• 드라이브 ㆍ 컨트롤
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• 제11권1호
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• pp.8-13
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• 2014

Hydraulic servo valves are widely used in various fluid power systems because of their fast response and precision control. In this paper, we studied the effect of metering notch shapes and amount of their openings on the flow characteristics within the spool valve using a computational fluid dynamic (CFD) code, FLUENT. To obtain the results for more realistic operating conditions, viscous heating due to the jet flow and viscosity variation of the hydraulic fluid with temperature were considered. For two types of notch shape, streamlines, oil temperature and viscosity distributions, and variations of flow and friction forces acting on spool were showed. The flow and friction forces affected by the metering notch shapes and their openings, and oil temperature rise near metering notch was significant enough to results in the jamming phenomenon. A thermohydrodynamic (THD) flow analysis adopted in this paper can be used in optimum design of hydraulic servo valves.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.140-146
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• 2002

The fluid induced vibration (FIV) phenomena of a 2-D.O.F airfoil system have been investigated in low Reynolds number incompressible flow region. Unsteady flows with viscosity are computed using two-dimensional incompressible Navier-stokes code. To validate developed Navier-Stokes code, steady and unsteady flow fields around airfoil are analyzed. The present fluid/structure interaction analysis is based on the most accurate computational approach with computational fluid dynamics (CSD) and computational structural dynamics (CSD) techniques. The highly nonlinear fluid/structure interaction phenomena due to severe flow separations have been analyzed fur the low Reynolds region (R$_{N}$ =500~5000) that has a dominancy of flow viscosity. The effect of R$_{N}$ on the fluid/structure coupled vibration instability of 2-DOF airfoil system is presented and the effect of initial angle of attack on the dynamic instability are also shown.own.

• ETRI Journal
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• 제38권6호
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• pp.1179-1189
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• 2016

A chemorheological analysis of a no-flow underfill was conducted using curing kinetics through isothermal and dynamic differential scanning calorimetry, viscosity measurement, and solder (Sn/27In/54Bi, melting temperature of $86^{\circ}C$) wetting observations. The analysis used an epoxy system with an anhydride curing agent and carboxyl fluxing capability to remove oxide on the surface of a metal filler. A curing kinetic of the no-flow underfill with a processing temperature of $130^{\circ}C$ was successfully completed using phenomenological models such as autocatalytic and nth-order models. Temperature-dependent kinetic parameters were identified within a temperature range of $125^{\circ}C$ to $135^{\circ}C$. The phenomenon of solder wetting was visually observed using an optical microscope, and the conversion and viscosity at the moment of solder wetting were quantitatively investigated. It is expected that the curing kinetics and rheological property of a no-flow underfill can be adopted in arbitrary processing applications.

• 전기학회논문지
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• 제65권8호
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• pp.1376-1382
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• 2016

The discharge characteristics of inductively coupled $Ar/CH_4$ plasma were investigated by fluid simulation. The inductively coupled plasma source driven by 13.56 Mhz was prepared. Properties of $Ar/CH_4$ plasma source are investigated by fluid simulation including Navier-Stokes equations. The schematics diagram of inductively coupled plasma was designed as the two dimensional axial symmetry structure. Sixty six kinds of chemical reactions were used in plasma simulation. And the Lennard Jones parameter and the ion mobility for each ion were used in the calculations. Velocity magnitude, dynamic viscosity and kinetic viscosity were investigated by using the fluid equations. $Ar/CH_4$ plasma simulation results showed that the number of hydrocarbon radical is lowest at the vicinity of gas feeding line due to high flow velocity. When the input power density was supplied as $0.07W/cm^3$, CH radical density qualitatively follows the electron density distribution. On the other hand, central region of the chamber become deficient in CH3 radical due to high dissociation rate accompanied with high electron density.

• Tribology and Lubricants
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• 제37권1호
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• pp.14-24
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• 2021

This study shows the effect of the thermal boundary condition around the tilting pad journal bearing on the static and dynamic characteristics of the bearing through a high-precision numerical model. In many cases, it is very difficult to predict or measure the exact thermal boundary conditions around bearings at the operating site of a turbomachine, not even in a laboratory. The purpose of this study is not to predict the thermal boundary conditions around the bearing, but to find out how the performance of the bearing changes under different thermal boundary conditions. Lubricating oil, bearing pads and shafts were modeled in three dimensions using the finite element method, and the heat transfer between these three elements and the resulting thermal deformation were considered. The Generalized Reynolds equation and three-dimensional energy equation that can take into account the viscosity change in the direction of the film thickness are connected and analyzed by the relationship between viscosity and temperature. The numerical model was written in in-house code using MATLAB, and a parallel processing algorithm was used to improve the analysis speed. Constant temperature and convection temperature conditions are used as the thermal boundary conditions. Notably, the conditions around the bearing pad, rather than the temperature boundary conditions around the shaft, have a greater influence on the performance changes of the bearing.

• 한국지반공학회논문집
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• 제19권4호
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• pp.145-153
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• 2003

공진주 실험은 탄성파 이론을 이용하여 흙의 동적 물성, 즉 전단변형률의 크기에 따른 전단탄성계수와 재료감쇠비를 측정하는 실험이다. 공진주 실험에 의한 시료의 동적물성의 측정은 공진주 실험 시스템의 동적 거동에 대한 이해를 전제로 한다. 공진주 실험의 시료 및 실험장치의 구성은 고정단-자유단 경계조건을 가지고 있는 연속보로 단순화할 수 있어서, Richart, Hall and Woods는 공진주 실험 시스템에 대한 파동방정식을 유도하였으나, 시료를 단순히 탄성으로 가정하였고 시료의 점성을 고려하지는 않았다. 그리고, Hardin은 파동방정식의 유도에서 시료의 점탄성을 고려하였으나, 시료의 전단탄성계수를 결정하기 위하여 시료의 점탄성을 가정하여야 하는 문제점을 가지고 있었다. 본 연구에서는 기존의 연구자들이 시도했던 공진주 실험 시스템에 대한 파동방정식을 새로운 측면에서 유도하였으며, 새로이 유도된 파동방정식의 해법을 제안하였다. 한편, 일반적으로 시스템에 대한 동적 거동을 이해하는 방법으로, 시스템의 운동방정식을 이용하는 방법이 있으나, 공진주 실험 시스템에 대한 동적 거동의 해석방법으로 이와 같은 운동방정식을 이용하는 해석방법을 연구한 경우는 거의 없었다. 운동방정식에 의한 해법은 시스템의 동적 증폭계수와 동적 응답에 대한 위상각을 구할수 있기 때문에 파동방정식에 대한 해법보다 더 많은 정보를 활용할 수 있는 장점이 있다. 따라서, 본 연구에서는 공진주 실험 시스템에 대한 보다 기본적이고 많은 정보를 도출하기 위하여, 공진주 실험 시스템에 대한 운동방정식을 유도하였으며, 이를 이용하여 공진주 실험자료를 해석하는 새로운 해석기법의 제안을 위한 근간을 마련하였다. 그리고, 공진주 실험 시스템에 대한 유한요소 해석을 수행하여, 본 연구에서 제안한 공진주 실험시스템의 이론적 모델링의 타당성과 합리성을 검증하였다.

• Food Science and Biotechnology
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• 제17권1호
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• pp.52-57
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• 2008

The effects of transglutaminase (TG) on the pasting and rheological properties of different wheat cultivars ('Sharpshooter', 'Russ', and 'AcAriss') blended with barley (40%) or soy (20%) flour were investigated. In the rapid visco-analyzer (RVA) pasting profile, the addition of barley or soy flour to wheat flour samples induced a decrease in peak, trough, final viscosity, breakdown and setback values. However, TG treatment of these blends significantly increased peak viscosity and breakdown (p<0.05). In particular, TG treatment greatly increased the breakdown of wheat flour blended with soy flour, indicating that the cross-linking of proteins through TG may somehow be related to an increase in starch granule rupturing in pastes. Storage (G') and loss (G") moduli of the sample pastes increased with an increase in frequency ($\omega$), while complex viscosity (${\eta}*$) decreased. In all wheat cultivars, G', G", and $\eta$ were decreased by the addition of barley or soy flour, or TG treatment. Results suggest that protein cross-linking by TG can produce unique and improved properties in wheat flours blended with barley or soy flour.

• Asian-Australasian Journal of Animal Sciences
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• 제26권6호
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• pp.896-904
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• 2013

Cattle breeds have a striking effect on milk, including milk composition and technological characteristics. This study aims to compare milk composition, acidification activity, viscosity, milk dispersion system stability and casein molecular weight among three buffalo breeds in China. The technological characteristics of milk produced by three cattle breeds of river buffalo (Murrah), crossbreed 1st generation ($F_1$), crossbreed multiple generation ($F_H$, $H{\geq}3$) buffaloes were investigated. Cattle breeds showed evident effect on milk protein, fat and total solids content, but little effect on most of buffalo casein molecular weight. Milk fat, protein content and the viscosity of buffalo milk from river buffalo were lower than those of $F_1$ and $F_H$, so was the buffer capacity. The viscosity was negatively correlated to temperature and concentration. Results of stability coefficient showed that milk dispersion system had the best dynamic stability characteristics under pH 6.6 and 6 times dilution, while zeta potential of Murrah milk was slightly higher than that of hybrid offspring ($F_1$, $F_H$). SDS-PAGE results showed that buffalo ${\alpha}_s$-casein had a slightly faster mobility than standard ${\alpha}_s$-casein; while buffalo ${\beta}$-casein showed a slightly slower mobility than standard ${\beta}$-casein. There is no clear differences in molecular weight of ${\alpha}_s$-, ${\beta}$-, and ${\kappa}$-casein among Murrah, $F_1$ and $F_H$.

• Composites Research
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• 제14권2호
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• pp.1-7
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• 2001

본 논문은 항공기 노스콘(nose cone) 제작에 사용되는 Kevlar/Epoxy 프리프레그의 조성과 경화거동을 연구한 것이다. 이 소재의 경화거동을 dielectrometer와 시차주사열분석기를 사용하여 연구하였다. 이 프리프레그는 $120^{\circ}C$ 부근에서 가장 낮은 이온점도를 보였으며, 이 이후 경화반응의 진행과 함께 점도가 $200^{\circ}C$ 까지는 상승하는 경향을 보여 주었다. 이것은 이 프리프레그의 경화반응이 $120^{\circ}C$ 부근에서 개시됨을 의미하며, 이 온도 이후부터 가속화된 분자간 가교화 반응을 통해서 분자량이 현저히 커짐을 의미한다. 본 프리프레그의 dynamic scan에 따른 loss factor 및 tan $\delta$값을 측정/연구하였는데, 매트릭스의 유동성과 매우 밀접한 관계에 있는 loss factor 거동은 이온점도 거동과 매우 유사하였다. 본 프리프레그의 열반응 특성을 시차주사열분석기를 사용해서 연구하였다.

• 한국식품조리과학회지
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• 제33권3호
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• pp.300-306
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• 2017

Purpose: This study aimed to prepare sea tangle vinegar and test its applicability as a vinegar-based functional salad dressing in terms of physicochemical properties. Methods: Sea tangle vinegar was prepared by mixing sea tangle with sugar and vinegar and fermenting the mixture at room temperature for 3 months. The resulting sea tangle vinegar was examined for its physicochemical properties and antioxidant activity with brewed vinegar and persimmon vinegar as controls. Results: The sea tangle vinegar showed significantly higher viscosity than control vinegars, and shear thinning behavior that is typical for salad dressing containing polymers. In addition, storage modulus (G′) of sea tangle vinegar was relatively high in dynamic viscosity measurement while that of control vinegars remained negligible. Together with the high soluble solids content of sea tangle vinegar, rheological behavior indicates that sea tangle vinegar had soluble polysaccharides extracted from sea tangle, consequently leading to an increase in viscosity. Titratable acidity (TA) and pH were 2.52% and 3.58, respectively, which satisfies the TA and pH requirements for microbiological safety of a salad dressing. Absorbance at 285 nm and Folin Ciocalteu's reagent method revealed that sea tangle vinegar contained antioxidative phenolic compounds. Conclusion: This study demonstrates that sea tangle vinegar could be potentially developed as a vinegar-based functional salad dressing when combined with sensory evaluation in the future.