• Journal of Hydrogen and New Energy
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• v.17 no.2
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• pp.193-203
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• 2006

A high-speed and initial helium jet flow has been analyzed by a developed four-dimensional digital speckle tomography. Multiple high-speed cameras have been used to capture movements of speckles in multiple angles of view simultaneously because a shape of a nozzle for the jet flow is asymmetric and the initial jet flow is fast and unsteady. The speckle movements between no flow and helium jet flow from the asymmetric nozzle controlled by a solenoid valve have been obtained by a cross-correlation tracking method so that those distances can be transferred to deflection angles of laser rays for density gradients. The four-dimensional density fields for the high-speed helium jet flow have been reconstructed from the deflection angles by a developed real-time tomography method.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.1
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• pp.15-22
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• 2014

Recently, parallel operation of dc-dc converters has been widely used in distributed power systems. In this paper, a control method to achieve parallel operation of three-phase bi-directional isolated interleaved dc-dc converters is discussed for the battery charging and discharging system which consists of the 32 battery charger/dischargers and two three-phase bi-directional isolated interleaved dc-dc converters. In the boost mode, the battery energy is delivered to the grid, whereas the grid energy is transferred to the battery in the buck mode operation. The average current sharing control method is employed to obtain an equal conducting of each phase current in the three-phase dc-dc converter. By using the proposed method, the imbalance factor is gratefully reduced from 8 percent to 1 percent. Two 2.5kW three-phase bi-directional dc-dc converter prototype have been built and the proposed method has been verified through experiments.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.2
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• pp.162-172
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• 1998

A numerical study of premixed combustion within a porous ceramic burner (PCB) is performed to understand flame behavior with respect to various model parameters. Basic flame structure within the porous ceramic burner and species profiles such as NO and CO are examined. Sensitivity analysis of flame speed, gas and solid temperature, NO and CO emission from the burner with respect to reaction steps and various physical properties of the ceramic material is applied to find the most significant parameters in selection of porous materials for the porous ceramic burner. Effects of thermal conductivity, extinction coefficient and scattering albedo on the burner characteristics are studied through the sensitivity analysis. The results of sensitivity study reveal the order of importance in ceramic material properties to get suitable burner performance. Scattering albedo, which governs the ratio of absorbed energy by the ceramic material to total radiative energy transferred, is one of the most important parameters in the material properties since it affects the actual absorbed radiation rate and thus it largely affects the flame structure. Through the study, it is found that the sensitivity study can be used to estimate the flame behavior within the porous ceramic burner more effectively.

• Journal of the Semiconductor & Display Technology
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• v.9 no.2
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• pp.103-109
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• 2010

An ink transfer is modeled and experimentally verified using roll-to-roll electric direct gravure printing process. The ink transfer model based on the physical mechanism for the maximum ink transfer rate is proposed, and experimented by the electric printing machine in FDRC for the relations of the maximum ink transfer rates to the printing pressure, the operating speed, the operating tension, the surface roughness of substrates, and the contact angle between substrate and silver ink. The free ink split coefficient and immobilized ink under the maximum ink transfer rate are calculated by the physical parameter in a printing process and contact angle between substrates and ink. Numerical simulations and experimental studies were carried out to verify performances of the proposed ink transfer model. Results showed that the proposed ink transfer model was effective for the prediction of the amount of transferred ink to the substrate in a direct gravure printing systems.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.11
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• pp.109-115
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• 2020

Surfaces with various roughnesses were produced through laser processing, and the anisotropy and hydrophobicity of the surfaces were examined in the context of the microstructures. The fine particles transferred to the glass surface exhibited different sizes, and the roughness increased. Due to the change in the roughness, the liquid could not penetrate the space between the fine particles, and it was thus exposed to the air. We analyzed this phenomenon using the combined Wenzel and Cassie-Baxter models. Excessive fine particle formation on the substrate tended to increase the roughness and surface energy. The silver-glass-air contact analysis could clarify the mechanism of the reduction of the contact angle and differences in the metastable and stable states when the particles did not completely cover the glass substrate. The formation of microstructures with fine particles through the laser selective deposition led to the generation of an anisotropic surface as the water droplets diffused toward the glass substrate with a relatively high surface energy level.

• Journal of Wind Energy
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• v.10 no.4
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• pp.20-27
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• 2019

High-speed shaft coupling in a wind power system transmits power and absorbs variations in length and spindle dislocation between the gearbox and generator. Furthermore, the coupling has an insulation function that prevents electrical corrosion caused by the flow of the generator's current into the gearbox and prevents overload resulting from sudden power failure from being transferred to the gearbox. Its design, functions, and part verification are described in the IEC61400 and GL Guidelines, which specify that the part must have a durability life of 20 years or longer under distance variation and axial misalignment between the gearbox and the generator. This study presents the design of a high-speed coupling through composite stiffness calculation, structural analysis, and comparative analysis of test and theory to identify the characteristics of high-speed coupling for a large-capacity 6 MW wind power generator. A prototype was fabricated by optimizing the manufacturing process for each part based on the design, and the reliability of the fabricated prototype was verified by evaluating the performance of the target quantitative evaluation items.

• Journal of the Korean Society of Industry Convergence
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• v.27 no.5
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• pp.1089-1098
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• 2024

Recently, the demand for energy storage has increased, serial cell configurations are commonly used for high-capacity secondary batteries. Initially, when identical cells are configured in series, the battery cells operate without voltage differences. However, over time, voltage imbalances occur due to differences in the environmental and physical properties of the cells. In addition, the unique characteristics of cells change during charging and discharging, which greatly affects to the degradation of battery efficiency and performance. Various cell balancing techniques have been proposed to achieve high efficiency and performance in battery. This paper proposes a minimum voltage selective balancing topology based on a flyback converter for module balancing of batteries based on active cell balancing techniques. In the proposed topology, the output voltage of each battery is shared through a single transformer, the energy from the converter's primary side is transferred to the battery modules with the minimum voltage. The proposed module balancing circuit can be easily applied to the battery reuse industry. The proposed minimum voltage battery module selective balancing topology was verified through PSIM simulations and experiments.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.7
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• pp.595-600
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• 2014

The characteristics of kinetic energy transfer during a collision between a rigid target particle on a surface and a fragile bullet particle moving at a high velocity were analyzed using molecular dynamics simulation. Bullet particles made of $CO_2$ were considered and their size, temperature, and velocity were varied over a wide range. The fraction of kinetic energy transferred from the bullet particle to the target particle was almost independent of the former's size or velocity; however, it was sensitively dependent on its temperature, which can be attributed to the change in the bullet rigidity with temperature. This fraction was nearly twice as high for $CO_2$ bullets as for Ar bullets. This result explains the reason for the more superior cleaning performance of $CO_2$ bullets than Ar bullets with regard to contaminants in the 10 nm size range.

• The Korean Journal of Nuclear Medicine
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• v.16 no.2
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• pp.81-84
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• 1982

To evaluate the in-vivo and in-vitro stability of methylene diphosphonate $(MDP)-^{99m}Tc$, relative ligand exchange rates in phosphate buffer between $MDP-^{99m}Tc$ and human serum albumin (HSA), and between pyrophosphate$(PYP)-^{99m}Tc$ and HSA have been measured. Gel permeation chromatography has also been carried out to estimate relative rates of ligand exchange between polysaccharide and the $^{99m}Tc-bone$ agents. The in-vitro stability was further correlated with its specific radioactivity. The results indicated that the $MDP-^{99m}Tc$ is more stable than the $PYP-^{99m}Tc$ but less stable than $MIDA-^{99m}Tc$, $HIDA-^{99m}Tc$, and $DTPA-^{99m}Tc$ etc. in refering to other data. In stability point of view, $MDP-^{99m}Tc$ is considered to be a better bone agent than $PYP-^{99m}Tc$ since $MDP-^{99m}Tc$ can be accumulated at bone by a smooth transfer of $^{99m}Tc$ to hydroxyapatite, whereas in case of $PYP-^{99m}Tc$, most of the $^{99m}Tc$ is transferred to HSA before arriving to the hydroxyapatite.

• Journal of KIISE:Computer Systems and Theory
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• v.37 no.1
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• pp.55-59
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• 2010

Most applications for solar-powered wireless sensor networks are usually deployed in remote areas without a continuous connection to the external networks and a regular maintenance by an administrator. In this case, sensory data has to be stored in the network as much as possible until it is uploaded by the data mule. For this purpose, a balanced data distribution over the network should be performed, and this can be achieved efficiently by taking the amount of available energy and storage into account, in the system layer of each node. In this paper, we introduce a simple but very efficient data distribution algorithm, by which each solar-powered node utilizes the harvested energy and the storage space maximally. This scheme running on each node determines the amount of energy which can be used for a data distribution as well as the amount of data which should be transferred to each neighbor, by using the local information of energy and storage status.