• Journal of the Semiconductor & Display Technology
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• v.22 no.4
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• pp.66-71
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• 2023

This paper describes a hybrid cleaning method of silicon wafer combining nano-bubble and ultrasound to remove sub-micron particles and contaminants with minimal damage to the wafer surface. In the megasonic cleaning process of semiconductor manufacturing, the cavitation induced by ultrasound can oscillate and collapse violently often with re-entrant jet formation leading to surface damage. The smaller size of cavitation bubbles leads to more stable oscillations with more thermal and viscous damping, thus to less erosive surface cleaning. In this study, ultrasonic energy was applied to the wafer surface in the DI water to excite nano-bubbles at resonance to remove contaminant particles from the surface. A patented nano-bubble generator was developed for the generation of nano-bubbles with concentration of 1×10⁹ bubbles/ml and nominal nano-bubble diameter of 150 nm. Ultrasonic nano-bubble technology improved a contaminant removal efficiency more than 97% for artificial nano-sized particles of alumina and Latex with significant reduction in cleaning time without damage to the wafer surface.

• The KSFM Journal of Fluid Machinery
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• v.17 no.2
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• pp.41-47
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• 2014

Experimental results are given for the vertical motion of water in the water chambers for wave energy converter aligned along the wave propagation direction in order to avoid the impulsive wave forces. This paper mainly focuses on the property of the amplitude of the vertical motion of the water surface in the chambers. The amplification has been investigated by dimensionless parameters of wave period to resonance period ratio of the U-shaped oscillation, $T/T_r$, chamber size to wave length ratio, l/L, water depth to wave length ratio, h/L, amplitude of up-down motion of water particles to draft of the front wall ratio, ${\zeta}/D$. It has been shown that l/L should be less than 0.1 and as $T/T_r$ approaches unity the up-down of the water in the chambers is amplified. Also, the structure of the walls which form th water chambers has been examined roughly. It is deduced that the chambers set on both sides of the hull of a single-point moored floating vessel is preferable to those set along a fixed structure such as breakwaters.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.7
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• pp.579-589
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• 2015

This study aims to understand the internal flow and the evaporation characteristics of a deionized water droplet subjected to vertical forced vibrations. To predict and evaluate its resonance frequency, the theories of Lamb, Strani, and Sabetta have been applied. To visualize the precise mode, shape, and internal flow inside a droplet, the experiment utilizes a combination of a high-speed camera, macro lens, and continuous laser. As a result, a water droplet on a hydrophobic surface has its typical shape at each mode, and complicated vortices are observed inside the droplet. In particular, large symmetrical flow streams are generated along the vertical axis at each mode, with a large circulating movement from the bottom to the top and then to the triple contact line along the droplet surface. In addition, a bifurcation-shaped flow pattern is formed at modes 2 and 4, whereas a large ellipsoid-shape flow pattern forms at modes 6 and 8. Mode 4 has the fastest internal flow speed and evaporation rate, followed by modes 8 then 6, with 2 having the slowest of these properties. Each mode has the fastest evaporation rate amongst its neighboring frequencies. Finally, the droplet evaporation under vertical vibration would lead to more rapid evaporation, particularly for mode 4.

• Journal of Power System Engineering
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• v.9 no.4
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• pp.71-76
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• 2005

Marine structures are often in contact with inner or outer fluid as stern, ballast and oil tanks. The effect of interaction between fluid and structure has to be taken into consideration when we estimate the dynamic response of the structure appropriately. Fatigue damages can also be sometimes observed in these tanks which seem to be caused by resonance. Thin walled tank structures in ships which are in contact with water and located near engine or propeller where vibration characteristics are strongly affected by the added mass of containing water. Therefore it is essentially important to estimate the added mass effect to predict vibration characteristics of tank structures. But it is difficult to estimate exactly the magnitude of the added mass because this is a fluid-structure interaction problem and is affected by the free surface, vibration modes of structural panels and the depth of water. I have developed a numerical tool of vibration analysis of 3-dimensional tank structure using finite elements for plates and boundary elements for fluid region. In the present study, the effect of added mass of containing water, the effect of structural constraint between panels on the vibration characteristics are investigated numerically and discussed. Especially a natural frequencies by the fluid interaction between 2 panels and a breath mode of the water tank are focused on.

• Current Optics and Photonics
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• v.3 no.3
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• pp.199-203
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• 2019

The characteristics of a photonic crystal fiber sensor with reuleaux triangle are studied by using the finite element method. The wavelength sensitivity of the designed optical fiber sensor is related to the arc radius of the reuleaux triangle. Whether the core area is solid or liquid as well as the refractive index of the liquid core contributes to wavelength sensitivity. The simulation results show that larger arc radius leads to higher sensitivity. The sensitivity can be improved by introducing a liquid core, and higher wavelength sensitivity can be achieved with a lower refractive index liquid core. In addition, the specific channel plated with gold film is polished and then analyte is deposited on the film surface, in which case the position of the resonance peak is the same as that of the complete photonic crystal fiber with three analyte channels being filled with analyte. This means that filling process becomes convenient with equivalent performance of designed sensor. The maximum wavelength sensitivity of the sensor is 10200 nm/RIU and the resolution is $9.8{\times}10^{-6}RIU$.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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• pp.517-527
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• 1997

Magnetic Resonance Spectroscopic Imaging is a methodology combining the imaging and spectroscopy. It can provide the spectrum of each areas of image so that one can easily compare the spectrum of one position to another position of the image. In this study, we developed pulse sequence or the spectroscopic imaging method, RF wave forms or the saturation of water signal, computer simulations to validate our method, and confirmed the methodology with phantom experiment. Then we applied the spectroscopic method to human subject and identified a few important metabolites in in vivo. To develope a water saturating RF waveform, we used Shinnar-Le-Roux algorithm and obtained maximum phase RF waveform. With this RF pulse, it could suppress the water signal to 1:1000. The magnet is shimmed to under 1.0ppm with auto-shimming technique. The saturation bandwidth is 80Hz(2ppm). The water and fat seperation is 3.3ppm(about 140Hz at 1 Tesla magnet), the bandwidth is enough to resolve the difference. But we are more concerned about the narrow window in between the two peaks, in which the small quantity of metabolites reside. We performed the computer simulation and phantom experiments in 8*8 matrix form and showed good agreement in the image and spectrum. Finally we applied spectroscopic imaging to the brain of human subject. Only the lipid signal was shown in the periphery region which agrees with the at distribution in human head surface area. The spectrum inside the brain shows the important metabolites such as NAA, Cr/PCr, Choline. We here have shown the spectroscopic imaging which is normally done above 1.5 Tesla machine can be performed in the 1 Tesla Magnetic Resonance Imaging Unit.

• Journal of Ocean Engineering and Technology
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• v.26 no.3
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• pp.33-38
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• 2012

The aim of this experimental study was to analyze the effect of the shape parameters and chamber pressure of a land-based oscillating water column (OWC) in regular incident waves. The magnitude of the free surface elevations inside the chamber was measured in a two-dimensional wave tank for various chamber skirt drafts and bottom slope angles. The surface elevations were also measured under both open chamber and partially open chamber conditions. From these measurements, the optimum shape of the OWC device could be predicted for the maximum wave energy conversion efficiency. It was found that the resonance frequency of the OWC system associated with incident waves moved toward the long wave region with increments of the draft of the chamber skirt and bottom slope. The behavior of the free surface elevation inside the chamber was also found to be dependent on the chamber pressure.

• Journal of Ocean Engineering and Technology
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• v.26 no.6
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• pp.53-58
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• 2012

An experimental study on the hydrodynamic performance of a backward bent duct buoy (BBDB) was performed in a 2D wave tank. The BBDB is one of the promising oscillating water column (OWC) types of floating wave energy converters. Two different corner-shaped BBDBs (sharp-corner and round-corner) were used to measure the maximum chamber surface elevations and body motions for various incident wave conditions, and their hydrodynamic characteristics were compared. In order to investigate the effect of the pneumatic pressure inside the chamber, the heave and pitch angle interacted with elevations were compared for both open chamber and partially open chamber BBDBs. From the comparison study, the deviation in the chamber surface elevations between the two shapes of BBDBs was found to be significant near the resonance period, which may be explained by viscous energy loss. It was also found that the pneumatic pressure noticeably affected the chamber surface elevation and body motions.

• Membrane and Water Treatment
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• v.15 no.2
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• pp.79-88
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• 2024

Modification of Polyvinylidene fluoride (PVDF) hollow fiber membranes (HFMs) characteristics and performance were investigated via post treatment using different oxidants. sodium hypochlorite (NaOCl), hydrogen peroxide (H₂O₂) and potassium persulfate (KPS). Fourier transform infrared (FTIR) and Proton nuclear magnetic resonance (¹H-NMR) results revealed no structural differences after post treatment. Cross-sectional micrographs show finger-like structures at the outer and inner walls of the HFMs and sponge-like structures in middle, where NaOCl and KPS post treated fibers exhibited a decrease in finger-like structures in addition to aggregates appearing on the surface, consequently leading to an increase in the surface roughness (Ra) from 48 nm to 52.8nm and 56 nm, respectively. Hydrogen peroxide post treatment only was observed to decrease the water contact angle from 98° to 81.4°. It was also observed that the elongation at break and the modulus deceased after NaOCl post treatment from 34.5 to 28.5% and from 19.3 Mpa to 16.6 Mpa, respectively. Moreover, pure water flux after H₂O₂ post treatment increased from 87.8 LMH/bar to 113 LMH/bar at 0.45 bar, while no changes were detected for the methylene blue dye rejection (74%) between raw and hydrogen peroxide post treated fibers at the same pressure. According to the findings hydrogen peroxide post treated PVDF HFMs have the most uniform surfaces, with almost no alterations in structural and mechanical properties or porosities with enhanced hydrophilicity and pure water flux maintaining appropriate rejection. Therefore, it is considered an efficient surface modifying agent for UF/NF membranes or low-pressure separators.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.5
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• pp.110-116
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• 2011

Water on a road surface can lower the coefficient of friction of vehicle tires and it involves lots of risks. One way to prevent water from staying is to cut many "rain grooves" into the edges of the pavement parallel. Such grooves, however, can exert unwanted side forces, particularly on passenger tires, which cause "Groove Wander" making the drivers uncomfortable. The "Groove Wander" is somewhat related to vehicle geometry, but is more strongly related to interaction between road grooves and tire tread's longitudinal grooves. This thesis tries to examine principles to estimate "Groove Wandering" effect focusing on the design of longitudinal groove. Additionally, it studied how to reduce pipe resonance longitudinal grooves form in the contact patch.