• 방사성폐기물학회지
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• 제14권1호
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• pp.1-9
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• 2016

In this study, thermal-hydrological-chemical modeling for the alteration of a bentonite buffer is carried out using a simulation code TOUGHREACT. The modeling results show that the water saturation of bentonite steadily increases and finally the bentonite is fully saturated after 10 years. In addition, the temperature rapidly increases and stabilizes after 0.5 year, exhibiting a constant thermal gradient as a function of distance from the copper tube. The change of thermal-hydrological conditions mainly results in the alteration of anhydrite and calcite. Anhydrite and calcite are dissolved along with the inflow of groundwater. They then tend to precipitate in the vicinity of the copper tube due to its high temperature. This behavior induces a slight decrease in porosity and permeability of bentonite near the copper tube. Furthermore, this study finds that the diffusion coefficient can significantly affect the alteration of anhydrite and calcite, which causes changes in the hydrological properties of bentonite such as porosity and permeability. This study may facilitate the safety assessment of high-level radioactive waste repositories.

• 한국디지털건축인테리어학회논문집
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• 제12권4호
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• pp.59-66
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• 2012

This study is interested in identifying the effectiveness of alkali-activated fire protection material compounds including the alkali-activator such as potassium hydroxide, sodium silicate and fly ash as the fire resistant finishing materials. Also, this paper is concerned with change in compressive strength and pore structure of the alkali-activated fire protection material at high temperatures. The testing methods of fire protection materials in high temperature properties are make use of TG-DSC and mercury intrusion porosimetry measurements. This study results show that compressive strength is rapidly degraded depending on a rise of heating temperature. Porosity showed a tendency to increase irrespective of specimen types. This is due to both the outbreak of collapse of gel comprising the cement and a micro crack by heating. However, alkali-activated fire protection material composed of potassium hydroxide, sodium silicate and fly ash has the thermal stability of the slight decrease of compressive strength and porosity at high temperature. These thermal stability is caused by the ceramic binding capacity induced by alkali activation reaction by the reason of the thermal analysis result not showing the decomposition of calcium hydrate.

• 한국화재소방학회논문지
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• 제23권3호
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• pp.103-109
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• 2009

콘크리트의 온도에 의한 재료적 특성에 대한 저감은 두 가지 메커니즘에 기인한다. 첫 번째 메커니즘은 온도범위에 따른 구성성분의 상변화이다. 초기 구성성분들은 온도 증가로 인해 다른 성분들로 상변화를 일으킨다. 두 번째 메커니즘은 온도에 의한 각 구성성분의 역학적 특성 변화이다. 따라서 고온에 노출된 콘크리트의 재료적 특성에 관한 모델 역시 이 두 가지 메커니즘을 함께 고려하여 제시되어야 한다. 본 연구는 위에서 언급한 두 가지 메커니즘을 고려한 고온에 노출된 콘크리트의 재료적 특성 모델을 제안하기 위한 기반연구로서, 온도범위에 따른 상변화를 고려한 경화된 시멘트 페이스트의 공극률에 대한 이론적 모델을 제시한다.

• Structural Engineering and Mechanics
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• 제85권6호
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• pp.717-728
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• 2023

The effect of temperature dependent material properties on the free vibration of FG porous beams is investigated in the present paper. A quasi-3D shear deformation solution is used involves only three unknown function. The mechanical properties which are considered to be temperature-dependent as well as the porosity distributions are assumed to gradually change along the thickness direction according to defined law. The beam is supposed to be simply supported and lying on variable elastic foundation. The differential equation system governing the free vibration behavior of porous beams is derived based on the Hamilton principle. Navier's method for simply supported systems is then used to determine and compute the frequencies of FG porous beam. The results of the present formulation are validated by comparing with those available literatures. Finally, the effects of several parameters such as porosity distribution and the parameters of variable elastic foundation on the free vibration behavior of temperature-dependent FG beams are presented and discussed in detail.

• 한국분말재료학회지
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• 제7권4호
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• pp.237-243
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• 2000

The property and performance of the $Al_2O_3/Ni$ nanocomposites have been known to strongly depend on the structural feature of Ni nanodispersoids which affects considerably the structure of matrix. Such nanodispersoids undergo structural evolution in the process of consolidation. Thus, it is very important to understand the microstructural development of Ni nanodispersoids depending on the structure change of the matrix by consolidation. The present investigation has focused on the growth mechanism of Ni nanodispersoids in the initial stage of sintering. $Al_2O_3/Ni$ powder mixtures were prepared by wet ball milling and hydrogen reduction of $Al_2O_3$ and Ni oxide powders. Microstructural development and the growth mechanism of Ni dispersion during isothermal sintering were investigated depending on the porosity and structure of powder compacts. The growth mechanism of Ni was discussed based upon the reported kinetic mechanisms. It is found that the growth mechanism is closely related to the structural change of the compacts that affect material transport for coarsening. The result revealed that with decreasing porosity by consolidation the growth mechanism of Ni nanoparticles is changed from the migration-coalescence process to the interparticle transport mechanism.

• 대한토목학회논문집
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• 제33권2호
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• pp.573-584
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• 2013

본 연구에서는 유수실 상부 덮개가 있는 케이슨 방파제의 전면벽 유공률 변화에 따라서 전면벽 파압 분포가 어떻게 달라지는지 실험적으로 고찰하였다. 우선 전면벽 유공률이 0인 무공 케이슨에 대해서 파압을 측정하여 이를 Goda(1974)의 파압 분포와 비교하였다. 분석 결과, 계측된 파압분포는 Goda의 파압 공식과 대체로 잘 일치하였으며, 이를 통해서 본 실험에서 파압이 정확하게 측정되었음을 확인하였다. 한편, 유공 케이슨의 경우 전면벽 유공률을 0.2, 0.25, 0.3으로 변화시키면서 실험을 수행하였다. 대부분의 실험 조건에서는 유공률에 따른 전면벽 파압 분포에 차이가 거의 없었던 반면, 비교적 파고 및 주기가 큰 일부 실험파의 경우에는 유공률이 클수록 파압이 근소하게 증가하는 경향이 나타났다. 그러나 전면벽 총파력은 대체로 유공률에 따른 차이가 미미하였다.

• 한국주조공학회지
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• 제12권4호
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• pp.346-354
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• 1992

In Al-Pb monotectic alloys Pb particles are difficult to uniformly distribute over the Al matrix because of the gravity segregation of pb element. Therefore the effects of centrifugally spray casting process on microstructures and distributions of Pb particle were investigated. As the preform thickened the sine of Pb particle became larger, the amount of porosity became lower and microstructures showed the change from spray-deposition microstructures in the lower part of the preform to spray-casting microstructures in the upper part of it. The size of Pb particles, amount of porosity and splat layer boundaries in hot forged preform showed still less than of as-deposited preform.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2004년도 학술.기술논문발표회
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• pp.33-37
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• 2004

Recently, Growing tendency for structure surface to use water repellent agent has increased steadily. But investigation of it's protection and durability property is not sufficient. Therefore, this paper shows the investigation about repellent property and micro structure's change in surface layer of mortar that is applied by water repellent agent. Water repellent property, absorption coefficient, air permeability, porosity and observation of micro construct was investigated according to water repellent agent type. The test results indicated that mortar applied water repellent agent appears tiny absorption coefficient, but air permeability is maintained. The reason is because silane solution is coating at capillary surface of a wall and minute pore structure is changeless.

• Advances in materials Research
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• 제6권1호
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• pp.45-63
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• 2017

In this article, static deflection and buckling of functionally graded (FG) nanoscale beams made of porous material are carried out based on the nonlocal Timoshenko beam model which captures the small scale influences. The exact position of neutral axis is fixed, to eliminate the stretching and bending coupling due to the unsymmetrical material change along the FG nanobeams thickness. The material properties of FG beam are graded through the thickness on the basis of the power-law form, which is modified to approximate the material properties with two models of porosity phases. By employing Hamilton's principle, the nonlocal governing equations of FG nanobeams are obtained and solved analytically for simply-supported boundary conditions via the Navier-type procedure. Numerical results for deflection and buckling of FG nanoscale beams are presented and validated with those existing in the literature. The influences of small scale parameter, power law index, porosity distribution and slenderness ratio on the static and stability responses of the FG nanobeams are all explored.

• 오토저널
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• 제4권3호
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• pp.40-47
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• 1982

Heat transfer on packed bed is considered to be important for the effective designs of chemical reaction equipment, air conditioning system, and storage type heat exchanger, etc. Currently studies are being carried out quite actively in this field in order to increase the heat transfer efficiency. The effect of heat transfer is closely relater to materials, shapes, porosities and packing states of packed bed as well as mutual dimensional relations between particles and the container. Investigation shows that heat transfer results appear to be influenced by such parameters as fluid velocity through packed bed, mass flow, and thermal properties. It is noted that viscosity is also considered to be an important factor in this problem. In this study, effective thermal conductivities on packed bed, effects of thermal conductivity (Ke) and friction factor (Fk) according to change of porosity(.epsilon.) and Reynolds number(Reh(, and pressure loss of the fluid, are experimentally investigated. Results show that the effective thermal conductivity increases and the friction factor decreased, as against the increase of Reynolds number. But as the increase of porosity increase them both.