• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.1974-1987
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• 2023

The load-following operation of small modular reactors (SMRs) requires accurate prediction of transient behaviors that can occur in the balance of plants (BOP) and the nuclear steam supply system (NSSS). However, 1-D thermal-hydraulics analysis codes developed for safety and performance analysis have conventionally excluded the BOP from the simulation by assuming ideal boundary conditions for the main steam and feed water (MS/FW) systems, i.e., an open loop. In this study, we introduced a lumped model of BOP fluid system and coupled it with NSSS without any ideal boundary conditions, i.e., in a closed loop. Various methods for coupling boundary conditions at MS/FW were tested to validate their combination in terms of minimizing numerical instability, which mainly arises from the coupled boundaries. The method exhibiting the best performance was selected and applied to a transient simulation of an integrated NSSS and BOP system of a SMART. For a transient event with core power change of 100-20-100%, the simulation exhibited numerical stability throughout the system without any significant perturbation of thermal-hydraulic parameters. Thus, the introduced boundary-condition coupling method and BOP fluid system model can expectedly be employed for the transient simulation and performance analysis of SMRs requiring daily load-following operations.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3B
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• pp.297-306
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• 2008

In order to determine the effects of lock gate expansion at the Lake Youngsan and Yeongam as well as increase in the width of the connecting channel of the two lakes on flood control downstream of the Youngsan River, an unsteady hydraulic flood routing was conducted by combining the Lake Youngsan and Yeongam as a single connected system. The coupled operation of the two lakes was found to have little effect when the widths of the lock gates and the connecting channel are set at the current level. It was also found that increasing the width of the connecting channel as well as the lock gate of the Lake Yeongam is an effective means of reducing the stage of the Lake Youngsan, whereas an increase in the width of the Lake Youngsan's lock gate had a relatively smaller effect. The extended width of the connecting channel leads to a rise in the stage of the Lake Yeongam. In order to reduce the elevated stage, The Lake Yeongam's lock gate must be expanded along with the Lake Yeongsan's lock gate. The analysis found that the stage of the Lake Yeongsan can be effectively controlled through adjustment of opening and shutting criteria of the connecting channel's lock gate, when diversion discharge between the lakes is increased as a result of expanding the width of the connecting channel.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3B
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• pp.277-284
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• 2010

To examine how the width of connecting channels, the width of the Kumho lock gate, and the opening/shutting criteria of the Yeongam connecting channel lock gate affect the flood stage of Lake Yeongsan, Lake Yeongam, and Lake Kumho, located in the lower reaches of the Yeongsan River, unsteady flood routing was performed by connecting the three lakes into a single interlinked system. The coupled operation of the three lakes was found to have little effect when the widths of the lock gates and the Yeongam and Kumho connecting channels are set at the current level. The most effective way to lower the water level in Lake Yeongsan was to widen the Yeongam connecting channel, but this caused the water level in Lake Yeongam to rise. To lower the increased water level in Lake Yeongam by utilizing the water storage capacity of Lake Kumho, it was necessary to widen both the Kumho lock gate and the Kumho connecting channel. It was found that the optimum opening/shutting criterion for the Yeongam connecting channel lock gate is approximately EL.(+)0.8 m under the simulated conditions used in this study and the criterion allows of maximal lowering of the water levels in Lake Yeongam and Lake Kumho while maintaining a near-constant water level in Lake Yeongsan.

• Smart Structures and Systems
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• v.29 no.4
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• pp.577-588
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• 2022

Oil refineries' Fluid Catalytic Cracking Units (FCCU) when in full operation may exhibit strong fluid dynamics caused by turbulent flow in the piping system that may induce vibrations in other mechanical and structural components of the Unity. This paper reports on the experimental-theoretical-computational program performed to get the vibration properties and the dynamic response amplitudes to find out alternative solutions to attenuate the excessive vibrations that were causing fatigue fractures in components of the bottle like reactor-regenerator of an FCC unit in operation in an existing oil refinery in Brazil. Solutions to the vibration problem were sought with the aid of a 3D finite element model calibrated with the results obtained from experimental measurements. A short description of the found solutions is given and their effectiveness are shown by means of numerical results. The solutions were guided by the concepts of structural stiffening and dynamic control performed by a nonlinear pendulum controller whose mechanical design was based on parameters determined by means of a parametric study carried out with 2D and 3D mathematical models of the coupled pendulum-structure system. The effectiveness of the proposed solutions is evaluated in terms of the fatigue life of critical welded connections.

• Journal of the Korean Association of Geographic Information Studies
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• v.12 no.3
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• pp.76-87
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• 2009

Most distributed models have been developed for data interchange between model for hydrological analysis and GIS(Geographic Information System). And some interface systems between them have been developed to operate the model conveniently. This study is about developing integrated system between model and GIS not coupled system based on file interchange or interface system. In this study, HyGIS-GRM which is integrated system between GRM(Grid based Rainfall-runoff Model) which is physically based distributed rainfall-runoff model and HyGIS(Hydro Geographic Information System) have been developed. HyGIS-GRM can carry out all the processes from preparing input data to appling them to model in the same system, and this operation environment can improve the efficiency of running the model and analyzing modeling results. HyGIS-GRM can provide objective modeling environment through establishing the process of integrated operation of GIS and distributed model, and we can obtain fundamental technologies for developing integrated system between GIS and water resources model.

• Journal of Advanced Research in Ocean Engineering
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• v.1 no.4
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• pp.252-267
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• 2015

Offshore structures might encounter several environmental and operating conditions during their lifetime of several decades. In order to predict the dynamic behavior of offshore structures, several simulation cases should be considered to deal with all the combinations of ocean environments and operating conditions. Because a sophisticated time-domain coupled dynamic analysis requires an extremely large amount of computational time to handle all the possible cases, an efficient preliminary process to prescreen the probability of severe environmental conditions can be helpful in downsizing the number of simulation cases and computational effort. In this study, a prescreening procedure to reduce the number of environmental conditions for dynamic analyses of offshore structures is proposed. For the efficiency of the procedure, frequency-domain theories were adopted to estimate the platform offset, using quasi-static analyses in line tension prediction. The results were validated by comparing with those of dynamic analysis coupled between platform and mooring lines, and reasonable agreement was observed. In addition, the characteristics of environmental conditions classified to be severe to the system were investigated through the application of the developed prescreening scheme to several actual environmental conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.3
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• pp.157-166
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• 2009

The pulverized coal combustion behavior in the coal fired utility boiler has been investigated with the CFD and process analysis techniques. The used commercial software were CFX and PROATES, and these were coupled each other to get more reliable boundary condition set-up, resulting in more reliable solution. For two cases which were the actual operation condition of A power plant, the calculated values from the coupled CFD and process analysis for thermal energy system were compared with the plant data, and the good agreements were obtained for Case 1 and 2. The calculated temperature distributions on the surface of heat exchangers were compared with the plant data for the steam temperatures across heat exchangers, and these explained the actual operating situation very well. The temperature deviation across the final superheater tube, which was believed to be the main cause of the frequent tube failure, were also explained very well with the calculated distributions of gas temperature and radiation on the plane of the final superheater.

• International Journal of Automotive Technology
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• v.6 no.5
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• pp.445-451
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• 2005

Most of the pollutants from passenger cars are emitted during the cold-transient phase of the FTP-75 test. In order to reduce the exhaust emissions during the cold-transient period, it is essential to warm up the catalyst as fast as possible after the engine starts, and the Unburned Exhaust Gas Ignition (UEGI) technology was developed through our previous studies to help close-coupled catalytic converters (CCC) reach the light-off temperature within a few seconds after cold-start. The UEGI system operates by igniting the unburned exhaust mixture by glow plugs installed upstream of the catalyst. The flame generates a high amount of heat, and if the heat is concentrated on a specific area of monolith surface, then thermal crack or failure of the monolith could occur. Therefore, it is very important to monitor the temperature distribution in the CCC during the UEGI operation, so the local temperatures in the monolith were measured using thermocouples. Experimental results showed that the temperature of CCC rises faster with the UEGI technology, and the CCC reaches the light-off temperature earlier than the baseline case. Under the conditions tested, the light-off time of the baseline case was 62 seconds, compared with 33 seconds for the UEGI case. The peak temperature is well under the thermal melting condition, and temperature distribution is not so severe as to consider thermal stress. It is noted that the UEGI technology is an effective method to warm up the catalyst with a small amount of thermal stress during the cold start period.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.3
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• pp.115-125
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• 2008

Recently, Exhaust Gas Recirculation (EGR) system which re-flow a cooled exhaust gas from vehicles burning diesel as fuel to a combustion chamber of engine has been used to solve the serious air pollution. For the design and mass production of EGR system, it is essential to ensure structural integrity evaluation. The EGR system consisted of ten dimpled oval core rectangular tubes, two fix-plates, two coolant pipes, shell body and two flanges in this study. To confirm the safety of the designed system, finite element modeling about each component such as the dimpled oval core tube with the dimpled shape and others was carried out. The reliability of EGR system against exhaust gas flow with high temperature was investigated by flow and pressure analysis in the system. Also, thermal and strength analysis were verified the safety of EGR system against temperature change in the shell and tubes. Furthermore, modal analysis using ANSYS was also performed. From the results of FE analysis, there were confirmed that EGR system was safe against the flow of exhaust gas, temperature change in EGR system and vibration on operation condition, respectively.

• Transactions of the KSME C: Technology and Education
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• v.4 no.1
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• pp.19-26
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• 2016

This paper presents the measurement and analysis results for the performance of HGCHP system using a cooling tower as a supplemental heat rejector. In order to demonstrate the performance of the hybrid approach, we installed the monitoring equipments including sensors for measuring temperature and power consumption, and measured operation parameters from February 1, 2014 to February 28, 2015. Leaving load temperatures to building showed an average value of $11.7^{\circ}C$ for cooling and $39.5^{\circ}C$ for heating, respectively. From the analysis, the daily PF of hybrid GCHP system varied from 2.6 to 6.6 over the measurement period.