• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.20-24
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• 2011

In this paper, numerical simulation of cavitation flow for modified NACA66 hydrofoil was made by using the multi-phase RANS equation based on pseudo-compressibility. The Homogeneous mixture model comprised of the mixture continuity, mixture momentum and liquid volume fraction equations was utilized. A vertex-centered finite-volume method was used in conjunction 2nd-order Roe's FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing The Spalart-Allmaras one equation model was employed for the closure of turbulence. Reasonable agreements were obtained between the calculation results and the experiment for pressure coefficients on the hydrofoil surface.

• Journal of Theoretical and Applied Mechanics
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• v.2 no.1
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• pp.15-29
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• 1996

A fair portion of the dream to acquire the solutions to the Navier-Stokes equations has come true through the remarkable development of computers and solution algorithms in recent years. However, it is also true that there still remain serious hurdles in simulating general fluid flows. A few numerical trials to overcome the existing difficulties are introduced. The issues in numerical simulations of high-Reynolds-number flows, flows characterized by complex body geometry, and multi-phase flows, are scrutinized. The future of computational fluid dynamics as a promising tool for flow analyses is illuminated by this review.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.389-391
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• 2005

This paper describes experimental analysis of UPFC, which is composed of cascaded H-bridge modules and single-phase multi-winding transformers for isolation. The operational characteristic was analyzed through experimental works with a scaled model, and simulation results with PSCAD/EMTDC. The UPFC proposed In this paper can be directly connected to the transmission line without series injection transformers. It has flexibility to expand the operation voltage by increasing the number of H-bridge modules. The analysis results can be utilized to design the actual UPFC system applicable for the transmission system.

• Journal of the military operations research society of Korea
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• v.16 no.1
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• pp.130-141
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• 1990

This paper presents an allocation model of test times of software modules. An evaluation measure of modules which is based on the data flow path between modules is used at test phase. An evaluation measure is expressed by the possible path number of data flow for each module, which can be interpreted as an importance of individual module. Three criteria : module test time, module reliability, and system reliability is considered in this model. Multi-objective programming, hence, is used to solve this model.

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.507-513
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• 2009

The cooling technology of power conversion semiconductors in the propulsion system for the HEMU(High Electrical Multi Unit) are applied in water cooling method and phase change method such as the immersed type and the heat pipe type. Both of cooling systems need a condenser and a fan through forced wind to emit that is radiated heat from electric power conversion semiconductor(IGBT) stack effectively, now in the case of Japanese Fastec 360S, is using ram-air that is flowed in establishing cooling passage to propulsion system for cooling of condenser. In this research, it is that achieved the computing numerical analysis using ADINA of commertial program to examine flow characteristics and pressure distribution of ram-air for a condenser in cooling passage.

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.249-256
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• 2009

The cooling technology of power conversion semiconductors in the propulsion system for the HEMU(High Electrical Multi Unit) are applied in water cooling method and phase change method such as the immersed type and the heat pipe type. This research designs and manufactures the water cooling system that could cool about heat load Q=2kW and performance tests to apply it by an electric power conversion semiconductors(IGBT) cooling technology. Experimental condition made change of a flow rate, an air velocity and a heat load to confirm operation characteristics of water cooling device, and when is heat load 2kW, air velocity 20 m/s, and water flow rate 7kg/s, it is about $80^{\circ}C$ to temperature of cooling plate.

• Journal of Korea Water Resources Association
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• v.53 no.6
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• pp.395-408
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• 2020

This paper aims to develop and apply three different machine learning approaches (i.e., artificial neural networks (ANN), adaptive neuro-fuzzy inference systems (ANFIS), and wavelet-based neural networks (WNN)) combined with an evolutionary optimization algorithm and the k-fold cross validation for multi-step (days) streamflow forecasting at the catchment located in Algeria, North Africa. The ANN and ANFIS models yielded similar performances, based on four different statistical indices (i.e., root mean squared error (RMSE), Nash-Sutcliffe efficiency (NSE), correlation coefficient (R), and peak flow criteria (PFC)) for training and testing phases. The values of RMSE and PFC for the WNN model (e.g., RMSE = 8.590 ㎥/sec, PFC = 0.252 for (t+1) day, testing phase) were lower than those of ANN (e.g., RMSE = 19.120 ㎥/sec, PFC = 0.446 for (t+1) day, testing phase) and ANFIS (e.g., RMSE = 18.520 ㎥/sec, PFC = 0.444 for (t+1) day, testing phase) models, while the values of NSE and R for WNN model were higher than those of ANNs and ANFIS models. Therefore, the new approach can be a robust tool for multi-step (days) streamflow forecasting in the Seybous River, Algeria.

• Journal of the Korean Society of Radiology
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• v.82 no.3
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• pp.626-637
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• 2021

Purpose To explore cerebrovascular reservoir (CVR) and arterial transit time (ATT) changes using acetazolamide-challenged multi-phase arterial spin labeling (MP-ASL) perfusion-weighted MRI in chronic cerebrovascular steno-occlusive disease. Materials and Methods This retrospective study enrolled patients with chronic steno-occlusion who underwent acetazolamide-challenged MP-ASL between June 2019 and October 2020. Cerebral blood flow, CVR, basal ATT, and ATT changes associated with severe stenosis, total occlusion, and chronic infarction lesions were compared. Results There were 32 patients (5 with bilateral steno-occlusion) in our study sample. The CVR was significantly reduced during total occlusion compared with severe stenosis (26.2% ± 28.8% vs. 41.4% ± 34.1%, respectively, p = 0.004). The ATT changes were not significantly different (p = 0.717). The CVR was marginally lower in patients with chronic infarction (29.6% ± 39.1% vs. 38.9% ± 28.7%, respectively, p = 0.076). However, the ATT was less shortened in patients with chronic infarction (-54 ± 135 vs. -117 ± 128 ms, respectively, p = 0.013). Conclusion Acetazolamide-challenged MP-ASL provides an MRI-based CVR evaluation tool for chronic steno-occlusive disease.

• Economic and Environmental Geology
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• v.56 no.2
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• pp.167-183
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• 2023

Gases originated from the final SNF (spent nuclear fuel) disposal site are very mobile in the barrier and they may also affect the migration of radioactive nuclides generated from the SNF. Mechanisms of gas-nuclide migration in the multi-barrier and their influences on the safety of the disposal site should be understood before the construction of the final SNF disposal site. However, researches related to gas-nuclide coupled movement in the multi-barrier medium have been very little both at home and abroad. In this study, properties of gas generation and migration in the SNF disposal environment were reviewed through previous researches and their main mechanisms were summarized on the hydrogeological evolution stage of the SNF disposal site. Gas generation in the SNF disposal site was categorized into five origins such as the continuous nuclear fission of the SNS, the Cu-canister corrosion, the oxidation-reduction reaction, the microbial activity, and the inflow from the natural barriers. Migration scenarios of gas in porous medium of the multi-barrier in the SNF repository site were investigated through reviews for previous studies and several gas migration types including ① the free gas phase flow including visco-capillary two-phase flow, ② the advection and diffusion of dissolved gas in pore water, ③ dilatant two-phase flow, and ④ tensile fracture flow, were presented. Reviewed results in this study can support information to design the further research for the gas-nuclide migration in the repository site and to evaluate the safety of the Korean SNF disposal site in view points of gas migration in the multi-barrier.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.1
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• pp.1-5
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• 2009

In this study, we performed growth of InGaN/GaN multi quantum well (MQW) structures on semi-polar (1-10]) GaN facet on 8-degree off oriented stripe patterned (100) Si substratcs by MOVPE. The structural and optical properties of the InGaN/GaN multi quantum well (MQW) structures grown on (1-101) GaN stripe depend on $NH_3$ flow rate, TMI flow rate and growth temperature are characterized by cathodoluminescence (CL) and scanning electron microscopy (SEM). With the decrease of $NH_3$ flow rate, the threading dislocation of (1-101) GaN is considerably reduced. We could control the transition wavelength of InGaN/GaN MQW structures from 391.5 nm to 541.2 nm depend on the growth conditions.