• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.45-48
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• 2008

Micro power generators have been studying to provide high power that micro systems require. Micro power generators need micro combustor. Swiss-roll combustor has been studied about scale, geometry, material. From previous study experiments have shown that swiss-roll combustors require thin walls with low thermal conductivity for maximum performance at small scales. In this work, polyimide combustors with low thermal conductivity and thin thickness are built and tested.

• Journal of the Korea Convergence Society
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• v.7 no.4
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• pp.181-190
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• 2016

The objective of this study is to find the effective stiffness and compressive strengths of a unit-cell pinwheel truss and double pinwheel truss model designed following a double helical geometry similar to that of the DNA (deoxyribonucleic acid) structure in biology. The ideal solution for their derived relative density is correlated with a ratio of the truss thickness and length. To validate the relative stiffness or relative strength, ABAQUS software is used for the computational model analysis on five models having a different size of truss diameter from 1mm to 5mm. Applied material properties are stainless steel type 304. The boundary conditions applied were fixed bottom and 5 mm downward displacement. It was assumed that the width, length, and height are all equal. Consequently, it is found that the truss model has a lower effective stiffness and a lower effective yielding strength.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1516-1521
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• 2004

Mixing in Y-channel micro mixer is analyzed through computational fluid dynamics. In the case of passive mixing, we investigate the effect of geometric parameters on the mixing efficiency, such as shape of throttling geometry and angle between two inlets. Mixing performance improves as two fluids join not just horizontally but both vertically and horizontally, and it also improves when channel follows throttling shapes. A numerical results substantiate the highly efficient mixing performance. It is highly beneficial to fabrication process since the proposed throttling geometry is simple, but allows high mixing ratio.

• Transactions of Materials Processing
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• v.13 no.3
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• pp.230-235
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• 2004

A new design based on the appropriate geometry of molded part and type of runner system under the optimal processing conditions was proposed to minimize the micro weld lines on the sub deco surface molded by two shot molding. Theoretical and experimental studies were conducted to examine the cause of the weld lines during the overmolding process in two shot molding. Various dimensions and geometries of substrate$(1^{st}shot)$ and the wall thickness of overmold$(2^{nd}shot)$ have been proposed to avoid the weld lines which are the most inevitable appearance defects occurred on the sub deco. The each design proposal was analyzed by mold flow analysis after part modeling. The analysis results were compared with molded part from mass production tool. It could be seen that from the analysis that the proper geometry of plastic part and type of runner system considering pressure drop under the optimal processing conditions were the most influential factors to avoid weld lines occured on the sub deco.

• Transactions on Electrical and Electronic Materials
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• v.18 no.1
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• pp.25-29
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• 2017

This paper presents a unique pressure sensor design for environmental applications. The design uses a new geometry for a multi bossed beam-membrane structure with a SOI (silicon-on-insulator) substrate and a mechanical transducer. The Intellisuite MEMS CAD design tool was used to build and analyze the structure with FEM (finite element modeling). The working principle of the multi bossed beam structure is explained. FEM calculations show that a sensing diaphragm with Mises stress can provide superior linear response compared to a stress-free diaphragm. These simulation results are validated by comparing the estimated deflection response. The results show that, the sensitivity is enhanced by using both the novel geometry and the SOI substrate.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.802-810
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• 2003

In this paper, the modified singular fracture process zone (S-FPZ) model is proposed to consider variation of a fracture criterion for continuous crack propagation in concrete. The fracture properties of the proposed fracture model are strain energy release rate at a micro-crack tip and crack closure stress (CCS) versus crack opening displacement (COD) relationship in the FPZ. The proposed model can simulate the estimated fracture energy of experimental results. The analysis results of the experimental data shows that specimen geometry and loading condition did not affect the CCS-COD relation. But the strain energy release rate is a function of not only specimen geometry but also crack extension. Until 25 mm crack extension, the strain energy release rate is a constant minimum value, and then it increased linearly to the maximum value. The maximum fracture criterion occurred at the peak load for an large size specimen. The fracture criterion remains the maximum value after the peak load. The variation of the fracture criterion is caused by micro-cracking and micro-crack localizing. The fracture criterion of strain energy release rate can simply be the size effect of concrete fracture, and it can be used to quantify the micro-tracking and micro-crack localizing behaviors of concrete.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1888-1893
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• 2007

In this study, the microchannel plated heat exchanger were numerically studied for the enhancement of heat transfer in the channel configuration. Unit cold and hot fluid region with the microchannel were modeled and periodic boundary condition at the side wall was applied to continuously repeating geometry. The material of micro-structured plate is STS304 and working fluid is water. Triangular obstacles were placed in micro channel to enhance heat transfer. The performance of microchannel plated heat exchangers were numerically investigated with various obstacle configuration and Reynolds number under the parallel and counter flows. Heat transfer rate has increased about 18% compared with straight channel, but pressure drop also increased about 3.5 times. The main factor of increasing of pressure drop and heat transfer rate is considered that the momentum was lost to collide against obstacles, generation of secondary flow and boundary layer separation, wake and vortex forming phenomena.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1145-1150
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• 2005

The aim of this paper is to investigate the effect of surface texturing on metal surface and to understand the potential of friction reduction through micro-scale dimple to fabricate by photolithography on pin-on-disk test using flat-on-flat contact geometry. It was verify that the friction property with respect to the same pitch has been influence on the size of dimple under lubricated sliding contact. Also, we can recognize from Stribeck curve that the friction property has a connection with the size of dimple. It can explain a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. The friction property has been an effect on the size of surface texture on reduction friction, not only because the density of dimple, but also because the ratio of diameter/pitch. This ratio of approximately 0.5 is recommend under the tested friction condition. It suggested that the ratio of d/p is an important parameter for surface texture design.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.30-37
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• 2001

A Numerical simulation for the propulsion of axisymmetric body by contractive and dilative motion is carried out. The present analysis shows that a propulsive force can be obtained in highly viscous fluid by a contractive and dilative motion of axisymmetric body. An axisymmetric analysis code is developed with unstructured grid system for the simulation of complicated motion and geometry. The developed code is validated by comparing with the results of stokes approximation with the problem of uniform flow past a sphere in low Reynolds number($R_n=1$). The validated code is applied to the simulation of contractive and dilative motion of body. The simulation is extended to the analysis of waving surface with projecting part for finding out the difference of hydrodynamic performance according to the variation of waving surface configuration. The present study will be the basic research for the development of the propulsor of an axisymmetric micro-hydro-machine.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.5
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• pp.708-713
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• 2012

The indented geometry for rockwell hardness indenter has been configured by using Confocal Laser Scanning Microscopy (CLSM). For this purpose, the CLSM can be well suited to construct the three-dimensional indented volume from the indented surface by rockwell hardness tester. Furthermore, the height data of HEI(height encoded image) by CLSM must be acquired at first and converted to indented surface later. And the indented surface patterns enable us to predict the indenter shape and volume. This volume can be used to study the rockwell hardness model as a volume parameter. As a result, the technique performed in this study by combining the CLSM with compensation technique is an excellent one to obtain the geometries of indented surfaces over a wide range of surface resolution in a micro scale. And it can be used for micro volume calculation.