• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.1 s.71
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• pp.1-13
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• 2006

An analytical procedure to analyze reinforced concrete(RC) beams and columns subject to monotonic and cyclic loadings is proposed on the basis of the layered section method. In contrast to the classical nonlinear approaches adopting the perfect bond assumption, the bond slip effect along the reinforcing bar is quantified with the force equilibrium and compatibility condition at the post cracking stage and its contribution is implemented into the reinforcing. The advantage of the proposed analytical procedure, therefore, will be on the consideration of the bond slip effect while using the classical layered section method without additional consideration such as taking the double nodes. Through correlation studies between experimental data and analytical results, it Is verified that the proposed analytical procedure can effectively simulate the cracking behavior of RC beams and columns accompanying the stiffness degradation caused by the bond slip.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.5
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• pp.1-9
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• 2013

Variable area nozzle, where both throat and exit area vary, is required for optimal expansion and optimal nozzle shape upon operation of after-burner. Steady-state and transient analyses are carried out for each condition with and without afterburner operation and as a function of the location of the nozzle flap. Effects of that nozzle displacement on flow and thrust characteristics are analyzed from numerical results. With variable area nozzle adopted, the combustion field is variable in time, leading to periodically variable thrust. For off-design conditions, flow separation shows up due to over expansion at the flap tips and shock wave does in the nozzle due to under expansion. The undesirable phenomena can be solved by control of variable area nozzle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.7
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• pp.477-484
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• 2016

In a multi-effect solar distiller, a feeding rate of seawater to each effect should be decreased as the effect number is increased. In previous studies, the feed rate of seawater was not reduced evenly between the effects, which is unreasonable, since the thermal energy input of each effect decreases by the same amount. In this work, numerical analysis was carried out in order to elucidate this discrepancy. The results showed that the amount of distillates produced was almost the same for both evenly and unevenly reduced flow rates between the effects. Optimum feed rates of seawater with various energy inputs from exhaust gas heat exchanger were also obtained. The results showed that the optimum feed rate of the first effect increased linearly or reached a steady state depending on the heat flux.

• Transactions of the KSME C: Technology and Education
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• v.3 no.1
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• pp.1-13
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• 2015

In this study, a new dynamic VRF-type heat pump simulation model is proposed which incorporates frosting and defrosting models. Toward this end, a simple frosting model based on the perfect analogy, and lumped system based defrost model, are proposed. Then, frosting and defrosting models are incorporated into a dynamic heat pump model which adopts segment-by-segment local heat exchanger model and map-based variable speed compressor model. Thus, the model can naturally represent locally uneven frosting and defrosting on the heat exchanger surface. Developed simulation model is validated against available experimental data to show good agreement within 10% error for capacity and COP. Finally, developed dynamic heat pump model is applied to annual heating season simulation to show that seasonal COP of heat pump is degraded by 7% due to frosting and defrosting.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.1
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• pp.39-48
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• 2013

This paper develops a 2-D moving least squares(MLS) difference method for Stefan problem by extending the 1-D version of the conventional method. Unlike to 1-D interfacial modeling, the complex topology change in 2-D domain due to arbitrarily moving boundary is successfully modelled. The MLS derivative approximation that drives the kinetics of moving boundary is derived while the strong merit of MLS Difference Method that utilizes only nodal computation is effectively conserved. The governing equations are differentiated by an implicit scheme for achieving numerical stability and the moving boundary is updated by an explicit scheme for maximizing numerical efficiency. Numerical experiments prove that the MLS Difference Method shows very good accuracy and efficiency in solving complex 2-D Stefan problems.

• Journal of the Korean Geotechnical Society
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• v.28 no.9
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• pp.31-45
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• 2012

This study was conducted to estimate the stability of a quay wall in case of wave overtopping under the combined action of an earthquake and tsunami using limit equilibrium method. The tsunami force was calculated by using a numerical program called TWOPM-3D (3-D one-field Model for immiscible TWO-Phase flows). Especially, the wave force acting behind the quay wall after a tsunami wave overtopping was estimated by treating back fill as a permeable material. The stability of the quay wall was assessed for both the sliding and overturning modes under passive and active conditions. The variation in the stability of the quay wall with time was determined by parametric studies, including those for the tsunami wave height, seismic acceleration coefficient, internal friction angle of the soil, wall friction angle, and pore water pressure ratio. When the earthquake and tsunami were considered simultaneously, the tsunami induced wave overtopping increased the stability of the quay wall under the passive condition, but in the active condition, the safety factors decreased.

• KSBB Journal
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• v.21 no.1 s.96
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• pp.11-15
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• 2006

The biological activities of extracts from the fruit, stem, and leaf of Hovenia dulcis were examined. In the batch mode of operation, the fruit, stem, and leaf of Hovenia dulcis were extracted with hot water for 10 hr. The fruit extract of Hovenia dulcis gave the highest activity for decreasing alcohol concentration which was 138% of control. The equilibrium between bioactive compound in the fruit (size : 4 mm) and hot water solution was reached within 6 hr and the recovery was 95% by three-times extraction. The fruit extract of Hovenia dulcis showed significant alcohol decrease in blood and hepatoprotective activity against $CCl_4$-toxicity in rat. The fruit extract significantly inhibited the elevation of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) levels.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.513-520
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• 2005

The uniform truss mechanism is widely accepted as a shear transfer mechanism in reinforced concrete members. However, the uniform truss action cannot be expected when the bond stress distribution is not constant along longitudinal bars. A test method in which only the truss action takes place is developed and conducted to investigate the truss actions under various bond contributions. Based on the experimental results and analysis, the following findings can be obtained: 1) The bond stress distribution depends on the axial compression force, the amount of shear reinforcement and loading conditions. 2) The analysis using the combined truss model consisting of uniform and fan-shape trusses can predict the experimental results

• Korean Chemical Engineering Research
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• v.43 no.3
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• pp.360-365
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• 2005

SMB (simulated moving bed) is a continuous chromatographic process by shifting periodically port position. Binary of mixture, Blue dextran and Orange G, was separated by SMB. These components have unique color individually, that is, Blue dextran is blue and Orange G is orange. It is easy to understand SMB process by observing the shift of color changes in SMB. These components was not adsorbed to stationary phase and isolated by difference of size exclusion factor. Mass transfer coefficient was determined by single pulse test under several flow rate conditions. Operation condition was obtained by standing wave theory and optimized for high purities in extract and raffinate streams. Experiment was performed in open loop 4 zone (2-2-2-2) SMB. There are several advantages in open loop SMB, where extract is product for high purity. It is also easy to control flow rate and monitor experimental state during operation. Experimental, extract and raffinate history is well fitted with simulation results, however, column concentration profile is a little different from simulation results. Purities were 99.5％ for extract and 98.9％ for raffinate and extract and raffinate yields were obtained as 98.9％ and 99.4％ respectively.

• Journal of Energy Engineering
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• v.23 no.2
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• pp.7-12
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• 2014

Molecular simulation was performed to evaluate the possibility of hydrogen storage of carbon nanotubes. The equilibrium state of hydrogen adsorbed on carbon nanotubes was simulated by grand canonical Monte Carlo method at constant temperature and pressure. The interaction energy between hydrogen molecule and carbon nanotube was calculated by Lennard-Jones potential model. According to the interaction energy calculated, more hydrogen molecules were adsorbed on the inside than the outside of nanotubes. Whereas the adsorption strength was higher outside than inside. Adsorption capacity was investigated for various temperature and pressure. The maximum capacity of carbon nanotube for hydrogen storage was 2.5wt% at 200 K and 200 bar.