• Steel and Composite Structures
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• v.47 no.3
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• pp.355-363
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• 2023

The main purpose of this study is to characterize the size-dependent strain rate sensitivity in structural steel using the continue stiffness measurement (CSM) indentation. A series of experiments, such as CSM indentation and optical microscope examination, has been performed at the room temperature at different rate conditions. The results indicated that indentation hardness, strain rate, and flow stress showed size-dependent behavior. The dependency of indentation hardness, strain rate, and flow stress on the indentation size was attributed to the transition of the dislocation nucleation rate and the dislocation behaviors during the indentation process. Since both hardness and strain rate showed the size-dependent behavior, SRS tended to depend on the indentation depth. The results indicated that the SRS was quite high over 2.0 at the indentation depth of 240 nm and quickly dropping to 0.08, finally around 0.046 at large indents. The SRS values at large indentations strongly agree with the general range reported for several types of low-carbon steel in the literature (Chatfield and Rote 1974, Nguyen et al. 2018b, Luecke et al. 2005). The results from the present study can be used in both static and dynamic analyses of structures as well as to assess and understand the deformation mechanism and the stress-state of material underneath the indenter tip during the process of the indentation testing.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.93-100
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• 2013

The objective of present study is to investigate the sensitivity of aerostatic force coefficients of twin box girder of Yi Sun-sin Bridge according to the Reynolds numbers. This paper presents the 1:30 scale sectional model tests conducted at high speed wind tunnel in Korea Air Force Academy. Comparison with results at low Reynolds number obtained in KOCED Wind Tunnel Center in Chonbuk National University is also provide. The Reynolds number dependency of aerodynamic force coefficients were observed at present streamlined twin box girder. The drag coefficient revealed significant decrease of nearby 23% at supercritical region. The boundary layer trip strip was found to reduce the Reynolds number dependency of aerodynamic forces by fixing the location of flow transition.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.4
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• pp.387-394
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• 2020

A parametric study of a 2.5 kW class propeller type micro hydraulic turbine was performed. In order to analyze the internal flow characteristics in the hydraulic turbine, three dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model were used and the hexahedral grid system was used to construct computational domain. To secure the reliability of the numerical analysis, the grid dependency test was performed using the grid convergence index method based on the Richardson extrapolation, and the grid dependency was removed when about 1.7 million nodes were used. For the parametric study, the axial distance at shroud span (L) between the inlet guide vane and the runner, and the inlet and outlet blade angles (β₁, β₂) of the runner were selected as the geometric parameters. The inlet and outlet angles of the runner were defined in the 3 spans from the hub to tip, and a total of 7 geometric parameters were investigated. It was confirmed that the outlet angles of the runner had the most sensitive effect on the power and efficiency of the micro hydraulic turbine.

• Korean Journal of Food Science and Technology
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• v.28 no.3
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• pp.538-544
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• 1996

A highly viscous biopolymer from alkali-tolerant Bacillus sp. was purified and its rheological properties were studied. 1% (w/v) solution of purified biopolymer showed pseudoplastic fluid behavior with the yield stress similar to those of xanthan and guar gum, and its consistency index was exponentially dependent on concentration and temperature. The concentration dependency of consistency index exhibited two rectilinear plots with different slopes at 1% concentration and pseudoplastic property increased with the increase of biopolymer concentration. The biopolymer solution exhibited a low temperature dependency and the activation energy of flow was 1.16 kacl/g mol. The apparent viscosity was very dependent on the change of pH and the addition of salt. However, no organic solvent effects were observed effects of viscosity synergism with the addition of viscosifier were not observed.

• Journal of KIISE:Information Networking
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• v.30 no.2
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• pp.143-154
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• 2003

There is a growing trend in developing system for distributed mobile system that supports services - job flow management, video conference, replicated data management and resource allocation. Supporting these services, applications have to use causally ordered message delivery. Previous proposals that provide causally ordered message delivery have problems such as communication overhead, message delaying, scalability, computing overload of mobile host. In this paper, we proposed efficient protocol for causally ordered message delivery using the methods that MSS maintains dependency information matrix between MSS and MH, Piggybacking dependency information about each immediate predecessor message. Proposed algorithm, when compared with previous proposals, provides a low message overhead, and low probability of unnecessary inhibition in delivering messages. Also, it consider resource restriction of MH and low bandwidth of wireless communication by computing most of algorithm at MSS, and reduce processing delay by executing causally ordered message delivery a unit of MH.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2279-2284
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• 2007

This study is intended to analyze the effect of thin ink-film thickness around rotating printing roll on the printing quality in the gravure printing process which is used for making electronics circuit like a RFID tag with a conductive ink. The present work numerically estimates the film thickness around rotating roller partially immersed in ink, for which the volume of fluid (VOF) method was adopted to figure out the film formation process around rotating roller. Parameter studies were performed to compare the effect of ink viscosity, surface tension, roller rotating speed, immersed angle on the film thickness. The result indicates that the film thickness has a strong dependency on the fluid viscosity, while the surface tension has negligible effect.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.299-304
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• 2001

An approach is developed for parametric investigation of the influence of the surface roughness on thermohydrodynamic analysis with film conditions which systemically occur in journal bearings. A parametric investigation is performed for predicting the bearing behaviors such as pressure and temperature distributions in lubricating films between the stationary and moving surfaces determined by absorbed layers and interfaces on the statistical method for rough surface with Gaussian distribution. The layers expressing the effects of surface roughness are expressed as functions of the standard deviations (${\sigma}$) of each surface and surface orientation (j) to explain the flow patterns between both rough surfaces. The coupled effect of surface roughness and shear zone dependency on hydrodynamic pressure and temperature has been found by solving the present model in non-contact mode and contact mode, respectively.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.11a
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• pp.357-362
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• 1996

LOFT LBLOCA test, LP-02-6 was analyzed using RELAP5/MOD3.2. It has a distinguished thermal-hydraulic phenomenon of a positive bottom-up core flow in tile blowdown phase. A modified nodalization which is based on that used in LP-LB-1 calculation by Lubbesmeyer was used in the calculation. RELAP5/MOD3.2 predicted overall system hydraulic behavior relatively well. However, the bottom-up quenching in the middle part of the core was not predicted sufficiently. It was demonstrated also that the peak cladding temperature can be predicted well by adjusting a discharge coefficient. But more improvements are needed in order to apply this code to actual plants with less user dependency.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.316-321
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• 1997

The mixing vane effect on the Critical Heat Flux (CHF) is discussed with focus on the vortex now effect. In the subchannel approach, this effect is not quantified by the calculation model, but directly taken into account by the CHF correlation itself through data analysis. The vortex now effect is identified the two Westinghouse correlations, and then the CHF margin issue given rise to by the Vantage-5H design change is evaluated and discussed. It is noted that deficiency about CHF dependency on the vortex flow effect could induce an error in the Departure from Nucleate Boiling Ratio (DNBR) sensitivity Calculation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.12 s.255
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• pp.1155-1163
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• 2006

Calculation was carried out for phase velocity and deformation wave decay in a layer of viscoelastic material fixed tightly on the solid substrate. Analysis has been performed regarding the inner structure of the wave, i.e., the proportions between the vertical and horizontal displacements and their profiles. The wave characteristics depend strongly on media compressibility factor. The effect of viscous losses on parameters of the main oscillation mode was studied in detail. Results were compared with the model of coating with local deformation. A new experimental approach was made in order to measure such wave properties of a compliant coating as the dependency of deformation wave velocity on frequency and decay factor was made. The method for estimation of coating parameters enabling the drag reduction in turbulent flow was then refined.