• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.2
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• pp.67-75
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• 2004

This study aims to investigate the dynamic behaviour of a parabolic arch with initial deflection by using the elasto-plastic finite element model where the von-Mises yield criteria have been adopted. The initial deflection of arch was assumed by the high order polynomial of ${\omega}_i$ = ${\omega}_o$${(1-{(2x/L)}^m)}^n$) and the sinusoidal profile of ${\omega}_i$ = ${\omega}_o$$\sin$(n$\pi$x/L). Several numerical examples were tested considering symmetric initial deflection modes when the maximum initial deflection of an arch is fixed as L/500, L/1000, L/2000 or L/5000. The effects of polynomials order on the dynamic behavior of arch were not conspicuous. The most unfavorite dynamic response occurs when the maximum initial deflection varies from L/1000 to L/4000 if the initial deflection mode is represented by high order polynomials.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.5
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• pp.616-624
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• 2011

The flow characteristics and heat transfer augment on the periodically arranged semi-circular ribs in a rectangular channel for turbulent flow has been investigated numerically. The aspect ratio of the rectangular channel was AR=5, the rib height to hydraulic diameter ratio were 0.07 and rib height to channel height ratio was set as e/H=0.117 for various PR(rib pitch-to-rib height rate) between 8~14, respectively. The SST k-${\omega}$ turbulence model and v2-f turbulence model were used to find out the heat transfer and the flow characteristics of near the wall which are suited to obtain realistic phenomena. The numerical analysis results show turbulent flow characteristics, heat transfer enhancement and friction factor as observed experimentally. The results predict that turbulent kinetic energy(k) is closely relative to the diffusion of recirculation flow. and v2-f turbulence model simulation results have a good agreement with experimental values.

• Nutrition Research and Practice
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• v.15 no.4
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• pp.468-478
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• 2021

BACKGROUND/OBJECTIVES: This study aimed to analyze the association between dietary omega-3 fatty acid intake and depression in postmenopausal women using data from the Korea National Health and Nutrition Examination Survey (KNHANES) VI. SUBJECTS/METHODS: The KNHANES is a cross-sectional nationwide health and nutrition survey. Dietary data, including omega-3 fatty acids, were assessed using the 24-h recall method. Depression was evaluated using a survey questionnaire. The association between dietary omega-3 fatty acids and depression was evaluated using multivariate logistic regression analysis. Depression, according to the dietary omega-3 fatty acid intake, was expressed as the odds ratio (OR) with a 95% confidence interval (CI). A total of 4,150 postmenopausal women were included in the analysis. RESULTS: In the fully-adjusted model, the group with the highest dietary omega-3 fatty acid intake significantly showed lower prevalence of depression than the group with the lowest intake (OR, 0.52; 95% CI, 0.33-0.83); a significant linear trend was detected (P for trend = 0.04). According to the dose-response analysis using cubic restricted spline regression, this association was linear and monotonic (P for non-linearity = 0.32). CONCLUSIONS: In this study, the dietary omega-3 fatty acid intake in postmenopausal women was inversely proportional to depression in a dose-response manner. Large cohort studies are needed to verify the causality between omega-3 fatty acids and depression in Korean postmenopausal women.

• Journal of the East Asian Society of Dietary Life
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• v.8 no.2
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• pp.126-136
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• 1998

This study was designed to determine the effects of linoleic acid contents and $\omega$ 6/$\omega$3 ratios on the induction of gastric ulcer by water immersion and restraint stress. Sprague-Dawley rats were fed 5diets containing 7% fat(w/w) for 6weeks. These diet groups were Lh, Mh, Hh, Mm, Ml, : 3 different linoleic acid levels(0.3% of energy(L). 3.5(M), 10(H) and 3 different $\omega$6/$\omega$3 ratios (11(1), 33(m), 100(h) with beef tallow, sunflower or fish oil. The Lh group showed a significantly higher ulcer index (UI) than the Mh and Hh groups(p<0.05). At the same linoleic levels, the UI had no significant difference within the $\omega$6/$\omega$3 ratios. The Mh group showed significantly higher (p<0.05) PGE2 and TBX2 content than any other group. Pearson's correlation coeffcients between UI and PGE2 and TBX2 had a negatively significant correlation(p<0.05). Linoleic acid of gastric mucosal phospholipids was reflected by the diet, but was not significantly different. The most significant finding of this study is that not only the absolute amount of linoleic acid, but also the $\omega$6/$\omega$3 ratios are important factors for the prevention of gastric ulcer.

• International Journal of Aerospace System Engineering
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• v.2 no.2
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• pp.67-72
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• 2015

The main concern of this study is to integrate the EARSM into an industrial RANS solver in conjunction with the $k-{\omega}$ model, as proposed by Hellsten (EARSMKO2005). In order to improve the robustness, particular limiters are introduced to turbulent conservative variables, and a suitable full-approximation storage (FAS) multi-grid (MG) strategy is designed to incorporate turbulence model equations. The present limiters and MG strategy improve both robustness and efficiency significantly but without degenerating accuracy. Two discretization approachs for velocity gradient on cell interfaces are implemented and compared with each other. Numerical results of a three-dimensional supersonic square duct flow show that the proper discretization of velocity gradient improves the accuracy essentially. To assess the capability of the resulting EARSM $k-{\omega}$ model to predict complex engineering flow, the case of Common Research Model (CRM, Wing-Body) is performed. All the numerical results demonstrate that the resulting model performs well and is comparable to the standard two-equation models such as SST $k-{\omega}$ model in terms of computational effort, thus it is suitable for industrial applications.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.3
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• pp.252-261
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• 2016

A spar-type floating substructure that is being widely used for offshore wind power generation is vulnerable to resonance in the heave direction because of its small water plane area. For this reason, the stable dynamic response of this floating structure should be ensured by accurately identifying the resonance characteristics. The purpose of this study is to analyze the characteristics of the combination resonance between the excitation frequency of a regular wave and natural frequencies of the floating substructure. First, the nonlinear equations of motion with two degrees of freedom are derived by assuming that the floating substructure is a rigid body, where the heaving motion and pitching motions are coupled. Moreover, to identify the characteristics of the combination resonance, the nonlinear term in the nonlinear equations is approximated up to the second order using the Taylor series expansion. Furthermore, the validity of the approximate model is confirmed through a comparison with the results of a numerical analysis which is made by applying the commercial software ANSYS AQWA to the full model. The result indicates that the combination resonance occurs at the frequencies of ${\omega}{\pm}{\omega}_5$ and $2{\omega}_{n5}$ between the excitation frequency (${\omega}$) of a regular wave and the natural frequency of the pitching motion (${\omega}_{n5}$) of the floating substructure.

• Journal of The Korean Astronomical Society
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• v.28 no.1
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• pp.61-65
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• 1995

We discuss a model4-dimensional Friedmann cosmology which may have evolved from a model of 4+D dimensions which admits spontaneous compactification of D dimensions (or N-dimensional variants of the Brans-Dicke (BD) theory). The BD parameter appearing in dimensional reduction is negative $-1<\omega<0$ (for the N-dimensional variants of the BD theory, $-1.5{\leq}{\omega})$. We find that if there had been inflationary transtion to the standard big-bang model, the Universe can undergoe a polar-type expansion during when the gravitational coupling becomes negative. The unique feature is that for the negative w, the density parameter of the post-inflationary Universe falls in a range 0<0<1 even if the Universe is geometrically flat (k = 0).

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.603-608
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• 2000

The characteristics of laminar and turbulent slot impinging jet flows are examined using segregated FEM with SUPG. Turbulent flows are modeled using $Wilcox^{(1)}$ $k-\;{\omega}$ turbulence model. The results are validated by comparing with velocity field of the existing experimental data. The distance of the target plate from the nozzle varies between 2, 4 and 5 times the slot jet width. Present study shows that the $k-\;{\omega}$ model gives results which agree well with the existing experimental data. In turbulence flows, the velocity profile of present calculation is more accurate than the existing numerical calculations. In laminar flows, We found tertiary vortex which was not found in the previous numerical study by M. $chen^{(6)}$ et al due to the numerical difference.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.420-427
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• 2011

In this study, numerical simulations of transonic aircraft configurations are performed with various turbulence models and the effect of turbulence models on flow separation are examined. A three-dimensional RANS code and three turbulence models are used for the study. The turbulence models incorporated to the code include Menter's ${\kappa}-{\omega}$ model, Coakley's $q-{\omega}$, and Huang and Coakley's ${\kappa}-{\omega}$, model. Using the code, numerical simulations of DLR-F6 configurations obtained from AIAA CFD Drag Prediction Workshop are conducted. Flow separations on the wing-body juncture and the wing lower surface near pylon are observed. and flow features of the regions are compared with experimental data and other numerical results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.173-174
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• 2006

In this paper we proposed transient model for NPT(Non Punch-Through) IGBT(Insulated Gate Bipolar Transistor) with gate resistances. As gate resistance increases, turn-off time increases. But If gate resistance is small, overshoot voltage increase. To analyze the effect of gate resistance, the transient model is made and the experiments are conducted. We used gate resistances of values; 8[$\Omega$], 140[$\Omega$], 810[$\Omega$] for simulations and experiments. We compared theoretical and experimental results and obtained good agreements.