• Advances in aircraft and spacecraft science
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• v.10 no.4
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• pp.303-315
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• 2023

The primary goal of this research is to investigate flow separation phenomena using various turbulence models. Also investigated are the effects of free-stream turbulence intensity on the flow over a NACA 0018 airfoil. The flow field around a NACA 0018 airfoil has been numerically simulated using RANS at Reynolds numbers ranging from 100,000 to 200,000 and angles of attack (AoA) ranging from 0° to 18° with various inflow conditions. A parametric study is conducted over a range of chord Reynolds numbers for free-stream turbulence intensities from 0.1 % to 0.5 % to understand the effects of each parameter on the suction side laminar separation bubble. The results showed that increasing the free-stream turbulence intensity reduces the length of the separation bubble formed over the suction side of the airfoil, as well as the flow prediction accuracy of each model. These models were used to compare the modeling accuracy and processing time improvements. The K- SST performs well in this simulation for estimating lift coefficients, with only small deviations at larger angles of attack. However, a stall was not predicted by the transition k-kl-omega. When predicting the location of flow reattachment over the airfoil, the transition k-kl-omega model also made some over-predictions. The Cp plots showed that the model generated results more in line with the experimental findings.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.20 no.3
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• pp.119-130
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• 2015

Impacts of Argo temperature assimilation on the analysis fields in the East Sea is investigated by using DAESROM, the East Sea Regional Ocean Model with a 3-dimensional variational assimilation module (Kim et al., 2009). Namely, we produced analysis fields in 2009, in which temperature profiles, sea surface temperature (SST) and sea surface height (SSH) anomaly were assimilated (Exp. AllDa) and carried out additional experiment by withdrawing Argo temperature data (Exp. NoArgo). When comparing both experimental results using assimilated temperature profiles, Root Mean Square Error (RMSE) of the Exp. AllDa is generally lower than the Exp. NoArgo. In particular, the Argo impacts are large in the subsurface layer, showing the RMSE difference of about $0.5^{\circ}C$. Based on the observations of 14 surface drifters, Argo impacts on the current and temperature fields in the surface layer are investigated. In general, surface currents along the drifter positions are improved in the Exp. AllDa, and large RMSE differences (about 2.0~6.0 cm/s) between both experiments are found in drifters which observed longer period in the southern region where Argo density was high. On the other hand, Argo impacts on the SST fields are negligible, and it is considered that SST assimilation with 1-day interval has dominant effects. Similar to the difference of surface current fields between both experiments, SSH fields also reveal significant difference in the southern East Sea, for example the southwestern Yamato Basin where anticyclonic circulation develops. The comparison of SSH fields implies that SSH assimilation does not correct the SSH difference caused by withdrawing Argo data. Thus Argo assimilation has an important role to reproduce meso-scale circulation features in the East Sea.

• Journal of Food Hygiene and Safety
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• v.18 no.4
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• pp.177-182
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• 2003

Saururus chinensis Baill (Saururaceae) is a perennial plant that has been used for therapy of edema, jaundice and gonorrhea in Korean folk medicine. This study was carried out to investigate the inhibitory effects of Saururus chinensis Baill(SCB) on hepatoprotective effects in accutely Carbone Tetrachloride ($CCl_4$) treated rats. Saururus chinensis Baill (100 mg/kg) was administered into rats intraperitoneally for 2 weeks, after the injection of CCl4 (3.3 ml/kg). We dxamined the biochemical parameters by measuring the levels of Aspartate aminotransferase (AST), Alanine aminotransferase (ALT), Total cholesterol, Triglyceride (TG), HDL-cholesterol, and LDL-cholesterol in serum and Malonedialdehyde (MDA) in liver tissue of rats. cholesterol was siginificantly elevated in $CCl_4$-treated abnormal group (CTA). The higher level of HDL-cholesterol was found is Saururus chinensis Baill and CCl4 administered group (SCT), which showed the lower levels of Total-cholesterol and LDL-cholesterol. TG content in the SCT was decreased compared to CTA by 0.93 times. MDA content in the SCT was inhibited compared to CTA by 33.00%. These findings indicate that Saururus chinensis. Baill may have a protective effect against CCl4-treated hepatotoxicity in rats.

• Journal of the Korean Society of Safety
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• v.35 no.3
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• pp.96-104
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• 2020

The numerical simulations were conducted to investigate the thermal-fluid phenomena occurred inside the experimental apparatus during a PCCS, used to remove heat released in accidents from a containment of light water nuclear power plant, operation. Numerical simulations of the flow and heat transfer caused by wall condensation inside the containment simulation vessel (CSV), which equipped with 18 vertical heat exchanger tubes, were conducted using the commercial computational fluid dynamics (CFD) software ANSYS-CFX. Shear stress transport (SST) and the wall condensation model were used for turbulence closure and wall condensation, respectively. The simulation using the actual size of the apparatus. However, rather than simulating the whole experimental apparatus in consideration of the experimental cases, calculation resources, and calculation time, the simulation model was prepared only in CSV. Selective simulation was conducted to verify the effects of non-condensable gas(NC gas) concentration, CSV internal pressure, and wall sub-cooling conditions. First, as a result of the internal flow of CSV, it was observed that downward flow due to condensation occurred surface of the vertical tube and upward flow occurred in the distant place. Natural convection occurred actively around the heat exchanger tube. Due to this rising and falling internal flow, natural circulation occurred actively around the heat exchanger tubes. Next, in order to check the performance of built-in condensation model using according to the non-condensable gas concentration, CSV internal flow and wall sub-cooling, the heat flux values were compared with the experimental results. On average, the results were underestimated with and error of about 25%. In addition, the influence of CSV internal pressure and wall sub-cooling was small, but when the condensate was highly generated due to the low non-condensable gas concentration, the error was large compared to the experimental values. This is considered to be due to the nature of the condensation model of the CFX code. However, in spite of the limitations of CFD, it is valid to use the built-in condensation model of CFD for PCCS performance prediction from a conservative perspective.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.4
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• pp.401-409
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• 2018

A numerical investigation has been conducted to find the effects of pressure losses by struts and rakes, and averaging methods on the performance of a multi-stage axial fan and a multi-stage axial compressor. Struts and rakes which produce pressure losses are installed upstream of the aerodynamic inlet plane in the fan and the compressor rigs. Some of normal stator vanes are substituted with thick vanes with total pressure probes to measure total pressure between stages. Three-dimensional Reynolds-averaged Navier- Stokes equations with $k-{\omega}$ SST turbulence model were applied to analyze the pressure losses by the struts, inlet rakes, and thick instrumented vanes. The hexahedral grids were used to construct computational domain. Inlet pressure losses were evaluated for the compressor as a function of Mach number. The passage pressure losses due to the instrumented vanes were evaluated at the two speed lines in the fan. Total properties, such as pressure and temperature, were evaluated at the exit of the fan and the compressor with two different averaging methods which are area-averaging and mass-averaging, respectively.

• Journal of Food Hygiene and Safety
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• v.18 no.3
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• pp.166-170
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• 2003

This study was carried out to investigate the inhibitive effect of Saururus chinenesis Baill (SCB) on lipid peroxidation in Sprague-Dawely rat (SD-rat) accutely exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Saururus chinenesis Baill (200 mg/kg) was administered into rats intraperitoneally for four weeks, seven days after the injection of TCDD (1 ${\mu}$g/kg). we examined th lipid parameters by measuring the levels of Total Cholestero, Triglyceride(TG), HDL-Cholestero, and LDL-Cholesterol in serum and Malone Dialdehyde (MDA) in liver tissue of rats. Cholesterol was siginificantly elevated in TCDD-treated abnormal group (TTA). The higher level of HDL-Cholesterol was found in Saururus chinenesis Baill and TCDD administered group (STT), which showed the lower levels of Total-Cholesterol and LDL-Cholesterol. TG content in the TTA was 34.84% increased compared to Non TCDD-treated group (NTT). That of STT was inhibited by 18.90% compared to TTA. MDA content in the TTA was 44.72% increased compared to NTT. That of STT was inhibited by 17.14% compared to TTA.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.875-882
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• 2019

The effects of Triangle Groove Strips (TGS) on Vortex-induced Vibration (VIV) suppression of marine riser are numerically investigated using Computational Fluid Dynamics (CFD) method. The range of Reynolds number in simulations is 4.0 × 10⁴ < Re < 1.2 × 10⁵. The two-dimensional unsteady Reynolds-Averaged Navier-Stokes (RANS) equations and Shear Stress Transport (SST) k-ω turbulence model are used to calculate the flow around marine riser. The Newmark-β method is employed for evaluating the structure dynamics of marine riser. The effect of the height ratio (ε) of TGS on VIV suppression is evaluated. The amplitude responses, frequency responses, vortex patterns and the flow around the structures are discussed in detail. With the increase of the height ratio of TGS, the suppression effect of TGS on VIV suppression is improved firstly and then weakened. When ε=0.04, the suppression effect of TGS is the best. Compared with the VIV responses of smooth marine riser, the amplitude ratio is reduced by 38.9%, the peak of the lift coefficient is reduced by 69% and the peak of the drag coefficient is reduced by 40% when Re=6.0 × 10⁴. With the increase of Reynolds number, the suppression effect of TGS on VIV suppression is improved firstly and then weakened. When the Reynolds number is 7.0 × 10⁴, the amplitude ratio can be reduced by 40.1%. As to the large-amplitude vibration cases, the TGS show nice suppression effect on VIV.

• Journal of Korean Society for Atmospheric Environment
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• v.25 no.6
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• pp.481-492
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• 2009

The characteristic of cold water by upwelling in the southeast of the Korean Peninsula and the effect of sea breeze in this region are investigated. The coastal upwelling around the southeast coast of the Korea Peninsula is analyzed by using Coastal Oceanographic Data statistical analyses for 5 years were carried out. The period of an cold water event, on the average, was observed southwesterly wind events. The analysis suggests that strong and persistent southwesterly winds in period of an cold water play an important role of bring the moisture to the surface, generating persistent cyclone as jangma. In order to investigate the effect of cold water on sea breeze, we considered two case. First, Exp. 1 is not occurred coastal upwelling on sea breeze. Second, Exp. 2 is occurred cold water on sea breeze. Two experiments were completed separately to the effects of cold water by upwelling. The results show the sea breeze is stronger in Exp. 2, when the cold water occurs, and weaker in Exp. 1, when there is no cold water. In order to verify the effect of the sea breeze on the cold water by upwelling, on the intensification and change of direction of the prevailing wind, the sea breeze effectively intensify cold water condition.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.6
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• pp.494-502
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• 2016

The accurate assessment of hull-appendage interaction in the early design stage is important to control the inflow to the propeller plane, which can cause undesirable hydrodynamic effects in terms of cavitation phenomenon. This paper describes a numerical analysis for the flow around a fully appended surface ship model for which KRISO has carried out a model test in the Large Cavitation Tunnel(LCT). This numerical study was performed with the LCT model test in a complementary manner for a good reproduction of the wake distribution of surface ships. A second order accurate finite volume method provided by a commercial computational fluid dynamics(CFD) program was used to solve the governing Reynolds Averaged Navier-Stokes(RANS) equations, where the SST $k-{\omega}$ model was used for turbulence closure. The numerical results were compared to available LCT experimental data for validation. The calculations gave good predictions for the boundary layer profiles on the walls of the empty cavitation tunnel and the wake at the propeller plane of the fully appended hull model in the LCT.

• Journal of the Korean Society of Physical Medicine
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• v.19 no.2
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• pp.1-16
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• 2024

PURPOSE: This study examined the effects of four weeks of gaze stabilization exercises and balance training on the static and dynamic balance functions. METHODS: The study was an assessor-blinded randomized controlled trial conducted at Daegu University in South Korea. Thirty subjects who fulfilled the inclusion criteria were selected and divided randomly into three groups containing ten each. The first group received balance exercises with gaze stabilizing exercises (BGG). The second group received a balance exercise (BEG), and the third group received gaze-stabilizing exercise (GEG). Each group exercised for 40 minutes, three times a week for four weeks. The subjects were asked to complete the following static balance test: 1) one-leg standing test, 2) sharpened Romberg test, dynamic balance test, 3) Y-balance test, and 4) single-leg stand-squat-stand test. The static and dynamic balance were measured before and after four weeks to determine the effect of exercise on balance. RESULTS: The static (OLS and SRT) and dynamic (YBT and SST) balance tests showed significant differences in the surface and length of the three groups (p < .05), and the y-balance score effect size, 11.477 (p < .05), was improved significantly. On the other hand, the change in BGG value was larger than those of BEG and GEG, and the improvements in balance control were the most significant. CONCLUSION: After four weeks of exercise, BGG showed the best improvement in static and dynamic balance, suggesting that this specific type of gaze stabilization exercise with balance exercise may benefit healthy young adults.