• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.49-59
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• 2003

The factors affecting the vertical loads acting on embankment piles can be classified into two factors on pile and soil. Factor on pile is the space between pile cap and factors on soil are embankment height and soil parameters(c, $\phi$). Therefore, a series of model tests were performed both to investigate the extent of influence of these factors and to verify the reliability of the proposed theoretical analysis. In the model tests, the piles were installed in the 6 columns $\times$ 6 rows(or 5 columns $\times$ 5 rows) below the embankment and the isolated pile caps with the area of 2.5cm $\times$ 2.5cm were installed on each pile head. The portion of the embankment load carried by model pile caps decreases with increment of the space between pile caps and increases with increment of the embankment height and the relative density(or internal friction angle) of fill. Also, the experimental results showed good agreement with theoretical predictions.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.530-533
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• 2010

This paper presents numerical analysis and design optimization of various turbine blade cooling techniques with three-dimensional Reynolds-averaged Navier-Stokes(RANS) analysis. The fluid flow and heat transfer have been performed using ANSYS-CFX 11.0. A fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness with the radial basis neural network method. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. The impingement jet cooling has been performed to investigate heat transfer characteristic with geometry variables. Distance between jet nozzle exit and impingement plate, inclination of nozzle and aspect ratio of nozzle hole are considered as geometry variables. The area averaged Nusselt number is evaluated each geometry variables. A rotating rectangular channel with staggered array pin-fins has been investigated to increase heat transfer performance ad to decrease friction loss using KRG modeling. Two non-dimensional variables, the ratio of the eight diameter of the pin-fins and ratio of the spacing between the pin-fins to diameter of the pin-fins selected as design variables. A rotating rectangular channel with staggered dimples on opposite walls are formulated numerically to enhance heat transfer performance. The ratio of the dimple depth and dimple diameter are selected as geometry variables.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.6
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• pp.1365-1373
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• 1994

A Monte-Carlo simulation model, developed to predict size distribution of air bubbles in turbulent shear flow, is applied to a laboratory-scale problem. Sensitivity to various numerical and physical parameters of the model is analyzed. Practical applicability of the model is explored through comparisons of results with experimental measurements. Bubble size increases with air-water discharge ratio and friction factor. Bubble size decreases with increasing mean flow velocity, but the total bubble surface area in the aeration region remains fairly constant. The effect on bubble size distribution of the longitudinal length increment in the simulation model is negligible. A larger radial length increment yields more small and large bubbles and fewer in between. Bubble size distribution is significantly affected by its initial distribution and the location of air injection. Collision efficiency is introduced to explain the discrepancy between collisions with and without coalescence.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.1
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• pp.78-84
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• 2012

Mold may experience deterioration of molding quality as the abrasion of mold occurring due to friction between mold and molded product works as allowance in the course of press process. Therefore, to improve the wear-resistance of mold, methods like nitriding, carburizing, flame and induction surface hardening treatment etc have been applied. However, as such methods are accompanied by problems like shape limitation or product deformation etc, laser surface treatment technology is under review as surface treatment method that can solve such problems. Therefore, in this study, mold material cast iron was surface-treated by using high power diode laser. In previous report 1 and report 2, the heat treatment characteristics were compared by the differences of die materials and shapes, then this paper observed microstructure by using optical microscope and scanning electronic microscope to analyze the structural difference of hardened zone, interface area and base metal after heat treatment. And the structural condition was grasped through EDS. As a result of microstructure, hardened zone showed formation of acicular martensite.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.4
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• pp.356-363
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• 2015

Microbubbles moving in the turbulent boundary layer are visualized and investigated in the point of frictional drag reduction. The turbulent boundary layer is formed beneath the surface of the 2-D flat plate located in the tunnel test section. The microbubble generator produces mean bubble diameter of 30 – 50 μm. To capture the micro-bubbles passing through the tiny measurement area of 5.6 mm² to 200 mm², the shadowgraphy system is employed appropriately to illuminate bubbles. The velocity field of bubbles reveals that Reynolds stress is reduced in the boundary layer by microbubbles’ activity. To understand the contribution of microbubbles to the drag reduction rate more, much smaller field-of-view is required to visualize the bubble behaviors and to find the 2-D void fraction in the inner boundary layer.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.723-728
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• 2014

Hydraulic experiments are performed in order to verify the swash effect of seashore structures installed to prevent scouring. However, a great deal of investment and time are required for producing the test apparatus and seashore structure used to perform the hydraulic experiment. The swash effect can be predicted, however, by using a numerical model and validation can be done based on comparisons of the numerical model and hydraulic experiment analysis results, thereby saving the cost and time required for producing the test apparatus and seashore structure. Taking a polyhedral rubble mound structure as the subject, this study performed a comparative analysis of wave run-up and run-down height of the numerical model interpretative results and the hydraulic experiment results, and validated the interpretative simulation wave test modeling technique. The study also predicted the swash effect by using the numerical interpretation approach method, whereby the volume ratio and friction area of the rubble mound were varied for different results.

• Fire Science and Engineering
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• v.25 no.4
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• pp.89-93
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• 2011

It is not recommended that elevator use for egress at (super) high rise buildings because elevator shaft main roles to spread of fire smoke. But in North America used to protect this area by elevator shaft pressurization. These tests are performed at high rise apartment to verify that elevator shaft pressurization can protect to spread of fire smoke or not. and verify to used for egress at fire. Pressurization at elevator shaft make pressure difference of 50 Pa all floor at 150 CMM because this method have low friction loss from air flow. Also when dwelling door and elevator door are opened that critical velocity is performed to protect of back-layering from fire room for escape routs by 180 CMM. Therefore through out these pressurization tests by elevator shaft are estimated to have less overpressure because supply air difference are low between to satisfy critical velocity at one door opened and maintain to pressure difference all doors closed. Finally we verified that disable or residual people can use elevator for egress at fire by elevator shaft pressurization.

• Magazine of the Korean Society of Agricultural Engineers
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• v.34 no.2
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• pp.73-84
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• 1992

The TIDE, finite element model for the simulation of tidal flow in shallow sea was tested for its applicability at the Saemangeum area. Several pre and post processors were developed to facilitate handling of the complicated and large amount of input and output data for the model developed. Also an operation scheme to run the model and the processors were established. As a result of calibration test using the observed data collected at 9 points within the region, linearlized friction coefficients were adjusted to be ranged 0.0027~0.0072, and water depths below the mean sea level at every nodes were changed to be increased generally by 1 meter. Comparisons of tidal velocities between the observed and the simulated for the 5 stations were made and obtained the result that the average relative error between simulated and observed tidal velocities was 11% for the maximum velocities and 22% for the minimum, and the absolute errors were less than 0.2m/sec. Also it was found that the average R.M.S. error between the velocities of observed and simulated was 0.119 m/sec and the average correlation coefficient was 0.70 showing close agreement. Another comparison test was done to show the result that R.M.S. error between the simulated and the observed tidal elevations at the 4 stations was 0.476m in average and the correlation coefficients were ranged 0.96~0.99. Though the simulated tidal circulation pattern in the region was well agreed with the observed, the simulated tidal velocities and elevations for specific points showed some errors with the observed. It was thought that the errors mainly due to the characteristics of TIDE Model which was developed to solve only with the linearized scheme. Finally it was concluded that, to improve the simulation results by the model, a new attempt to develop a fully nonlinear model as well as further calibration and the more reasonable generation of finite element grid would be needed.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.4
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• pp.42-52
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• 1997

The basic principle of underwater ram-jet as a unique marine propulsion concept showing vary high cruise speed range(e. g. 80-100 knots) is the thrust production by the transfer of the potential energy of compressed gas to the operating liquid through kinetic mixing process. This paper is aimed to investigate the propulsive efficiency of the nozzle flow in underwater ram-jet at the speed of 80 knots for the buried type vessel. The basic assumption of the theoretical analysis is that mixture of water and air can be treated as incompressible gas. For an optimized nozzle configuration obtained from the performance analysis, preliminary data for performance evaluation are obtained and effects of nozzle inner wall friction, ambient temperature, ambient pressure, water density, gas velocity, bubble radius, flow velocity, diffuser area ratio, mass flow ratio and water velocity gradient are investigated.

• Journal of Powder Materials
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• v.14 no.6
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• pp.372-379
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• 2007

The microstructure, mechanical and electrochemical properties of plasma electrolytic coatings (PEO) coatings on Mg-4.3 wt%Zn-1.0 wt%Y and Mg-1.0 wt%Zn-2.0 wt%Y alloys prepared by gas atomization, followed by compaction at 320 for 10 min under the pressure of 700 MPa and sintering at 380 and 420 respectively for 24 h, were investigated, which was compared with the cast Mg-1.0 wt%Zn alloy. All coatings consisting of MgO and $Mg_2SiO_4$ oxides showed porous and coarse surface features with some volcano top-like pores distributed disorderly and cracks between pores. In particular, the surface of coatings on Mg-1.0 wt%Zn-2.0 wt%Y alloy showed smaller area of pores and cracks compared to the Mg-4.3 wt%Zn-1.0 wt%Y and Mg-1.0 wt%Zn alloys. The cross section micro-hardness of coatings on the gas atomized Mg-Zn-Y alloys was higher than that on the cast Mg-1.0 wt%Zn alloy. Additionally, the coated Mg-1.0 wt%Zn-2.0 wt%Y alloy exhibited the best corrosion resistance in 3.5%NaCl solution. It could be concluded that the addition of Y has a beneficial effect on the formation of protective and hard coatings on Mg alloys by plasma electrolytic oxidation treatment.