• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.8
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• pp.711-719
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• 2016

In this study, we derived an theoretical equation, using a simplified spring-mass model for the rolling stock, to obtain the overriding behavior of a leading vehicle, which is considered as the main factor in train accidents. To verify the derived equation, we created a simple 2D model based on the theoretical model, and a simple 3D model considering the characteristics of the power bogie. We then compared the theoretical results with the simulation results obtained using LS-DYNA. The maximum relative derivations in the vertical displacements at the first end-buffer, which is the most important point in overriding, were 3.5 [%] and 1.7 [%] between the two results. Further, we evaluated collision-induced overriding displacements using the theoretical equation for a rubber draft gear, a hydraulic buffer under various collision conditions. We have suggested a theoretical approach for the realization of overriding collision accidents or the energy absorption design of the front end of trains.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.2-11
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• 2006

In the processes of hydrological cycle, when precipitation reaches the ground surface, water may become surface runoff or infiltrate into soil and then possibly further percolate into groundwater aquifer. A part of the water is returned to the atmosphere through evaporation and transpiration. Soil moisture dynamics driven climate fluctuations plays a key role in the simulation of water transfer among ground surface, unsaturated zone and aquifer. In this study, a one-layer canopy and a four-layer soil representation is used for a coupled soil-vegetation modeling scheme. A non-zero hydraulic diffusivity between the deepest soil layer modeled and groundwater table is used to couple the numerical equations of soil moisture and groundwater dynamics. Simulation of runoff generation is based on the mechanism of both infiltration excess overland flow and saturation overland flow nested in a numerical model of soil moisture dynamics. Thus, a comprehensive hydrological model integrating canopy, soil zone and aquifer has been developed to evaluate water resources in the plain region of Huaihe River basin in East China and simulate water transfer among precipitation, surface water, soil moisture and groundwater. The newly developed model is capable of calculating hydrological components of surface runoff, evapotranpiration from soil and aquifer, and groundwater recharge from precipitation and discharge into rivers. Regional parameterization is made by using two approaches. One is to determine most parameters representing specific physical values on the basis of characterization of soil properties in unsaturated zone and aquifer, and vegetations. The other is to calibrate the remaining few parameters on the basis of comparison between measured and simulated streamflow and groundwater tables. The integrated modeling system was successfully used in the Linhuanji catchment of Huaihe plain region. Study results demonstrate that (1) on the average 14.2% of precipitation becomes surface runoff and baseflow during a ten-year period from 1986 to 1995 and this figure fluctuates between only 3.0% in drought years of 1986, 1988, 1993 and 1994 to 24.0% in wet year of 1991; (2) groundwater directly deriving from precipitation recharge is about 15.0% t of the precipitation amount, and (3) about half of the groundwater recharge flows into rivers and loses through evaporation.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.3
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• pp.304-311
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• 2014

In this study, to apply hydrogen energy to ship engine and to generate effective hydrogen production, we investigated the effects of high temperature $H_2SO_4$ feed rate and cooling water rate to pump parts with fixed frequency needed to reciprocate motion and a simulation was conducted at each condition. In the fixed frequency and cooling water inlet flow rate of 0.5 Hz and 3.9 kg/s, we changed the high temperature $H_2SO_4$ flow rate to 47.46 kg/s (it is 105 % of 45.2 kg/s), 49.72 kg/s (110 %), and 51.98 kg/s (115 %). Also, at 0.5 Hz and 45.2 kg/s of frequency and high temperature $H_2SO_4$ flow, the thermal hydraulic analysis was performed at the condition of 95 % (3.705 kg/s), 90 % (3.51 kg/s), and 85 % (3.315 kg/s). In overall simulation cases, the physical properties of materials are more influential to the temperature increase in the pump part rather than the changes on the feed rate of high temperature $H_2SO_4$ and cooling water. A continuous operation of pump was also capable even if the excess feed of high temperature $H_2SO_4$ of about 15 % or the less feed of cooling water of about 15 % were performed, respectively. When the increasing feed of high temperature $H_2SO_4$ of up to 5 %, 10 %, and 15 % were compared with base flow (45.2 kg/s), the deviation of time period rose to a certain temperature and ranged from 0 to 4.5 s in the same position (same material). In case of cooling water, the deviation of time period rose to a certain temperature and ranged from 0 to 5.9 s according to the decreasing feed changes of cooling water at 5 %, 10 %, and 15 % compared to a base flow (3.9 kg/s). Finally, the additional researches related to the two different materials (Teflon and STS for Pitch and End-plate), which are concerned about the effects of temperature changes to the parts contacting different materials, are needed, and we have a plan to conduct a follow-up study.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.3
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• pp.143-149
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• 2012

Groundwater flow simulations were performed to obtain data of groundwater flow used in a safety assessment for a hypothetical geological disposal facility assumed to be located in the KURT (KAERI Underground Research Tunnel) site. A regional scale modeling of the groundwater flow system was carried out to make boundary conditions for a local scale modeling. And, fracture zones identified at the study site were involved in the local scale groundwater flow model. From the results of the local scale modeling, a hydraulic head distribution was indicated and it was used in a particle tracking simulation for searching pathway of groundwater from the location of the hypothetical disposal facility to the surface where the groundwater reached. The flow distance and discharge rate of the groundwater in the KURT site were calculated. It was thought that the modeling methods used in this study was available to prepare the data of groundwater flow in a safety assessment for a geological disposal facility of radioactive wastes.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.11
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• pp.772-779
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• 2012

For improving performance of conical air diffuser generating fine bubble, both experimental and numerical simulation method were used. After adapting diffusers inner real scale bubble column, suitable for various diffuser submergence, the effect of diffuser submergence on oxygen transfer performance such as Oxygen Transfer Coefficient ($K_{L}a_{20}$) and Standard Oxygen Transfer Efficiency (SOTE) was investigated empirically. As flow patterns for various diffuser number and submergence were revealed throughout hydrodynamic simulation for 2-phase fluid flow of air-water, the cause of the change for oxygen transfer performance was cleared up. As results of experimental performance, $K_{L}a_{20}$ was increased slightly by 7% and SOTE was increased drastically by 39~72%, 5.6% per meter. As results of numerical analysis, air volume fraction, air and water velocity in bioreactor were increased with analogous flow tendency by increasing diffuser number. As diffuser submergence increased, air volume fraction, air and water velocity were decreased slightly. Because circulative co-flow is determinant factor for bubble diffusion and rising velocity, excessive circulation intensity can result to worsen oxygen transfer by shortening bubble retention time and amount.

• Journal of Korea Water Resources Association
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• v.38 no.7 s.156
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• pp.545-554
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• 2005

The detailed interdisciplinary surveys were conducted on the pattern of habitat use of dominant fishes during the spawning and adult stage. The hydraulic parameters of the depth and velocity, discharge, substrate cover streams, and distribution of fish in the Yeonggang, WiCheon, HoeCheon, GeochangwiCheon, CheongdoCheon, DanjangCheon (the Nakdong River Basin) were measured. The Habitat Suitability Criteria was developed for the two fish species (Zacco Platypus and Zacco Temmincki) and life stages(spawning and adult), habitat conditions (depth, velocity and covet). The Physical Habitat Simulation of the Instream Flow Incremental Methodology was applied to calculate for optimal flow and the ecological flow recommendation was proposed by choosing the largest one in the optimal flow. The ecological flow recommendation was $5.0\;m^3/s{\sim}10.0\;m^3/s$ (e.g., $6.5\;m^3/s$ in the NaeseongCheon). Also, the ecological flow recommendations were compared with the existing ecological flow and flow duration analysis.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.4
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• pp.265-282
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• 2008

Based on the site characterization works in a low and intermediate level waste(LILW) repository site, the numerical simulations for groundwater flow were carried out in order to understand the groundwater flow system of repository site. To accomplish the groundwater flow modeling in the repository site, the discrete fracture network(DFN) model was constructed using the characteristics of fracture zones and background fractures. At result, the total 10 different hydraulic conductivity(K) fields were obtained from DFN model stochastically and K distributions of constructed mesh were inputted into the 10 cases of groundwater flow simulations in FEFLOW. From the total 10 numerical simulation results, the simulated groundwater levels were strongly governed by topography and the groundwater fluxes were governed by locally existed high permeable fracture zones in repository depth. Especially, the groundwater table was predicted to have several tens meters below the groundwater table compared with the undisturbed condition around disposal silo after construction of underground facilities. After closure of disposal facilities, the groundwater level would be almost recovered within 1 year and have a tendency to keep a steady state of groundwater level in 2 year.

• Economic and Environmental Geology
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• v.37 no.5
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• pp.499-508
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• 2004

Changwon City first constructed riverbank filtration plants in Book-Myeon and Daesan-Myeon in Korea in the year 2001. This study evaluated hydrogeological characteristics and groundwater flow simulation between the Nakdong River and the fluvial aquifers adjacent to the river in Book-Myeon, Changwon City. The groundwater simulation calculated the influx rate from the Nakdong River and the fluvial aquifers to pumping wells through the riverbank filtration system. The groundwater flow model utilized drilling, grain size analysis, pumping test, groundwater level measurements, river water discharge and rainfall data. Hydraulic heads calculated by the steady-state model closely matched measured heads in pumping and observation wells. According to the transient flow model, using a total pumping amount of 14,000 $m^3$/day, the flux into the pumping wells from the Nakdong River accounts for 8,390 $m^3$/day (60%), 590 $m^3$/day (4%) is from the aquifer in the rectilinea. direction to the Nakdong River, and 5,020 $m^3$/day (36%) is from the aquifer in the parallel direction to the Nakdong River. The particle tracking analysis shows that a particle from the Nakdong River moves toward the pumping wells at a rate of about 1.85 m/day and a particle from the aquifer moves toward the pumping wells at a rate of about 0.75 m/day. This study contributes to surface water/groundwater management modeling, and helps in understanding, how seasonal change affects pumping rates, water quality, and natural recharge.

• Journal of the Korean Association of Geographic Information Studies
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• v.13 no.1
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• pp.101-113
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• 2010

Recently actual rainfall pattern is decreasing rainy days and increasing in rainfall intensity and the frequency of flood occurrence is also increased. To consider recent situation, Engineers use deterministic methods like a PMP(Probable Maximum Precipitation). If design storm wouldn't occur, increasing of design criteria is extravagant. In addition, the biggest structure cause trouble with residents and environmental problem. And then it is necessary to study considering probability of rainfall parameter in each sub-basin for design of water structure. In this study, stochastic rainfall patterns are generated by using log-ratio method, Johnson system and multivariate Monte Carlo simulation. Using the stochastic rainfall patterns, hydrological analysis, hydraulic analysis and 2nd flooding analysis were performed based on GIS for their applicability. The results of simulations are similar to the actual damage area so the methodology of this study should be used about making a flood risk map or regidental shunting rout map against the region.

• Journal of Korea Water Resources Association
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• v.48 no.2
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• pp.127-136
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• 2015

In general, XP-SWMM regards manholes as nodes, so it can not consider local head loss in surcharged manhole depending on shape and size of the manhole. That might be a reason why XP-SWMM underestimates inundated-area compared with reality. Therefore, it is necessary to study how we put the local head loss in surcharged manhole in order to simulate storm drain system with XP-SWMM. In this study, average head loss coefficients at circular and square manhole were estimated as 0.61 and 0.68 respectively through hydraulic experiments with various discharges. The estimated average head loss coefficients were put into XP-SWMM as inflow and outflow energy loss of nodes to simulate inundation area of Gunja basin. Simulated results show that not only overflow discharge amount but inundated-area increased considering the head loss coefficients. Also, inundation area with considering head loss coefficients was matched as much as 58% on real inundation area. That was more than simulated results without considering head loss coefficients as much as 18 %. Considering energy loss in surcharged manholes increases an accuracy of simulation. Therefore, the averaged head loss coefficients of this study could be used to simulate storm drain system. It was expected that the study results will be utilized as basic data for establishing the identification of the inundation risk area.