• International Journal of Aeronautical and Space Sciences
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• v.1 no.1
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• pp.36-47
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• 2000

Three-dimensional compressible turbulent flow fields within the passage of a diffusing S-duct have been simulated by solving the Navier-Stokes equations with SIMPLE scheme. The average inlet Mach number is 0.6 and the Reynolds number based on the inlet diameter is $1.76{\times}10^6$ The extended $k-{\varepsilon}$ turbulence model is applied to modeling the Reynolds stresses. Computed results of the flow in a circular diffusing S-duct provide an understanding of the flow structure within a typical engine inlet system. These are compared with experimental wall static-pressure, total-pressure fields, and secondary velocity profiles. Additionally, boundary layer thickness, skin friction values, and streamlines in the symmetric plane are presented. The computed results depict the interaction between the low energy flow by the flow separation and the high energy flow by the reversed duct curvature. The computed results obtained using the extended $k-{\varepsilon}$ turbulence model.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.07a
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• pp.582-584
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• 2011

This paper presents a Channel DiVision (CDV) scheme for transform-domain distributed video coding. In the proposed system, we employ the symmetric motion estimation to generate high quality side information for Wyner-Ziv (WZ) frames. Also, the decoder estimates the distortion of the side information, which is used to classify the transmitting channels for WZ frames. Each channel has a different expected noise. Then, the encoder allocates an appropriate number noise. Then, the encoder allocates an appropriate number present rate-distortion performance results and comparisons with existing state-of-the-art algorithms and H.264.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.76-80
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• 2001

Unsteady compressible Euler equation is solved and the high-order, high-resolution numerical solver, physical boundary condition, adaptive nonlinear artificial dissipation model and conformal mapping are applied to computation of steady transonic flow and unsteady acoustics. The acoustic characteristics of axi-symmetric duct and two dimensional straight/S channel are studied and the computation results shows good agreements with linear analysis. In transonic case, local time stepping and canceling-the-residual techniques are used for convergence acceleration. The aspect of flow and acoustics in S-channel and the Pattern of noise radiation is changed by inflow Mach no. and static pressure at fan-face.

• 한국가시화정보학회:학술대회논문집
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• 2004.11a
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• pp.72-75
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• 2004

The present study describes a computational work to investigate detailed behaviors of the twin shock waves discharged from the exits of two-parallel ducts. In computations, the Yee-Roe-Davis's TVD scheme was used to solve the unsteady, three-dimensional, inviscid, compressible, Euler equations. The distance between two ducts is varied and the Mach number of the incident shock wave is changed below 2.0. The results obtained show that on the symmetric axis between two-parallel ducts, the maximum pressure achieved by the merge of twin shock waves and its location strongly depend upon the distance between two-parallel ducts and the Mach number of the incident shock wave. It is also found that the twin shock waves discharged from the exits of two-parallel ducts leads to the complicated flow fields, such as Mach stem, spherical waves, and vertical structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.10
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• pp.1619-1625
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• 1997

This paper concerns a 2-axis PR type pneumatic manipulator system translating in vertical and rotating in horizontal directions. A simplified linear model is mathematically formulated similar to the pneumatic acturators in dynamic responses in order to devise an appropriate position control scheme. A PD controller preceding the on/off solenoid valve turns out not only economical but also effective in reducing rise time and amplitude of limit cycles, if its control gains are determined on the basis of frequency response. And, additional implementation of symmetric or asymmetric deadband at the PD controller output greatly helps minimize valve opening numbers, positional error, and undesirable direction-dependent property due to the gravitational load. Such a control concept is synthesized through numerical simulations and next applied to the experimental set-up, featuring enhanced positional servo characteristics.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.5
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• pp.548-553
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• 2015

The conventional ejector-diffuser system makes use of high pressure primary stream to propel the secondary stream through pure shear action for the purposes of transport or compression of fluid. It has been widely used in many industrial applications such as seawater desalination, solar refrigeration, marine engineering, etc. The present study is performed numerically to study the performance of a two-stage ejector-diffuser system. The detailed flow phenomenon of the ejector-diffuser system has been critically predicted by means of the numerical approach using compressible Reynolds averaged Navier-Stokes (RANS) equations. The axi-symmetric supersonic ejector-diffuser flow has been solved by a fully implicit finite volume scheme with a two-equation k-omega turbulence model. The numerical results are validated with existing experimental data. Detailed flow physics and their contributions on ejector performance are detected to compare both single-stage and two-stage ejectors. The performance improvement on the ejector-diffuser system is discussed in terms of the mass flux ratio and the coefficient of power.

• Journal of Mechanical Science and Technology
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• v.14 no.2
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• pp.188-196
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• 2000

In this paper, our aim is to develop a model for two cooperating flexible manipulators handling a rigid object by using lumped parameters. This model is in turn analyzed on MATLAB. In order to validate the model, a precise simulation model is developed using $ADAMS^{TM}$ (Automatic Dynamic Analysis of Mechanical System). Moreover, to clarify the discussion, the motions of a dual-arm experimental flexible manipulator are considered. Using the developed model, we control a robotic system with a symmetric hybrid position/force control scheme. Finally, experiments and simulations are performed, and a comparison of simulation results with experimental results is given to a rerify the validity of our model.

• Structural Engineering and Mechanics
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• v.65 no.1
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• pp.69-79
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• 2018

This paper is devoted to two new techniques for free vibration analysis of concrete arch dam-reservoir systems. The proposed schemes are quadratic ideal-coupled eigen-problems, which can solve the originally non-symmetric eigen-problem of the system. To find the natural frequencies and mode shapes, a new special-purpose eigen-value solution routine is developed. Moreover, the accuracy of the proposed approach is thoroughly assessed, and it is confirmed that the new scheme is very accurate under all practical conditions. It is also concluded that both decoupled and ideal-coupled strategy proposed in the previous works can be considered as special cases of the current more general procedure.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.42-47
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• 1999

In this study, we adopt the point symmetric Gauss-Seidel relaxation algorithm to obtain the steady state solution of the Navier-Stokes equations for the thermal and chemical nonequilibrium flow of air. All of the inviscid, viscous flux Jacobians and thermochemical source Jacobians are included in the implicit part Numerical simulation is performed for the thermal and chemical nonequilibrium flow over blunt body and computational results are presented. The convergence history and CPU time of the present computation are compared with the LU-SGS scheme which employs the approximate Jacobians.

• 한국전산유체공학회:학술대회논문집
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• 1996.05a
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• pp.68-73
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• 1996

The full incompressible Navier-Stokes equations are numerically integrated to solve the unsteady channel flow using a new numerical scheme of second-order accuracy developed by the authors. It is well known that in spite of the symmetry in the boundary condition and geometry, asymmetry can develop with time-dependency in a channel with sudden expansion. The instability of the shear flow and the cross-channel pressure contribute to such asymmetric flow. In this paper, we successfully generated a channel flow in which vortex waves were propagated downstream due to the harmonically oscillating inlet flow. The structure of the eddies and wall vorticity are parametrically investigated.