• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2005년도 ICCAS
• /
• pp.123-128
• /
• 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.

• 대한기계학회논문집B
• /
• 제31권1호
• /
• pp.51-61
• /
• 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.

• 에너지공학
• /
• 제23권4호
• /
• pp.112-122
• /
• 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
• /
• 제40권7호
• /
• pp.605-612
• /
• 2016

버블젯 타입 마이크로 엑츄에이터의 설계변수에 따른 유동특성에 관한 수치해석적 연구를 수행하였다. 수치 모델은 저장소로 부터의 잉크 유동과 기포의 성장 및 소멸, 노즐을 통한 액적의 토출과 리필 과정을 포함한다. 기포의 거동은 전체 엑츄에이터의 성능에 중요한 영향을 미치는 요소이기 때문에, 본 연구에서는 open pool 해석을 통하여 기포의 성장과 소멸 및 소멸시의 캐비테이션 현상에 대해 살펴보았다. 또한 마이크로 엑츄에이터의 노즐 형상의 변화, 챔버와 리스트릭터의 기하학적 변화에 따른 액적의 토출과 잉크 리필과정에 대한 수치예측을 수행하였다. 설계변수의 변화에 따른 수치해석의 결과는 마이크로 엑츄에이터의 성능특성을 예측할 수 있으며 또한 마이크로 엑츄에이터의 최적설계에 유용하리라 판단된다.

• Nuclear Engineering and Technology
• /
• 제51권5호
• /
• pp.1279-1288
• /
• 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
• /
• 제36권3호
• /
• pp.153-160
• /
• 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 ㎛.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.1892-1897
• /
• 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
• /
• 제37권3호
• /
• pp.91-98
• /
• 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 ㎛.

• 농약과학회지
• /
• 제9권4호
• /
• pp.292-302
• /
• 2005

206종의 농약성분을 신속하게 분석하기 위한 가스크로마토그래피-질량분석기 이용방법을 최적화 하였다. Wide-bore 컬럼을 채택함으로써 기존의 캐필러리 컬럼을 이용할 때에 비해 분리능을 비슷하게 유지하면서도 분석시간이 1/2이상 단축되고, 감도는 더욱 개선되었다. 시료의 성분이 복잡하고 분석대상 농약이 많은 경우에도, EI와 CI 스크리닝 결과를 비교함으로써 방해물질에 의한 허위정보(False Positive)를 상쇄할 수 있었다. 허위정보에 대한 위험이 적어지면서 시험용액의 정제를 간소화 할 수 있어 전체적인 분석과정을 간소화 할 수 있었다. 또한 검출이 예상되는 성분에 대해서만 확인실험을 함으로써 검사시간을 절약하고 검사의 정확도를 향상시킬 수 있었다.