• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.9
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• pp.907-913
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• 2012

High-order perturbation solutions have been obtained for the simple physical model describing the liquid pool spreading with a continuous spill, and these are shown to improve over first-order perturbation solutions. The non-dimensional governing equations for the model are derived to obtain more general solutions. Non-dimensional parameters are sought as the governing parameters for the non-dimensional equations, and the non-dimensional evaporation rate is used as the perturbation parameter. The results show that the high-order solutions exhibit an improvement over the first-order solutions with respect to the pool volume as well as the spreading radius. In addition, as the order of the perturbation solutions increases, the difference between the numerical solutions and the perturbation solutions is significantly reduced. Finally, it is revealed that the third-order solutions are reasonable because they almost agree with the numerical solutions.

• The Journal of the Acoustical Society of Korea
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• v.29 no.8
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• pp.491-496
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• 2010

Thermoacoustic power generation by a spiral heater in the Rijke tube was analyzed numerically. In the analysis, variables were normalized by the angular frequency of the sound and the thermal diffusivity of the air. The effect of the heater wire diameter d, the spacing between wires P-d, and the air-current velocity $U_0$, upon the power generation was obtained and discussed. When the spacing is broad enough, the normalized velocity is $U_0{\approx}0.8$ and the diameter is $d{\approx}4$ for the maximum power generation. With decrease of the spacing, however, the power generation increases more than 5 times and becomes maximum around $d{\approx}2$, $P-d{\approx}3$. And the velocity $U_0{\approx}0.8$ for the maximum power generation is almost independent of the wire spacing.

• Geotechnical Engineering
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• v.6 no.1
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• pp.43-58
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• 1990

In order to get ultimate pullout resistance of ground anchor, the position of failure surface, normal stress and friction angle on the failure surface should be known. In this study, the position of failure surface is obtained by observing deformation of ground around anchor, and stresses on the anchor surface are analyzed by measuring normal and shear stresses on the anchor surface through model anchor test in plane strain. In addition, the relationship between lateral earth pressure and the position of failure surface is analyzed and the formula for calculating ultimate pullout resistance of anchor is proposed by using non-dimensional coefficient of ultimate pullout resistance.

• Elastomers and Composites
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• v.39 no.1
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• pp.23-35
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• 2004

In this work, effects of hyper-elastic rubber material properties on the indentation load-deflection curve and subindenter deformation are first examined via finite element (FE) analyses. An optimal data acquisition spot is selected, which features maximum strain energy density and negligible frictional effect. We then contrive two normalized functions, which map an indentation load vs. deflection curve into a strain energy density vs. first invariant curve. From the strain energy density vs. first invariant curve, we can extract the rubber material properties. This new spherical indentation approach produces the rubber material properties in a manner more effective than the common uniaxial tensile/compression tests. The indentation approach successfully measures the rubber material properties and the corresponding nominal stress-strain curve.

• Water for future
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• v.29 no.4
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• pp.187-198
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• 1996

A numerical model for unsteady dispersion of horizontal line source in turbulent shear flow is developed. A fractional step finite difference method is used which splits the unsteady two-dimensional advective diffusion equation into the longitudinal advection and the vertical diffusion equations, and solves them alternately for half time intervals by the Holly-Preissmann scheme and the Crank-Nicholson scheme, respectively. The developed numerical model is verified using a semi-analytic solution for steady dispersion in turbulent shear flow. Dispersion of an instantaneous plane source in turbulent shear flow is analyzed using the model. The degree of mixing at the same dimensionless time is almost the same regardless of the friction factor, and the travel distance required to reach a certain degree of mixing is inversely proportional to the square root of the friction factor.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.235-235
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• 2018

홍수 시의 산지하천 만곡부는 2차류 발생과 편수위 상승에 따른 하상세굴 및 홍수범람 위험이 크다. 만곡부 외측에 주로 설치되어 있는 콘크리트 옹벽호안은 표면이 매끄러워 홍수피해를 가중 시킨다. 이러한 피해를 저감시키기 위해 콘크리트 옹벽에 돌출줄눈을 설치하여 유속조감 및 설치효과를 분석한 바 있다. 본 연구에서는 기존에 제안된 직사각형 단면의 돌출줄눈보다 내구성을 추구한 사다리꼴 단면의 돌출줄눈을 제시하여 수리모형 실험을 수행하였다. 수리모형 실험은 개수로 직선수로에서 수로경사 0.0035 조건에서 수로 출구 게이트를 조절하면서 이루어졌다. 모형 돌출줄눈의 조도높이는 3cm로 하였으며, 사다리꼴 밑각은 $45^{\circ}$로 완만한 경우이다. 설치간격은 무차원 돌출줄눈 간격을 기준으로 ?형 조도인 6으로 하였다. 돌출줄눈의 설치 유무에 따라 유량에 따른 수위를 측정하고 유속을 산정하여, 마찰저항의 변화를 파악하였다. 공급유량에 따른 Froude 수는 0.168~0.359 범위였으며, 유량이 증가에 따라 Manning의 조도계수는 감소하였다. Froude 수가 0.25보다 큰 경우 돌출줄눈설치의 조도계수가 미설치보다 큰 것으로 파악되었다. 그러나 사다리꼴 돌출줄눈의 흐름저항효과는 직사각형 돌출줄눈에 비해 상대적으로 작았다. 수로 횡단면의 수위분포에 따르면, 돌출줄눈 설치 측벽 주변에서 흐름저항에 따른 유속감소와 수위상승 효과가 나타나는 것으로 파악되었다. 이번 사다리꼴 돌출줄눈은 흐름저항 효과가 크지 않았기 때문에 사다리꼴 밑각을 조정하여 새로운 단면에 대한 추가적인 실험이 필요할 것으로 보인다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.6
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• pp.393-401
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• 2021

In this paper, we proposed a numerical model based on moment-curvature, to evaluate the resistance of reinforced concrete (RC) members subjected to blast loading. To consider the direct shear failure mode, we introduced a dimensionless spring element based on the empirical direct shear stress-slip relation. Based on the dynamic increase factor equations for materials, new dynamic increase factor equations were constructed in terms of the curvature rate for the section which could be directly applied to the moment-curvature relation. Additionally, equivalent bending stiffness was introduced in the plastic hinge region to consider the effect of bond-slip. To verify the validity of the proposed model, a comparative study was conducted against the experimental results, and the superiority of this numerical model was confirmed through comparison with the analytical results of the single-degree of freedom model. Pressure-impulse (P-I) diagrams were produced to evaluate the resistance of members against bending failure and direct shear failure, and additional parametric studies were conducted.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.3
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• pp.228-234
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• 2012

Two-dimensional hydraulic experiments for wave overtopping under non-breaking wave condition are conducted. The wave overtopping formula for vertical structure is suggested and the results are compared with EurOtop (2007). The relative water depth coefficient (${\gamma}_{kh}$) shows that almost the same coefficient is obtained for certain range (kh > 1.55) regardless of relative water depth, that is, although the relative water depth becomes larger, the relative water depth coefficient is almost same. When the wave steepness becomes larger the wave steepness coefficient decreases. The overtopping formula are expressed by relative freeboard(R) and non-dimensional wave overtopping rate(Q) and this formula has the form of exponential function. In this formula, the effects of wave period on wave overtopping are quantitatively investigated and suggested through the relative water depth coefficient(${\gamma}_{kh}$) and wave steepness coefficient(${\gamma}_s$).

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.669-677
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• 2009

Twenty-four beam specimens were tested to examine the effect of the maximum aggregate size on the shear behavior of lightweight concrete continuous beams. The maximum aggregate size varied from 4 mm to 19 mm and shear span-to-depth ratio was 2.5 and 0.6 in each all-lightweight, sand-lightweight and normal weight concrete groups. The ratio of the normalized shear capacity of lightweight concrete beams to that of the company normal weight concrete beams was also compared with the modification factor specified in ACI 318-05 for lightweight concrete. The microphotograph showed that some unsplitted aggregates were observed in the failure planes of lightweight concrete beams, which contributed to the enhancement of the shear capacity of lightweight concrete beams. As a result, the normalized shear capacity of lightweight concrete continuous beams increased with the increase of the maximum aggregate size, though the increasing rate was lower than that of normal weight concrete continuous beams. The modification factor specified in ACI 318-05 was generally unconservative in the continuous lightweight concrete beams, showing an increase of the unconservatism with the increase of the maximum aggregate size. In addition, the conservatism of the shear provisions of ACI 318-05 was lower in lightweight concrete beams than in normal weight concrete beams.

• Tunnel and Underground Space
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• v.13 no.5
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• pp.389-396
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• 2003

It is shown that the cubic law can be modified regarding the steady-state Navier-Stokes equations by using perturbation approximation method for a sinusoidal aperture variation. In order to adopt the perturbation theory, the sinusoidal function needs to be non-dimensionalized for the amplitude and wavelength. Then, the steady-state Navier-Stokes equations can be solved by expanding the non-dimensionalized stream function with respect to the small value of the parameter (the ratio of the mean aperture to the wavelength), together with the continuity equation. From the approximate solution of the Navier-Stokes equations, the basic cubic law is successfully modified for the steady-state condition and a sinusoidal aperture variation. A finite difference method is adopted to calculate the pressure within a fracture model, and the results of numerical experiments show the accuracy and applicability of the modified cubic law. As a result, it is noted that the modified cubic law, suggested in this study, will be used for the analysis of fluid flow through aperture geometry of sinusoidal distributions.