• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.271-277
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• 2014

Internal structures, especially those located in the upstream of a reactor core, may have a significant influence on the core inlet flow rate distribution depending on both their shapes and the relative distance between the internal structures and the core inlet. In this study, to examine the effect of the reactor internal structure geometry treatment method on the prediction accuracy for the scale-down APR+ flow distribution, simulations with real geometry modeling were conducted using ANSYS CFX R.14, a commercial computational fluid dynamics software, and the predicted results were compared with those of the porous medium assumption. It was concluded that the core inlet flow distribution could be predicted more accurately by considering the real geometry of the internal structures located in the upstream of the core inlet. Therefore, if sufficient computational resources are available, an exact representation of these internal structures, for example, lower support structure bottom plate and ICI nozzle support plate, is needed for the accurate simulation of the reactor internal flow.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.10
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• pp.710-716
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• 2013

New and renewable energy sources have drawn attention because of climate change. Many studies have been carried out in waste-to-energy field. Fast pyrolysis of waste lignocelluosic biomass is one of the waste-to-energy technologies. Bubbling fluidized bed (BFB) reactor is widely used for fast pyrolysis of the biomass. In BFB pyrolyzer, bubble behavior influences on the chemical reaction. Accordingly, in the present study, hydrodynamic characteristics and fast pyrolysis reaction of waste lignocellulosic biomass occurring in a BFB pyrolyzer are scrutinized. The computational fluid dynamics (CFD) simulation of the fast pyrolysis reactor is carried out by using Eulerian-Granular approach. And two-stage semi-global kinetics is applied for modeling the fast pyrolysis reaction of waste lignocellulosic biomass. To summarize, generation and ascendant motion of bubbles in the bed affect particle behavior. Thus biomass particles are well mixed with hot sand and consequent rapid heat transfer occurs from sand to biomass particles. As a result, primary reaction is observed throughout the bed. And reaction rate of tar formation is the highest. Consequently, tar accounts for 66wt.% of the product gas. However, secondary reaction occurs mostly in the freeboard. Therefore, it is considered that bubble behavior and particle motions hardly influences on the secondary reaction.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.8
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• pp.711-719
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• 2017

Bladeless fan is becoming increasingly popular owing to its advantages, such as improved safety, easy to clean, and attractive shape. However, many people are reluctant to purchase it because of several disadvantages, such as noise and moderate wind; therefore, research on how improve wind generation without increasing the motor speed is required. This study investigates the optimization of the shape of the nozzle and nearby surface using CFD (Computational Fluid Dynamics) simulation, ANSYS fluent. The results are analyzed by ANOM (analysis of mean) and interaction analysis; therefore this study suggests the variables of affecting Coanda effect and satisfy the govern equation, the conservation of momentum. The optimal combination was found through a predictive equation. In this study, factors and levels that affect the mass flow rate were selected and experimental points were arranged using the orthogonal array table. The value of the mass flow rate was confirmed by ANSYS fluent, which is a CFD program. Through the ANOM, it was confirmed that the nozzle distance is the most influential parameter affecting the mass flow rate. Furthermore, the mass flow rate obtained from the predictive equation and the mass flow rate from the CFD correspond to the largest values. Results from this study confirmed that the mass flow rate is increased by a change in the shape, even if the motor speed did not increase.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.6
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• pp.613-619
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• 2017

Recently, the size of container ships has been progressively increasing, and much attention is required for safe navigation in shallow areas such as coastal waters and ports due to increases in draft. It is necessary to understand the characteristics of ship motion not only in still waters but also with waves. Especially in shallow regions, squat due to the vertical movement of the ship can be an important evaluation factor for the safe navigation, and wave drift force acting in the horizontal direction can have a great influence on the maneuverability of a ship. In this study, a numerical simulation using computational fluid dynamics has been performed for the wave exciting force acting in the vertical direction and the wave drift force acting in the horizontal direction for a very large container vessel sailing in shallow zone. As a result, it was found that total resistance in still waters greatly increased in shallow water. Wave drift force was shown to decrease given longer wavelengths regardless of water depth. It was observed that the wave exciting force in shallow water was considerably larger than at other water depths. As wave height against the central part of the ship lowered, the aft side rose.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.5
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• pp.647-655
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• 2021

The IMO (International Maritime Organization) is discussing the improvement of energy ef iciency of ships in order to reduce greenhouse gas emissions from ships. Currently, by applying an ORC power generation system using waste heat generated from ships, high energy conversion efficiency can be expected from ships. This technology uses an organic medium based on Freon or hydrocarbons as the working fluid, which evaporates at a lower temperature range than water. Through this, it is possible to generate steam (gas) and generate power at a low and low temperature relatively. In this study, the analysis of heat flow between the refrigerant and waste heat in the ORC power generation system, which is an organic Rankine cycle, is analyzed using 3D simulation techniques to determine the temperature change, velocity change, pressure change, and mass change of the fluid flowing of the WHRU (Waste Heat Recovery Unit) inside and the outside the structure. The purpose of this study is to analyze how the mass change affects the structure, and this study analyzed the heat transfer of the heat exchanger from the refrigerant and the exhaust gas of the ship's main engine in the ORC power generation system using this technique.

• Clean Technology
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• v.25 no.1
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• pp.63-73
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• 2019

Numerical analysis was done to evaluate the chemical reaction and the reduction rate inside of selective non-catalytic reduction to denitrification in combustion process. The $NO_X$ reduction in selective non-catalytic reduction is converted to not only nitrogen but also nitrous oxide. Simultaneous $NO_X$ reduction and nitrous oxide generation suppressing is required in selective non-catalytic reduction because nitrous oxide influences the global warming as a greenhouse gas. The current study was performed compare the computational analysis in the same temperature and amount of NaOH, and in comparison with the previous research experiments and confirmed the reliability of the computational fluid dynamics. Additionally, controlling the addition amount of NaOH to predict the $NO_X$ reduction efficiency and nitrous oxide production. Numerical analysis was done to check the mass fraction of each material in the measurement point at the end of selective non-catalytic reduction. Experimental Value and simulation value by numerical analysis showed an error of up to 18.9% was confirmed that a generally well predicted. and it was confirmed that the widened temperature range of more than 70% $NO_X$ removal rate is increased when the addition amount of NaOH. So, large and frequent changes of the reaction temperature waste incineration facilities are expected to be effective.

• KEPCO Journal on Electric Power and Energy
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• v.5 no.1
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• pp.33-38
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• 2019

Thermal power generation accounts for the highest percentage of domestic power generation, among which coal-fired boiler generation accounts for the highest percentage. Coal boilers generate harmful substances and fine dust during coal combustion and have a serious effect on air pollution. So, fluidized-bed boilers have been introduced as eco-friendly coal boilers. It uses a fluid medium which affect the combustion temperature of coal. Because of it fluidized-bed boilers emit less pollutants than original one. Water-wall tubes play an important role in this fluidized bed boiler. Due to the fluid medium, the wall damage is more severe than the existing boiler. However, there is no quantitative maintenance technique in Korea yet. Remote field eddy current testing is a non-destructive evaluation technique that is often used for inspection of inner and outer wall of tube. it can inspect with non-contact and high speed. However, it is an inspection that proceeds from inside the pipe, and the water-wall tube is not able to enter the interior. In this study, we designed and simulated an external remote field eddy current sensor suitable for water-wall tube of a fluidized - bed boiler using simulations. By obtaining a signal similar to the existing remote field eddy current test, the criteria for the external remote field eddy current sensor design can be presented.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.2
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• pp.377-384
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• 2022

Vortex-induced vibration (VIV) occurs owing to the vortex generated from the back side of the appendages of ships and submarines during operation. Recently, the importance of high-order modes (HOMs) vibration and fatigue failure has become increasingly emphasized by increasing the speed of ships and the size of structures. In addition, predicting the vibration of HOMs is significantly necessary as the VIV becomes stronger in the fast flow speed condition than in the low flow speed condition. This study introduces a methodology according to HOMs hybrid Fluid Structure Interaction (FSI) for predicting the HOMs VIV on the hydrofoils. The HOMs FSI system is verified by comparing the VIV results from the FSI simulation with the experimental results. Finally, the effectiveness of the HOMs FSI is determined by applying the maximum von-Mises stress obtained from the VIV on the hydrofoil to the S-N curve released from Det Norske Veritas (DNV). VIV results from the HOMs FSI include the lock-in characteristics as well as a significant increase of more than 10 times compared with that of low-order modes (LOMs) FSI. In the future works, advanced studies will be required for improving cantilever boundary conditions and the shape of hydrofoils.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.7
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• pp.1244-1251
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• 2022

Marine accidents due to a loss of stability, have been gradually increasing over the last decade. Measures must be taken on the roll reduction of a ship. Amongst the measures, building an anti-roll tank in a ship is recognized as the most simple and effective way to reduce the roll motion. Therefore, this study aims to develop a computational model for a U-tube type anti-roll tank and to validate it by experiment. In particular, to validate the developed computational model, the height of the free surface in the tank was measured in the experiment. To develop a computational model, the mesh dependency test was carried out. Further, the effects of a turbulence model, time step size, and the number of iterations on the numerical solution were analyzed. In summary, a U-tube type anti-roll tank simulation had to be performed accurately with conditions of a realizable k-𝜖 turbulence model, 10^-2s time step size, and 15 iterations. In validation, the two cases of measured data from the experiment were compared with the numerical results. In the present study, STAR-CCM+ (ver. 17.02), a RANS-based commercial solver was used.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.250-261
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• 2023

In this study, the noise contributions by the duct, stator and rotor, which are the propulsor components, are evaluated to identify the flow noise source in cavitation and non-cavitation conditions on pumpjet propulsion and the noise levels in both conditions are compared. The unsteady incompressible Reynolds averaged Navier-Stokes (RANS) equation based on the homogeneous mixture assumption is applied on the suboff submarine hull and pumpjet propeller in the cavitation tunnel, and the Volume of Fluid (VOF) method and Schnerr-Sauer cavitation model are used to describe the two-phase flow. Based on the flow simulation results, the acoustic analogy formulated by Ffowcs Williams and Hawkings (FW-H) equation is applied to predict the underwater radiated noise. The noise contributions are evaluated by using the three types of impermeable integral surface on the duct, stator and rotor, and the two types of permeable integral surface surrounding the propulsor. As a result of noise prediction, the contribution by the stator is insignificant, but it affects the generation of flow noise source due to flow separation in the duct and rotor, and the noise is predominantly radiated into the upward and right where the flow separations are. Also, the noise is radiated into the thrust direction due to pressure fluctuation between suction and pressure sides on the rotor blades, and the it can be seen that the cavitation effect into the noise can be considered through the permeable integral surface.