• Journal of Aerospace System Engineering
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• v.17 no.4
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• pp.118-125
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• 2023

The wind tunnel test is one of the essential processes in the development of guided missile systems, and various wind tunnel facilities exist depending on the test requirements, various conditions, and their purposes. The Ludwieg tube is very useful in the development of guided missile systems, and we have necessitated the upgrade of the Ludwieg tube in ADD to acquire various test requirements, such as high angle of attack, repeatability, and stability. In this paper, upgrading the nozzle, vacuum tank, and model support is suggested to improve the Ludwieg tube performance, and we demonstrate a result of the solution through pressure measurement.

• Journal of Korean Society on Water Environment
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• v.36 no.4
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• pp.300-313
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• 2020

The Bayesian approach can be used to estimate hydrologic model parameters from the prior expert knowledge about the parameter values and the observed data. The purpose of this study was to compare the performance of the two Bayesian methods, the Metropolis-Hastings (MH) algorithm and the Generalized Likelihood Uncertainty Estimation (GLUE) method. These two methods were applied to the TANK model, a hydrological model comprising 13 parameters, to examine the uncertainty of the parameters of the model. The TANK model comprises a combination of multiple reservoir-type virtual vessels with orifice-type outlets and implements a common major hydrological process using the runoff calculations that convert the rainfall to the flow. As a result of the application to the Nam River A watershed, the two Bayesian methods yielded similar flow simulation results even though the parameter estimates obtained by the two methods were of somewhat different values. Both methods ensure the model's prediction accuracy even when the observed flow data available for parameter estimation is limited. However, the prediction accuracy of the model using the MH algorithm yielded slightly better results than that of the GLUE method. The flow duration curve calculated using the limited observed flow data showed that the marginal reliability is secured from the perspective of practical application.

• Journal of Korean Society on Water Environment
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• v.22 no.5
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• pp.856-864
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• 2006

For estimating the minimum discharge to maintain a river, low flow analysis is required and long term runoff records are needed for the analysis. However, runoff data should be estimated to run a hydrologic model for ungaged river basin. For the reason, parameter estimation is crucial to simulate rainfall-runoff events for those basins using Tank model. In this study, only runoff data recorded for dry season are used for parameter estimation, which is different to other methods based on runoff data recorded for wet and dry seasons. The Harmony Search algorithm is used to determine the optimum parameters for Tank model. The coefficient of determination ($R^2$) is served as the objective function in the Harmony Search. In cases that recorded data are insufficient, the recording interval is changed and Empirical CDF is adopted to analyze the estimated parameters. The suggested method is applied to Yongdam dam, Soyanggang dam, Chungju dam and Seomjingang dam basins. As results, the higher $R^2s$ are obtained when the shorter recording interval, the better recorded data quality, and the more rainfall events recorded along with certain rainfall amount is. Moreover, when the total rainfall is higher than the certain amount, $R^2$ is high. Considering the facts found from this study for the low flow analysis, it is possible to estimate the parameters for Tank model properly with the desired confidence level.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.432-432
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• 2015

농업용 저수지의 하류유역은 저수지로부터 농업용수를 공급받는 관개지구와 산림지 등 관개를 실시하지 않는 비관개지구의 수문순환이 복합적으로 연계된다. 이러한 저수지 하류유역의 하천유량은 배후 유역에서 발생하는 유역 유출량, 관개지구의 농업용수 회귀수량, 저수지에서 방류되는 환경용수 방류량과 제한수위 및 만수위 방류량, 그리고 지하수 유출량 등으로 구성된다. 본 연구에서는 저수지 하류의 하천유량 구성 요소를 해석하는 하천망 모형을 구성하였고, 대상지구의 자료를 구축하였으며, 모형의 보정 및 검정을 수행하였다. 비관개지구의 유출량 모의는 수정 3단 Tank 모형을 이용하였다. 관개지구의 배수량은 논 포장 배수량과 용수로 배수량을 구분하여 모의하며, 논 포장 배수량은 논 물수지식을 기반으로 모의하였다. 저수지 방류량은 저수지 유입량과 저수지 운영방식을 고려하여 모의하도록 구성하였다. 하도 추적은 Muskingum 방법을 이용하였다. 연구 대상지로 이동저수지 유역을 선정하여 기상, 지형, 수문, 그리고 영농 자료를 수집하여 모형의 입력 자료를 구축하였다. 모형의 평가를 위한 통계적 지표는 Nash-Sutcliffe efficiency (NSE), root mean square error-observations standard deviation ratio (RSR), 그리고 percent bias (PBIAS)를 이용하였다. 보정 및 검정 결과 구성된 모형의 모의 결과는 실측치의 경향을 잘 반영하는 것으로 나타났다. 본 연구 결과는 우리나라 농촌유역 물순환에 대한 이해를 넓히며, 저수지 하류유역 유량 해석을 위한 기초자료로 이용될 수 있을 것으로 사료된다.

• Journal of Korean Society of Disaster and Security
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• v.12 no.4
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• pp.1-13
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• 2019

Recently, as the occurrence frequency of sudden floods due to climate change increased, it is necessary to install the facilities that can cope with the initial stormwater. Most researches have been conducted on the design of facilities applying the Low Impact Development (LID) and the reduction effect on rainfall runoff to examine with 1D or 2D numerical models. However, the studies on the examination about flow characteristics and stability of pipe network systems were relatively insufficient in the literature. In this study, the stability of the pipe network system in rainwater storage tank was examined by using 3D numerical model, FLOW-3D. The changes of velocity and dynamic pressure were examined according to the number of rainwater storage tank and compared with the design criteria to derive the optimal design plan for a rainwater storage tank. As a results of numerical simulation with the design values in the previous study, it was confirmed that the velocity became increased as the number of rainwater storage tank increased. And magnitude of the velocity in pipes was formed within the design criteria. However, the velocity in the additional rainwater storage pipe was about 3.44 m/s exceeding the allowable range of the design criteria, when three or more additional rainwater storage tanks were installed. In the case of turbulence intensity and bottom shear stress, the bottom shear stress was larger than the critical shear stress as the additional rainwater storage was increased. So, the deposition of sediment was unlikely to occur, but it should be considered that the floc was formed by the reduction of the turbulence intensity. In addition, the dynamic pressure was also satisfied with the design criteria when the results were compared with the allowable internal pressure of the pipes generally used in the design of rainwater storage tank. Based on these results, it was suitable to install up to two additional rainwater storage tanks because the drainage becomes well when increasing of the number of storage tank and the velocity in the pipe becomes faster to be vulnerable to damage the pipe. However, this study has a assumption about the specifications of the rainwater storage tanks and the inflow of stormwater and has a limitation such that deriving the suitable rainwater storage tank design by simply adding the storage tank. Therefore, the various storage tank types and stormwater inflow scenarios will be asked to derive more efficient design plans in the future.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.675-683
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• 2017

In this study, a theoretical analysis was performed to the flow of refilling stage in a safety injection tank, which is the core cooling system of nuclear power plant in an emergency. A theoretical model was proposed with a nonlinear governing equation defining on the flow of the refilling process of the coolant. Utilizing the Taylor-series expansion, the $1^{st}$ - order approximation flow equation was obtained, along with its analytic solution of closed type, which could predict accurately the variations of free surface height and flow rate of the coolant. The availability of theoretical result was confirmed by comparing with previous experimental results.

• Journal of Korean Society on Water Environment
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• v.33 no.2
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• pp.187-196
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• 2017

To ensure hygienic safety of drinking water in a water storage tank, the concentrations of residual chlorine should be above a certain regulation level. In this study, we conducted model simulations to investigate the effects of temperature on residual chlorine in water storage tank conditions typically used in Seoul. For this, values of model parameters (decomposition rate constant, sorption coefficient, and evaporation mass transfer coefficient) were experimentally determined from laboratory experiments. The model simulations under continuous flow conditions showed that the residual chlorine concentrations were satisfied the water quality standard level (0.1 mg/L) at all the temperature conditions ($5^{\circ}C$, $10^{\circ}C$, $15^{\circ}C$, $20^{\circ}C$ and $25^{\circ}C$). Meanwhile, when the tanks had a no flow condition (i.e., no tap-water influent due to a sudden shut-down), the concentrations became lower than the regulatory level after certain periods. The findings from this modeling works simulating Seoul's water storage tanks suggested disappearance rate of residual chlorine could be reduced through the tanks design optimization with maintenance of low water temperature, minimization of air flow and volume, suppression of dispersion and the use of wall materials with low sorption ability.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.5
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• pp.17-26
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• 2021

It is challenging to estimate the fatigue life of construction equipment consisting of a welded joint using field structure test owing to the uncertainty of the S-N curve. IIW recommends different S-N curves for various welded joint types. However, there is no way to define an appropriate curve considering complex design shape and strain gauge characteristics. This paper proposes an equivalent S-N curve method based on the relationship between IIW effective notch stress and virtual stress using finite element analysis. Moreover, a case study was conducted for the excavator fuel tank. The proposed method is expected to enhance accuracy and consistency in calculating the fatigue life for the welded structure of construction equipment.

• Journal of the Korean Institute of Gas
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• v.26 no.6
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• pp.9-15
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• 2022

In order to verify the durability of the high-pressure hydrogen tank in the operating pressure range, a hydraulic rupture test should be performed. However, if the bubbles generated by the initial injection process of water are attached to the inner wall of the tank and remain, a sudden pressure change of the bubbles during the rupture of the pressurized tank may cause shock and noise. Therefore, in this study, the flow velocity required to remove the bubbles remaining on the inner wall of the tank was predicted through simplified formulas, and the shape of the injection nozzle to maintain the flow velocity was determined based on the shape of the hydrogen tank for the hydrogen bus. In addition, a numerical model was developed to predict the change in flow velocity according to the inlet pressure, and an experiment was performed through a model tank to prove the validity of the prediction result. As a result of the experiment, the flow velocity near the tank wall was similar to the predicted value of the analysis model, and when the inlet pressure was 1.5 to 5.5 bar, the minimum size of the removable bubble was predicted to be about 2.2 to 4.6 mm.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.4
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• pp.64-76
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• 1999

In this paper hydroelastic experimental techniques of very large floating offshore structures are suggested based on the model test carried out in the UOU Ocean Engineering Wide Tank. The prototype is a box-shaped floating structure with length of 300m, breadth of 60m, depth of 2m and draft of 0.5m and longitudinal bending rigidity as $4.87{\times}10^{10}kgm^2$. The scale ratio is 1/42.857. The model is realized by aluminum square pipes with the section dimension of $20mm{\times}20mm$. The numbers of longitudinal and transverse pipes are 7 and 35 respectively. Heave motions at selected points are measured with potentiometers and bending moments with strain gages.