• Journal of the Korean Society of Groundwater Environment
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• v.6 no.4
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• pp.188-193
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• 1999

Transport of pollutants in aquifer largely depends on groundwater flow which is governed by aquifer hydraulic parameters. Determination of these parameters and associated groundwater modeling become essential for adequate remediation of contaminate groundwater. The objective of this paper is to analyze groundwater flow and determine the optimum hydraulic parameters by performing groundwater modeling based on sensitivity analysis for unconfined sandy gavel aquifer constructed in a laboratory scale under various boundary condition. Results revealed that the simulated drawdown was lower than the observed drawdown irrespective of boundary conditions. and specific yield (S$_{y}$) had less effect on the grondwater flow than permeability (K) in the aquifer. Water balance analysis showed that the measured drawdown in neighboring observation wells during pumping was higher than either simulated or recovered water table. The indicated that a difference might exist in the water tables between aquifer and wells. The difference was investigated by time domain reflectometry (TDR) measurements on water contents in the region of water table and capillary fringe, and explained by a delayed response of water table during gravitational drainage as the water table was lowered as a result of pumping.g.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.9
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• pp.816-825
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• 2007

With a view to building up a program used in conceptual design of liquid rocket engine system, a preliminary performance-based code for an integrated engine system has been developed by incorporating sub-modular programs for each essential engine component. Modular descriptions for each component were formulated mathematically with essential parameters. In the whole iterative circuits for predicting engine performance, matching conditions of mass flow rate and pressure drop through each engine component have been considered. Mass balance calculations at each inter-component boundary are found smoothly converged. All the pressure drops through engine components as a function of mass flow rate are added up to provide turbo-pump outlet condition. In this paper, the flow chart for each iterative circuit and design methodologies are presented. Resultant predictions are validated with real engine data.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.5
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• pp.545-550
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• 2012

Steam generator is one of the major components of nuclear power plant and steam generator tubes are the pressure boundary between primary and secondary side, which makes them critical for nuclear safety. As the operating time of nuclear power plant increases, not only damage mechanisms but also scaled deposits on steam generator tubes are known to be problematic causing tube support flow hole blockage and heat fouling. The ability to assess the extent and location of scaled deposits on tubes became essential for management and maintenance of steam generator and eddy current bobbin data can be utilized to measure thickness of scale on tubes. In this paper, tube reference standards with various thickness of scaled deposit has been set up to provide information about the overall deposit condition of steam generator tubes, providing essential tool for steam generator management and maintenance to predict and prevent future damages. Also, methodology to automatically measure scale thickness on tubes has been developed and applied to field data to estimate overall scale amount.

• Journal of Sensor Science and Technology
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• v.26 no.2
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• pp.122-127
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• 2017

Graphene grown on copper-foil substrates by chemical vapor deposition (CVD) has been attracting interest for sensor applications due to an extraordinary high surface-to-volume ratio and capability of large-scale device fabrication. However, CVD graphene has a polycrystalline structure and a high density of grain boundaries degrading its electrical properties. Recently, processes such as electropolishing for flattening copper substrate has been applied before growth in order to increase the grain size of graphene. In this study, we systemically analyzed the effects of the process condition of electropolishing copper foil on the quality of CVD graphene. We observed that electropolishing process can reduce surface roughness of copper foil, increase the grain size of CVD graphene, and minimize the density of double-layered graphene regions. However, excessive process time can rather increase the copper foil surface roughness and degrade the quality of CVD graphene layers. This work shows that an optimized electropolishing process on copper substrates is critical to obtain high-quality and uniformity CVD graphene which is essential for practical sensor applications.

• Journal of the Korean Vacuum Society
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• v.14 no.1
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• pp.7-16
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• 2005

Oil-Hydraulic pump consisting of swing twin-cylinder becomes to be used as a next generation of low vacuum pump. However, there is no enough flow-analysis for design improvement. It is essential to develope a numerical method for flow-analysis before manufacturing, in economic sense. Using a commercial code (Fluent), developed for flow-analysis, useful informations for design of pump were provided. Two-dimensional analysis has been performed to investigate the flow parameters such as pressure and velocity distributions between the swing twin-cylinder and the fixed cylinder. This numerical method will be used to design a better performance of pump consisting of swing twin-cylinder.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.496-500
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• 2004

A new, commercially available polishing process called magnetorheological finishing is used to polish and figure precision optics. To understand and model this process correctly it is important to determine the mechanical properties of the fluid under the influence of the magnetic field. Magnetorheological (MR) fluids are commonly modeled as Bingham fluids, so one of the essential properties to measure is the yield stress. Since MR fluids are inherently anisotropic, the yield stress will depend on the mutual orientation of the magnetic field and the direction of deformation. The relative orientation of the field and deformation in polishing does not coincide with common rheological setups, so a new rheometer has been designed and tested. This new magnetorheometer design has been shown to give correct stresses during calibration experiments using Newtonian fluids with a known viscosity. The measured stress has also been shown to have a magnitude consistent with published finite element approximations for magnetic fluids. The design of the instrument was complicated because of the requirements imposed upon the magnetic field, and the difficulty in satisfying the no slip boundary condition. Our results show the importance of having a homogeneous field in the test region during measurements. The solutions to these problems and discussion of the measurements on nonmagnetic and magnetic fluids are given.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.9
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• pp.109-115
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• 2008

The cleaning process of contaminant particles adhering to the microchips, integrated circuits (ICs) or the like is essential in modern microelectronics industry. In the cleaning process particularly working with the application of inert gases, the removal of contaminant particles of submicron scale is very difficult because the particles are prone to reside inside the boundary layer of the working fluid, The use of cryogenic $CO_2$ cleaning method is increasing rapidly as an alternative to solve this problem. In contrast to the merits of high efficiency of this process in the removal of minute particles compared to the others, even fundamental parametric studies for the optimal process design in this cleaning process are hardly done up to date, In this study, we attempted to measure the cleaning efficiency with the variations of some principal parameters such as mass flow rate, injection distance and angle, and tried to draw out optimal cleaning conditions by measuring and evaluating an effective cleaning width called $d_{50}$.

• International Journal of Highway Engineering
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• v.7 no.3 s.25
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• pp.23-30
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• 2005

Predicting distribution and variation of humidity inside concrete is essential to improve curing quality of concrete at field. The concrete humidity is predicted by numerical analysis using surface humidity as boundary condition. However, ambient humidity has been used instead of the surface humidity because the surface humidity could not be ccurately measured. Because it is hard to accurately measure the surface humidity, owever, the ambient humidity has been used instead of the surface humidity in the numerical analysis. In this paper, a methodology to accurately measure the surface humidity is suggested, and the ambient humidity and the humidity at the surface and inside the concrete measured by a series of laboratory tests are presented. The cause of low concrete humidity immediately after placement was investigated by a separately performed test. A surface humidity prediction model was developed using the measured humidity, and consequently validated through an additional test.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.1
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• pp.73-83
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• 1990

A theorectical method is presented for the calculation of the effective wake in an axisymmetric sheared inflow. The effective wake is essential in the design of optimal propulsor and in the reduction of propulsor induced vibration and noise. The nominal wakes are mathematically modelled and the effective wakes are calculated using the computer program developed on the basis of the linear momentum theory. The results show that shear effects arc dominant near the hub and the effective wakes reveal some differences near the hub for the moderately and heavily loaded propulsors but they arc well coincided with the other experimental or theorectical results for the lightly loaded propulsors. To improve the results it may be necessary to consider nonlinear terms neglected in this study and body boundary condition on hub.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1738-1743
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• 2004

Turbo-pump system, an essential component of liquid rockets and induced weapons, adopts a partial admission axial turbine which drives pump. And the turbine of a turbo-pump system is usually operated at supersonic condition due to its high loading chracteristics. Therefore, reseaches about flow and performance characteristics of a partial admission supersonic turbine must be preceeded to progress the aerospace and defense industries as well as the development of turbo-pump systems. In this study, flow characterisitics within blades of the partial admission supersonic turbine are numerically investigated by using Fine Turbo, a commercial CFD Code. Before performing the numercial analyses, to verify accuracy of the numerical result computed by Fine Turbo, I performed the comparison between the numerical results with J.J.Cho' experimental results. It is found that the numerical results show good agreement with the experimental results. Computations about the partial admission supersonic turbine have been performed to investigate flow characteristics including shock patterns. It is also found that the flow and performance of partial admission supersonic turbine are largely depend on shocks ocurred in the nozzle and at the leading edge of blades, expansion or compression at exit of nozzle and separations occurred in passage.