• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.735-740
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• 2003

In this study, a numerical optimization to find the optimal shape of streamwise periodic ribs mounted on both of the principal walls is performed to enhance turbulent heat transfer in a rectangular channel. The optimization is based on Navier-Stokes analysis of flow and heat transfer with $k-{\varepsilon}$ turbulence model and is implemented using response surface method. The width-to-height ratio of a rib, rib height-to-channel height ratio, rib pitch to rib height ratio and distance between opposite ribs to rib height ratio are chosen as design variables. The object function is defined as a function of heat transfer coefficient and friction drag coefficient with weighting factor. Optimum shapes of the rib have been investigated for the range of 0.0 to 0.1 of weighting factor.

• 한국유체기계학회 논문집
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• 제10권2호
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• pp.7-15
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• 2007

A numerical procedure for optimizing the shape of three-dimensional channel with V-shaped ribs extruded on both walls has been carried out to enhance the turbulent heat transfer. The response surface based optimization is used as an optimization technique with Reynolds-averaged Wavier-stoked analysis. Shear stress transport (SST) turbulence model is used as a turbulence closure. Computational results for average heat transfer rate show good agreements with experimental data. The objective function is defined as a linear combination of heat transfer and friction loss-related terms with a weighting factor. Three dimensionless variables such as, rib pitch-to-rib height ratio, rib height-to-channel height ratio, and the attack angle of the rib are chosen as design variables. Nineteen training points obtained by D-optimal designs for three design variables construct a reliable response surface. In the sensitivity analysis, it is found that the objective function is most sensitive to the ratio of rib height-to-channel height ratio. And, optimal values of design variables have been obtained in a range of the weighting factor.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.313-316
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• 2008

Although the positioning accuracy of the Global Positioning System (GPS) has been studied extensively and used widely, it is still limited due to errors from sources such as the ionospheric effect, orbital uncertainty, antenna phase center variation, signal multipath and tropospheric influence. This investigation addresses the tropospheric effect on GPS height determination. Data obtained from GPS receivers and co-located surface meteorological instruments in 2003 are adopted in this study. The Ministry of the Interior (MOl), Taiwan, established these GPS receivers as continuous operating reference stations. Two different approaches, parameter estimation and external correction, are utilized to correct the zenith tropospheric delay (ZTD) by applying the surface meteorological measurements (SMM) data. Yet, incorrect pressure measurement leads to very poor accuracy. The GPS height can be affected by a few meters, and the root-mean-square (rms) of the daily solution ranges from a few millimeters to centimeters, no matter what the approach adopted. The effect is least obvious when using SMM data for the parameter estimation approach, but the constant corrections of the GPS height occur more often at higher altitudes. As for the external correction approach, the Saastamoinen model with SMM data makes the repeatability of the GPS height maintained at few centimeters, while the rms of the daily solution displays an improvement of about 2-3 mm.

• Journal of Advanced Marine Engineering and Technology
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• 제38권10호
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• pp.1237-1243
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• 2014

The aim of the present paper is to analyze the friction and mass flow in a rough microchannel using Lattice Boltzmann Method (LBM). The LBM is a kinetic method based on the particle distribution function, so it can be fruitfully used to study the flow dependence on Knudsen number including slip velocity, pressure drop in rough microchannel. The surface roughness elements are taken to be considered as a series of circular shaped riblets throughout the channel with relative roughness height up to a maximum 10% of the channel height. The friction coefficients in terms of Poiseuille number (Pn), mass flow rate and the flow behaviors have been discussed in order to study the effect of surface roughness in the slip flow regime at Knudsen number (Kn), ranging from 0.01 to 0.10. It is seen that the friction factor and the flow behaviors in a rough microchannel strongly depend on the rarefaction effect and the relative roughness height. The friction factor in a rough microchannel is higher than that in smooth channel but the mass flow rate is lower than that of smooth channel. Moreover, it is seen that the friction factor increased with relative roughness height but decreased with increasing the Kundsen number (Kn) whereas the mass flow rate is decreased with increasing both of surface roughness height and Knudsen number.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.210-213
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• 1995

In this study,the effect of both process parameters (wheel velocity, friction coefficients between die and billet, etc) and die-shape (abutment height and shape, flash gap, etc.) on the surface defect on forming process is theoretically investigated. For this work, computer simulation was performed by using the DEFORM, a commercial FEM code. Through numerous simulations with different parameters and die shapes, We propose one optimal die shape for CONFORM process which can remove surface defect.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.157-163
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• 1995

This paper presents an algorithm to deternine the tool path height for rough machining of sculptured surface. To minimize rough machining of sculptured surface, it is necessary to determine the tool path heights of contour planes. the proposed algorithm searches for the height at which maximum metal removal rate is obtained. This bisection method is accomplished until all shoulder heights are within roughing tolerance. The machining experiment demonstrates the superiority of the algorithm presented in this thesis.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.429-434
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• 2002

The Synthetic Aperture Radar (SAR) data are considered to contain the greatest amount of information among various microwave techniques developed for measuring ocean variables from aircraft or satellites. They have the potential of measuring wavelength, wave direction and wave height of the ocean waves. But, it is difficult to retrieve significant ocean wave heights and surface current from conventional SAR data, since the imaging mechanism of ocean waves by a SAR is determined by the three basic modulation processes arise through the tilt modulation, hydrodynamic modulation and velocity bunching which are poorly known functions. Along-Track Interferometric (ATI) SAR systems can directly detect the Doppler shift associated with each pixel of a SAR image and have been used to estimate wave fields and surface currents. However, the Doppler shift is not simply proportional to the component of the mean surface current. It includes also contributions associated with the phase velocity of the Brags waves and orbital motions of all ocean waves that are longer than Brags waves. In this paper, we have developed a new method for extracting the surface current vector using multiple-frequency (L- & C-band) ATI SAR data, and have generated surface wave height information.

• 대한물리의학회지
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• 제11권3호
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• pp.97-104
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• 2016

PURPOSE: Bridge exercise is widely used in rehabilitation exercise for trunk stabilization through various applications in clinical practice. However, there is a lack of studies changing the base of support for the shoulders. The purpose of this study is to investigate the changes in the base of support for the shoulders of trunk muscle activation during bridge exercise. METHODS: 20 healthy subjects (10 men, 10 women) in their twenties were participated in this study. They performed 5 bridge exercises (bridge exercise with their shoulders on a stable table (1/2 knee height, knee height), and on a sling (1/2 knee height, knee height), conventional bridge exercise. The surface electromyography were used for rectus abdominis (RA), internal oblique (IO), external oblique (EO), and erector spinae (ES). RESULTS: During bridge exercise that their shoulders on the sling of 1/2 knee height, the RA, EO, IO muscle activities were significant increased. And during bridge exercise that their shoulders on the stable surface of knee height, the IO/RA ratio were higher than other positions but there were no significant difference between positions for EO/RA, IO/RA ratio. CONCLUSION: Based on this result, using various bases of support and changing the height of bridging exercise may be used to provide effective trunk stabilization exercises.

• Journal of Periodontal and Implant Science
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• 제49권5호
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• pp.310-318
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• 2019

Purpose: Surface alterations of titanium discs following instrumentation with either a nylon brush or a metal brush were evaluated. Methods: A total of 27 titanium discs with 3 surface types (9 discs for each type), including machined (M) surfaces, sandblasted and acid-etched (SA) surfaces, and surfaces treated by resorbable blast media (RBM), were used. Three discs were instrumented with a nylon brush, another 3 discs were instrumented with a metal brush, and the remaining 3 discs were used as controls for each surface type. Surface properties including the arithmetic mean value of a linear profile (Ra), maximum height of a linear profile (Rz), skewness of the assessed linear profile (Rsk), arithmetic mean height of a surface (Sa), maximum height of a surface (Sz), developed interfacial area ratio (Sdr), skewness of a surface profile (Ssk), and kurtosis of a surface profile (Sku) were measured using confocal microscopy. Results: Instrumentation with the nylon brush increased the Ra, Sa, and Sdr of the M surfaces. On the SA surfaces, Ra, Sa and Sdr decreased after nylon brush use. Meanwhile, the roughness of the RBM surface was not affected by the nylon brush. The use of the metal brush also increased the Ra, Sa, and Sdr of the M surface; however, the increase in Sdr was not statistically significant (P=0.119). The decreases in the Rz, Sz, Ra, Sa, and Sdr of the SA surfaces were remarkable. On the RBM surfaces, the use of the metal brush did not cause changes in Ra and Sa, whereas Rz, Sz, and Sdr were reduced. Conclusions: Titanium surfaces were altered when instrumented either with a nylon brush or a metal brush. Hence, it is recommended that nylon or metal brushes be used with caution in order to avoid damaging the implant fixture/abutment surface.

• 한국구조물진단유지관리공학회 논문집
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• 제24권5호
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• pp.126-134
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• 2020

유체 저장 구조물은 지진 시 유체의 출렁임에 의해 동수압이 발생한다. 이 때, 유체의 동수압은 지진의 강도뿐만 아니라 유체 자유수면의 출렁임 높이(sloshing height)에 의해서도 변화한다. 이러한 하중 변화에 영향을 미치는 인자로는 지진파의 형상, 최대지진강도, 유체 저장구조물의 크기, 구조물의 폭, 유체의 높이 등이 있으며, 본 연구에서는 유체높이와 구조물 폭의 비가 유체의 출렁임 특성에 미치는 영향을 규명하고자 한다. 이를 위하여 구조물의 폭이 500mm인 수조에 구조물의 전체 높이 대비 50%인 200mm와 35%인 140mm의 유체를 담아 실지진파를 적용시켜 유체 자유수면의 출렁임 높이를 측정하였다. 또한 수치해석기법 중 하나인 SPH기법을 통하여 실험과 해석의 유사성을 검증하였다. 실험과 해석의 비교를 통하여 유체의 자유 수면이 유사한 형상을 나타냄을 확인하였으며, 이를 바탕으로 SPH기법을 적용하여 유체높이와 구조물 폭의 비를 다양하게 변화시키면서 유체 자유수면의 출렁임 형상을 분석하였다. 이상의 결과를 바탕으로 지진시 유체 자유수면의 최대 높이 및 최소높이를 예측할 수 있는 식을 제안하였으며, 제안식에 의해 예측된 유체 자유수면의 최대 높이 및 최소 높이의 오차는 최대 3% 이내임을 확인하였다.