• 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.

• Journal of Korea Water Resources Association
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• v.36 no.3 s.134
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• pp.465-480
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• 2003

The interception capabilities of storm water grate inlet were analyzed in this paper. The hydraulic model lot gutter flow was used to estimate the interception capability. With the consideration of width and length of road, gutter discharges were ranged of 4-15l/sec. The transverse slopes of gutter were selected 4, 7 and 10%. The longitudinal slopes were 0, 2, 5 and 7%. The four sizes of storm water grate inlet were used in this experiments ($30\times40cm,\;40\times50cm,\;40\times100cm,\;40\times150cm$). The total number of experimental cases were 240. As the transverse slopes of gutter increased, the interception capability also increased. As the flow width in gutter and the discharge were lower, the interception efficiencies increased and the longitudinal slopes of road increased, the interception efficiencies decreased. The empirical formula with the factors of total inflow discharge, the longitudinal slope and the transverse slope of gutter were derived. These equations could be used to estimate the intercepting discharge of grate inlet. The reasonable construction space of grate inlet for the road widths, the longitudinal slopes, the transverse slopes and the grate inlet sizes were suggested.

• Korean Journal of Agricultural Science
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• v.17 no.2
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• pp.102-114
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• 1990

This study was carried out to analyze the operation of the sluice gates by taking Sabkyo Reservoir as the model, and to examine the formulae of the design criteria for the Agricultural Land Improvement Project by hydraulic model experiments. The results were summarized as follows ; 1. According to the records of gate operation for 9 years, the mean height of the opened gates was 4.13 m, the mean number of operated gates were 4.04, the average annual number of operation were 67 times, the average annual operating time were 192.5 hours, and the average operating time were 2.88 hours. 2. The water supplied through Sabkyo Reservoir was 88.15 megatons per year, which was about 1.4 times the effective storage capacity. And the annual volume of pumping in May, which is the most water demanding season, was 29.56 megatons in average. 3. As the submerged orifice was transformed into the surface orifice, the suggested formulae for the orifice flow on the design criteria for the Agricultural Land Improvement Project showed a discontinuous line on the transition zone. It should be improved, because it is different from the real hydraulic phenomena. 4. The formulae for the orifice flow which are divided into the submerged and surface orifices are being used. However, these formulae could be substituted for the formular, $q=C{\cdot}W\sqrt{2gH_1}$, if the discharge coefficient considering the reservoir water level, the sea water level, and the gate opening height is used.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.3
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• pp.82-92
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• 2022

In recent years, coastal and port structures have attempted to prevent wave-overtopping or provide waterfront areas by installing superstructures on the structural crowns. In general, in the design stage, the Goda formula acting on the front the structure is applied to calculate the wave pressure acting on the superstructure in consideration of the wave-runup of the design wave. However, the wave pressure exceeding the Goda wave pressure could generate depending on the installation location of the superstructure where the wave-overtopping occurs. This study analyzed the applicability of the Goda formula to the wave pressure calculation for the superstructure of the vertical structures through hydraulic model experiments and numerical simulations. Furthermore, this study investigated the magnitude of the wave pressure acting on the superstructure based on detailed numerical results. As a result, the wave pressure acting on the superstructure was up to 120% higher than the maximum wave pressure on the still water surface. In addition, the wave pressure increases exponentially with the Froude number computed by the overtopping water depth at the crown of the structure, and we proposed an empirical formula for predicting the wave pressure based on the Froude number.

• Nuclear Engineering and Technology
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• v.50 no.3
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• pp.356-367
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• 2018

A series of tests dedicated to station blackout (SBO) accident scenarios have been recently performed at the $Prim{\ddot{a}}rkreislauf-Versuchsanlage$ (primary coolant loop test facility; PKL) facility in the framework of the OECD/NEA PKL-3 project. These investigations address current safety issues related to beyond design basis accident transients with significant core heat up. This work presents a detailed analysis using the best estimate thermal-hydraulic code TRACE (v5.0 Patch4) of different SBO scenarios conducted at the PKL facility; failures of high- and low-pressure safety injection systems together with steam generator (SG) feedwater supply are considered, thus calling for adequate accident management actions and timely implementation of alternative emergency cooling procedures to prevent core meltdown. The presented analysis evaluates the capability of the applied TRACE model of the PKL facility to correctly capture the sequences of events in the different SBO scenarios, namely the SBO tests H2.1, H2.2 run 1 and H2.2 run 2, including symmetric or asymmetric secondary side depressurization, primary side depressurization, accumulator (ACC) injection in the cold legs and secondary side feeding with mobile pump and/or primary side emergency core coolant injection from the fuel pool cooling pump. This study is focused specifically on the prediction of the core exit temperature, which drives the execution of the most relevant accident management actions. This work presents, in particular, the key improvements made to the TRACE model that helped to improve the code predictions, including the modeling of dynamical heat losses, the nodalization of SGs' heat exchanger tubes and the ACCs. Another relevant aspect of this work is to evaluate how well the model simulations of the three different scenarios qualitatively and quantitatively capture the trends and results exhibited by the actual experiments. For instance, how the number of SGs considered for secondary side depressurization affects the heat transfer from primary side; how the discharge capacity of the pressurizer relief valve affects the dynamics of the transient; how ACC initial pressure and nitrogen release affect the grace time between ACC injection and subsequent core heat up; and how well the alternative feeding modes of the secondary and/or primary side with mobile injection pumps affect core quenching and ensure stable long-term core cooling under controlled boiling conditions.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.7 no.6
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• pp.61-74
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• 2004

Hydraulic engineers and scientists working on river restoration recognize the need for a deeper understanding of natural streams as a complex and dynamic system, which involves not only abiotic elements(flow, sediments) but also biotic components. From this point of view, the role played by riverine vegetation dynamics and flow conditions becomes essential. Hydro-mechanic interaction between flow and flexible plants covering a river bed is studied in this paper and some previous works are discussed. Measurements of turbulence and flow resistance in vegetated open channel were performed using rigid and flexible tube. Measuring detailed turbulent velocity profiles within and above submerged and flexible stems allowed to distinguish different turbulent regimes. Some interesting relationships were obtained between the velocity field and the deflected height of the plants, such as a reduced drag coefficient in the flexible stems. Turbulent intensities and Reynolds stresses were measured showing two different regions : above and inside the vegetation domain. In flexible vegetated open channel, the maximum values of turbulent intensities and Reynolds stresses appear above the top of canopy. Method to predict a flow resistance in flexible vegetated open channel is developed by modifying an analytical model proposed by Klopstra et al. (1997). Calculated velocity profiles and roughness values correspond well with flume experiments. These confirm the applicability of the presented model for open channel with flexible vegetation. The new method will be verified in the real vegetated conditions in the near future. After these verifications, the new method should be applied for nature rehabilitation projects such as river restorations.

• Nuclear Engineering and Technology
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• v.26 no.1
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• pp.1-8
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• 1994

The flame speed correlation considering thermal-hydraulic phenomena under severe accidents is proposed and correction coefficients are defined. This correlation modifies the pressure dependency in Iijima-Takeno correlation and adds the steam suppression effects to it in the anticipated hydrogen and steam concentration ranges under severe accidents. The existing models of flame speed due to hydrogen combustion under severe accidents are based on the experiments which were performed merely at room temperature and atmospheric pressure. They have difficulty in predicting a accurate flame speed in a case of high temperature and pressure during severe accidents. Thus the flame structure is assumed as a prerequisite to the reliable determination of flame speed and theoretical model is developed. To examine the validity, flame speeds in various conditions calculated by this model are compared with those obtained by the calculation of the existing correlations of the codes such as improved HECTR and MAAP. Also the steam suppression ratio is quantified and the steam suppression coefficient is defined as a composition of mixture. Initial temperature and pressure dependencies are investigated and correction coefficents are determined. More experimental studies can be recommended to improve this correlation to its further works.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.2
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• pp.182-190
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• 2009

For RANS equation model using VOF scheme Lin and Liu (1999) developed internal wave-maker method to generate target wave trains by using designed mass source functions of the continuity equation. By using this method studies on various numerical wave experiments has been achieved without the problem caused by wave reflection due to an external wave-maker. In this study, the wave-maker method to generate target wave trains by using a momentum source function was proposed. The computational results obtained by applying the mass and momentum source functions into FLUENT were compared with each other. To see its applicability, the hydraulic experiment of Luth et al. (1994) were numerically simulated and their measurements are compared with the computations, and the vertical variations of computed results were shown and investigated.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.2
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• pp.97-111
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• 2006

Using the eigenfunction expansion method, a mathematical model has been developed to calculate the reflection and transmission of regular waves from a multiple-row curtainwall-pile breakwater. In addition, hydraulic model experiments have been conducted with different values of porosities between the piles, drafts of the curtain walls, and distances between the rows of the breakwater. It is found that the reflection and transmission coefficients decrease and increase, respectively, with decreasing relative water depth, but they bounce to increase and decrease, respectively, as the relative water depth decreases further. When either the porosity between the piles or the draft of the curtain wall is changed with other parameters fixed, the relative magnitudes of the reflection and transmission coefficients have been changed, but the general trend remained the same. When the wavelength is the same as the distance between the rows of the breakwater, a rapid change was observed for the reflection and transmission coefficients. A good agreement between the measurement and prediction was also founded for three-row breakwaters.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.1
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• pp.19-28
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• 2018

Numerous research papers have been accumulated due to the development and computerization of bibliometrics. This made it difficult to review all of the related papers published worldwide to conduct the study. However, due to the development of Natural language processing techniques, the tendency analysis of published research papers has become easier. In this study, text mining analysis using the statistical computing language R was carried out based on the bibliographic information of SCOPUS DB (Data Base) in the field of coastal and ocean engineering. As expected, the term 'wave' predominates, and it was confirmed that numerical analysis and hydraulic experiments were still dominant from the terms 'numerical model', 'numerical simulation', and 'experimental study'. In addition, recent use of the term 'wave energy' related to marine energy has been recognized. On the other hand, it was quantitatively confirmed that the frequency of connection between 'wave', and 'height' or 'energy' prevailed, and suggested the possibility of high resolution analysis by detailed field and period in the future.