• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.2
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• pp.86-97
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• 2005

Accurate estimation of the wave-induced pore water pressure in the seabed is key factor in studying the stability of the seabed in the vicinity of coastal structure. Most of the existing numerical models for wave structure seabed interaction have been linked through applying hybrid numerical technique which is analysis method separating the wave field and seabed regime. Therefore, it is necessary to develope a numerical model f3r simulating accurately wave$\cdot$structure$\cdot$ seabed interaction under wave loadings by the single domain approach for wave field and seabed regime together. In this study, direct numerical simulation is newly proposed. In this model, modeled fluid drag has been used to detect the hydraulic properties according to the varied geometrical shape inside the porous media by considering the turbulence resistance as well as laminar resistance. Contrary to hybrid numerical technique, direct numerical simulation avoids the explicit formulation of the boundary conditions at the fluid/porous media interface. A good agreement has been obtained by the comparison between existed experimental results by hydraulic model test and direct numerical simulation results far wave $\cdot$structure$\cdot$seabed interaction. Therefore, the newly proposed numerical model is a powerful tool for estimating the nonlinear dynamic responses among a structure, its seabed foundation and water waves.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.3
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• pp.157-165
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• 2000

A small hydraulic winch system with an automatic tension control unit was designed to improve the work efficiency of coastal small vessels and the dynamic response characteristics of the winch system operated in the open loop condition was investigated. The inlet and the outlet pressures in hydraulic motor, the torque and the rotating speed of winch drum were measured as a function of time, and the behaviour in autotension mode for stepped load changes was analyzed. The results obtained are summarized as follows : 1. The developed winch system for coastal small vessels will result in better fishing with improved efficiency and lower manpower consumption by remote control of winch system. 2. The rotating delay times of winch drum for on/off operations of solenoid valve were 0.09 see at CW mode and 0.04 sec at CCW mode, respectively. After the solenoid valve was controlled, response characteristics were unstable slightly but showed good tracking behaviour over short time. 3. The driving torque of winch system in autotension mode was kept almost constant of 55.9 kgf·m, and 11.1 then the rotating speed of winch drum was kept almost constant of 5.1 rpm in the larger torque than 55.9 kgf·m and 11.1 rpm in the lower torque than that. 4. The 5% settling times in the transient response characteristics of autotension mode under rapid increasing and decreasing conditions of load were 0.12 sec and 0.2 sec, respectively, and then the rotating speeds were 11 rpm and 5.3 rpm, respectively. 5. The tracking behaviour of torque and rotating speed by remote control operation were stable within 0.23 sec at CW mode and 0.37 sec at CCW mode, respectively.

• Journal of The Korean Society of Agricultural Engineers
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• v.49 no.5
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• pp.11-20
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• 2007

In this study, we reviewed the optimal space for the fishway and fish storage establishment in the section between the downstream of the Hwacheon dam and the confluence of the Pungsan river. The hydraulic stability of these facilities was also examined. In the section between the downstream of Hwacheon dam and the confluence of Pungsan river, the release flow of Hwacheon dam was set at $5,495m^3/s,\;6,110m^3/s$ and $7,537m^3/s$, and numerical simulations were executed for each instance using the HEC-RAS model and RMA-2. In the analysis of the flow velocity distributions in the subject section by release flows of Hwacheon dam, it was shown that there was over 5.0m/s of high flow velocity at Sta. $#1{\sim}Sta.$ #3, Sta. $#4{\sim}Sta.$ #6, and Sta. $#12{\sim}Sta.$ #13 of the sections analyzed in this study. The Sta. $#0{\sim}Sta.$ #1 was considered appropriate for the fishway and fish storage establishment. As seen in the results of the numerical stability review by release flow conditions of Hwacheon dam subject to the selected available areas fur fishway and fish storage, the topographically available section for the establishment of fishway and fish storage exists at Sta. $#1{\sim}Sta.$ #3 when the release flow of Hwacheon dam is $5,495m^3/s$, whereas Sta. $#0{\sim}Sta.$ #1 should be reviewed for the subject section for the establishment of fishway at release flows of $6,110m^3/s$ and $7,537m^3/s$, in addition to the figures gathered at the $5,495m^3/s$ release flow. Finally, the available section for the establishment of fishway and fish storage was determined to be Sta. $#0{\sim}Sta.$ #3. Further, if fishway and fish storage are established in the outer bank within this section, the high flow velocity section should be avoided. An alternative would be to establish for the fishway in the inner band on the section of Sta. #1 or Sta. #3.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.9
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• pp.995-1005
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• 2005

The study with laboratory sandbox model has been carried out to address potential use of reclaimed water, as a countermeasure artificially recharging the coastal aquifer, to effectively prevent from seawater intrusion due to overexploitation. It also investigated plausibility for either preserving or recovering the freshwater interface facing with seawater intrusion. To do this, we assessed hydraulic properties in artificial aquifer seawater/freshwater interface) depending upon the variation of extraction, storage and injection of reclaimed water. The variation of interface between freshwater and seawater were visualized by Surfer 8(Golden Software, USA) according to given experimental conditions. The interface between seawater and freshwater has been sensitively influenced by the change of extraction rate, where seawater zone migrated much faster into freshwater zone even though extraction rate became decreased. However, decreasing recharge rate could slow down moving of saline water zone toward freshwater zone. When the recharge was solely introduced into the sand box model, saline water intrusion was retarded than those of recharge and extraction working together. And also, the level of salinity of saline water was diluted by artificial recharge. It finally revealed that the artificial recharge would hydraulically avoid seawater intrusion while the freshwater sources could be conservatively utilized.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.6
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• pp.603-612
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• 2006

The study with laboratory sandbox model has been carried out to address potential use of reclaimed water, as a way for artificially recharging the coastal aquifer, to effectively prevent from seawater intrusion. To do this, we assessed hydraulic and geochemical properties depending upon various extraction and recharging conditions. While solely being recharged, the intrusion could be significantly retarded than those of recharge and extraction implied together. At 0.5 to 2 for the ratio of the extraction over the recharge rate, the fresh water was exploited from the tank, where the void regime was simultaneously saturated with the recharged water. In the meantime, the saline water zone was diluted and back-tracked by the recharged water due to forming a hydraulic geochemical barrier around the injection well. However, if the ratio was being increased to greater than 4, saltwater more deeply intruded to the freshwater zone because the artificial recharge was not sufficiently supplied to timely back-fill the void space. When the aquifer water was intermittently extracted at the ratio of $0.5{\sim}2$ over the recharge rate, the value of S.M.I. decreased, but increasing it to more than 4 unlikely escalated the value of S.M.I as much as $3{\sim}47%$ indicating that the salt water intruded. It finally revealed that the proper ratio of extraction/recharge or intermittent extraction would efficiently retracted seawater intrusion while the freshwater sources could be conservatively utilized.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.500-504
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• 2008

The objective of this paper is to evaluate the feasibility of using an optimization model as a effective way to search conjunctive operation scheme to meet two conditions; one is to minimize the electric cost for pumping and another is to meet the water demand for satisfying customers. The feasibility is confirmed as comparing the best combinations of pumps between multi-regional water supply networks from multiple sources which are obtained through an optimization modeling and EPAnet modeling. KModsim model, a network optimization model, was used to determine conjunctive operation scheme in the pipe system. KModsim, based on Lagrangian Relaxation algorithm, is useful for modeling network system and obtaining simultaneously pump combination and water allocation with given input option such as energy unit cost supplying from a source into a consumer, operating pumping combination. This study develops the procedure of determining optimal conjunctive operation scheme with using KModsim model. As a study region, the water supplying systems of the Geojae-city in the Geongsang Namdo Province was selected and investigated. The EPAnet hydraulic simulation result(Ryu et al, 2007, KSWW) gave input data for optimization model; energy unit price(won/$m^3$), water service available area etc.. It was assured that the combination of pump operation through optimum conjunctive operation is to be optimum scheme to obtain the best economic water allocation with comparison to the hydraulic simulation result such as electric cost and pump combination cases. The results obtained through the study are as follows. First, It was found that a well-allocated water supply scheme, the best combination of pump operation through optimum joint operation, promises to save the electric cost and satisfy all operational goals such as stability and revenues during the period. Second, an application of KModSim, a network model, gave the amount of water allocation from each source to a consumer with consideration of economic supply. Finally, in a service area available to supply through conjunctive operation of existing inter-regional water supply networks within short distance, a conjunctive operation is useful for determining each transmission pipeline's service area and maximizing the effectiveness of optimizations in pumping operation time.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.3
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• pp.229-240
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• 1987

Carbonation of concrete is one type of a chemical process. The reaction mechanism is very complex for the case when low-calcium fly ash and blast furnace slag is added. When fly ash and blast furnace slag is used as an admixture in concrete, they improve compressive strength in the long term, permeability and chemical resistance of concrete by a pozzolanic reaction and latent hydraulic property. On the other hand, the pozzolanic reaction of fly ash and latent hydraulic property of the blast furance slag leads to a reduction of the alkalinity of the concrete. It has been pointed out that this will accelerate the carbonation of the concrete and the corrosion of reinforcement steel embedded in the concrete. In order to clarify the effect of fly ash and blast furance slag on the carbonation of concrete, an accelerated carbonation testing of concrete was carried out by varying the conditions of concrete and the initial curing period in water. The test results of accelerated carbonation were compared to the carbonation test results of concrete stored for 15 years in open air, but protected from rain. As a result, the equation for the rate of carbonation based on compressive strength of concrete was proposed.

• Journal of the Korean Geotechnical Society
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• v.21 no.9
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• pp.13-23
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• 2005

The prefabricated vertical drains (PVDs) are one of the most widely used techniques to accelerate the consolidation of soft clay deposits and dredged soil. Discharge capacity is one of the factors affecting the behavior of PVDs. In the field, a PVD is confined by clay or dredged soil, which is normally remolded during PVD installation. Under field conditions, soil particles may enter the PVD drainage channels, and the consolidation settlement of the improved subsoil may cause 131ding of the PVD. These factors will affect the discharge capacity of the PVDs. In this study an experimental study was carried out to estimate the discharge capacity of three different types of PVDs by utilizing the large-scale laboratory model testing and small-scale laboratory model testing equipments. The several factors such as confinement condition (confined by soft marine clay or dredged soil) and variations of the discharge capacity were studied with time under soil specimen confinement, The test results indicated that discharge capacity decreases with increasing load, time, and hydraulic gradient. With load application, the cross-sectional area of the drainage channel of PVD decreases because the filter of PVD is pressed into the core. The discharge capacity of the soft marine clay-confined PVDs is much lower than that of the dredged soil-confined PVDs.

• Journal of Aquaculture
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• v.10 no.3
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• pp.335-346
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• 1997

Denitrification is one of the important processes of removing nitrate from in recirculating aquaculture systems. And this process is affected by many factors such as external organic carbon sources, hydraulic retention time (HRT), COD/NO3--N (C:N) ratio, etc. However, not many studies were done for the optimum conditions of denitrification in the recirculation system for aquaculture. Therefore, this study was conducted to find out the optimum removal condition of NO3--N using submerged denitrification biofilter. The combinations of two external organic carbon sources (glucose and methanol), two HRT (4 and 8-hour) and four differnent C : N ratios (3, 4, 5, 6) were tested. The removal efficiencies of NO3--N and total inorganic nitrogen (TIM) at 8-hour HRT were better than those at 4-hour's (P<0.05). The maximum removal efficiency of NO3--N by methanol (97.8%) was achieved at HRT and C : N ratio were 8-hour and 4.0 respectively. The efficiencies of methanol for the removal of NO3--N and TIN were always better than those of glucose (P<0.05). The maximum removal efficiencies of total inorgainc nitrogen (TIN) were gained at C : N ration of 5.0. The maximum removel efficiencies of TIN using methanol and glucose were 96.9% and 71.5% respectively. Anaerobic condition which is necessary for denitrification process was not made until the 8-hour HRT and higher C : N ratio (5.0). Removal of NO3--N at 4-hour HRT and C : N ration lower than 5.0 were inhibited by oxygen and/or low quantity of external organic carbon. Removal efficiencies of NO3--N were also inhibited by high C : N (6.0) ratio when HRT was 8-hour.

• Journal of Korea Water Resources Association
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• v.51 no.11
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• pp.989-998
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• 2018

Connectivity between water source and demand node can be served as a critical system performance indicator of the degree of water distribution network (WDN)' failure severity under abnormal conditions. Graph theory-based approaches have been widely applied to quantify the connectivity due to WDN's graph-like topological feature. However, most previous studies used undirected-unweighted graph theory which is not proper to WDN. In this study, the directed-weighted graph theory was applied for WDN connectivity analyses. We also proposed novel connectivity indicators, Source-to-Node Shortest Pathway (SNSP) and SNSP-Degree (SNSP-D) which is an inverse of the SNSP value, that does not require complicate hydraulic simulation of a WDN of interest. The proposed SNSP-D index was demonstrated in total 42 networks in J City, South Korea in which Pearson Correlation Coefficient (PCC) between the proposed SNSP-D and four other system performance indicators was computed: three resilience indexes and an energy efficiency metric. It was confirmed that a system representative value of the SNSP-D has strong correlation with all resilience and energy efficiency indexes (PCC = 0.87 on average). Especially, PCC was higher than 0.93 with modified resilience index (MRI) and energy efficiency indicator. In addition, a multiple linear regression analysis was performed to identify the system hydraulic characteristic factors that affect the correlation between SNSP-D and other system performance indicators. The proposed SNSP is expected to be served as a useful surrogate measure of resilience and/or energy efficiency indexes in practice.