• 한국해양학회지
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• v.30 no.4
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• pp.355-364
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• 1995

A heavy fluid is injected to a rotating cylindrical container of flat or inclined bottom filled with homogeneous lighter fluid. Continuous flow-in and spreading patterns over the bottom of the container are observed and at the same time upper-layer motions induced by the movement of the heavy fluid are traced by thymol blue solution. Regardless of bottom geometry, the injected denser fluid is deflected toward "western wall" and continuous its path along the boundary with radial spreading which occurs in the bottom boundary layer to make a quite asymmetric flow. When the bottom contains a slope(${\beta}$-plane), increased pressure gradient causes the fluid move faster to produce a stronger Coriolis force. This makes the width of the flow narrower than that of f-plane. But, when the denser flow reaches the southern part of the container, a local-depth of denser fluid increases (much greater than the Ekman-layer depth) such that the spreading velocity along the wall is reduced and the interfacial slope increases to make the upper-layer adjust geographically to have oppositely directed upper-layer motion along the interfacial boundary. The role of the denser fluid in terms of vorticity generation in the upper-layer is such that it produces local topographic effect over the western half of the container and also induces vortex-tube stretching which is especially dominant in the f-plane.

• Journal of Korea Water Resources Association
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• v.49 no.7
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• pp.635-644
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• 2016

This study investigates variation of flow characteristics due to variation of branch channel width and discharge ratio at bifurcation channel using 2D numerical model. The calculated result considering secondary flow is more accurate and stable than without considering one. The diversion flow rate ($Q_3/Q_1$) is reduced by flow stagnation effect according to the interaction of the secondary flow and flow separation zone in branch channel. The less upstream inflow or the lower upstream velocity, the bigger variation of diversion flow rate by changing branch channel width. At uniform downstream boundary condition, the rate of change in Froude number of downstream of main channel($Fr_2$)-diversion flow rate ($Q_3/Q_1$) relations is similar about -2.4843~-2.6675 when branch channel width ratio (b/B) is decreased. At uniform diversion flow rate ($Q_3/Q_1$) condition, the width of recirculation zone in branch channel is decreased when branch channel width ratio (b/B) is decreased. The less upstream inflow in the case of increasing branch channel width or the narrower branch channel width in the case of increasing upstream inflow, the bigger reduction ratio of recirculation zone width. At uniform inflow discharge ($Q_1$) condition, diversion flow rate, the width and length of recirculation zone in branch channel are decreased when branch channel width ratio (b/B) is decreased.

• International Journal of Highway Engineering
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• v.8 no.3 s.29
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• pp.77-88
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• 2006

The maintenance / repair of concrete pavements has become an issue as a result of increasing of concrete pavements' service year. Asphalt overlay is applied to the concrete pavements after partial repairs on all occasions. This thesis discusses the application standard, evenness, skid resistance, noise, economical efficiency, extension of life span, etc. of diamond grinding, a method of maintenance about concrete pavements. Based on this, it was applied to the field and measured the performance. It was measured the longitudinal evenness of before and after the construction through measurement equipment. and surveyed the skid resistance the each lane classified using the SN standard value. In case of noise, it is selected the kind of vehicle, velocity, then measured the noise between control and constructed site. In addition, it is evaluated the average texture depth. As a result of the analysis, longitudinal evenness is improved about $6{\sim}40%$, skid resistance is improved 66% at first section,37% at second section. Noise is reduced 3.4dB average, and average texture depth is 79% deeper than control section. Therefore, it can be concluded that diamond grinding is suitable as maintenance / repair method of concrete pavements.

• Journal of Korea Soil Environment Society
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• v.4 no.2
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• pp.137-147
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• 1999

Fluidized-bed thermal desorber coupled with a heat pipe was investigated for the remediation of soil contaminated with diesel oils. Thermal gravimetric analysis by Cahn-balance indicated that the desorption of diesel oils from the soil particles was mainly governed by the internal diffusion at low concentration of less than 0.5 wt. % of oils in the soil particles. In fluidized-bed experiments. increase of fluidizing gas velocity reduced the residual oils of the contaminated soils, the increase of soil feed rate decreased efficiency of fluidized-bed desorber. A mathematical model was developed by incorporating Fickian diffusion kinetics into the Kunii-Levenspiel model Simulation results showed reasonable agreement for the performance of fluidized-bed thermal desorber.

• Analytical Science and Technology
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• v.13 no.5
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• pp.584-591
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• 2000

The separation of Nd from the simulated $U_3Si/Al$ spent fuel solution with sequential two-step anion exchange separation has been studied. To prepare the simulated $U_3Si/Al$ spent nuclear fuel, unirradiated $U_3Si/Al$ whose composition consists of small $U_3Si$ particle dispersed in an Al matrix with Al cladding was dissolved with a mixture of 4 M HCl and 10 M $HNO_3$ and 8 or 15 fission product elements were added to the dissolved solution. The trace amount of silica in the solutions was removed by evaporating to dryness with HF and the U was adsorbed on the first anion exchange resin. Neodymium can be purely isolated from the fission product elements with a methanol-nitric acid eluent using the second anion exchange resin. A large excess of Al didn't influence on the elution velocity of Nd, but reduced the eluted contents of Nd, Al, Eu, Gd, Sm and Sr, A large amount of Al was removed first from the column with 3 mL of loading solution (0.8 M $HNO_3$/99.8% MeOH) before Nd elution by the eluent [0.04 M $HNO_3$-99.8% MeOH(1:9)]. The recovery of Nd was more than 94%, regardless of Al contents. Taking the 9 to 13 mL fraction of eluate was effective to purely isolate Nd.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.69-77
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• 2002

To acquire the dynamic response and design the controller of the airship, the longitudinal motion of the airship with respect to the vertical gust, which is the nonlinear system, was studied. The effects of the apparent mass and moment of the airship delay the dynamic response and the settling time, which are slower than those of conventional airplanes. The current object of the airship is designed to cruise at 500~1000m altitude. At that height, the atmospheric conditions are generally unstable by wind gust. In this paper, it has been studied for the case of vertical gust, since the apparent mass effects are dominant in has been studied for the case of vertical gust, since the apparent mass effects are dominant in that plane. In addition to the study of the dynamic responses of the airship, the controller was designed using the PID-controller. When the gust was applied, airship responses were recovered of equilibrium states. However, it takes too ling time for recovery and the speed of airship is reduced. So, the aim in this paper was to fasten the recovery speed and to get back the cruising velocity. The control parameters were determined from the stability mode analysis, and the control inputs were the thrust and the elevator deflection angle.

• Imaging Science in Dentistry
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• v.50 no.3
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• pp.199-208
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• 2020

Purpose: This study was performed to introduce an in vivo hybrid multimodality technique involving the coregistration of micro-computed tomography (micro-CT) and high-resolution magnetic resonance imaging (HR-MRI) to concomitantly visualize and quantify mineralization and vascularization at follow-up in a rat model. Materials and Methods: Three adult female rats were randomly assigned as test subjects, with 1 rat serving as a control subject. For 20 weeks, the test rats received a weekly intravenous injection of 30 ㎍/kg zoledronic acid, and the control rat was administered a similar dose of normal saline. Bilateral extraction of the lower first and second molars was performed after 10 weeks. All rats were scanned once every 4 weeks with both micro-CT and HR-MRI. Micro-CT and HR-MRI images were registered and fused in the same 3-dimensional region to quantify blood flow velocity and trabecular bone thickness at T0 (baseline), T4 (4 weeks), T8 (8 weeks), T12 (12 weeks), T16 (16 weeks), and T20 (20 weeks). Histological assessment was the gold standard with which the findings were compared. Results: The histomorphometric images at T20 aligned with the HR-MRI findings, with both test and control rats demonstrating reduced trabecular bone vasculature and blood vessel density. The micro-CT findings were also consistent with the histomorphometric changes, which revealed that the test rats had thicker trabecular bone and smaller marrow spaces than the control rat. Conclusion: The combination of micro-CT and HR-MRI may be considered a powerful non-invasive novel technique for the longitudinal quantification of localized mineralization and vascularization.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.3
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• pp.147-154
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• 2014

In the context of an increasing need for safety in concrete structures under blast and impact loading condition, the behavior of concrete under high strain rate condition has been an important issue. Since concrete subjected to impact loading associated with high strain rate shows quite different material behavior from that in the static state, several material models are proposed and used to describe the high strain rate behavior under blast and impact loading. In the process of modelling high strain rate conditions with these material models, mesh dependency in the used finite element(FE) is the key problem because simulation results under high strain-rate condition are quite sensitive to applied FE mesh size. This paper introduces an criterion which can minimize the mesh-dependency of simulation results on the basis of the fracture energy concept, and HJC(Holmquist Johnson Cook) model is examined to trace sensitivity to the used FE mesh size. To coincide with the purpose of the perforation simulation with a concrete plate under a projectile(bullet), the residual velocities of projectile after perforation are compared. The analytical results show that the variation of residual velocity with the used FE mesh size is quite reduced and accuracy of simulation results are improved by applying a unique failure strain value determined according to the proposed criterion.

• Composites Research
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• v.18 no.3
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• pp.38-46
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• 2005

In order to characterize the outstanding performance of three-dimensional (3D) composites, the low velocity impact test has been carried out. 3D fiber structures have been achieved by using the automated tape placement (ATP) process and a stitching method. Materials for the ATP and the stitching process were carbon/epoxy prepreg tapes and Kevlar fibers, respectively. Two-dimensional composites with the same stacking sequence as 3D counterparts have also been fabricated for the comparison of damage tolerance. For the assessment of damage after the impact loading, specimens were subjected to C-Scan nondestructive inspection. Compression after impact (CAI) tests were conducted to evaluate residual compressive strength. The damage area of 3D composites was greatly reduced $(30-40\%)$ compared with that of 2D composites. Although the CAI strength did not show drastic improvement for 3D composites, the ratio of retained strength was $5-10\%$ higher than 2D samples. The effect of stitching on the impact performance was negligible above the energy level of 35 Joules.

• Journal of the Korean Society for Railway
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• v.18 no.4
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• pp.309-316
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• 2015

The contribution of exterior devices such as bogie fairings and pantographs to running resistance was estimated on the basis of coasting tests at up to 350 km/h with the help of the Korean Next Generation High speed train (HEMU-430X). In order to assess the reduction of air resistance by nose car's bogie fairing, coasting tests were conducted with a removable bogie fairing at various speed ranges. And, the contribution of the pantograph to air resistance was also estimated with coasting tests that include the pantograph's rising and descent modes. The linear regression method was used to examine decelerations from time-velocity data and the equation of resistance to motion is proposed from the deceleration data. From the aerodynamic term of the equation of resistance to motion, the contribution to air resistance by nose car's bogie fairing and pantograph was estimated. The results show that the air resistance was reduced by about 3.8% by the nose car's bogie fairing. And, the 3.9% increase of air resistance by the pantograph (open knee mode) has been found.