• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.132-144
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• 1987

This paper presents the theroetical analysis of the crack tip stress intensity factor for a center crack in a finite width plate with variable thickness. The analyses were based on Laurent's expansions of complex stress potentials where the expansion coefficients are determined from the boundary conditions. The perturbation method was employed in numerical calculations. The correction factor F(.lambda.)is given in the form of power series of .lambda. [a numerical formula] where .lambda.=a/w$^{1}$; Dimensionless crack length, .betha.=t$_{2}$/t; Thickness ratio .omega.=w$_{2}$/w$_{1}$; width ratio The correction factor values vary with the width ratio .omega. and the maximum variation occurs around .betha.=1. For the case of .betha.=1 or .betha.=0 (uniform thickness plate0, the correction factor values agree well with Feddersen's formula. In all cases, as .lambda. approaches to 1 (thickness interface), the correction factor values are decreased rapidly for .betha.>1, and increased rapidly for .betha.<1.

• Journal of the Korea Organic Resources Recycling Association
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• v.6 no.2
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• pp.45-57
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• 1998

The object of this experiment was to determine the optimum mixing ratio of paper mill sludge and sewage sludge with woodchips as a bulking agent. The bulking agent was mixed with the mixture of paper mill sludge and sewage sludge(2:1 by dried weight) at the rates of 0(W-0), 20(W-20), 33(W-33), and 50(W-50)% on volume basis, and then the mixtures were composted by forced aerated static pile. The changes of physicochemical properties of the mixtures were measured during the composting in order to evaluate the maturity of composts. The temperatures of W-30 and W-50 treatments increased rapidly as soon as the composting started, and reached $60^{\circ}C$ in the fifth day of composting. Reduction of hot water soluble C/N ratio of W-33 and W-50 treatments showed faster than that of W-0 and W-20 treatments at early stage of the composting. The contents of hot water soluble $NO_3{^-}-N$ showed little change in the early stage of the composting in all treatments, but increased rapidly after 20 days of the composting, and the contents of W-0 among all treatments were lower than the others. The G.I. values of W-50 treatment were over 80 before 20 days after starting the composting, those of W-0 treatment were over 80 after 30 days. As a result of evaluation of compost, W-33 and W-50 treatments were found very reasonable at the mixing ratio of a bulking agent. But it is very difficult to aerate compost pile for W-50 treatment than W-33 treatment due to intensified fluctuation of temperature. Considering cost, availability of a bulking agent, and productivity of compost, W-33 treatments more efficient than W-50 treatment.

• Journal of agriculture & life science
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• v.43 no.6
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• pp.111-115
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• 2009

This study was conducted to develop the ultrasonic dryer because present drying methods (heat convection, microwave, vacuum, etc.) could not improve the drying consumption energy, decrease of quality and drying ratio by physical limitation. The drying tests were conducted with four levels (No. 1 only non-heated air, No. 2 only ultrasonic, No. 3 only heated air and No. 4 ultrasonic with heated air) and measuring weight of samples after drying carrot and ginseng slices for 30 minutes. The result of test is that the drying ratio was highest in the level of No. 4 ultrasonic with heated air. The sliced carrot's drying ratio was 22.4% (w.b.)/h and sliced ginseng's drying ratio was 3.8% (w.b.)/h. The discoloration and twist of samples was appeared on using only heated air like No. 3.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.3
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• pp.1-8
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• 1997

The surface properties after plasma etching of TiW alloy using the chemistries of BCl$_{3}$ and SF$_{6}$ gases with varying mixing ratio have been investigated using XPS(X-ray photoelectron spectrocopy). The elements existed on the etched sampled have been extracted with BCL$_{3}$/SF$_{6}$ ratio and their chemical binding states have also been analysed. It was confirmed that the thickness of native oxide formed on the TiW films is thinner than 10nm by using Ar sputtering. At the same time, the roughness of etched surface has been esamnied using AFM (atomic force microscopy). on the basis of the basis of this results, the relations between the caanges of oxygen contents detected by XPS and the rouhness of etched surface have been discussed. And the etch rate and etched profile of Tiw films have been examined and the changes of the etch rate and etched prfile have been discussed with XPS results. From XPS results, the role of passivation layer consisted of Ti-S compound with XPS results. From XPS results, the role of passivation layer consisted of Ti-S compound has been proposed. Ti-S compound seems to make a role of passivation layer that surpresses Ti-O formation.ion.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.272-272
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• 2014

니켈-텅스텐 합금은 hydrogen evolution reaction의 electrocatalytic으로 이용가능하다. 니켈-텅스텐 합금 도금은 니켈에 비해 큰 텅스텐의 원자 부피에 의해 큰 internal stress를 갖는다. 니켈-텅스텐 합금과 낮은 adhesion을 갖는 물질에 도금을 하여 외부에서 stress를 가하면 큰 표면적을 갖는 니켈-텅스텐 편상 합금을 얻을 수 있다. 도금 시간 및 외부의 stress를 이용하여 다양한 크기의 니켈-텅스텐 편상 합금 분물을 얻을 수 있었다.

• Journal of Industrial Technology
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• v.16
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• pp.45-50
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• 1996

An experimental study os performed to examine the feasibility of using wastes steel furnace slag construction materials and its utility as a replacement for the natural resources to prevent the economic loss was investigated. A half factorial exprements was performed with the variables of W/C ratio, S/A, Coarse aggrigate/Slag ratio and slump as a preliminary study for optimum mix design of concrete. The results show that the W/C ratio and Slump ratio are the most important factor to the concrete strength. The substitute of waste Slag up to 100% has little influence, saying that it can substitute the coarse aggregate without damaging the concrete properties.

• Journal of the Korean Solar Energy Society
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• v.29 no.5
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• pp.73-80
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• 2009

A tidal current turbine is designed and analyzed numerically by using blade element momentum theory. The rated power has a limitation because the diameter of the tidal current turbine cannot exceed the depth of sea water. This study investigates a horizontal axis tidal-current turbine with a rated power of 500 kW. NACA-6 series laminar foil shape is used for basic airfoil along the blade span. The distributions of chord length and twist angle along the blade span are obtained from the hydrodynamic optimization procedure. Prandtl's tip loss correction and angle of attack correction considering the three-dimensional effect are applied for this study. The power coefficient curve shows maximum peak at the rated tip speed ratio of 6.0, and the maximum torque coefficient is developed at the tip speed ratio of 4. The drag coefficient reaches about 0.85 at the design tip speed ratio.

• Journal of the Korea Institute of Building Construction
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• v.4 no.2
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• pp.81-88
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• 2004

The purpose of this study is to investigate the chemical shrinkage and autogenous shrinkage of high strength cement paste and silica fume and fly ash and sand to cement ratio by the method of volumetric tests, and also investigate the autogenous shrinkage of high measurement method, and compare the results of volumetric test and linear length measurement test. A series of cement paste which have W/C ratio of 25%, 35%, 45% respectively were planed to study the effect of the W/C ratio to the shrinkages, and a series of cement paste which were replaced the cement by the silica fume and fly ash with 5%, 10%, 15% as the mass of cement respectively were planed to investigate the effects of poazolana to the shrinkages. A series of mortar which have a C/S ratio of 1:1, 1:1.5, 1:2 respectively were planed to investigate the shrinkage resistant effect of aggregate.

• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1159-1168
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• 1994

We powders were synthesized from W powders in differnet particle sizes by Self-propagating High-temperature Synthesis process (SHS) using a chemical furnace. The effects of the mole ratio of chemical fuel content, pellet thickness and the mole ratio between carbon and tungsten (C/W Ratio) on synthesis were investigated with the tungsten powders have different particle size each other. Compositional and structural characterization of these powders was carried out by scanning electron microscope (SEM0 and x-ray diffractometer. Powder characterization was carried out by the measurement of particle size distribution with laser-particle size analyzer. The amounts of WC obtained by SHS process depend very much on the particle size of tungsten powder and heat contents given in a product, i.e. as the particle size of W powder is smaller, the amounts of WC produced increase. Also the more heat contents is given, the more amounts of WC increase. By optimizing the synthesis conditions, it is possible to fabricate WC powders which have little secondary phases (W2C, C).

• Journal of the Society of Cosmetic Scientists of Korea
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• v.24 no.3
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• pp.129-133
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• 1998

We have studied a relationship between the pattern of complex modulus change versus internal phase volume ratio and the rheological consistency of concentrated W/O emulsions with Magnesium Sulfate in the range 0.0 to 0.5 wt% and with different oil polarities, respectively. The rheological consistency with time of concentrated W/O emulsion was checked using Fudoh Rheometer and the coalescence of deformed water droplets was examined using polarized light microscope(LEICA DMRP). To find the pattern of complex modulus change of the concentrated emulsions versus internal phase volume ratio, the effect of varying water phase volume fraction from 0.78 up to 0.85 on viscoelastic measurements was investigated using rotational rheometer (HAAKE Rheostress RS 50). The rheological consistency was mainly destroyed by the coalescence of the deformed water droplets. The greater the increase of complex modulus was, the less coalescence occurred and the more consistent the concentrated emulsions were. And the pattern of complex modulus increase versus volume ratio has been explained with the resistance to coalescence of the deformed interfacial film of water droplets in concentrated W/O emulsion.