• Structural Engineering and Mechanics
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• v.64 no.5
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• pp.621-640
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• 2017

This paper reports the numerical investigation conducted to study the influence of Local-Distortional (L-D) interaction mode buckling on post buckling strength erosion in fixed ended lipped channel cold formed steel columns. This investigation comprises of 81 column sections with various geometries and yield stresses that are carefully chosen to cover wide range of strength related parametric ratios like (i) distortional to local critical buckling stress ratio ($0.91{\leq}F_{CRD}/F_{CRL}{\leq}4.05$) (ii) non dimensional local slenderness ratio ($0.88{\leq}{\lambda}_L{\leq}3.54$) (iii) non-dimensional distortional slenderness ratio ($0.68{\leq}{\lambda}_D{\leq}3.23$) and (iv) yield to non-critical buckling stress ratio (0.45 to 10.4). The numerical investigation is carried out by conducting linear and non-linear shell finite element analysis (SFEA) using ABAQUS software. The non-linear SFEA includes both geometry and material non-linearity. The numerical results obtained are deeply analysed to understand the post buckling mechanics, failure modes and ultimate strength that are influenced by L-D interaction with respect to strength related parametric ratios. The ultimate strength data obtained from numerical analysis are compared with (i) the experimental tests data concerning L-D interaction mode buckling reported by other researchers (ii) column strength predicted by Direct Strength Method (DSM) column strength curves for local and distortional buckling specified in AISI S-100 (iii) strength predicted by available DSM based approaches that includes L-D interaction mode failure. The role of flange width to web depth ratio on post buckling strength erosion is reported. Then the paper concludes with merits and limitations of codified DSM and available DSM based approaches on accurate failure strength prediction.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.6
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• pp.63-73
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• 2014

In this study, the large scale test was performed to investigate the behavior of failure on the embankment and spillway transitional zone by overtopping. The pore water pressure, earth pressure, settlement and failure behaviors according to several reinforcing method were compared and analyzed. The pore water pressure showed a small change in the spillway transition zone and core, indicating that the riprap and geotextile efficiently reinforced the embankment, but non-reinforcement showed a largely change in pore water pressure. The earth pressure by riprap and geotextile at upstream slope and bottom core increased rapidly with the infiltration of the pore water by overtopping. And the earth pressure at crest showed a smally change due to effect of the inclined core. A settlement by riprap showed a small change and the geotextile decreased a rapidly due to failure of crest. The width of failure by riprap at intermediate stage (50 min) showed a largely due to sliding of crest. But, the width and depth of the seepage erosion after the intermediate overtopping period (100 min) were very small due to the effect of riprap than geotextile and non-reinforcement which delayed failure. It has the effect that protect reservoir embankment from erosion in the central part. The pore water pressure at the spillway transition zone due to overtopping increased a rapidly in the case of non-reinforcement, but the reinforced methods by geotextile and riprap showed a smally change. Therefore, the reinforced method by riprap and geotextile was a very effective method to protect permanently and the emergency an embankment due to overtopping, respectively.

• Journal of Welding and Joining
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• v.26 no.4
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• pp.85-91
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• 2008

The grooving corrosion is caused mainly by the different microstructures between the matrix and weld which is formed during the rapid heating and cooling cycle in welding. By this localized corrosion reaction of pipes, it evolves economic problems such as the early damage of industrial facilities and pipe lines of apartment, and water pollution. So lots of researches were carried out already about grooving corrosion mechanism of ERW carbon steel pipe but there is seldom study for water hammer happened by fluid phenomenon and corrosion rate by flow velocity. In this study, the analysis based on hydrodynamic and fracture mechanics was carried out. ANSYS, FLUENT and STAR-CD were used for confirmation of flow phenomenon and stress on the pipe. As the results, fatigue failure is able to be happened by water hammer and grooving corrosion rate is increased cause by turbulent. Grooving corrosion is happened on the pipe, then friction loss of fluid is occurred from corroded part. Erosion can be happened enough in corroded region of microscopic size that wear "V" form. Also pipe is able to be damaged by water hammer effects because of corroded region is general acting as a notch effects. Corrosion depth was more than half of total thickness, it can be damaged from water hammer pressure.

• Journal of Ocean Engineering and Technology
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• v.28 no.3
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• pp.236-244
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• 2014

This study considered a seagrass habitat in order to analyze the characteristics of a marine environment of seagrass located in the Seomjin river estuary, through an analysis of the distribution of the water depth, field observation, and three-dimensional numerical experiments using an EFDC model. The seagrass habitat was usually distributed at D.L(-) 0.5~0.0 m, and was hardly seen in the intertidal zone higher than that range. The distribution of the water temperature was within the range of $7.0{\sim}23.2^{\circ}C$, and the seagrass was demonstrated to have a strong tolerance to changes in the water temperature. In addition, the salinity distribution was found to be 27.2~31.0 psu, with suspended solids of 32.1 mg/L, which were higher than the previous research results (Huh et al., 1998), implying that there may be a reduction in the amount of deposits caused by the suspended solids. As for the sedimentary facies, they were comprised of 62.7% sand, 19.1% silt, and 18.2% clay, indicating that the arenaceous was superior and the sedimentary facies were similar to that of Dadae Bay. According to a numerical experiment, the maximum tidal current was 75 cm/s, while the tidal residual current was 10 cm/s, confirming that it sufficiently adapted to strong tidal currents. The erosion and deposition are predicted to be less than 1.0 cm/year. Thus, it is judged that the resuspension of sediments due to tidal currents and the changes in sedimentary facies are insignificant.

• Journal of Soil and Groundwater Environment
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• v.22 no.6
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• pp.94-103
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• 2017

Surface soil is one of the most important resources that have many functions for human needs such as conservation of water resource, purification of contaminated materials, and productivity of food or energy. However, the surface soil is a limited resource that cannot be recovered readily for a long time once it is lost by erosion. In Korea, the Ministry of Environment enacted the notification on the investigation of surface soil erosion and corresponding countermeasures. As the results, database of soil quality assess criteria (biomass, groundwater recharge, habitat, carbon storage, buffer, and soil loss) was established, and the web-based system that can evaluate surface soil conditions was developed. However, non-experts have difficulties in using the system because the system requires in-depth knowledge about soil qualities. In this study, the Web Geographic Information System (GIS) watershed-based surface soil information system was developed to improve usability of the system and accessibility of soil quaility database. The system provides the current condition of surface soil characteristics and GIS-based soil data at selected locations. The users are able to download soil quality data in different districts, watersheds, and special regions allocated by TauDEM module. The system developed in this study would valuable surface soil information for studies of soil quality and its environmental effects, and thereby contributing to establishing more appropriate and robust soil conservation laws.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.2
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• pp.13-23
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• 2019

In this study, an overtopping model experiments and three dimensional seepage characteristics at the deteriorated homogeneous reservoirs were performed to investigate the behavior of failure for embankment and spillway transitional zone due to overtopping. The failure pattern, pore water pressure, earth pressure and settlement by overtopping were compared and analyzed. The pattern of the failure by overtopping was gradually enlarged towards reservoirs crest from the spillway transition zone at initial stage. In the rapid stage and peak stage, the width and depth of failure gradually increased, and the pattern of the failure appeared irregular and several direction of the erosion. In the early stage, the pore water pressure at spillway transitional zone was more affected as its variation and failure width increased. In the peak stage, the pore water pressure was significantly increased in all locations due to the influence of seepage. The earth pressure increased gradually according to overtopping stage. The pore pressure by the numerical analysis was larger than the experimental value, and the analysis was more likely to increase steadily without any apparent variation. The horizontal and vertical displacements were the largest at the toe of slope and at the top of the dam crest, respectively. The results of this displacement distribution can be applied as a basis for determining the position of reinforcement at the downstream slope and the crest. The collapse in the overtopping stage began with erosion of the most vulnerable parts of the dam crest, and the embankment was completely collapsed as the overtopping stage increased.

• Journal of Coastal Disaster Prevention
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• v.4 no.1
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• pp.7-19
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• 2017

In this study, waves and currents observed by acoustic AWAC, VECTOR and Aquadopp Profiler in Anmok coastal waters were analysed to account for the variability of wave and current and to understand the mechanism of sediment transport generated by wave-induced current in the surf-zone. The monthly variation of wave and residual currents were analysed and processed with long-term observed AWAC data at station W1, located at the water depth of about 18m measured during from February 2015 to September 2016. Wave-induced currents were also analysed with intensive field measurements such as wave, current, suspended sediment, and bathymetry data observed at the surf-zone during in winter and summer. The statistical result of wave data shows that high waves coming from NNE and NE in winter (DEC-FEB) are dominant due to strong winds from NE. But in the other season waves coming from NE and ENE are prevalent due to the seasonal winds from E and SE. The residual currents with southeastern direction parallel to the shoreline are dominant throughout a year except in winter showing in opposite direction. The speed of ebb-dominant southeastern residual currents decreasing from surface to the bottom is strong in summer and fall but weak in winter and spring. By analysing wave-induced current, we found that cross-shore current were generated by swell waves mainly in winter with incoming wave direction about $45^{\circ}$ normal to the shoreline. Depending on the direction of incoming waves, longshore currents in the surf-zone were separated to southeastern and northwestern flows in winter and summer respectively. The variation of observed currents near crescentic bars in the surf-zone shows different direction of longshore and cross-shore currents depending on incoming waves implying to the reason of beach erosion generating the beach cusp and sandbar migration during high waves at Anmok.

• Journal of Wetlands Research
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• v.22 no.3
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• pp.194-199
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• 2020

Unlike in the past, the world is facing water shortages due to climate change and difficulties in simultaneously managing the risks of flooding. The Four Major Rivers project was carried out with the aim of realizing a powerful nation of water by managing water resources and fostering the water industry, and the construction period was relatively short compared to the unprecedented scale. Therefore, the prediction and analysis of how the river environment changes after the Four Major Rivers Project is insufficient. Currently, part of the construction section of the Four Major Rivers Project is caused by repeated erosion and sedimentation due to the effects of sandification caused by large dredging and flood-time reservoirs, and the head erosion of the tributaries occurs. In order to solve these problems, the riverbed maintenance work was installed, but it resulted in erosion of both sides of the river and the development of new approaches and techniques to keep the river bed stable, such as erosion and excessive sedimentation, is required. The water agent plays a role of securing a certain depth of water for the main stream by concentrating the flow so much in the center and preventing levee erosion by controlling the flow direction and flow velocity. In addition, Groyne products provide various ecological environments by forming a natural form of riverbeds by inducing local erosion and deposition in addition to the protection functions of the river bank and embankment. Therefore, after reviewing the method of determining the shape of the Groyne structure currently in use by utilizing the mobile limit flow rate and marginal reflux force, a new Critical Movement Velocity(${\bar{U}}_d$) and a new resistance coefficient formula considering the mathematical factors applicable to the actual domestic stream were developed and the measures applicable to Groyne installation were proposed.

• Korean Journal of Environmental Agriculture
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• v.26 no.4
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• pp.343-350
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• 2007

Three different experiments were carried out to investigate the runoff and erosion losses of endosulfan from sloped-field by rainfall. The mobility of endosulfan and which phase it was transported by were examined in adsorption study, the influence of rainfall pattern and slope degree on the pesticide loss were evaluated in simulated rainfall study, and the pesticide losses from soybean-grown field comparing with bare soil were measured in field lysimeter study. Adsorption parameter (K) of endosulfan ranged from 77 to 131 by adsorption method and K values by the desorption method were higher than those by the adsorption method. By the SSLRC's classification for pesticide mobility endosulfan was classified as non-mobile class ($K_{oc}>4,000$). Runoff and erosion loss of endosulfan by three rainfall scenarios ranged from 3.4 to 5.6%and from 4.4 to 15.6%of the amount treated. Endosulfan residues were mainly remained at the top 5 cm of soil depth after the simulated rainfall study. Pesticide loss in case of 30%-slope degree ranged from 0.6 to 0.9 times higher than those in case of 10%-slope degree. The difference of pesticide runoff loss was related with its concentration in runoff water and the difference of pesticide erosion loss would related closely with the quantity of soil eroded. Endosulfan losses from a series of lysimeter plots in sloped land by rainfall ranged from 5 to 35% of the amount treated. The erosion rate of endosulfan from soybean-plots was 66% of that from bare soil plots. The effect of slope conditions was not great for runoff loss, but was great for erosion loss as increasing to maximum $4{\sim}12$ times with slope degree and slope length. The peak runoff concentration of endosulfan in soybean-plots and bare soil plots ranged from 8 to 10 and from 7 to $9{\mu}gL^{-1}$ on nine plots with different slope degree and slope length. Therefore the difference of the peak runoff concentrations between bare soil plots and soybean-plots were not great.

• Journal of Navigation and Port Research
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• v.27 no.5
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• pp.527-537
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• 2003

The characteristics of ship induced waves caused by navigation become widely different from both ship's speed and water depth condition. The ship induced waves specially generated in coastwise routes frequently give rise to call unforeseen danger for swimmers and small boats as well as shoreline erosion or sea wall destruction in coastal zones. The main concern of ship induced wave study until now is either how to reduce ship resistance or how to manoeuvre the ship safely under a constant water depth in the view point of shipbuilding engineers. Moreover, due to the trends for appearance of the high speed ships at the shallow coastal water, we are confronted with the danger of damages from those ship induced waves. Therefore, it is necessary to examine the development of ship induced waves and the influence of their deformation effects according to its propagation ray. In present study, in order to predict the development of the ship induced waves and their propagation under the conditions of complicate and variable shallow water depth with varying ship's speed, we constructed a computer model using Boussinesq equation with a fixed coordinate system and verified the model results by comparison with experimental results. Additionally, the model was applied under the variable water depth based on actual passage and we then confirmed the importance of the variable water depth consideration.