• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.123-128
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• 2005

A novel tri-mode ultraprecision positioning system for machine tools and measuring machine is proposed. The basic coarse mode uses a Twist-roller Friction Drive (abbr. TFD), and controls several tens of millimeters of the machine-table travel with nanometer order of positioning resolution. The fine mode also utilizes the TFD with a fine adjusting mechanism. The resolution of the fine mode is in the range of sub-nanometer. For realizing picometer positioning, the ultra-fine mode is executed by using an active aerostatic guideway. On the bearing surface of this active guideway, several Active Inherent Restrictors (abbr. AIRs) are embedded for controlling the table position. An AIR unit consists of a piezoelectric actuator having a through hole, one end of the hole on the bearing surface acts as an inherent restrictor. Owing to the aerostatic mechanism of the AIR, the deformation of the piezoelectric actuator in the AIR unit causes much reduced table displacement. Such motion reduction is effective for ultraprecision positioning. Current positioning resolution of the ultra-fine mode is 50pm, however the final goal of the positioning resolution is expected to be in the order of picometer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.1 s.256
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• pp.51-61
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• 2007

This paper presents numerical and theoretical studies of acoustic wave interactions in slightly compressible liquids within piezoelectrically driven inkjet print heads. The interconnected flow channels may cause jet crosstalk, resulting in poor printing quality. It should be reduced by modifying the channel structure with the acoustic wave interactions considered. Compressible gas flow driven by the sudden movement of a top wall in the channel is calculated using Flow3D and is validated with the narrow gap theory. Limited compressibility model of the Flow3D is employed to calculate pressure waves of slightly compressible ink flow. It is found that reducing restrictor width can damp out the jet crosstalk by inhibiting the pressure wave propagation. The degree of crosstalk has been quantified using the maximum values of cross-correlations between neighboring channels and a critical channel dimension for acceptable crosstalk has been proposed. This finding is verified by drop visualization experiments using silicon-micromachined piezo inkjet print heads that are fabricated by our group.

• Journal of Energy Engineering
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• v.23 no.4
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• pp.112-122
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• 2014

A main steam line break (MSLB) test at the ATLAS facility was simulated using the best-estimate thermal-hydraulic system code, MARS-KS. This has been performed as an activity at the third domestic standard problem for code benchmark (DSP-03) that has been organized by Korea Atomic Energy Research Institute (KAERI). The results of the MSLB experiment and the MARS input data prepared for the previous DSP-02 using the ATLAS facility were provided to participants. The preliminary MSLB simulation using the base input data, however, showed unphysical results in the primary-to-secondary heat transfer. To resolve the problems, some improvements were implemented in the MARS input modelling. These include the use of fine meshes for the bottom region of the steam generator secondary side and proper thermal-hydraulics calculation options. Other input model improvements in the heat loss and the flow restrictor models were also made and the results were investigated in detail. From the results of simulations, the limitations and further improvement areas of the MARS code were identified.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.7
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• pp.605-612
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• 2016

A numerical analysis was performed on the effect of the design parameters of a bubble jet type microactuator on its liquid flow characteristics. The numerical models included the ink flow from the reservoir, bubble formation and growth, ejection through the nozzle, and dynamics of the refilling process. Because the bubble behavior is a very important parameter for the overall actuator performance, the bubble growth and collapse phenomena in an open pool were simulated in the present study. The drop ejection and refill process were numerically predicted for various geometries of the nozzle, chamber, and restrictor of the bubble jet microactuator. The numerical results from varying the design parameters can help with predicting the performance and optimizing the design of a microactuator.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1279-1288
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• 2019

The vortex-type fluidic diode (FD) is a key safety component for inherent safety in various advanced reactors such as the sodium fast reactor (SFR) and the molten salt reactor (MSR). In this study, topology optimization is conducted to optimize the design of the vortex-type fluidic diode. The optimization domain is simplified to 2-dimensional geometry for a tangential port and chamber. As a result, a design with a circular chamber and a restrictor at the tangential port is obtained. To verify the new design, experimental study and computational fluid dynamics (CFD) analysis were conducted for inlet Reynolds numbers between 2000 and 6000. However, the results show that the performance of the new design is no better than the original reference design. To analyze the cause of this result, detailed analysis is performed on the velocity and pressure field using flow visualization experiments and 3-D CFD analysis. The results show that the discrepancy between the optimization results in 2-D and the experimental results in 3-D originated from exclusion of an important pressure loss contributor in the optimization process. This study also concludes that the junction design of the axial port and chamber offers potential for improvement of fluidic diode performance.

• Tribology and Lubricants
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• v.36 no.3
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• pp.153-160
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• 2020

In this paper, we present a hydrostatic bearing design and rotordynamic analysis of a pump-and-drive turbine module for a 250-kW supercritical CO₂ cycle application. The pump-and-drive turbine module consists of the pump and turbine wheel, assembled to a shaft supported by two hydrostatic radial and thrust bearings. The rated speed is 21,000 rpm and the rated power is 143 kW. For the bearing operation, we use high-pressure CO₂ as the lubricant, which is supplied to the bearing through the orifice restrictor. We calculate the bearing stiffness and flow rate for various orifice diameters, and then select the diameter that provides the maximum bearing stiffness. We also conduct a rotordynamic analysis based on the design parameters of the pump-and-drive turbine module. The predicted Campbell diagram shows that there is no critical speed below the rated speed, owing to the high stiffness of the bearings. Furthermore, the predicted damping ratio indicates that there is no unstable mode. We conduct the operating tests for the pump and drive turbine modules within the supercritical CO₂ cycle test loop. The pressurized CO₂, at a temperature of 136℃, is supplied to the turbine and we monitor the shaft vibration during the test. The test results show that there is no critical speed below the rated speed, and the shaft vibration is controlled to below 3 ㎛.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1892-1897
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• 2003

A new thermal inkjet printer head on SOI wafer with virtual valve was proposed. It was composed of two rectangular heaters with same size. So we could call it T-jet(Twin jet). T-jet has a lot of merits. It has the advantage of being fabricated with one wafer and is easy to change the size of chamber, nozzle, restrictor and so on. However, above all, It is the best point that T-jet has a virtual valve. And it was manufactured on SOI wafer. The chamber was formed in its upper silicon whose thickness was 40um. The chamber's bottom layer was silicon dioxide of SOI wafer and two heaters were located underneath the chamber's ceiling. And the restirctor was made beside the chamber. Nozzle was molded by process of Ni plating. Ni was 30um thick. Nozzle ejection test was performed by printer head having 56 nozzles in 2 columns with 600NPI(nozzle per inch) and black ink. It measured a drop velocity of 12m/s, a drop volume of 30pl, and a maximum firing frequency of 12KHz for single nozzle ejection. Throwing out the ink drop in whole nozzles at the same time, it was observed that the uniformity of the drop velocity and volume was less than 4%.

• Tribology and Lubricants
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• v.37 no.3
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• pp.91-98
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• 2021

This paper presents a hydrostatic bearing design and rotordynamic analysis of a turbo expander for a hydrogen liquefaction plant. Th~e turbo expander includes the turbine and compressor wheel assembled to a shaft supported by two hydrostatic radial and thrust bearings. The rated speed is 75,000 rpm and the rated power is 6 kW. For the bearing operation, we use pressurized air at 8.5 bar as the lubricant that is supplied to the bearing through the orifice restrictor. We calculate the bearing stiffness and flow rate for various gauge pressure ratios and select the orifice diameter providing the maximum bearing stiffness. Additionally, we conduct a rotordynamic analysis based on the calculated bearing stiffness and damping considering design parameters of the turbo expander. The predicted Cambell diagram indicates that there are two critical speeds under the rated speed and there exists a sufficient separation margin for the rated speed. In addition, the predicted rotor vibration is under 1 ㎛ at the rated speed. We conduct the operating test of the turbo expander in the test rig. For the operation, we supply pressurized air to the turbine and monitor the shaft vibration during the test. The test results show that there are two critical speeds under the rated speed, and the shaft vibration is controlled under 2.5 ㎛.

• The Korean Journal of Pesticide Science
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• v.9 no.4
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• pp.292-302
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• 2005

Condition of Ion-Trap gas chromatography-mass spectrometry (GC-MS) for rapid screening of 206-pesticides residues in agricultural foodstuffs was optimized. As applying a wide-bore column (10 m${\times}$0.53 mm, DF 0.25 um) connected with a fused silica restrictor (0.6 m${\times}$0.1 mm), a significant retention time reduction was obtained. Additionally, the shape of peaks was sharper and higher than classical GC's and GC-MS's, which allowed lower detection limits. To easily manage many spectral data, both of Electron Ionization(EI) and Chemical Ionization(CI) techniques were adopted in screening procedure. At the following steps, MS-MS technique were used to confirm screened analytes in complicated matrices.