• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.11
• /
• pp.205-212
• /
• 2018

In order to overcome shortcomings of commercial analysis program for solving certain geotechnical problems, finite element method adopting isoparametric quadrilateral element was selected as a tool for analyzing soil behavior and calculating process was programmed. Two examples were considered in order to verify reliability of the developed program. One of the two examples is the case of acting isotropic confining pressure on finite element and the other is the case of acting shear stress on the sides of the finite element. Isoparametric quadrilateral element was considered as the finite element and displacements in the element can be expressed by node displacements and shape functions in the considered element. Calculating process for determining strain which is defined by derivatives using global coordinates was coded using the Jacobian and the natural coordinates. Four point Gauss rule was adopted to convert double integral which defines stiffness of the element into numerical integration. As a result of executing analysis of the finite element under isotropic confining pressure, calculated stress corresponding to four Gauss points and center of the element were equal to the confining pressure. In addition, according to the analyzed results for the element under shear stress, horizontal stresses and vertical stresses were varied with positions in the element and the magnitudes and distribution pattern of the stresses were thought to be rational.

• Korean Journal of Remote Sensing
• /
• v.36 no.6_3
• /
• pp.1643-1652
• /
• 2020

To investigate the characteristics of detailed flows in a building-congested district, we coupled a computation fluid dynamics (CFD) model to the local data assimilation and prediction system (LDAPS), a current operational numerical weather prediction model of the Korea Meteorological Administration. For realistic numerical simulations, we used the meteorological variables such as wind speeds and directions and potential temperatures predicted by LDAPS as the initial and boundary conditions of the CFD model. We trilinearly interpolated the horizontal wind components of LDAPS to provide the initial and boudnary wind velocities to the CFD model. The trilinearly interpolated potential temperatures of LDAPS is converted to temperatures at each grid point of the CFD model. We linearly interpolated the horizontal wind components of LDAPS to provide the initial and boundary wind velocities to the CFD model. The linearly interpolated potential temperatures of LDAPS are converted to temperatures at each grid point of the CFD model. We validated the simulated wind speeds and directions against those measured at the PKNU-SONIC station. The LDAPS-CFD model reproduced similar wind directions and wind speeds measured at the PKNU-SONIC station. At 07 LST on 22 June 2020, the inflow was east-north-easterly. Flow distortion by buildings resulted in the east-south-easterly at the PKNU-SONIC station, which was the similar wind direction to the measured one. At 19 LST when the inflow was southeasterly, the LDAPS-CFD model simulated southeasterly (similar to the measured wind direction) at the PKNU-SONIC station.

• Journal of the Korean earth science society
• /
• v.43 no.3
• /
• pp.386-404
• /
• 2022

From April 29 to 30, 2011, under the influence of Asian dust originated from Mongolia, a high concentration of Asian dust was observed nationwide for 4 days in Korea. This study investigated the causes and characteristics of and weather conditions associated with Asian dust at high concentrations at its source in Mongolia. For analysis, Asian dust weather data, Asian dust monitoring tower data, satellite data, backward trajectory data, observation data (PM₁₀ and OPC data), and ECMWF reanalysis data were used. In the synoptic analysis, it was observed that the intervals of isobars were densely distributed in the central region of Mongolia and the pressure gradient force was strong. It could be inferenced that Asian dust occurred due to strong winds. The temperature was relatively high, above 10℃, just before the occurrence of Asian dust, and it decreased sharply at the onset of the dust. The relative humidity had a low value of less than approximately 40%. After the occurrence of Asian dust, it increased sharply to over 50% and then showed a tendency to decrease. In the aerosol index shown by the COMS satellite, a high concentration value of over 25 was detected in Inner Mongolia, and it was consistent with the observations made with naked eyes. In the 72-hour backward trajectory, the northwest airflow streamed into Korea, and on May 2, Heuksando showed the highest PM₁₀ concentration of 1,025 ㎍ m^-3(times the average). Especially, in kinematic vertical analysis, it was observed that low pressure on the ground was strengthened by cyclonic relative vorticity developed in the upper layer. Also, the vertical velocity development is considered to have played a major role in the occurrence of high concentration Asian dust.

• Journal of the Korean Geotechnical Society
• /
• v.25 no.11
• /
• pp.105-115
• /
• 2009

The Jeju sand was sampled from the beach in Jeju Island and its basic properties were analyzed. The cementation effect of Jeju coastal sediments was evaluated from in-situ tests such as SPT, CPT, and the Suspension-PS test. It was shown from test results that the Jeju sand has high extreme void ratios due to the angularity of grains and the intra-particle voids of hollow particles, similar to typical calcareous sands. From cone penetration test in the calibration chamber, it was found that the cone resistance($q_c$)-relative density($D_R$)-vertical effective stress(${\sigma}_v'$) relation of Jeju sand almost matches that of high compressible quartz sand. However, the $q_C-D_R-{\sigma}_v'$ correlation suggested for uncemented Jeju sand overestimates the relative density of coastal sediments of Jeju Island due to the cementation effect. From the analysis of the relation of cone resistance, N value, and small strain shear modulus measured in-situ, it seems reasonable to assume that the coastal sediment of Jeju Island is a naturally cemented one.

• Journal of the Korean Geotechnical Society
• /
• v.25 no.10
• /
• pp.99-110
• /
• 2009

In order to provide the design criteria, the characteristics of consolidation for soft ground improvement have been investigated using the field banking test performed by the vertical drain method at the northern container section in Busan New Port. Field test results indicated that the estimated degree of consolidation in design stage decreased by about 7% compared with the measured one. This difference is attributed to the fact that the conservative geological properties were applied with relatively high amount of maximum clay mixture ratio during the design stage. Based on this findings, another laboratory oedometer test was implemented to consider various combination of mixture ratio. It was found that the consolidation degree increased in accordance with the increase of sand/silt mixture ratio. Also, the proportion of 10%, 50%, and 40% for sand, silt, and clay, respectively, was observed as the best combination of mixture ratio to the actual measurement, which is very similar to the average grain size distribution in the banking test area. Therefore, it is suggested that the overall geological characteristics as well as the grain size distribution should be considered in design stage to improve the soft ground that contains mixture of sand, silt, and clay.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.30 no.1B
• /
• pp.89-100
• /
• 2010

The performance evaluation of a conventional Wave Resonator at the entrance of harbors against solitary wave has been performed using 3D numerical wave flume. A wave resonator has been designed for the attenuation of the transmitted wave energy by trapping the short periodic incident waves only. In this study, however, the controlled performance of the wave resonator by its various widths has been numerically investigated for solitary waves. Source distribution method based on the Green function and the 3D one-field Model for immiscible TWO-Phase flows (TWOPM-3D) using 3D numerical wave flume were used for the short-periodic waves and the solitary waves, respectively, and these models were verified through the comparisons with the previous experimental and numerical results by other researchers. It was confirmed that the wave resonator is effective enough to control the solitary waves as well as the periodic waves when it compares with the case of no resonance system. Further, it was found that there is the optimal width of a wave resonator to attenuate the target solitary waves.

• Journal of Environmental Impact Assessment
• /
• v.32 no.6
• /
• pp.473-487
• /
• 2023

Korea's multi-purpose dams, which were constructed in the 1970s and 1980s, have a single outlet located near the bottom for hydropower generation. Problems such as freezing damage to crops due to cold water discharge and an increase the foggy days have been raised downstream of some dams. In this study, we analyzed the effect of water intake depth on the reservoir's water temperature stratification structure and outflow temperature targeting Hapcheon Reservoir, where hypolimnetic withdrawal is drawn via a fixed depth outlet. Using AEM3D, a three-dimensional hydrodynamic water quality model, the vertical water temperature distribution of Hapcheon Reservoir was reproduced and the seasonal water temperature stratification structure was analyzed. Simulation periods were wet and dry year to compare and analyze changes in water temperature stratification according to hydrological conditions. In addition, by applying the intake depth change scenario, the effect of water intake depth on the thermal structure was analyzed. As a result of the simulation, it was analyzed that if the hypolimnetic withdrawal is changed to epilimnetic withdrawal, the formation location of the thermocline will decrease by 6.5 m in the wet year and 6.8 m in the dry year, resulting in a shallower water depth. Additionally, the water stability indices, Schmidt Stability Index (SSI) and Buoyancy frequency (N²), were found to increase, resulting in an increase in thermal stratification strength. Changing higher withdrawal elevations, the annual average discharge water temperature increases by 3.5℃ in the wet year and by 5.0℃ in the dry year, which reduces the influence of the downstream river. However, the volume of the low-water temperature layer and the strength of the water temperature stratification within the lake increase, so the water intake depth is a major factor in dam operation for future water quality management.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.35 no.6
• /
• pp.128-137
• /
• 2023

In this study, the bearing pressure on the rubble mound of a gravity-based harbor structure with an arbitrarily shaped bottom was targeted. Assuming that the bottom of the structure is a rigid body, the rubble mound was modeled as a linear spring uniformly distributed on the bottom that resists compression only, and the bearing pressure evaluation formula was derived. It was confirmed that there were no errors in the derivation process by showing that when the bottom was square, the derived equation was converted to the equation used in the design. In addition, the validity of the derived equation was proven by examining the behavior and convergence value of the bearing pressure when an arbitrarily shaped bottom converges into a square one. In order to examine the adequacy of the method used in the current design, the end bearing pressure for the pre-designed breakwater cross-section was calculated and compared with the values in the design document. As a result, it was shown that the method used for design was not appropriate as it gave unsafe results. In particular, the difference was larger when the eccentricity of the vertical load was large, such as in the case of extreme design conditions.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.17 no.3
• /
• pp.227-235
• /
• 2015

Using eddy covariance method, net ecosystem exchange (NEE) of $CO_2$ ($F_{CO_2}$), $H_2O$ (LE), and sensible heat (H) can be approximated as the sum of eddy flux ($F_c$) and storage flux term ($F_s$). Depending on strength and distribution of sink/source of scalars and magnitude of vertical turbulence mixing, the rates of changes in scalars are different with height. In order to calculate $F_s$ accurately, the differences should be considered using scalar profile measurement. However, most of flux sites for agricultural lands in Asia do not operate profile system and estimate $F_s$ using single-level scalars from eddy covariance system under the assumption that the rates of changes in scalars are constant regardless of the height. In this study, we measured $F_c$ and $F_s$ of $CO_2$, $H_2O$, and air temperature ($T_a$) using eddy covariance and profile system (i.e., the multi-level measurement system in scalars from eddy covariance measurement height to the land surface) at the Chengmicheon farmland site in Korea (CFK) in order to quantify the differences between $F_s$ calculated by single-level measurements ($F_s_{-single}$ i.e., $F_s$ from scalars measured by profile system only at eddy covariance system measurement height) and $F_s$ calculated by profile measurements and verify the errors of NEE caused by $F_s_{-single}$. The rate of change in $CO_2$, $H_2O$, and Ta were varied with height depending on the magnitudes and distribution of sink and source and the stability in the atmospheric boundary layer. Thus, $F_s_{-single}$ underestimated or overestimated $F_s$ (especially 21% underestimation in $F_s$ of $CO_2$ around sunrise and sunset (0430-0800 h and 1630-2000 h)). For $F_{CO_2}$, the errors in $F_s_{-single}$ generated 3% and 2% underestimation of $F_{CO_2}$ during nighttime (2030-0400 h) and around sunrise and sunset, respectively. In the process of nighttime correction and partitioning of $F_{CO_2}$, these differences would cause an underestimation in carbon balance at the rice paddy. In contrast, there were little differences at the errors in LE and H caused by the error in $F_s_{-single}$, irrespective of time.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.10 no.3
• /
• pp.155-166
• /
• 2007

We carried out a study on the marine environment, such as water temperature, salinity, density and chlorophyll ${\alpha}$, and the distribution of phytoplankton community, such as species composition, dominant species and standing crops in the Southwestern Sea of Korea during early summer 2005. According to the analysis of a T-S diagram, three characteristics of water masses were identified. We classified them into Korean and Chinese coastal water, the cold water and the oceanic water. The first was characterized by high temperature and low salinity in the surface layer influenced by river run offs from China and Korea, the second by low temperature and salinity in bottom layer originated from the bottom cold water of the Yellow Sea, and the third by high temperature and high salinity influenced by Tsushima warm currents. The internal discontinuous layer among them was formed at the intermediate depth (about $10{\sim}20\;m$ layer). And the thermal front appeared in the central parts between Tsushima warm currents and Korean and Chinese coastal waters in the Southwestern Sea of Korea. Chlorophyll ${\alpha}$ concentration was high values in the Korean coastal waters and sub-surface layers. But It was low concentration in the Tsushima warm currents regions. The $Chl-{\alpha}$ maximum layers appeared in the sub-surface layer below thermocline. The phytoplankton community in the surface and stratified layers was composed of a total of 40 species belonging to 26 genera. Dominant species were 2 diatoms, Paralia sulcata, Skeletonema costatum and a dinoflagellate, Scripsiella trochoidea. Standing crops of phytoplankton in the surface layer were very low with cell density ranging from 5 to $3.8\;{\times}\;10^3\;cells/L$. Diatoms were controlled by the expanded low salinity coastal waters of the low salinity with high concentrations of nutrients. Otherwise phytoflagellates were dominant in the high temperature regions where the Tsushima warm currents approches the Southwestern Sea of Korea in early summer.