• Journal of Korea Foundry Society
• /
• v.16 no.6
• /
• pp.550-555
• /
• 1996

A stochastic model, based on the coupling of the finite volume(FV) method for macroscopic heat flow calculation and a two-dimensional cellular automaton(CA) model for treating microstructural evolution was applied-for the prediction of microstructural evolution in squeeze casting. The interfacial heat transfer coefficient at the casting/die interface was evaluated as a function of time using an inverse problem method in order to provide a quantitative simulation of solidification sequences under high pressure. The effects of casting process variables on the formation of solidification grain structures and on the columnar to equiaxed transition of an Al-4.5wt%Cu alloy in squeeze casting were investigated. The calculated solidification grain structures were in good agreement with those obtained experimentally.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.6 no.1
• /
• pp.1-9
• /
• 2006

We introduce our in-house program, NANOCAD, for the modeling and simulation of carrier transport in nanoscale MOSFET devices including quantum-mechanical effects, which implements two kinds of modeling approaches: the top-down approach based on the macroscopic quantum correction model and the bottom-up approach based on the microscopic non-equilibrium Green’s function formalism. We briefly review these two approaches and show their applications to the nanoscale bulk MOSFET device and silicon nanowire transistor, respectively.

• Journal of the Korean Electrochemical Society
• /
• v.8 no.1
• /
• pp.47-54
• /
• 2005

This article covers the fundamentals of stress-induced diffusion, focusing on the theoretical model for hydrogen transport through self-stressed electrode. First, the relationship between hydrogen diffusion and macroscopic deformation of the electrode specimen was briefly introduced, and then it was classified into the diffusion-elastic and elasto-diffusive phenomena. Next, the transport equation for the flux of hydrogen caused simultaneously by both the concentration gradient and the stress gradient was theoretically derived. Finally, stress-induced diffusion was discussed on the basis of the numerical solutions to the derived transport equation under the permeable and impermeable boundary conditions.

• Smart Structures and Systems
• /
• v.15 no.3
• /
• pp.609-625
• /
• 2015

Management of infrastructure stock is essential in sustainability of society, and its analysis and optimization are studied in the light of control system modeling in this paper. At the first part of the paper, cost of stock management is analyzed based on macroscopic statistics on infrastructure stock and economical growth. Stock management burden relative to economy is observed to become larger at low economic growth periods in developed economies. Then, control system modeling of stock management is introduced and by augmenting maintenance actions as control input, dynamic behavior of stock is simulated and compared with existing time history statistics. Assuming steady state conditions, applicability of the model to cross sectional data is also demonstrated. The proposed model is enhanced so that both preventive and corrective maintenance can be included as system inputs, i.e., feedforward and feedback control inputs. Optimal management strategy to achieve specified deteriorated stock level with minimal cost, expressed in terms of preventive and corrective maintenance actions, is derived based on estimated parameter values for corrosion of steel bridges. Relative cost effectiveness of preventive maintenance is shown when target deteriorated stock level is lower.

• Structural Engineering and Mechanics
• /
• v.24 no.2
• /
• pp.181-194
• /
• 2006

The masonry is a complex heterogeneous material and its shear deformation and fracture is associated with very complicated progressive failures in masonry structure, and is investigated in this paper using a mesoscopic mechanical modelling, Considering the heterogeneity of masonry material, based on the damage mechanics and elastic-brittle theory, the newly developed Material Failure Process Analysis (MFPA) system was brought out to simulate the cracking process of masonry, which was considered as a three-phase composite of the block phase, the mortar phase and the block-mortar interfaces. The crack propagation processes simulated with this model shows good agreement with those of experimental observations by other researchers. This finding indicates that the shear fracture of masonry observed at the macroscopic level is predominantly caused by tensile damage at the mesoscopic level. Some brittle materials are so weak in tension relative to shear that tensile rather than shear fractures are generated in pure shear loading.

• Journal of Magnetics
• /
• v.10 no.3
• /
• pp.113-117
• /
• 2005

Some polycrystalline ferromagnetic mms are composed of continuously connected nanometer scale islands with random crystallite orientations. The nanometer perturbations of the mm introduce a large number of nearly degenerate local field configurations that are indistiguishable on a macroscopic scale. As a first step, this situation is modelled as a thin ferromagnetic disc coupled by exchange and dipole interactions to a homogeneous ferromagnetic plane, where the disc and plane have different easy axes. The model is solved to find the partial $N\acute{e}el$ domain walls that minimize the magnetic energy. The two solutions give a bistable configuration that, for appropriate geometries, provides an important microsopic ferromagnetic degree of freedom for the mm. These results are used to interpret recent measurements of exchange biased bilayer films.

• Proceedings of the KSR Conference
• /
• 2007.05a
• /
• pp.1319-1324
• /
• 2007

Many researches have been performed to analyze the smoke movement in tunnel fires by using field model. Recently, FDS(Fire Dynamics Simulator) v.4, which is one of the field model and developed from NIST(National Institute of Standards and Technology), is widely used. In tunnel fires, FDS can show detail results in local point, but it has difficulties in boundary condition and taking long computing time as the number of grid increases. So, there is a need to use alternative method for tunnel fire simulation. A zone model is different kind of CFD method and solves ordinary differential equation based on conservation and auxiliary equations. It shows good macroscopic view in less computing time compared to field model. In this study, therefore, to confirm the applicability of CFAST in tunnel fire analysis, numerical simulations using CFAST are conducted to analyze smoke movement in longitudinal ventilation reduced-scale tunnel fires. Then the results are compared with experimental results. The differences of temperature and critical velocity between numerical results and experimental data are over $30^{\circ}C$ and 0.9m/s, respectively. These values are out of error range. It shows that CFAST 6.0 is hard to be used for tunnel fire simulation.

• Computers and Concrete
• /
• v.21 no.4
• /
• pp.471-484
• /
• 2018

Refined analysis depicting mass transportation and physicochemical reaction and reasonable computing load with acceptable DOFs are the two major challenges of numerical simulation for concrete durability. Mesoscopic numerical simulation for chloride diffusion considering binder, aggregate and interfacial transition zone is unable to be expended to the full structure due to huge number of DOFs. In this paper, a multiscale approach of combining both mesoscopic model including full-graded aggregate and equivalent macroscopic model was introduced. An equivalent conversion of chloride content at the Interfacial Transition Layer (ITL) connecting both models was considered. Feasibility and relative error were discussed by analytical deduction and numerical simulation. Case study clearly showed that larger analysis model in multiscale model expanded the diffusion space of chloride ion and decreased chloride content in front of rebar. Difference for single-scale simulation and multiscale approach was observed. Finally, this paper addressed some worth-noting conclusions about the chloride distribution and rebar corrosion regarding the configuration of rebar placement, rebar diameter, concrete cover and exposure period.

• Computers and Concrete
• /
• v.23 no.1
• /
• pp.69-80
• /
• 2019

Modeling approach for mesoscopic model of concrete depicting mass transportation and physicochemical reaction is important since there is growing demand for accuracy and computational efficiency of numerical simulation. Mesoscopic numerical simulation considering binder, aggregate and Interfacial Transition Zone (ITZ) generally produces huge number of DOFs, which is inapplicable for full structure. In this paper, a three-dimensional multiscale approach describing three-phase structure of concrete was discussed numerically. An effective approach generating random aggregate in polygon based on checking centroid distance was introduced. Moreover, ITZ elements were built by parallel expanding the surface of aggregates on inner side. By combining mesoscopic model including full-graded aggregate and macroscopic model, cases related to diffusivity and thickness of ITZ, volume fraction and grade of aggregate were studied regarding the consideration of multiscale compensation. Results clearly showed that larger analysis model in multiscale model expanded the diffusion space of chloride ion and decreased chloride content in front of rebar. Finally, this paper addressed some worth-noting conclusions about the chloride distribution and rebar corrosion regarding the configuration of, rebar diameter, concrete cover and exposure period.

• Journal of The Korean Association For Science Education
• /
• v.27 no.8
• /
• pp.677-692
• /
• 2007

In this study, university students were provided with repeated opportunities to represent their ideas graphically, and to examined via their drawings the extent to which they could visualize macroscopic phenomena microscopically. These drawings provided insight into the students' basic understanding of solution chemistry, revealing three conceptual models: the Undifferentiated Symbolic Model, the Particulate Model, and the Symbolic Ionic Model. Generally speaking, students who had poor conceptual understanding tended to exhibit the Undifferentiated Symbolic Model, whereas students with deeper understanding tended to employ the Symbolic Ionic Model. Students' conceptual comprehension was predictable from their graphical representations, which better elucidated what they actually comprehended about the phenomena, as opposed to their ambiguous verbal descriptions alone. The results of this study demonstrated a lack of development in university students' conceptions of solutions. Their weakness in understanding at the molecular-level became more obvious when they were asked to represent their ideas in drawings. Few students exhibited expert knowledge, and several common misconceptions were found, which indicated typical difficulties students have perceiving common phenomena at the molecular level. The findings of this study illustrate how eliciting graphical representations can be used to assess students' conceptual understandings.