• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.2
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• pp.100-107
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• 1998

Diamond wheels with fine grains and multi-porous structures are newely trial developed for smoothing and mirror finishing materials. Grinding wheel must have performed both to remove tool marks efficienitly and to contact elastically with curved surfaces, that are employed for ultra precision and high performance grinding of difficult-to materials such as tungsten carbide alloy using tool and die materials, Diamond grains are bonded by a melamine resin to prevent the decrease of machining efficiency due to grain sinking within the bond materials. Also, highly foamed structures are developed to increase the flexibility of the grinding wheel, and to induce self-sharpening by increasing contact pressure between the grinding wheel and workpiece surfaces. In this paper, melamine-bonded diamond wheels try to manufacture, then the forming method of grinding wheel are suggested, and the grinding characteristics of melamine-bonded diamond grinding wheel are also illustrated.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.315-318
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• 2002

Light emitting thin film structures based on organic luminophors embedded in porous alumina matrixes are discussing. The optical properties of the luminophors in a matrix differ greatly from their properties in usual crystalline state or in a solution and they depend on the concentration of luminophors molecules of up to 10-2 mol/l. Successful experiments on filling of pores with organic luminophors and the investigation of their luminescent and optical properties were carried out.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.185-191
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• 2003

A numerical study on the hydrodynamic properties of a floating flexible breakwater consisting of triple vertical porous membrane structures attached to a floating rigid pontoon restrained by moorings is carried out in the context of two-dimensional linear wave-flexible body interaction theory. The tensions in the triple membranes are achieved by hanging a clump weight from its lower ends. The clump weight is also restrained properly by moorings. The dynamic behavior of the breakwater was described through an appropriate Green function, and the fluid multi-domains are incorporated into the boundary integral equation. Numerical results are presented which illustrate the effects of the various wave and structural parameters on the efficiency of the breakwater as a barrier to wave action. It is found that the wave reflection and transmission properties of the structures depends strongly on the membrane length taking major fraction of water column, the magnitude of tensions on membrane achieving by the clump weight, proper mooring types and stiffness, the permeability on the membrane dissipating wave energy.

• Coupled systems mechanics
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• v.3 no.1
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• pp.53-71
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• 2014

Accurate prognoses of the durability of concrete structures require a detailed description of the continuously running aging processes and a consideration of the complete load history. Therefore, in the framework of continuous porous media mechanics a model is developed, which allows a detailed analysis of the most important aging processes of concrete as well as a flexible coupling of different processes. An overview of the prediction model and the balance equations is given. The material dependent model equations, the consequences of coupling different processes and the solution scheme are discussed. In two case studies the aging of concrete due to hydration and chloride penetration are presented, which illustrate the capabilities and the characteristics of the developed model.

• Nuclear Engineering and Technology
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• v.56 no.2
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• pp.636-643
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• 2024

The coolability of the debris bed with a simulant of solidified corium is experimentally studied, focusing on the effects of the structure of the axial stratified debris bed on the dryout heat flux (DHF). DHF was obtained for the four structures with different particle sizes for the axial stratified debris bed under top flooding. The experimental results show that the dryout position of the axial stratified debris bed is formed at the stratified interface indicated by the temperature rise, and the DHF of the axial stratified bed is much lower than that of the homogeneous bed packed with the upper small particles. To predict the dryout heat flux of the stratified debris beds, by considering the properties of the mixed area, a one-dimensional dryout heat flux model of the porous medium is derived from a water and vapor momentum equation for porous medium, two-phase permeability modifications, interfacial drag, and the correlation between capillary pressure and liquid saturation and verified with the experimental data. The modified model can give reasonable results under different structures.

• 한국방재학회:학술대회논문집
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• 2009.02b
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• pp.87.2-87.2
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• 2009

• Polymer(Korea)
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• v.39 no.1
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• pp.151-156
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• 2015

Herein, novel porous structures were fabricated from monomer solutions of dimethylsiloxane and benzene by directional crystallization in twice. First, a honeycomb-like structure was fabricated by $1^{st}$ directional crystallization of solvent. By infiltration of the solution and subsequent $2^{nd}$ directional crystallization, novel structures of different pores in the honeycomb-like structure were fabricated. The porous materials prepared by the repeated directional crystallization have higher indentation modulus and hardness than those of the samples prepared by single directional crystallization. When a higher solution concentration was used in $2^{nd}$ directional crystallization, the maximum increase (indentation modulus: 2140% increase, indentation hardness: 2330% increase) was obtained. On the other hand, porosity and contact angle were lower in the samples from $2^{nd}$ directional crystallization than those from $1^{st}$ directional crystallization. A large decreases was observed, when a relatively high concentration was used in $2^{nd}$ directional crystallization (porosity: 21% decrease, contact angle: 36% decrease).

• Nuclear Engineering and Technology
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• v.47 no.4
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• pp.398-406
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• 2015

In this study, R-123 flow boiling experiments were carried out to investigate the effects of nanoparticle deposition on heater surfaces on flow critical heat flux (CHF) and boiling heat transfer. It is known that CHF enhancement by nanoparticles results from porous structures that are very similar to layers of Chalk River unidentified deposit formed on nuclear fuel rod surfaces during the reactor operation period. Although previous studies have investigated the surface effects through surface modifications, most studies are limited to pool boiling conditions, and therefore, the effects of porous surfaces on flow boiling heat transfer are still unclear. In addition, there have been only few reports on suppression of wetting for decoupled approaches of reasoning. In this study, bare and $Al_2O_3$ nanoparticle-coated surfaces were prepared for the study experiments. The CHF of each surface was measured with different mass fluxes of $1,600kg/m^2s$, $1,800kg/m^2s$, $2,100kg/m^2s$, $2,400kg/m^2s$, and $2,600kg/m^2s$. The nanoparticle-coated tube showed CHF enhancement up to 17% at a mass flux of $2,400kg/m^2s$ compared with the bare tube. The factors for CHF enhancement are related to the enhanced rewetting process derived from capillary action through porous structures built-up by nanoparticles while suppressing relative wettability effects between two sample surfaces as a highly wettable R-123 refrigerant was used as a working fluid.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.6
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• pp.491-497
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• 2017

In recent years, 3D printing has received increasing attention due to its potential for direct fabrication beyond the traditional rapid prototyping. 3D printing has the advantage of being able to manufacture complicated shapes that were thought impossible to produce by traditional manufacturing processes. This advantage has driven applications of 3D printing to direct manufacturing of functional parts, such as lightweight structures and component integration. In this study, a porous shell structure is designed for the purpose of weight reduction and ventilation. Finite element (FE) analyses are performed to compare the effective stiffness of the porous structure with the conventional solid structure. Structural reinforcements are also considered in order to make up the stiffness reduction due to the porosity, and the relevant FE analyses are performed to investigate the effect of the reinforcement design on the bending stiffness. The optimized reinforced structure is then proposed through response surface analysis.

• Korean Journal of Materials Research
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• v.31 no.9
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• pp.502-510
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• 2021

Hierarchically porous carbon materials with high nitrogen functionalities are extensively studied as high-performance supercapacitor electrode materials. In this study, nitrogen-doped porous carbon textile (N-PCT) with hierarchical pore structures is prepared as an electrode material for supercapacitors from a waste cotton T-shirt (WCT). Porous carbon textile (PCT) is first prepared from WCT by two-step heat treatment of stabilization and carbonization. The PCT is then nitrogen-doped with urea at various concentrations. The obtained N-PCT is found to have multi-modal pore structures with a high specific surface area of 1,299 m² g^-1 and large total pore volume of 1.01 cm³ g^-1. The N-PCT-based electrode shows excellent electrochemical performance in a 3-electrode system, such as a specific capacitance of 235 F g^-1 at 1 A g^-1, excellent cycling stability of 100 % at 5 A g^-1 after 1,000 cycles, and a power density of 2,500 W kg^-1 at an energy density of 3.593 Wh kg^-1. Thus, the prepared N-PCT can be used as an electrode material for supercapacitors.