• Journal of the Society of Naval Architects of Korea
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• v.60 no.1
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• pp.1-9
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• 2023

In order to improve the propeller cavitation performance composed of Cavitation Inception Speed (CIS), cavitation extent and pressure fluctuation, it needs to improve the wake distribution that flows into the propeller. The warship propeller cavitation is strongly influenced by the wake created at the V-strut of various appendages. The inflow characteristics of the V-strut were investigated using Computational Fluid Dynamics (CFD) and the twisted angles of the V-strut were aligned with upstream flow. The resistance and self-propulsion tests for the model ship with the existing and modified V-struts were conducted in Towing Tank (TT), and wake distribution, CIS, cavitation observation and pressure fluctuation tests were conducted in Large Cavitation Tunnel (LCT). The propeller behind the modified V-strut showed better cavitation characteristics than that behind the existing V-strut. Another model test was conducted to investigate rudder cavitation performance by the change of the V-strut. The rudder cavitation characteristics were not improved by the change of the operating conditions. On the basis of the present study, it is thought that the stern appendages for better propeller cavitation performance would be developed.

• The Journal of the Convergence on Culture Technology
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• v.10 no.2
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• pp.531-536
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• 2024

Control drones, which are recently classified as smart agricultural machines in the agricultural field, are striving to build smart control and automatic control systems by combining hardware and software in order to shorten working hours and increase the effectiveness of control in the aging era of rural areas. In this paper, the characteristics of the nozzle dedicated to the control drone were analyzed as a basic study for the establishment of management control and automatic control systems. In order to consider various variables such as the type of various drone models, controller, wind, flight speed, flight altitude, weather conditions, and UAV pesticide types, related studies are needed to be able to present the drug spraying criteria in consideration of the characteristics and versatility of the nozzle. Therefore, to enable the consideration of various variables, flow analysis (CFD) simulation was conducted based on the self-designed nozzle, and the theoretical and experimental values of the droplet distribution were compared and analyzed through water reduction experiments. In the future, we intend to calculate accurate scattering in consideration of various variables according to drone operation and use it in management control and automatic control systems.

• Journal of Korea Water Resources Association
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• v.50 no.6
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• pp.373-386
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• 2017

This study simulated water quality item and flow rate of subbasin for Saemangeum watershed using Soil and Water Assessment Tool (SWAT) model and Environmental Fluid Dynamics Code (EFDC) model which simulate hydraulic and water quality in three-dimensions. The simulated values corresponded to observed value well. The result of simulation for floodgate operations at the M3 and M5 points, it exceeds water quality standard and at the M3 and D3 points, change of range for concentration is too wide, and upstream of Saemangeum reservoir is sensitive to inflow flow rate. Compared to the annual average concentration for observed station according to the discharge conditions, improvement of water quality for upstream was apparently compared to the downstream. Range of influence for change of water quality presented that maximum discharge condition, the influence range is 22 km in the direction of the Saemangeum downstream from the Mankyung bridge, and 15 km in the downstream direction of saemangeum in the Dongjin bridge. This study result demonstrated that floodgate operating at upstream has significant influence on water quality management of Saemangeum reservoir and it needs to be considered in plans of water quality management for Floodgate operation on Saemangeum reservoir.

• Nuclear Engineering and Technology
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• v.42 no.4
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• pp.382-393
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• 2010

Thermal mixing by steam jets in a pool is dominantly influenced by a turbulent water jet generated by the condensing steam jets, and the proper prediction of this turbulent jet behavior is critical for the pool mixing analysis. A turbulent jet flow induced by a steam jet discharged through a vertical upward single hole into a subcooled water pool was subjected to computational fluid dynamics (CFD) analysis. Based on the small-scale test data derived under a horizontal steam discharging condition, this analysis was performed to validate a CFD method of analysis previously developed for condensing jet-induced pool mixing phenomena. In previous validation work, the CFD results and the test data for a limited range of radial and axial directions were compared in terms of profiles of the turbulent jet velocity and temperature. Furthermore, the behavior of the turbulent jet induced by the steam jet through a horizontal single hole in a subcooled water pool failed to show the exact axisymmetric flow pattern with regards to an overall pool mixing, whereas the CFD analysis was done with an axisymmetric grid model. Therefore, another new small-scale test was conducted under a vertical upward steam discharging condition. The purpose of this test was to generate the velocity and temperature profiles of the turbulent jet by expanding the measurement ranges from the jet center to a location at about 5% of $U_m$ and 10 cm to 30 cm from the exit of the discharge nozzle. The results of the new CFD analysis show that the recommended CFD model of the high turbulent intensity of 40% for the turbulent jet and the fine mesh grid model can accurately predict the test results within an error rate of about 10%. In this work, the turbulent jet model, which is used to simply predict the temperature and velocity profiles along the axial and radial directions by means of the empirical correlations and Tollmien's theory was improved on the basis of the new test data. The results validate the CFD model of analysis. Furthermore, the turbulent jet model developed in this study can be used to analyze pool thermal mixing when an ellipsoidal steam jet is discharged under a high steam mass flux in a subcooled water pool.

• Journal of the Korean Institute of Gas
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• v.27 no.2
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• pp.1-6
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• 2023

PE piping, which has advantages in terms of construction convenience and economy, is widely used for underground burial in the domestic urban gas field. These PE pipes use squeeze-off in many sites to block gas flow during maintenance and repair work. Squeeze-off refers to a method of compressing a PE pipe to block fluid flow, and damage may occur due to the nature of construction in which the pipe is deformed by physical force. In order to prevent damage to PE pipes due to squeeze-off, the main points to be reflected in the squeeze-off operation procedures such as proper compression range, use pressure, and diameter were derived through damage assessment and confidential test according to the compression rate. The compression experiment for PE pipe damage assessment was conducted while changing the compression rate (20%~40%), the pressure of use (2.8 kPa, 25 kPa, 70 kPa), and the pipe diameters (63 mm, 90 mm, 110 mm). As a result of damage assessment according to the compression rate, damage occurred in pipes with compression rates of 45%(110mm) and 73%(63mm), which are for analyzing the effect of excessive compression. In addition, the leakage test was conducted using Ar(argon) during the squeeze-off, and as a result of the experiment, leakage occurred under the conditions of 70kPa and 110mm of pipe. As a result of this study, it was confirmed that squeeze-off for airtightness should be carried out in pipes within a range not exceeding 25 kPa and 90 mm pipes, and the appropriate compression rate to prevent damage to PE pipes is 30%.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1802-1813
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• 2023

Conjugate heat transfer between liquid metal and solid is a common phenomenon in a liquid-metal-cooled fast reactor's fuel assembly and heat exchanger, dramatically affecting the reactor's safety and economy. Therefore, comprehensively studying the sophisticated conjugate heat transfer in a liquid-metal-cooled fast reactor is profound. However, it has been evidenced that the traditional Simple Gradient Diffusion Hypothesis (SGDH), assuming a constant turbulent Prandtl number (Pr_t,, usually 0.85 - 1.0), is inappropriate in the Computational Fluid Dynamics (CFD) simulations of liquid metal. In recent decades, numerous studies have been performed on the four-equation model, which is expected to improve the precision of liquid metal's CFD simulations but has not been introduced into the conjugate heat transfer calculation between liquid metal and solid. Consequently, a four-equation model, consisting of the Abe k - ε turbulence model and the Manservisi k_𝜃 - ε_𝜃 heat transfer model, is applied to study the conjugate heat transfer concerning liquid metal in the present work. To verify the numerical validity of the four-equation model used in the conjugate heat transfer simulations, we reproduce Johnson's experiments of the liquid lead-bismuth-cooled turbulent pipe flow using the four-equation model and the traditional SGDH model. The simulation results obtained with different models are compared with the available experimental data, revealing that the relative errors of the local Nusselt number and mean heat transfer coefficient obtained with the four-equation model are considerably reduced compared with the SGDH model. Then, the thermal-hydraulic characteristics of liquid metal turbulent pipe flow obtained with the four-equation model are analyzed. Moreover, the impact of the turbulence model used in the four-equation model on overall simulation performance is investigated. At last, the effectiveness of the four-equation model in the CFD simulations of liquid sodium conjugate heat transfer is assessed. This paper mainly proves that it is feasible to use the four-equation model in the study of liquid metal conjugate heat transfer and provides a reference for the research of conjugate heat transfer in a liquid-metal-cooled fast reactor.

• Korean Journal of Materials Research
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• v.17 no.1
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• pp.11-17
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• 2007

Turbulent in-situ mixing process is a new material process technology to get dispersed phase in nanometer size by controlling reaction of liquid/solid, liquid/gas, flow ana solidification speed simultaneously. In this study, mixing which is the key technology to this synthesis method was studied by computational fluid dynamics. For the simulation of mixing of liquid metal, static mixers investigated. Two inlets for different liquid metal meet ana merge like 'Y' shape tube having various shapes and radios of curve. The performance of mixer was evaluated with quantitative analysis with coefficient of variance of mass fraction. Also, detailed plots of intersection were presented to understand effect of mixer shape on mixing. The simulations show that the Reynolds number (Re) is the important factor to mixing and dispersion of $TiB_2$ particles. Mixer was designed according to the simulation, and $Cu-TiB_2$ nano composites were evaluated. $TiB_2$ nano particles were uniformly dispersed when Re was 1000, and cluster formation and reduction in volume fraction of $TiB_2$ were found at higher Re.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.15-20
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• 2015

The objective of this study was to examine numerically the heat transfer and flow characteristics of the heat pipe with a wick using the simplified heat transfer model to enhance the cooling effects of high heat flux devices and minimizing the energy consumption for electric vehicles. The heat pipe with a wick was analyzed using commercial software with COMSOL and water was used as the working fluid. The velocity and temperature characteristics of the heat pipe were simulated numerically along the heat pipe and the local and average Nusselt numbers were calculated. As a result, the driving force occurred because of the temperature difference between the hot side and the cold side. The heat transfer of the heat pipe occurred from the hot side to the cold side and increased toward the center position. In addition, the average Nusselt numbers were 1.88 for the hot side and 0.1 for the cold side, and the maximum Nusselt number was 4.47 for the hot side and 0.7 for the cold side.

• Clinical and Experimental Pediatrics
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• v.58 no.4
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• pp.154-157
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• 2015

Plastibell is one of the three most common devices used for neonatal circumcision in the United States, with a complication rate as low as 1.8%. The Plastibell circumcision device is commonly used under local anesthesia for religious circumcision in male neonates, because of cosmetic reasons and ease of use. Occasionally, instead of falling off, the device may get buried under the skin along the shaft of the penis, thereby obstructing the normal flow of urine. Furthermore, the foreskin of neonates is highly vascularized, and hence, hemorrhage and infection are possible when the skin is cut. Necrosis of penile skin, followed by urethral obstruction and renal failure, is a serious surgical mishap requiring immediate corrective surgery and medical attention. We report a case of fulminant urosepsis, acute renal failure, and pyelonephritis in a 4-day-old male neonate secondary to impaction of a Plastibell circumcision device. Immediate medical management was initiated with fluid resuscitation and mechanical ventilation; thereby correcting life threatening complications. Pediatricians and Emergency Department physicians should be cognizant of the complications from Plastibell circumcision device in order to institute appropriate and timely management in neonates.

• Wind and Structures
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• v.22 no.4
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• pp.477-501
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• 2016

Though hilly topography influences both wind speeds and directions aloft, only the influence on wind speeds, i.e. the speed-up effect, has been thoroughly investigated. Due to the importance of a model showing the spatial variations of wind directions above hilly terrains, it is worthwhile to systematically assess the applicability and limitations of the model describing the influence of hilly topographies on wind directions. Based on wind-tunnel test results, a model, which describes the horizontal and vertical variations of the wind directions separately, has been proposed in a companion paper. CFD (Computational Fluid Dynamics) techniques were employed in the present paper to evaluate the applicability of the proposed model. From the investigation, it has been found that the model is acceptable for describing the vertical variation of wind directions by a shallow hill whose primary-to-secondary axis ratio (aspect ratio) is larger than 1. When the overall hill slope exceeds $20^{\circ}$, the proposed model should be used with caution. When the aspect ratio is less than 1, the proposed model is less accurate in predicting the spatial variation of wind directions in the wake zone in a separated flow. In addition, it has been found that local slope of a hill has significant impact on the applicability of the proposed model. Specifically, the proposed model is only applicable when local slope of a hill varies gradually from 0 (at the hill foot) to the maximum value (at the mid-slope point) and then to 0 (at the hill top).