• The KSFM Journal of Fluid Machinery
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• v.13 no.3
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• pp.18-23
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• 2010

This paper predicts the unbalance and transient (start-up) response of a 5MW industrial gas turbine by using commercial rotordynamic tool, DYNAMICS 4.3. The gas turbine is operated at 12,975rpm on squeeze film dampers or tilting pad bearings. The stiffness and damping coefficients of the squeeze film dampers and tilting pad bearings are estimated. It is seen that the vibration amplitude of the gas turbine rotor is sufficiently small around the critical speeds and at the rated speed.

• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.148-154
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• 2008

The Wells turbine rotor consists of several symmetric airfoil blades arranged around a central hub, and the stagger angle is 90 degrees. These characteristics simplify the total construction of OWC type wave energy converters. Although the Wells turbine is simple, the turbine produces a complicated flow field due to the peculiar arrangement of blades, which can rotate in the same direction irrespective of the oscillating airflow. In order to understand these flows, flow visualization is carried out with an oil-film method in the water tunnel. This research aims to analyze the mechanism of the 3-D flows around the turbine with the flow visualization. The flow visualization explained the influence of attack angle, the difference between fan-shaped and rectangular wings, and the sweep angle.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.221-226
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• 2008

Numerical simulation is performed for microdroplet deposition on a pre-patterned micro-structure. The level-set method for tracking the liquid-gas interface is extended to treat the immersed (or irregular-shaped) solid surface. The no-slip condition at the fluid-solid interface as well as the matching conditions at the liquid-gas interface is accurately imposed by incorporating the ghost fluid approach based on a sharp-interface representation. The method is further extended to treat the contact angle condition at an immersed solid surface. The present computation of a patterning process using microdroplet ejection demonstrates that the multiphase characteristics between the liquid-gas-solid phases can be used to improve the patterning accuracy.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.221-226
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• 2008

Numerical simulation is performed for microdroplet deposition on a pre-patterned micro-structure. The level-set method for tracking the liquid-gas interface is extended to treat the immersed (or irregular-shaped) solid surface. The no-slip condition at the fluid-solid interface as well as the matching conditions at the liquid-gas interface is accurately imposed by incorporating the ghost fluid approach based on a sharp-interface representation. The method is further extended to treat the contact angle condition at an immersed solid surface. The present computation of a patterning process using microdroplet ejection demonstrates that the multiphase characteristics between the liquid-gas-solid phases can be used to improve the patterning accuracy.

• Journal of ILASS-Korea
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• v.20 no.1
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• pp.7-13
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• 2015

In this study, the behavior of water or nanofluid droplets impacting upon a hot surface was investigated by visualization of impacting phenomena with time-delayed photographic technique. Changing the mass ratio of nanofluid and the temperature of the heated surface, the characteristics of the spreading behavior and the diameter of spreading liquid film was compared between water and nanofluid droplets. The impacting droplet spreaded as a liquid film after impact and nanofluid droplets spreaded more widely than water droplets. After reaching the maximum diameter, water droplets shrinked more than nanofluid droplets. Based on this, the heat transfer area from a hot surface to impacting nanofluid droplets would be wider than that of impacting water droplets. Considering individual impacting droplet only, spray cooling using nanofluid would be better than using water.

• Tribology and Lubricants
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• v.18 no.1
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• pp.9-15
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• 2002

The nonlinear vibration characteristics of hydrodynamic journal bearings with a circumferential groove we analyzed numerically when the external sinusoidal disturbances are given to the rotor-bearing system continuously. Furthermore, a cavitation algorithm, implementing the Jakobsson-Floberg-Olsson boundary condition, is adopted to predict cavitation regions in a fluid film more accurately than the conventional analysis. which uses the Reynolds boundary condition. It is found that the difference between linear and nonlinear analysis is much more remarkable as the amplitude of external disturbance increases, and it depends upon the excitation frequency of the external disturbance. It is also shown that the cavity region in the fluid film increases as the amplitude or excitation frequency of the external disturbance increases. The whirling center of the steady state orbit moves closer to the bearing center as the amplitude or excitation frequency of the external disturbance increases.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.906-910
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• 2003

This paper numerically analyzes the dynamic characteristics of a spindle system supported by two identical journal bearings considering bearing span that has dynamic load due to its mass unbalance. The Reynolds equation is transformed to solve a herringbone grooved journal bearing. The Reynolds equations are solved using FEM in order to calculate the pressure distribution in a fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors, such as whirl radius or angular displacement of a rotor, are determined by solving its nonlinear equations of motion with the Runge-Kutta method. This research shows that the same bearing spans of upper and lower journal bearings produce the minimum runout and friction torque of a spindle system.

• Proceedings of the KIEE Conference
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• 2000.11c
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• pp.583-585
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• 2000

This study reports the fluidic handling method using hydrophobic patterns inside PDMS microchannels. In order to obtain hydrophobic patterns, we pattern fluorcarbon(FC) film surfaces by lift-off process. FC films are deposited by spin coating method and plasma polymerization method. Hydrophobic surfaces are used as the barriers to control fluid flow. Injected liquid is spontaneously filled up inside PDMS-microchannels by the capillary action. Liquid flow stops when it meets hydrophobic regions which can be the barrier against fluid flow. Then, again, when liquid is pressurized externally, liquid can move toward another hydrophilic region by external air pressure. Contact angle analyses are performed on fluorocarbon films to estimate the wettability of film surfaces.

• Archives of Pharmacal Research
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• v.28 no.3
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• pp.364-369
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• 2005

HPMC (Hydroxypropyl methylcellulose) was chemically modified, using maleic anhydrides, to obtain pH-sensitive HPMCAM (Hydroxypropyl methylcellulose acetate maleate) polymers for use as novel duodenum-specific coating agents. The pharmaceutical properties of HPMCAM, such as film forming, acid values, pH-sensitive values, water vapor permeability, tensile strength and Tg, were investigated, and found to show good film forming properties. The pH­sensitive values were 3.0 to 3.7. In vitro results demonstrate that HPMCAM could completely suppress drug release within 2h in a simulated gastric fluid (pH 1.2) and rapidly release the drug in a simulated pathological duodenal fluid (pH 3.4). These results indicate that HPMCAM might be a useful material for a duodenum-specific drug delivery system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.9 s.90
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• pp.779-784
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• 2004

This paper numerically analyzes the dynamic characteristics of a spindle system supported by two identical journal bearingsconsidering bearing span that has dynamic load due to its mass unbalance. The Reynolds equation is transformed to solve a herringbone grooved journal bearing. The Reynolds equations are solved using FEM in order to calculate the pressure distribution in a fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors, such as whirl radius or angular displacement of a rotor, are determined by solving its nonlinear equations of motion with the Runge-Kutta method. This research shows that the same bearing spans of upper and lower journal bearings produce the minimum runout and friction torque of a spindle system.