• Journal of the Korean Geotechnical Society
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• v.30 no.11
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• pp.25-37
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• 2014

Clay or sand does not exist alone but various sizes of soil are mixed in the field. In this study, the effect of water content on large deformation of such mixed soils is studied by using soil column tests and a particle method. A soil column with 7 cm in diameter and 13 cm in height, which was made out of kaolinite with sand content of 0, 10, 25, or 50%, was tested for large deformation. Its deformation was monitored with time. While increasing its water content from 40, 60, to 80%, a total of 12 types of soil column tests were carried out. The particle method simulated their deformation with time. A maximum plastic shear modulus, which was a function of undrained shear strength and plasticity index for soils with different water contents, was associated with soil viscosity to simulate large deformation of soil column. When a sand content of soil column was constant, the deformation of soil column increased with increasing water content. When a water content of soil column was constant, large deformation occurred with increasing the sand content. The maximum deformation, which was 22 cm in diameter, was observed in the case of water content of 80% and sand content of 50%. The particle method was able to relatively well simulate such large deformation and stress change of soils.

• Composites Research
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• v.16 no.1
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• pp.1-12
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• 2003

This study developed SiC$_{p}$/A1$_2$O$_3$$_{f}$/Al composites for electronic packaging to which reinforcements were added with the volume fractions of 49%, 56% and 63% by the squeeze casting method. 0.8 wt. % of the inorganic binder as well as the A1$_2$O$_3$ fiber and SiC Particles with the volume fraction of 1:10 were added to the composites, which were produced in the newly designed mold. For the produced SiC/Al composites, the CTEs (coefficients of thermal expansion) were measured from 30 to 300 and compared with the FEM numerical simulation to analyze the temperature dependent properties. The experiment showed the CTEs of SiC$_{p}$/A1$_2$O$_3$$_{f}$/Al composites that were intermediate values of those of Rule of Mixture and Turner's Model. The CTEs were close to Turner's Model in the room temperature and approached the Rule of Mixture as the temperature increases. These properties analyzed from the difference of the average stress acting between the matrix and the reinforcements proposed in this study.

• Journal of Korea Port Economic Association
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• v.27 no.4
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• pp.165-185
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• 2011

Transshipment traffic has significant meanings because it gives positive effects on increasing the container handling volumes in seaports, and revitalizes the regional and national development. Korean container port's transshipment traffic volumes, however, will slowly decrease due to the direct ships' calling into Chinese ports, which recently has a huge development plan. There are a lot of stress on forecasting the transshipment traffic volumes because the Korean container port development plans are designed based on this container traffic which consists of import and export traffic, and transshipment traffic. The transshipment traffic volumes are assumed to occupy 40% of total container traffic volumes. Despite of the importance of forecasting the transshipment traffic, a little studies are suggested using the concepts of the port competitiveness. In this respect, this study aims to estimate the Port Competitiveness Index and Transshipment traffic Volumes using the System Dynamics methodology. As a result, transshipment traffic volumes are predicted as: 20 million TEUs in Korea under the 4% annual increasing rates, 90 million TEUs in China under the 6% annual increasing rates, and 2.5 million TEUs in Japan under the 1% annual increasing rates respectively. The suggested results can be used to enhance the container port competitiveness and produce more transshipment traffic volumes.

• Journal of Sensor Science and Technology
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• v.6 no.5
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• pp.346-355
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• 1997

In this paper, the analyses of the stress disturibution and frequency characteristics of silicon microstructures for an accelerometer were performed using the general purpose finite element simulation program, ANSYS. From the analyses, we determined the parameter values of a new 6-beam piezoresistive accelerometer applicable to the accelerometer's specification in airbag system of automobile. Then, the mass paddle radius, beam length, beam width, and beam thickness of the designed accelerometer were$500{\mu}m$, $350{\mu}m$, $100{\mu}m$, and $5{\mu}m$, respectively and two different seismic masses with 0.4 mg and 0.8 mg were defined on the same sensor structure. The designed 6- beam accelerometers were fabricated on the selectively diffused (111)-oriented $n/n^{+}/n$ silicon substrates and the characteristics of the fabricated accelerometers were investigated. Then, we used a micromachining technique using porous silicon etching method for the formation of the micromechanical structure of the accelerometer.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.55-68
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• 2020

In order to investigate the hydraulic characteristics of a boundary layer streaming over the beach cusps appeared in swells prevailing mild seas, we numerically simulated the shoaling process of Edge waves over the beach cusp. Synchronous Edge waves known to sustain the beach cusps could successfully be duplicated by generating two obliquely colliding Edge waves in front of beach cusps. The amplitude A_B and length L_B of Beach Cusp were elected to be 1.25 m and 18 m, respectively based on the measured data along the Mang-Bang beach. Numerical results show that boundary layer streaming was formed at every phase of shoaling process without exception, and the maximum boundary layer streaming was observed to occur at the crest of sand bar. In RUN 1 where the shortest waves were deployed, the maximum boundary layer streaming was observed to be around 0.32 m/s, which far exceeds the amplitude of free stream by two times. It is also noted that the maximum boundary layer streaming mentioned above greatly differs from the analytical solution by Longuet-Higgins (1957) based on wave Reynolds stress. In doing so, we also identify the recovery procedure of natural beaches in swells prevailing mild seas, which can be summarized such as: as the infra-gravity waves formed in swells by the resonance wave-wave interaction arrives near the breaking line, the sediments ascending near the free surface by the Phase II waves orbital motion were carried toward the pinnacle of foreshore by the shoreward flow commenced at the steep front of breaking waves, and were deposited near the pinnacle of foreshore due to the infiltration.

• Korean Journal of Agricultural and Forest Meteorology
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• v.11 no.3
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• pp.87-99
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• 2009

We evaluated modified Soil-Plant-Atmosphere model's performance to simulate the seasonal variation of net ecosystem exchange (NEE) of carbon and examined the critical controlling mechanism on carbon exchange using the model over a deciduous forest at Gwangnung in 2006. The modified Soil-Plant-Atmosphere (mSPA) model was calibrated to capture the mean NEE during the daytime (1000-1400 LST) and used to simulate gross primary productivity (GPP). Ecosystem respiration ($R_e$) has been estimated using an empirical formula developed at this site. The simulation results indicated that the daytime mean stomatal conductance was highly correlated with daily insolation in the summer. Low stomatal conductance in high insolation occurred on the days with low temperature rather than with high vapor pressure deficit. It suggests that the forest rarely experienced water stress in the summer of 2006. The model captured the observed bimodal seasonal variation with a mid-season depression of carbon uptake. The model estimates of annual GPP, $R_e$ and NEE were $964\;gC\;m^{-2}\;yr^{-1}$, $733\;gC\;m^{-2}\;yr^{-1}$, and $-231\;gCm\;^{-2}\;yr^{-1}$, respectively. Compared to the observed annual NEE, the modeled estimates showed more carbon uptake by about $140\;gC\;m^{-2}\;yr^{-1}$. The uncertainty of the estimate of annual NEE in a complex terrain is discussed.

• Tunnel and Underground Space
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• v.30 no.1
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• pp.39-62
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• 2020

In this study, Barcelona Basic Model (BBM) was implemented into TOUGH2-MP/FLAC3D for the numerical analysis of coupled thermo-hydro-mechanical (THM) behavior of unsaturated soils and the prediction of long-term behaviors. Similar to the methodology described in a previous study for the implementation of BBM into TOUGH-FLAC, the User Defined Model (UDM) of FLAC based on the Modified Cam Clay Model (MCCM) and the FISH function of FLAC3D were used to extend the existing MCCM module in FLAC3D for the implementation of BBM into TOUGH2-MP/FLAC3D. In the developed BBM module in TOUGH2-MP/FLAC3D, the plastic strains due to change in suction increase (SI) in addition to mean effective stress are calculated. In addition to loading-collapse (LC) yield surface, suction increase (SI) yield surface is changed by hardening rules in the developed BBM module. Several numerical simulations were conducted to verify and validate the implementation of BBM: using an example presented in the FLAC3D manual for the standard MCCM, simulation results using COMSOL, and experimental data presented in SKB Reports. In addition, the developed BBM analysis module was validated by simultaneously performing a series of modeling tests that were performed for the validation of the Quick tools developed for the purpose of effectively deriving BBM parameters, and by comparing the Quick tools and Code_Bright results reported in a previous study.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.34-34
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• 2012

Heavy storms rainfall has caused many landslides and slope failures especially in the mountainous area of the world. Landslides and slope failures are common geologic hazards and posed serious threats and globally cause billions in monetary losses and thousands of casualies each year so that studies on slope stability and its failure mechanism under rainfall are being increasing attention of these days. Rainfall-induced slope failures are generally caused by the rise in ground water level, and increase in pore water pressures and seepage forces during periods of intense rainfall. The effective stress in the soil will be decreased due to the increased pore pressure, which thus reduces the soil shear strength, eventually resulting in slope failure. During the rainfall, a wetting front goes downward into the slope, resulting in a gradual increase of the water content and a decrease of the negative pore-water pressure. This negative pore-water pressure is referred to as matric suction when referenced to the pore air pressure that contributes to the stability of unsaturated soil slopes. Therefore, the importance is the study of saturated unsaturated soil behaviors in evaluation of slope stability under heavy rainfall condition. In an actual field, a series of failures may occur in a slope due to a rainfall event. So, this study attempts to develop a numerical model to investigate this failure mechanism. A two-dimensional seepage flow model coupled with a one-dimensional surface flow and erosion/deposition model is used for seepage analysis. It is necessary to identify either there is surface runoff produced or not in a soil slope during a rainfall event, while analyzing the seepage and stability of such slopes. Runoff produced by rainfall may result erosion/deposition process on the surface of the slope. The depth of runoff has vital role in the seepage process within the soil domain so that surface flow and erosion/deposition model computes the surface water head of the runoff produced by the rainfall, and erosion/deposition on the surface of the model slope. Pore water pressure and moisture content data obtained by the seepage flow model are then used to analyze the stability of the slope. Spencer method of slope stability analysis is incorporated into dynamic programming to locate the critical slip surface of a general slope.

• Journal of Korea Water Resources Association
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• v.46 no.5
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• pp.559-568
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• 2013

Surface compaction significantly impacts runoff and soil erosion under rainfall since it leads to changes of soil physical characteristics such as increase of bulk density and shear stress, change of microporosity, and decrease of hydraulic conductivity. This study addressed surface compaction effects on runoff and soil loss from bare and disturbed soils that are commonly distributed on construction sites. Thirty-six rainfall simulations from three replicates of each involving rainfall intensities (68.5 mm/hr, 95.6 mm/hr) and plot gradients ($5^{\circ}$, $12.5^{\circ}$, $20^{\circ}$) were conducted to measure runoff and soil loss for two different soil surface treatments (compacted surface, non-compacted surface). Compacted surface increased significantly soil bulk density and soil strength. However, the effect of surface treatments on runoff changed with rainfall intensity and plot gradient. Rainfall intensity and plot gradient had a positive effect on mean soil loss. In addition, the effect of surface treatments on soil loss responded differently with rainfall intensity and plot gradient. Compacted surfaces increased soil loss at gentle slope ($5^{\circ}$) while they decreased soil loss at steep slope ($20^{\circ}$). These results indicate that there exists transitional slope range ($10{\sim}15^{\circ}$) between gentle and steep slope by surface compaction effects on soil loss under disturbed bare soils and simulated rainfalls.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.302-307
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• 2016

The technology of multistage deep drawing has been widely applied in the metal forming industry, in order to reduce both the manufacturing cost and time. A battery can used for mobile phone production is a well-known example of multistage deep drawing. It is very difficult to manufacture a battery can, however, because of its large thickness to height aspect ratio. Furthermore, the production of the final parts may result in assembly failure due to springback after multistage deep drawing. In industry, empirical methods such as over bending, corner setting and ironing have been used to reduce springback. In this study, a bottoming approach using the finite element method is proposed as a practical and scientific method of reducing springback. Bottoming induces compression stress in the deformed blank at the final stroke of the punch and, thus, has the effect of reducing springback. Different cases of the bottoming process are studied using the finite element program, DYNAFORM, to determine the optimal die design. The results of the springback simulation after bottoming were found to be in good agreement with the experimental results. In conclusion, the proposed bottoming method is expected to be widely used as a practical method of reducing springback in industry.