• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.10-16
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• 1996

This study is aimed for investigating a decision of the saturated surface dry of crushed stone sand and measuring the moisture with increasing percentage of VFS(Very Fine Sand) replacement each crushed stone sand. The results indicated that moisture of crushed stone sand is generally increased with increasing percentage of VFS replacement and the rate of increase of moisture is about 30% every time that VFS replacement increases 3.5%. Also the saturated surface dry for crushed stone sane is proposed as a point of time where shape of flow-cone first slumps in this paper.

• Geomechanics and Engineering
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• 제2권1호
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• pp.29-44
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• 2010

Vertical vibration tests were conducted using model footings of different size and mass resting on the surface of finite sand layer with different height to width ratios which was underlain by either rigid concrete base, under both dry and saturated condition. The effect of saturation on the damping ratio of finite sand stratum underlain by a rigid base has been verified and compared with the results obtained for the case of finite dry sand stratum underlain by the rigid base. Comparison of results of the experimental study showed that the damping in both the cases is less than 10%. The damping ratio obtained for finite saturated sand stratum is marginally lower than that obtained on finite dry sand stratum at H/B ratio of 0.5. The difference between the two cases becomes significant when the H/B ratio increases to 3.0, indicating the significant influence of soil moisture on damping ratio of foundation- soil system with increase in the thickness of the finite sand stratum. Comparison of the predicted damping ratio for a homogeneous sand stratum with the experimental damping ratio obtained corresponding to the height to width ratio of 3.0 of the finite sand stratum underlain by the rigid concrete base indicates a significant reduction in damping ratio of the foundation-soil system for both the cases.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.153-156
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• 2005

Surface dry condition examination method on the KS F 2504(Testing method for specific gravity and absorption of fine aggregate) has dim detail prescriptions which can cause different ways of understanding based on one's convinence, not on correct means of rule. So we investigate the problems about the inconsistency on decisioing surface dry condition at management examination in the lab and scene. In conclusion, free-falling method is easier and faster than self-weight method. And we also found that the most important face on decisioning surface dry is compacting factor of tamping rod.

• Structural Engineering and Mechanics
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• 제68권4호
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• pp.443-457
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• 2018

In this article, a comparative study has been made to investigate the scattering behaviour of three layered structure model on torsional surface wave. For such model intermediate layer is taken as fiber reinforced composite, resting over a dry sandy Gibson substratum and underlying by different anelastic media. We consider two distinct mediums for topmost layer. In the first case, topmost layer has been taken as fluid saturated homogeneous porous layer, while in the second case the fluid saturated porous layer has been replaced by a transversely isotropic layer. Simple form expression for the secular equation of torsional surface wave has been worked out in both the cases by executing specific boundary conditions, which comprises Whittaker's function and its derivative, for imminent result that have been elaborated asymptotically. Some special cases have been constituted which are in excellent compliance with recorded literatures. For the sake of comparative study, numerical estimation and graphical illustration have been accomplished to identify the effects of the width ratio of the layers, Biot's gravity parameter, sandy parameter, porosity parameter and other heterogeneity parameters corresponding to the layers and half spaces, horizontal compressive and tensile initial stress on the phase velocity of torsional surface wave.

• Earthquakes and Structures
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• 제11권1호
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• pp.83-107
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• 2016

In this study, the response and behavior of machine foundations resting on dry and saturated sand was investigated experimentally. A physical model was manufactured to simulate steady state harmonic load applied on a footing resting on sandy soil at different operating frequencies. Total of (84) physical models were performed. The parameters that were taken into consideration include loading frequency, size of footing and different soil conditions. The footing parameters are related to the size of the rectangular footing and depth of embedment. Two sizes of rectangular steel model footing were used. The footings were tested by changing all parameters at the surface and at 50 mm depth below model surface. Meanwhile, the investigated parameters of the soil condition include dry and saturated sand for two relative densities; 30 % and 80 %. The dynamic loading was applied at different operating frequencies. The response of the footing was elaborated by measuring the amplitude of displacement using the vibration meter. The response of the soil to dynamic loading includes measuring the stresses inside soil media by using piezoelectric sensors. It was concluded that the final settlement (St) of the foundation increases with increasing the amplitude of dynamic force, operating frequency and degree of saturation. Meanwhile, it decreases with increasing the relative density of sand, modulus of elasticity and embedding inside soils. The maximum displacement amplitude exhibits its maximum value at the resonance frequency, which is found to be about 33.34 to 41.67 Hz. In general, embedment of footing in sandy soils leads to a beneficial reduction in dynamic response (displacement and excess pore water pressure) for all soil types in different percentages accompanied by an increase in soil strength.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제19권2호
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• pp.197-215
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• 2015

Modeling water flow in variably saturated, porous media is important in many branches of science and engineering. Highly nonlinear relationships between water content and hydraulic conductivity and soil-water pressure result in very steep wetting fronts causing numerical problems. These include poor efficiency when modeling water infiltration into very dry porous media, and numerical oscillation near a steep wetting front. A one-dimensional finite element formulation is developed for the numerical simulation of variably saturated flow systems. First order backward Euler implicit and second order Crank-Nicolson time discretization schemes are adopted as a solution strategy in this formulation based on Picard and Newton iterative techniques. Five examples are used to investigate the numerical performance of two approaches and the different factors are highlighted that can affect their convergence and efficiency. The first test case deals with sharp moisture front that infiltrates into the soil column. It shows the capability of providing a mass-conservative behavior. Saturated conditions are not developed in the second test case. Involving of dry initial condition and steep wetting front are the main numerical complexity of the third test example. Fourth test case is a rapid infiltration of water from the surface, followed by a period of redistribution of the water due to the dynamic boundary condition. The last one-dimensional test case involves flow into a layered soil with variable initial conditions. The numerical results indicate that the Crank-Nicolson scheme is inefficient compared to fully implicit backward Euler scheme for the layered soil problem but offers same accuracy for the other homogeneous soil cases.

• 조명전기설비학회논문지
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• 제29권1호
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• pp.64-69
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• 2015

This study investigates the Horizontal surface discharge characteristics of solid insulators by varying their materials, and the dew-point of dry-air. The methodology of this study is that a quasi-uniform field is first applied to a test chamber. Then, the chamber is filled with dry-air as an insulation gas which pressure is varied from 1 to 6atm while applying an AC voltage to the chamber. The used solid insulators are teflon, polyethlene and polyurethane. As the dew-point is lower and the pressure of dry-air is higher, the flashover voltage of all solid insulators increases more. When each characteristic of the solid insulators is compared under the same gas pressure, the flashover voltage of teflon is the highest. Then, the flashover voltage of polyethlene is higher than that of polyurethane. Moreover, it is observed that the flashover voltage increases as the horizontal distance between the electrodes of each solid insulator become larger, respectively. However, as the pressure is increased, flashover voltage of the solid insulators is saturated. Therefore, selection of cost-effective insulation is needed in order to appropriate pressure.

• 설비공학논문집
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• 제16권3호
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• pp.203-210
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• 2004

This paper describes the potential advantages in applying evaporative cooling to air-cooled condensers. The cooling characteristics of an air-cooled condenser with its surface fully covered with thin water film are investigated and compared with that of an air-cooled condenser with usual dry surface. By applying the evaporative cooling, the cooling performance of the condenser is shown to improve enormously. When the outdoor air is 35$^{\circ}C$ and 40% in relative humidity, the condensing temperature of the refrigerant is decreased by 2$0^{\circ}C$. Even when the incoming air is fully saturated with water vapor, the evaporation from the wet surface occurs to cause a decrease in the condensing temperature by 1$0^{\circ}C$. The main reason for this improvement is assessed as the addition of an efficient cooling mechanism which is the water evaporation resulting in latent heat absorption.

• 터널과지하공간
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• 제18권3호
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• pp.219-225
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• 2008

고준위폐기물처분장의 설계 및 장기 성능평가를 위한 입력자료를 확보하기 위해, 한국원자력연구원 지하처분연구시설 부지에서 실시된 경사시추에서 얻은 암석 코어를 이용하여 화강암의 열전도도를 측정하였다. 측정을 위한 시료는 다양한 지표면으로부터의 심도에서 채취되었으며, 건조 조건과 물로 포화된 조건에서 열전도도가 측정되었다. 건조 조건에서 화강암의 열전도도는 공극률이 증가함에 따라 감소하였으며, 2.1 W/mK에서 3.1 W/mK 사이의 범위에 있었다. 동일 암석 코어에서 얻은 화강암 시료에 대해 포화 조건에서 측정된 화강암의 열전도도는 건조 조건에서 특정된 값보다 큰 값을 나타내어 2.9 W/mK에서 3.6 W/mK 사이의 범위에 있었다. 조사부지 내 화강암의 열전도도에 대한 이방성의 영향은 작은 것으로 나타났다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권9호
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• pp.616-621
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• 1999

A planar inductively coupled $CH_4/H_2/Ar$plasma was used to investigate dry etch characteristics of GaN as a function of input power, RF bias power, and etch gas composition. Etch rate of GaN increased with input power up to 600 W and was saturated at the higher power. Also, the etch rates increased with increasing RF bias power, composition of $CH_4$ and Ar gas. We achieved the maximum etch rate of $930{\AA}$/min at the input power 400 W, RF bias power 250 W, and operational pressure 10 mTorr. This paper shows that smooth etched surface having roughness less than 1 nm in rms can be obtained by using planar inductively coupled plasma with $CH_4/H_2/Ar$ gas chemistry.