reynolds equation. A perturbation approach and finite difference numerical method is used to determine the static and dynamic performance of the bearing from the coupled fluid-structural model. The analysis result shows that the static and dynamic performance is enhanced by the bump friction.

• Tribology and Lubricants
• /
• v.24 no.1
• /
• pp.14-20
• /
• 2008

In this paper, the characteristics of trapezoidal air screws is studied. These screws can e applied to the elevator having column driving shaft. The generalized coordinate transformation technique is used to solve incompressible Reynolds' equation because the air lubricated plane is twisted. The transformed equation is discretized by the base of Finite difference method. Using Visual C++ language, a GUI program which can calculate he load carrying capacity for this kind of air screw is developed, then the design variables for these air screws is studied.

• 한국전산유체공학회:학술대회논문집
• /
• 1995.10a
• /
• pp.37-42
• /
• 1995

In the present study, an improved version of 4-equation low-Reynolds-number 4-equation model is proposed. The equations of the temperature variance ($k_{\theta}$) and its dissipation rate(${\varepsilon}_{\theta}$) are solved, in concert with the equations of the turbulent kinetic energy(k) and its dissipation rate(${\varepsilon}$). In the present model, the near-wall effect and the non-equilibrium effect are fully taken into consideration. The validation of the model is then applied to the turbulent flow behind a backward-facing step and the flow over a blunt body. The predicted results of the present model are compared and evaluated with the relevant experiments.

• 유체기계공업학회:학술대회논문집
• /
• 2005.12a
• /
• pp.803-809
• /
• 2005

This paper presents the theoretical model to investigate the effect of Coulomb damping in the sub-structure of a foil bearing. Foil deflection is restricted by friction of bumps. Equivalent viscous damping of the bump foils is derived from the Coulomb friction. Dynamic equation of the bumps is constituted by stiffness and damping terms. This point give the difference from Heshmat's frictionless and simple compliance bump model. The fluid is modeled with the compressible Reynolds equation. A perturbation approach is used to determine the static and dynamic performance of the bearing from the coupled fluid-structural model. The analysis result shows that the static and dynamic performance is enhanced by bump friction. This analysis technique would be extended to development of a high performance bearing.

• The KSFM Journal of Fluid Machinery
• /
• v.9 no.1 s.34
• /
• pp.47-55
• /
• 2006

This paper presents the theoretical model to investigate the effect of Coulomb damping in the sub-structure of a foil bearing. Foil deflection is restricted by friction of bumps. Equivalent viscous damping of the bump foils is derived from the Coulomb friction. Dynamic equation of the bumps is constituted by stiffness and damping terms. This point give the difference from Heshmat's frictionless and simple compliance bump model. The fluid is modeled with the compressible Reynolds equation. A perturbation approach is used to determine the static and dynamic performance of the bearing from the coupled fluid-structural model. The analysis result shows that the static and dynamic performance is enhanced by bump friction. This analysis technique would be extended to development of a high performance bearing.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.4
• /
• pp.764-770
• /
• 1989

This paper analyze the steady state performance of a self-acting air lubricated slider bearing in hard disk/head system. Modified Reynolds' equation is derived from the steady state compressible Navier-Stokes equation, under slip-flow conditions. Finite difference technique and numerical procedure are described by using Newton-Raphson iteration method to slove the non-linear equations. These techniques are applied to conventional slider bearings and the effects of molecular mean free path(MMFP) for a recording surface of hard disk are shown. The calculation procedure developed here, wide applicabilities in practical head design procedures, and converges rapidly.