• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.711-716
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• 2002

When judging the ground by core-logging, depth of coring might be stopped by coming into view of the moderately weathered rock and also considered as bedrock line. However, highly weathered rock may appear again, if coring more, because there are core-stones in the residual soil and highly weathered rock by the effect of hydraulic-thermal differentiation and does the irregular rock weathering or metamorphic rock region. Therefore, there are room for misunderstanding of diagnosing the moderately weathered rock. Even though the irregular ground where the corestones were come out will show clear geotechnical differences between the ground and the gradually weathered bedrock, nowadays, the construction sites do not take into account the characteristic of core-stone region. In conclusion, to study the failure-strength characteristics of soil layers containing core-stones, we made artificial core-stones and varied percentage of corestones, and measured cohesion and friction factors to adjust them to construction sites containing corestones such as slope, tunnel, and underground.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.137-147
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• 2013

It is essential to understand the hydraulic characteristics of rivers for increasing flood-control capacity and operating hydraulic structures efficiently. Multi-dimensional models can be the proper measures to obtain the detailed information on the hydraulic characteristics of rivers. But huge amount of data and time-consuming work have been the obstacle for applying multi-dimensional models. In this study, simulation technique with multi-dimensional model(EFDC), coupled with COSFIM and FLDWAV, has been developed and applied to the real river system for verification. Developed technique can offers spatial and grid unit information as well as line and section unit information from 1-D modeling. It is considered that the coupling simulation technique can provide useful hydraulic information for river management and treatment.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.3
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• pp.107-115
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• 2009

The labyrinth weir can be applied to increase the overflow rate, maintain constant water depth and improve water quality. This weir can be defined that the plane shape of overflow part is not straight line and is a kind of weir having overflow length increased by changing its plane shape. There are relatively few studies related to effect of maintaining the water depth which has been used to consider for various functions as hydraulic facilities and design conditions of labyrinth weirs. Thus, it is needed to conduct studies related to the maintenance of water depth by the labyrinth weir. This study was to provide fundamental data which may become a facilitator for more accurate and proper design of hydraulic facilities related to the maintenance of water depth. The ranges of constant water depth ($H_t/P=0.08\sim0.27$) were provided for the triangle type labyrinth weir, and the effect of maintaining water depth was analyzed using hydraulic laboratory experiments and 3D-numerical simulations(Flow-3D).

• Wind and Structures
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• v.26 no.5
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• pp.267-277
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• 2018

Numerical simulations are performed of a long flexible cylinder undergoing vortex-induced vibration at a Reynolds number of 500. The cylinder is pinned at both ends, having an aspect ratio of 100 (cylinder length to cylinder diameter) and a mass ratio of 4.2 (structural mass to displaced fluid mass). Temporal and spatial information on the cross-flow (CF) and in-line (IL) vibrations is extracted. High modal vibrations up to the $6^{th}$ in the CF direction and the $11^{th}$ in the IL direction are observed. Both the CF and IL vibrations feature a multi-mode mixed pattern. Mode competition is observed. The $2^{nd}$ mode with a low frequency dominates the IL vibration and its existence is attributed to a wave group propagating back and forth along the span. Distributions of fluid force coefficients are correlated to those of the CF and IL vibrations along the span. Histograms of the x'-y motion phase difference are evaluated from the total simulation time and a complete vibration cycle representing the standing or travelling wave pattern. Correlations between the phase difference and the vibrations are discussed. Vortex structures behind the cylinder show an interwoven near-wake pattern when the standing wave pattern dominates, but an oblique near-wake pattern when the travelling wave pattern prevails.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.2
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• pp.106-113
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• 1987

The Alaska pollack longline operations, which consist of baiting, shooting, hauling and arrangement of hooks, are dependant on manual labour up to the present. The automation against this traditional way is necessary to eliminate the manual operations and to reduce crew. We have developed a prototype longline system suitable for Alaska pollack longline gear, which is composed of an automatic baiting machine, an automatic line hauler, a hook cleaner and storage rails. The automatic bailing machine driven by hydraulic power is precise baiting method controlled sequentially, and the automatic line hauler is to haul up the mainline by means of hydraulic power and at the same time to split every hook and to carry it onto storage rail automatically. A series functioning tests on shooting and hauling apparatus were carried out in the laboratory and at sea. The results obtained are as follows ; 1. As for the baiting machine, the exciting time of solenoid which operates a directional valve, bait feeding and cutting time, is shortened according to the increase of pressure, and also, after cutting the bait, the over-rotated angle of the blade increased in accordance with the increase of pressure. 2. The baiting efficiency is about $90\%$ when using sand lance (Hypoptychus dybowskii), and the most proper pressure of the hydraulic circuit in feeding and cutting the bait is between $13\;kgf/cm^2\;and\;20\;kgf/cm^2$. 3. The hook splitting rate of the automatic line hauler is about $95.5\%$ regardless of hauling speed and materials of snood. 4. The case of unseparating hook is appeared when the snood gets entangled or the hook is sticked in the mainline.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.04a
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• pp.167-172
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• 2002

Seoul subway system has been constructed to solve traffic difficulties of Seoul metropolitan, and now is the major public transportation. However, the more line has added in the system the deeper the bottom of the tunnel base. And a huge amount of groundwater along the line has seeping into the tunnel. Several subway stations has pumping system to extract the groundwater to the outside and consequently, groundwater table along the line has declined gradually. Groundwater table has dropped about 40 meters at some areas, There was some study for the proper usage of the abstracted groundwater and the project to use the groundwater has launched already by the local government. However. more serious problem is expected on quality degradation of soil and groundwater as the decline of groundwater table along the subway line. This study suggests that the detailed groundwater environmental study should be made as soon as possible for this. If there is any pollution leaking at the surface area of the groundwater depression, the pollution will be seep into the subway tunnel in some day even though the time will be different with the soil material and hydraulic characteristics of the aquifer. And the polluted area of the soil and groundwater would be enlarged along the pathway The study on possibility of the soil subsidence and reducing surface water flow in small creek were also needed. This study suggest one of the counter measurement that restoring the declined groundwater table after groundwater environmental study

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.2
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• pp.3-14
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• 2004

This study was conducted to assess the possibility of the field application of the iceharbor-type precast fishway. When overflow depth of weir is 4.0 cm in model fishway, upper part velocities appear appropriate for upstream migration of fish and the lowest overflow wall (right line) in lower part has shown velocity distribution more or less inadequate for upstream migration. Except that right line, left and middle line revealed that velocities are appropriate for upstream migration of fish. Therefore, we concluded that this fishway owing to be not broad growth width of overflow velocities according to increasing discharges can correspond to variation of water level. Also We consider that various velocities in fishway were effective, because slow velocity line can guide flow for upstream migration. For low flow, the arrangement of different crest level or each overflow part (higher left, middle and lower right, or lower left, middle and higher right) was more effactive than unform crert level. Hole plays an important role as migration pass during drought and flood flow. Therefore, We concluded that this fishway can cope with water depth variation by various overflow wall height change and raise the field applicability with better performance hydraulically and structurally.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.208-216
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• 2004

The waterhammer occured when the pumps are started or stopped for the operation or tripped due to the power failure, the hydraulic transients occur as a result of the sudden change in velocity. The field tests of the waterhammer were carried out for PanGyo booster pumping station. The PanGyo pumuing station was installed booster pump of 6 sets and in-line pump of 2 sets. The main surge suppression device was equipped with the pump control valve and the surge relief valve as auxiliary. However, the pump control valve had not early controlled in the planned closing mode, and the slamming occurred to the valve of which abruptly closed during the large reverse flow. Because the pressure wave caused by the pump failure was superposed on the slam surge, the upsurge increased so extremely that the shaft of the valve was damaged. After the addition surge suppression device was equipped with air chamber. Further more in-line pump is needed surge suppression device that the pumping station acquired the safety and reliability for the pressure surge.

• Nuclear Engineering and Technology
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• v.53 no.3
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• pp.1029-1040
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• 2021

For the structural integrity evaluation of pressurized water reactor (PWR) steam generator (SG) tubes subjected to transient hydraulic loading, determination of the tube-to-tube gap velocity and static pressure distributions along the tubes is prerequisite. This paper addresses both computational fluid dynamics (CFD) and analytical approaches for predicting the tube-to-tube gap velocity and static pressure distributions during blowdown following a feedwater line break (FWLB) accident at a PWR SG. First of all, a comparative study on CFD calculations of the transient velocity and pressure distributions in the SG secondary sides for two different models having 30 or no tubes is performed. The result shows that the velocities of sub-cooled water flowing between any adjacent two tubes of a tubed SG model during blowdown can be roughly estimated by applying the specified SG secondary side porosity to those of the no-tubed SG model. Secondly, simplified analytical approximate solutions for the steady two-dimensional SG secondary flow velocity and pressure distributions under a given discharge flowrate are derived using a line sink model. The simplified analytical solutions are validated by comparing them to the CFD calculations.

• The Journal of Engineering Geology
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• v.18 no.4
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• pp.415-422
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• 2008

Pumping test was conducted to understand hydraulic conductivity for leaky confined aquifer with high permeability. Test aquifer was formed in $25{\sim}35\;m$ below ground surface at predetermined site of riverbank filtration which junction of Nakdong river and Milyang river in the Ttaan isle, Gimhae city, Korea Monitoring wells were located at intervals of 2 m and 5 m from pumping well in south-west direction (MW1 and MW2 wells) and northeast direction (MW3 and MW4 wells), respectively. Pumping test was continuously conducted for constant pumping rate of $2,500m^3/day$, hydraulic conductivity was estimated using AQTESOLV 3.5 program. Hydraulic conductivity were estimated to be $1.745{\times}10^{-3}m/sec$ for pumping well (PW), $2.452{\times}10^{-3}m/sec$ for between PW and MW1 wells, $2.161{\times}10^{-3}m/sec$ for between PW and MW2 wells, $2.270{\times}10^{-3}m/sec$ for between PW and MW3 wells and $2.591{\times}10^{-3}m/sec$ for between PW and MW4 wells. The function of hydraulic conductivity (K) as monitoring distance (d) were estimated to be logK = 0.0693logd - 2.671 for south-west direction (PW-MW1-MW2 line), logK = 0.0817logd - 2.655 for north-east direction (PW-MW3-MW 4 line). Scale exponent of hydraulic conductivity as test volume was estimated using Schulze-Makuch et al.(1999) method. Scale exponent of this aquifer was estimated to be 0.15. It means that test aquifer has very low heterogeneity. The radius of influence estimated using transmissivity, maximum groundwater level displacement, distance from pumping well and pumping rate during pumping test were 7.148 m for south-west direction and 6.912 m for north-east direction. The increasing rate of hydraulic conductivity from pumping well to maximum radius of influence were estimated to be 1.40 times for south-west direction and 1.49 times for north-east direction. Thus, heterogeneity of test aquifer was a little higher in north-east direction.