• Journal of Advanced Marine Engineering and Technology
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• v.31 no.7
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• pp.842-851
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• 2007

Oscillating foil propulsion, the engineering application of fish-like movement of a hydrofoil, has received in recent decades as a possible competitor for propellers. The oscillating foil produces an effective angle of attack, resulting in a normal force vector with thrust and lift components, and it can be expected to be a new highly effective propulsion system. We have explored propulsion hydrodynamics as a concept in wake flow pattern. The present study has been examined various conditions such as oscillating frequencies and amplitudes in NACA0010 profile. Flow visualizations showed that high thrust was associated with the generation of moderately strong vortices, which subsequently combine with trailing-edge vorticity leading to the formation of a reverse $K\acute{a}rm\acute{a}n$ vortex street. Vortex generation was inherent to jet production and playeda fundamental role in the wake dynamics. And it was shown that the strong thrust coefficient obtained as the Strouhal number was larger.

• Journal of Korean Institute of Industrial Engineers
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• v.36 no.1
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• pp.42-51
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• 2010

The semiconductor industry is highly capital and technology intensive. Technology advancement on circuit design and process improvement requires chip makers continuously to invest a new fabrication facility that costs more than 3 billion US dollars. Especially major semiconductor companies recently started to discuss 450mm fabrication substituting existing 300mm fabrication of which facilities were initiated to build in 1998. If the plan is consolidated, the yield of 450mm facility would be more than doubled compared to existing 300mm facility. In steps of this important investment, facility layout has been acknowledged as one of the most important factors to be competitive in the market. This research proposes a new concept of semiconductor facility layout using hexagonal floor plan and its compatible material flow pattern. The main objective of this proposal is to improve the productivity of the unified layout that has been popularly used to build existing facilities. In this research, practical characteristics of the semiconductor fabrication are taken into account to develop a new layout alternative based on the analysis of Chung and Tanchoco (2009). The performance of the proposed layout alternative is analyzed using computer simulation and the results show that the new layout alternative outperforms the existing layout alternative, unified layout. However, a few questions on space efficiency to the new alternative were raised in communication with industry practitioners. These questions are left for a future study.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.1
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• pp.11-18
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• 1996

Grown-in defects like OISF and FPD in the large diameter(> 8 inch)of silicon crystal are characterized. It was revealed that the presence of the ring-patterned OISF would deterorate the minority life time of the silicon crystal. Through the cooling experiment from the $1250^{\circ}C$, the nucleation of the OISF was confirmed to follow the homogeneous nucleation and growth process. In addition to OISF nucleus, crystal originated particle, which was known to be closely related with FPD (Flow Pattern Defects), was found to depend on the pulling rate of the crystal. Combination of the lower rate of the pulling and the faster cooling near the $950^{\circ}C$ is proposed to be effective method in reducing the generation of these grown-in defects.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.4 s.235
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• pp.504-511
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• 2005

The generation of fine relics of inorganic and metallic materials from precursor suspensions is of significant current interest as it holds the key to the fabrication of display and printed circuit board. Some novel printing methods depositing ceramic particles have been suggested in recent years. When a conducting liquid is supplied to a capillary nozzle at a low flow rate and when the interface between air and the liquid is charged to a sufficiently high electrical potential, the liquid meniscus takes the form of a stable cone, whose apex emits a microscopic jet. This is called as a cone-jet mode. In our experiments, an alumina particles flowing through a nozzle were subjected to electro-hydrodynamic printing in the cone-jet mode. The pattern of 'YONSEI' characters was tested at $10 {\mu}l/min$ of alumina ink flow rate and different applied voltages. At an applied voltage of 6 kV, feature size was in the range of $250 {\mu}m.$

• Journal of the Semiconductor & Display Technology
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• v.12 no.2
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• pp.79-84
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• 2013

Nanoimprint lithography (NIL) is the next generation photolithography process in which the photoresist is dispensed onto the substrate in its liquid form and then imprinted and cured into a desired pattern instead of using traditional optical system. There have been considerable attentions on NIL due to its potential abilities that enable cost-effective and high-throughput nanofabrication to the display device and semiconductor industry. Although one of the current major research trends of NIL is large-area patterning, the technical difficulties to keep the uniformity of the residual layer become severer as the imprinting area increases more and more. In this paper, with the rolling type imprinting process, a mold, placed upon the $2^{nd}$ generation TFT-LCD glass sized substrate($370{\times}470mm^2$), is rolled by a rubber roller to achieve a uniform residual layer. The prediction of residual layer thickness of the photoresist by rolling of the rubber roller is crucial to design the rolling type imprinting process, determine the rubber roller operation conditions-mpressing force & feeding speed, operate smoothly the following etching process, and so forth. First, using the elasticity theory of contact problem and the empirical equation of rubber hardness, the contact length between rubber roller and mold is calculated with consideration of the shape and hardness of rubber roller and the pressing force to rubber roller. Next, using the squeeze flow theory to photoresist flow, the residual layer thickness of the photoresist is calculated with information of the viscosity and initial layer thickness of photoresist, the shape of mold pattern, feeding speed of rubber roller, and the contact length between rubber roller and mold previously calculated. Last, the effects of rubber roller operation conditions, impressing force & feeding speed, on the residual layer thickness are analyzed with consideration of the shape and hardness of rubber roller.

• The KSFM Journal of Fluid Machinery
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• v.11 no.5
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• pp.50-56
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• 2008

Metal cutting operations involve generation of heat due to friction between the tool and the pieces. This heat needs to be carried away otherwise it creates white spots. To reduce this abnormal heat cutting fluid is used. Cutting fluid also has an important role in the lubrication of the cutting edges of machine tools and the pieces they are shaping, and in sluicing away the resulting swarf. As a cutting fluid, water is a great conductor of heat but is not stable at high temperatures, so to improve stability an emulsion type mixed fluid with water and oil is often used. It is pumped over the cutting site of cutting machines as a state of atomized water droplet coated with oil by using jet. In this paper, to develop cutting fluid supplying nozzle to obtain ultra thin oil film for coating water droplet, a numerical analysis of three dimensional mixed fluid Jet through multi-stage nozzle was carried out by using a finite volume method. Jet flow characteristics such as nozzle exit velocity, development of mixing region, re-entrance and jet intensity were analyzed. Detailed mixing process of fluids such as air, water and oil in the nozzle were also investigated. It is easy to understand complex flow pattern in multi-stage nozzle. Important flow Information for advance design of cutting fluid supplying nozzle was drawn.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.5
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• pp.596-606
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• 2002

The three-dimensional unsteady compressible Euler equation solver with ALE, CFD code, PAM-FLOW based on FEM method has been applied to analyze the flow field around the high speed train which is entering into a channel. From the present study, the pressure and flow transients were calculated and analyzed. The generation of compression wave was observed ahead of train and the high pressure in the gap between the train and the tunnel was also found due to the blockage effects. It was found that abrupt fluctuation in pressure exists in the region from train nose to shoulder of train corresponding to 10％ of total length of train during tunnel entry. Computed time history of aerodynamic forces of train during tunnel entry show that drag coefficient rapidly rises and saturates at about non-dimensional time 0.31. The total increase of drag coefficient before and after tunnel entry is about 1.1%. Transient profile of lift force shows similar pattern to drag coefficient except abrupt drop after saturation and lift force in the tunnel increases 0.08% more than that before tunnel entry.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3540-3550
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• 2022

The supercritical carbon dioxide (S-CO₂) Brayton cycle is an important energy conversion technology for the fourth generation of nuclear energy. Since the printed circuit heat exchanger (PCHE) used in the S-CO₂ Brayton cycle has narrow channels, Rayleigh-Bénard (RB) convection is likely to exist in the tiny channels. However, there are very few studies on RB convection in supercritical fluids. Current research on RB convection mainly focuses on conventional fluids such as water and air that meet the Boussinesq assumption. It is necessary to study non-Boussinesq fluids. PRB convection refers to RB convection that is affected by horizontal incoming flow. In this paper, the computational fluid dynamics simulation method is used to study the PRB convection phenomenon of non-Boussinesq fluid-supercritical carbon dioxide. The result shows that the inlet Reynolds number (Re) of the horizontal incoming flow significantly affects the PRB convection. When the inlet Re remains unchanged, with the increase of Rayleigh number (Ra), the steady-state convective pattern of the fluid layer is shown in order: horizontal flow, local traveling wave, traveling wave convection. If Ra remains unchanged, as the inlet Re increases, three convection patterns of traveling wave convection, local traveling wave, and horizontal flow will appear in sequence. To characterize the relationship between traveling wave convection and horizontal incoming flow, this paper proposes the relationship between critical Reynolds number and relative Rayleigh number (r).

• Journal of the Korean Institute of Gas
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• v.16 no.3
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• pp.1-7
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• 2012

Natural gas through pipeline is supplied to consumers after its pressure gets down compulsorily. The waste pressure energy of this process can be restored by use of turbo expander which can produce electricity. So, turbo expander conducts two functions - pressure reduction and power generation. The power amount is the enthalpy difference between the inlet and outlet states. The five main factors which affect economic profit are facility price, produced power amount, pre-heating amount, electricity cost, and fuel gas cost. Power generation depends mainly on flow amount because inlet and outlet states are fixed. A methodology to estimate economy in irregular flow pattern is proposed and using this way, a case study was carried out.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.5
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• pp.775-783
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• 1990

In this paper we implemented the fast thinning unit by modifying the pipeline architecture which was proposed by Stanley R. Sternberg. The unit is useful in preprocessing such as image representation and pattern recognition etc. This unit is composed of interface part, local memory part, address generation part, thinning processing part and control part. In thinning processing part, we shortened the thinning part which performed by means of look up table using window mapping table. Thus we improved the weakness of SAP, in which the number of delay pipeline and window pipeline are equal to image column size. Two independent memorys using tri-state buffer enable the two direction flow of address generated by address generation part. This unit avoids the complexity of architecture and has flexibility of image size by means of simple modification of logic bits.