• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2524-2533
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• 2024

When analyzing containment thermal-hydraulics, computational fluid dynamics (CFD) is a powerful tool because multi-dimensional and local analysis is required for some accident scenarios. According to the previous study, neglecting steam bulk condensation in the CFD analysis leads to a significant error in boundary layer profiles. Validating the condensation model requires the experimental data near the condensing surface, however, available boundary layer data is quite limited. It is also important to confirm whether the heat and mass transfer analogy (HMTA) is still valid in the presence of bulk condensation. In this study, the boundary layer measurements on the vertical condensing surface in the presence of air were performed with the rectangular channel facility WINCS, which was designed to measure the velocity, temperature, and concentration boundary layers. We set the laminar flow condition and varied the Richardson number (1.0-23) and the steam volume fraction (0.35-0.57). The experimental results were used to validate CFD analysis and HMTA models. For the former, we implemented a bulk condensation model assuming local thermal equilibrium into the CFD code and confirmed its validity. For the latter, we validated the HMTA-based correlations, confirming that the mixed convection correlation reasonably predicted the sum of wall and bulk condensation rates.

• Journal of applied mathematics & informatics
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• v.26 no.5_6
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• pp.1273-1287
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• 2008

In this paper, the numerical integration method for general singularly perturbed two point boundary value problems with mixed boundary conditions of both left and right end boundary layer is presented. The original second order differential equation is replaced by an approximate first order differential equation with a small deviating argument. By using the trapezoidal formula we obtain a three term recurrence relation, which is solved using Thomas Algorithm. To demonstrate the applicability of the method, we have solved four linear (two left and two right end boundary layer) and one nonlinear problems. From the results, it is observed that the present method approximates the exact or the asymptotic expansion solution very well.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.2319-2324
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• 2005

This paper proposes a intelligent gain and boundary layer based sliding mode control (SMC) method for robotic systems with unknown model uncertainties. For intelligent gain and boundary layer, we employ the self recurrent wavelet neural network (SRWNN) which has the properties such as a simple structure and fast convergence. In our control structure, the SRWNNs are used for estimating the width of boundary layer, uncertainty bound, and nonlinear terms of robotic systems. The adaptation laws for all parameters of SRWNNs and reconstruction error bounds are derived from the Lyapunov stability theorem, which are used for an on-line control of robotic systems with unknown uncertainties. Accordingly, the proposed method can overcome the chattering phenomena in the control effort and has the robustness regardless of unknown uncertainties. Finally, simulation results for the three-link manipulator, one of the robotic systems, are included to illustrate the effectiveness of the proposed method.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.571-574
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• 2010

Large-eddy simulation has been conducted to simulate turbulent boundary-layer flows over an array of regularly distributed obstacles considering various cases of a wind incident angle. The effect of wind direction was investigated in the square cube array that periodic boundary condition was imposed. Characteristics of the turbulent flow over the obstacle array have been found to be very sensitive to the direction of prevailing wind or of mean wind or of mean pressure gradient but varied with height, specially below the urban canopy. Turbulent statistics are changed sensitively with the direction of mean pressure gradient around 10 degree.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.945-956
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• 2000

The axisymmetric bodies considered in this study have hemispherical and ellipsoidal noses. The near-field pressure fluctuations over each nose model at $Re_D=2.43{\times}10^5$ were investigated in the laminar separation region and developing turbulent boundary layers using a 1/8' pin-holed microphone sensor. The wall pressure fluctuations were also measured in an axisymmetric boundary layer on a cylinder parallel to mean flow at a momentum thickness Reynolds number of 850 and a boundary layer thickness to cylinder radius ratio of 1.88.

• Bulletin of the Society of Naval Architects of Korea
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• v.18 no.2
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• pp.7-20
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• 1981

A method to predict the three-dimensional turbulent boundary layer on ship forms is introduced. The present differential method is in the scope of thin boundary layer theory and adopting the eddy-viscosity turbulence model. Two different numerical schemes are taken in this paper to handle the sign-changing cross-flows. The method is applied to predict the boundary layer development on real ship forms; SSPA Model 720($C_B$=0.675) and HSVA Tanker Model($C_B$=0.85). The results are qualitatively in good agreements with measurements except at the very stern. Therefore the method seems to be very promising if further developments are accomplished to handle the thick stern boundary layer effectively.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.309-314
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• 1999

This paper is concerned with the viscous interaction between rotor and stator The viscous interaction is caused by wakes from upstream blades. The cascade was composed with five blades and cylinders were placed to make wakes and their location was about 50 percent of blade chord upstream. The location of cylinders were varied in the cascade axis with 0, 20, 40, 60 and 80 percent of pitch length. The velocity distribution in the cascade passage were measured using single slanted hot-wire and the ones in the boundary layer using boundary probe. As a result, wakes decay more rapidly at suction surface and more slowly at pressure surface. And the measurement of momentum thickness of cascade shows that the momentum thickness is larger near the blade surface. From measurement of blade boundary layer, turbulent intensity is also larger near the blade surface because wakes collide the boundary layer And wakes make boundary layer thickness smaller and delay flow separation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.12
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• pp.5655-5660
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• 2012

The objective of this study is theoretically to suggest the effective heat exchanger design method using boundary layer analysis. The boundary layer formation and interruption on rectangular plate and round plate fins are explained and the heat transfer coefficients showed with the variation of the velocity and temperature boundary layer. In addition, the flow pattern on one plate fin surface considered as external flow and flow pattern between fins considered as internal flow. As a result, theoretical method for the boundary layer interruption avoidance is suggested and the heat transfer coefficient of the round plate fin was higher than that of the rectangular plate fin because of the less thermal and velocity boundary layer thickness except the centerline.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.780-788
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• 1989

An experimental study has been performed to investigate the process from nonequilibrium state to equilibrium state in redeveloping turbulent boundary layer beyond separation-reattachment using pitot tube and hot-wire anemometer. The model sued in the experiment has the form of a backward facing step which is assembled by a two-dimensional 4:1 half elipse and a plate. Measurements are carried out up to a distance of about 50 step height downstream of the step, where the reattachment observed at about x/h=6.5. The profiles of the shape factor H the Clauser parameter G and the coefficient of friction $C^{f}$ exhibited the characteristics similar to those of the equilibrium turbulent boundary layer from x/h=25, and the profiles of the trubulent quantities did from x/h=35. However, the wake region of the boundary layer does not seem to recover the equilibrium turbulent boundary layer even at x/h=50. By considering the distributions of the intermittency factor it has been noted that the turbulence structure changes gradually from a mixing layer to a turbulent boundary layer along downstream direction after reattachment. This becomes clearer as we analyse the one-dimensional energy spectra and the dissipation energy spectra which are measured and caculated at various downstream positions after the backward facing step.p.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.4
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• pp.243-252
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• 2021

The present study aims to investigate the interaction of a wire-type turbulence stimulator and the laminar boundary layer on a flat plate by flow field measurement. For the towing tank tests, a one-dimensional Laser Doppler Velocimetry (LDV) attached on a two-axis traverse was used to measure the streamwise velocity component of the boundary layer flow in zero pressure gradient, disturbed by a turbulence stimulator. The wire diameter was 0.5 and 1.0 mm according to the recommended procedures and guidelines suggested by the International Towing Tank Conference. Turbulence development by the stimulator was identified by the skin friction coefficient, mean and Root Mean Square (RMS) of the streamwise velocity. The laminar boundary layer with the absence of the wire-type stimulator was similar to the Blasius solution and previous experimental results. By the stimulator, the mean and RMS of the streamwise velocity were increased near the wall, showing typical features of the fully developed turbulent boundary layer. The critical Reynolds number was reduced from 2.7×10⁵ to 1.0×10⁵ by the disturbances caused by the wire. As the wire diameter and the roughness Reynolds number (Rek) increased, the disturbances by the stimulator increased RMS of the streamwise velocity than turbulent boundary layer.