• Structural Engineering and Mechanics
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• v.7 no.6
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• pp.533-550
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• 1999

Optimal design of raft-pile foundations is examined by combining finite element technique and the optimization approach. The piles and soil medium are modeled by three dimensional solid elements while the raft is modelled by shell elements. Drucker-Prager criterion is adopted for the soil medium while the raft and the piles are assumed to be linear elastic. For the optimization process, the approximate semi-analytical method is used for calculating constraint sensitivities and a constraint approximation method which is a combination of the extended Bi-point approximation and Lagrangian polynomial approximation is used for predicting the behaviour of the constraints. The objective function of the problem is the volume of materials of the foundation while the design variables are raft thickness, pile length and pile spacing. The generalized reduced gradient algorithm is chosen for solving the optimization process. It is demonstrated that the method proposed in this study is promising for obtaining optimal design of raft-pile foundations without carrying out a large number of analyses. The results are also compared with those obtained from the previous study in which linear analysis was carried out.

• Nuclear Engineering and Technology
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• v.53 no.3
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• pp.833-841
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• 2021

During the postulated severe accident of nuclear reactor, eutectic reaction leads to low-temperature melting of fuel cladding and early failure of core structure. In order to model eutectic melting with the moving particle semi-implicit (MPS) method, the eutectic reaction model is developed to simulate the eutectic reaction phenomenon. The coupling of mass diffusion and phase diagram is applied to calculate the eutectic reaction with the uniform temperature. A heat transfer formula is proposed based on the phase diagram to handle the heat release or absorption during the process of eutectic reaction, and it can combine with mass diffusion and phase diagram to describe the eutectic reaction with temperature variation. The heat transfer formula is verified by the one-dimensional melting simulations and the predicted interface position agrees well with the theoretical solution. In order to verify the eutectic reaction models, the eutectic reaction of uranium and iron in two semi-infinite domains is simulated, and the profile of solid thickness decrease over time follows the parabolic law. The modified MPS method is applied to calculate Transient Reactor Test Facility (TREAT) experiment, the penetration rate in the simulations are agreeable with the experiment results. In addition, a hypothetical case based on the TREAT experiment is also conducted to validate the eutectic reaction with temperature variation, the results present continuity with the simulations of TREAT experiment. Thus the improved method is proved to be capable of simulating the eutectic reaction in the severe accident.

• Korean Journal of Food Science and Technology
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• v.41 no.3
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• pp.272-277
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• 2009

In this research, three dimensional mathematical models were developed to predict the shelf life of tofu packaged in a semi-rigid plastic container. A model combining oxygen transfer through the package and oxygen consumption within the package was considered. According to the results, the model simulations estimated that the number of microorganisms in the filled water was higher than that in the tofu, suggesting the shelf life of packaged tofu was not affected by the number of microorganisms in the tofu product, but rather by the number of organisms in the filled water. Additionally, the effects of the physical properties of the packaging material, such as oxygen permeability through the package, oxygen diffusion coefficient, the initial oxygen concentration in the filled water, and the depth of the filled water in the packaged tofu, were also observed.

• Journal of environmental and Sanitary engineering
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• v.14 no.3
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• pp.130-138
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• 1999

The feasibility of municipal sewage sludge digestion was investigated by using thermophilic anaerobic sequencing batch reactor(ASBR). One-day settle time was enough for the high performance of solid-liquid separation. The conversion of semi-continuous mode to sequencing batch mode is easily achieved without any adverse effects, although the large amount of sludge equal to the volume ratio of 0.3~06 to reactor volume was added in the feed step of the start-up. The ASBRs had higher conversion capability of organics to biogas than the control reactor. Gas yields of the ASBRs were increased by the average of 50% over the control reactor across a range of hydraulic retention time(HRT)s from 10days to 5days. The thermophilic reactors showed higher gas production than mesophilic reactor. Removal efficiencies of organic matter exceeded 80% on the basis of supernatants, except that at the reactor. Solid-liquid separation was essential in the performance of the ASBR, especially, at the lower HFT. The ASBRs were highly efficient in the retention of activated biomass within the reactor. thus compensating for increased equivalent organic loading rate through increased solids retention times followed by the increased solids, while maintaining shorter HRTs.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.972-975
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• 2002

An understanding of tribological behavior in CMP(Chemical Mechanical Polishing) is one of the most important things to reveal the mechanism of material removal. In CMP, the contact type is thought to be semi-direct, elastohydrodynamic contact type from the Stribeck diagram, which is a combination of solid-solid direct contact and hydrodynamic lubrication with thin liquid film. This study is focused on the decay of friction force during CMP from two points of view, one of which is change of the real contact area and the other is the decrease of the elastic modulus of the pad caused by the increase of the temperature during CMP Experiments are implemented with elastic modulus measuring system and tool dynamometer. Results show that the decay of friction force during CMP results from the decrease of the real contact pressure working on an abrasive, which is induced by the decrease of elastic modulus of pad caused by the increase of temperature. And, the phenomenon is thought to be happen specially in the case that the weight concentration of abrasive in slurry is small enough.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.667-673
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• 2017

We investigated the temperature uniformity in an anode-supported solid oxide fuel cell, using the open source computational fluid dynamics (CFD) toolbox, OpenFOAM. Numerical simulation was performed in three different flow paths, i.e., co-flow, counter-flow, and cross-flow paths. Gas flow in a porous electrode was calculated using effective diffusivity while considering the effect of interconnect rib. A lumped internal resistance model derived from a semi-empirical correlation was implemented for the calculation of electrochemical reaction. The result showed that the counter-flow path displayed the most uniform temperature distribution.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.272-273
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• 2014

Existing the free-form concrete segments (FCS) mold is produced by state of solid such as steel, wood, Styrofoam that can not be recycled. Using FCS mold result in delay on schedule and decrease of productivity because it consists of irregular curved variety and it requires more time than fixed mold. Thus, FCS mold should be developed which can reduce the costs and also it can be used as semipermanent. The aim of this study is to suggest of flexible mold production process for using the phase change materials(PCM). PCM is maintain that its solid state at low temperature but it changes phase to liquid state by heating. PCM is suitable material for flexible mold due to change of phase in relatively high temperature compare to other phase change materials such as water. Flexible mold is possible that reuse semi-permanently made by PCM. Thus, this study is proposed the process of flexible mold production for using the PCM. The study results will be used as the basic theory for studies on production and installation of FCS.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.496-500
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• 1997

This paper describes an automated system for analyzing the stress intensity factors(SIFs) of three-dimensional (3D) cracks. A geometry model, i.e.a solid containing one or several 3D cracks is defined. Several distributions of local node density are chosen, and then automatically superposed on one another over the geometry model by using the fuzzy knowledge processing. Nodes are generated by the bucketing method, and ten-noded quadratic tetrahedral solid elements are generated by the Delauuay triangulation techniques. The singular elements such that the mid-point nodes near crack fornt are shifted at the quarter-points are automatically placed along the 3D crack front. THe complete finite element (FE) model generated, i.e the mesh with material properties and boundary conditions is given to one of the commercial FE codes, and a stress analysis is performed. The SIFs are calculated using the displacement extrapolation method. To demonstrate practical performance of the present system, a semi- elliptical surface crack in a plate subjected to tension is solved.

• Journal of Korea Foundry Society
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• v.15 no.5
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• pp.514-522
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• 1995

The microstructural evolution with isothermal stirring during semi-solid state processing of hypoeutectic Al-6.2wt%Si alloy was studied. Substructure of the individual primary solid particle in the slurry was investigated through transmission electron microscopy(TEM). Formation of subgrain boundaries on the rheocast Al-6.2wt%Si alloy is observed and the misorientation between the grains is shown typically under 2 degrees by analyzing selected area diffraction (SAD) and convergent beam electron diffraction (CBED) patterns. The existence of high angle grain boundaries are also observed in the alloy. Based upon these observations, mechanisms for the primary particles fragmentation are considered. With isothermal stirring, the dislocation density increases, and the evolution of dislocation cell structure takes place, which is interpreted as a process of achieving uniform deformation by dynamic recovery under applied shear stress.

• Journal of Microbiology
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• v.44 no.3
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• pp.263-268
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• 2006

Pleurotus ostreatus is a widely cultivated white-rot fungus. Owing to its considerable enzymatic versatility p. ostreatus has become the focus of increasing attention for its possible utility in biobleaching and bioremediation applications. Interactions between microorganisms can be an important factor in those processes. In this study, we describe the presence of a bacterial species associated with P. ostreatus strain G2. This bacterial species grew slowly (approximately 30 days) in the liquid and semi-solid media tested. When p. ostreatus was inoculated in solid media containing Tween 80 or Tween 20, bacterial microcolonies were detected proximal to the fungal colonies, and the relevant bacterium was identified via the analysis of a partial 16S rDNA sequence; it was determined to belong to the Burkholderia cepacia complex, but was not closely related to other fungus-isolated Burkholderiaceae. New specific primers were designed, and confirmed the presence of in vitro P. ostreatus cultures. This is the first time that a bacterial species belonging to the B. cepacia complex has been found associated with P. ostreatus.