• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.10
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• pp.83-92
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• 2019

A pump is considered to be submersible when a motor and a pump are integrated and operate while submerged in water. Submersible pumps mainly function as rejection pumps to prevent foods in densely populated areas, as cold water circulation pumps in large power plants, as pumps to supply irrigation water, as drainage pumps to prevent flooding of agricultural lands, as water supply intake pumps, and as inflow pumps for sewage treatment. The flow in such turbomachines (submersible pumps) inevitably involves various eddy currents. Since it is almost impossible to accurately grasp the complex three-dimensional flow structure and characteristics of a rotating turbomachine through actual testing, three-dimensional numerical analysis using computational fluid dynamics techniques measuring the flow field, velocity, and the pressure can be accurately predicted. In this study, the shape of the impeller was developed to reduce vibration and noise. This was done by increasing the efficiency of the existing submersible pump and reducing turbulence. In order to evaluate the pump's efficiency and turbulence reduction, we tried to analyze the flow using ANSYS Fluent V15.0, a commercial finite element analysis program. The results show that the efficiency of the pump was improved by 4.24% and the Reynolds number was reduced by 15.6%. The performance of a developed pump with reduced turbulence, vibration, and noise was confirmed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.8
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• pp.305-310
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• 2016

A thermal storage systems was designed to correspond to the temporal or quantitative variation in the thermal energy demand, and most of its heat is stored using the latent and sensible heat of the heat storage material. The heat storage method using latent heat has a very complex phenomenon for heat transfer and thermal behavior because it is accompanied by a phase change in the course of heating/cooling of the heat storage material. Therefore, many studies have been conducted to produce an experimentally accessible as well as numerical approach to confirm the heat transfer and thermal behavior of phase change materials. The purpose of this study was to investigate the problems encountered during the actual heat transfer from an internal storage tank through simulation of the process of storing and utilizing thermal energy from the thermal storage tank containing charged PCM. This study used analysis methods to investigate the heat transfer characteristics of the PCM with simultaneous heating/cooling conditions in the rectangular space simulating the thermal storage tank. A numerical analysis was carried out in a state considering natural convection using the ANSYS FLUENT(R) program. The result indicates that the slope of the liquid-solid interface in the analysis field changed according to the temperature difference between the heating surface and cooling surface.

• Journal of the Korea Society for Simulation
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• v.24 no.3
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• pp.77-87
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• 2015

Defense M&S (Modeling & Simulation) is utilized as a realistic method to analyze MOE (Measure of Effectiveness) of weapon systems by modeling weapons and their operational environment on the computer, and simulating them under various war scenarios. As weapon systems become complex in their structure and dynamics, model engineering are experiencing difficulties to construct simulation models on a computer. A model repository helps model developers to save model development time and cost by systematically storing predefined and already validated models. However, most repositories for Defense M&Shave not been successful partly due to limited accessability, vulnerability to security threats, and low level of dependability. In this paper, we propose W-Cloud (Weapon Cloud), a cloud model repository for reusing predefined weapon models. Clients can access W-Cloud on any platforms and various devices, yet security and confidentiality concerns are guaranteed by employing multi-tier information protection mechanism.

• Journal of Ginseng Research
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• v.45 no.6
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• pp.726-733
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• 2021

Background: Panax notoginseng is a highly valued medicinal herb used widely in China and many Asian countries. Its root and rhizome have long been used for the treatment of cardiovascular and hematological diseases. Imaging the spatial distributions and dynamics of metabolites in heterogeneous plant tissues is significant for characterizing the metabolic networks of Panax notoginseng, and this will also provide a highly informative approach to understand the complex molecular changes in the processing of Panax notoginseng. Methods: Here, a high-sensitive MALDI-MS imaging method was developed and adopted to visualize the spatial distributions and spatiotemporal changes of metabolites in different botanical parts of Panax notoginseng. Results: A wide spectrum of metabolites including notoginsenosides, ginsenosides, amino acids, dencichine, gluconic acid, and low-molecular-weight organic acids were imaged in Panax notoginseng rhizome and root tissues for the first time. Moreover, the spatiotemporal alterations of metabolites during the steaming of Panax notoginseng root were also characterized in this study. And, a series of metabolites such as dencichine, arginine and glutamine that changed with the steaming of Panax notoginseng were successfully screened out and imaged. Conclusion: These spatially-resolved metabolite data not only enhance our understanding of the Panax notoginseng metabolic networks, but also provide direct evidence that a serious of metabolic alterations occurred during the steaming of Panax notoginseng.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.2
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• pp.27-37
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• 2019

The shell and tube heat exchangers installed in the propulsion system test complex (PSTC) at the Naro Space Center heats cryogenic helium to 500 K with a heat transfer oil. As the experimental helium outlet temperature was lower than expected (less than 100 K), the boundary layer effect of the heat transfer oil is predicted to be the cause of the performance deterioration. A computational fluid dynamics (CFD) analysis was performed to verify where the boundary layer effect exists; however, the boundary layer effect has no significant impact on the performance of the heat exchanger. An alternative method to improve the performance of the heat exchanger by changing the heat transfer oil has been discussed in this paper. The low viscosity and high thermal conductivity at high temperature (~500 K) of heat transfer oil at the shell-side are required to improve the thermal performance of the heat exchanger. The experimental performance of the heat exchanger, used to exchange heat between the cryogenic helium and hot heat transfer oil at the PSTC are summarized in this paper.

• Journal of Power Electronics
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• v.19 no.1
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• pp.190-200
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• 2019

The flyback converter, which can be regarded as a nonlinear time-varying system, has complex dynamics and nonlinear behaviors. These phenomena can affect the stability of the converter. To simplify the modeling process and retain the information of the output capacitor branch, a special sampled-data model of a peak current-mode (PCM) controlled flyback converter is established in this paper. Based on this, its dynamic behaviors are analyzed, which provides guidance for designing the circuit parameters of the converter. With the critical stability boundary equation derived by a Jacobian matrix, the stable operation range with a varied output capacitor, proportional coefficient of error the amplifier, input voltage, reference voltage and slope of the compensation ramp of a PCM controlled flyback converter are investigated in detail. Research results show that the duty ratio should be less than 0.5 for a PCM controlled flyback converter without ramp compensation to operate in a stable state. The stability regions in the parameter space between the output capacitor and the proportional coefficient of the error amplifier are enlarged by increasing the input voltage or by decreasing the reference voltage. Furthermore, the ramp compensation also can extend to the stable region. Finally, time-domain simulations and experimental results are presented to verify the theoretical analysis results.

• Journal of Ocean Engineering and Technology
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• v.35 no.1
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• pp.50-58
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• 2021

The demand for eco-friendly energy is expected to increase due to the recently strengthened environmental regulations. In particular, the flow inside the pipe used in a cargo handling system (CHS) or fuel gas supply system (FGSS) of hydrogen transport ships and hydrogen-powered ships exhibits a very complex pattern of multiphase-thermal flow, including the boiling phenomenon and high accuracy analysis is required concerning safety. In this study, a feasibility study applying the boiling model was conducted to analyze the multiphase-thermal flow in the pipe considering the phase change. Two types of boiling models were employed and compared to implement the subcooled boiling phenomenon in nucleate boiling numerically. One was the "Rohsenow boiling model", which is the most commonly used one among the VOF (Volume-of-Fluid) boiling models under the Eulerian-Eulerian framework. The other was the "wall boiling model", which is suitable for nucleate boiling among the Eulerian multiphase models. Moreover, a comparative study was conducted by combining the nucleate site density and bubble departure diameter model that could influence the accuracy of the wall boiling model. A comparison of the Rohsenow boiling and the wall boiling models showed that the wall boiling model relatively well represented the process of bubble formation and development, even though more computation time was consumed. Among the combination of models used in the wall boiling model, the simulation results were affected significantly by the bubble departure diameter model, which had a very close relationship with the grid size. The present results are expected to provide useful information for identifying the characteristics of various parameters of the boiling model used in CFD simulations of multiphase-thermalflow, including phase change and selecting the appropriate parameters.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.18 no.3
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• pp.7-18
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• 2022

Secondary batteries used in electric vehicles have a potential risk of ignition and explosion. Various safety measures are being taken to prevent these risks. A numerical study was performed using a computational fluid dynamics code on the cases where pressure relief vents that can reduce the blast overpressures of batteries were installed in the through-compression test room, short-circuit drop test room, combustion test room, and immersion test room in facilities rleated to battery used in electric vehicles. This study was conducted using the weight of TNT equivalent to the energy release from the battery, where the the thermal runaway energy was set to 324,000 kJ for the capacity of the lithium-ion battery was 90 kWh and the state of charge (SOC) of the battery of 100%. The explosion energy of TNT (△H_TNT) generally has a range of 4,437 to 4,765 kJ/kg, and a value of 4,500 kJ/kg was thus used in this study. The dimensionless explosion efficiency coefficient was defined as 15% assuming the most unfavorable condition, and the TNT equivalent mass was calculated to be 11 kg. The internal explosion generated in a test room shows the very complex propagation behavior of blast waves. The shock wave generated after the explosion creates reflected shock waves on all inner surfaces. If the internally reflected shock waves are not effectively released to the outside, the overpressures inside are increased or maintained due to the continuous reflection and superposition from the inside for a long time. Blast simulations for internal explosion targeting four test rooms with pressure relief vents installed were herein conducted. It was found that that the maximum blast overpressure of 34.69 bar occurred on the rear wall of the immersion test room, and the smallest blast overpressure was calculated to be 3.58 bar on the side wall of the short-circuit drop test room.

• International Journal of Computer Science & Network Security
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• v.21 no.7
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• pp.211-220
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• 2021

The aim of the study is to implement a factor analysis of the determinants of pricing in a state-regulated competitive market using economic and mathematical modelling methods and to develop ways to improve the pricing environment of the market under study. The purpose of the work defines the main objectives: (i) to investigate the features of the competitive model of the Ukrainian flour market; (ii) to analyse the current price conjuncture of the flour market and the dynamics of the main determinants of pricing; (iii)to develop ways of improving the price situation on the flour market on the basis of the factor analysis on the results of economic and mathematical modelling. In order to ensure the reliability and validity of the research results, the following methods were applied: the logical-dialectical method of scientific knowledge in the study of the main theoretical aspects of flour market functioning, the method of logical generalisation and synthesis, comparison, factor analysis, correlation and regression analysis, the graphical method, etc. It has been shown that pricing in a state-regulated competitive market has its own characteristics. For example, in the flour market the price of goods cannot be influenced by producers (sellers) by any methods, therefore determinants of pricing by indirect influence have been taken into account. The five-factor power model of wheat flour price has been constructed. It was substantiated that the price of wheat flour in Ukraine is mostly influenced by consumer price index (0.92 %). The received complex model of wheat flour price may be used also for medium-term forecasting and working out the ways of price formation optimization in the flour market.

• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.2
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• pp.72-78
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• 2022

A vacuum brazed cooling passage for an aircraft engine controller was designed. In order to predict the total pressure loss, which is the main design factor of the cooling passage, theoretical and numerical methods for the major loss and the minor loss considering the overall shape of the cooling passage are presented. This design and evaluation method can predict the pressure loss of the complex cooling passage shape for various flow conditions at the initial design step.