• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.5
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• pp.563-573
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• 2015

For hard rock subsea tunnels the most challenging rock mass conditions are in most cases represented by major faults/weakness zones. Poor stability weakness zones with large water inflow can be particularly problematic. At the pre-construction investigation stage, geological and engineering geological mapping, refraction seismic investigation and core drilling are the most important methods for identifying potentially adverse rock mass conditions. During excavation, continuous engineering geological mapping and probe drilling ahead of the face are carried out, and for the most recent Norwegian subsea tunnel projects, MWD (Measurement While Drilling) has also been used. During excavation, grouting ahead of the tunnel face is carried out whenever required according to the results from probe drilling. Sealing of water inflow by pre-grouting is particularly important before tunnelling into a section of poor rock mass quality. When excavating through weakness zones, a special methodology is normally applied, including spiling bolts, short blast round lengths and installation of reinforced sprayed concrete arches close to the face. The basic aspects of investigation, support and tunnelling for major weakness zones are discussed in this paper and illustrated by cases representing two very challenging projects which were recently completed (Atlantic Ocean tunnel and T-connection), one which is under construction (Ryfast) and one which is planned to be built in the near future (Rogfast).

• Journal of Korean Society on Water Environment
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• v.31 no.3
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• pp.313-318
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• 2015

To study the influence of changes in river discharge on water quality of the main stem of the Geum River, we investigated variation of inflow load from tributaries with river discharge. We also studied the mixing behavior of pollutants during mixing of waters of the main stem and Gap Stream. For this study, we collected water quality data such as suspended solids (SS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) representing pre-monsoon, monsoon, and post-monsoon events of 2013 from a website of Water Information System. Based on inflow load, the Gap and Miho streams may be ones of tributaries which may largely influence water quality of main stem in upper river region. The Suksung and Nonsan Streams seemed to further affect water quality downstream. Results of modified EMMA indicated SS and TP may have another source(besides Gap Stream) at pre-monsoon, monsoon, and post-monsoon period. In contrast, TN and organic matter (BOD, COD, TOC) were conservative at pre-monsoon and post-monsoon. However, when river discharge increased, these pollutants may also came from unspecified non-point sources. Therefore, we need to attempt to find non-point sources for the pollutants in the main channel of upper Geum River region.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.177-180
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• 2002

The study on the design of pre-swirl stator vanes is performed. The pre-swirl stator vanes is an energy-saving device to improve propulsive performance by providing pre-swirl to the propeller inflow. The theoretical background and the design conditions for pre-swirl stator vanes are presented. The flow characteristics around the pre-swirl stator vanes attached ship hull are analyzed through the experimental method. The technique to determine the optimum location, angle and the number of stator vane is investigated and applied it to 310,000 TBW VLCC The flow velocities are measured using 5-hole Pilot tubes at the condition with and without a propeller.

• International Journal of Fluid Machinery and Systems
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• v.5 no.2
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• pp.49-59
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• 2012

The present study is devoted to the influence of a superposed radial inflow in a rotor-stator cavity with a peripheral opening. The flow regime is turbulent, the two boundary layers being separated by a core region. An original theoretical solution is obtained for the core region, explaining the reason why a weak radial inflow has no major influence near the periphery of the cavity but strongly affects the flow behavior near the axis. The validity of the theory is tested with the help of a new set of experimental data including the radial and tangential mean velocity components, as well as three components of the Reynolds stress tensor measured by hot-wire anemometry. The theoretical results are also in good agreement with numerical results obtained with the Fluent code and experimental data from the literature.

• Journal of Korean Society of Water and Wastewater
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• v.31 no.1
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• pp.103-114
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• 2017

A membrane bioreactor by sequentially alternating the inflow and by applying a two-stage coagulation control based on pre-coagulation was evaluated in terms of phosphorus removal efficiency and cost-savings. The MBR consisted of two identical alternative reaction tanks, followed by aerobic, anoxic and membrane tanks, where the wastewater and the internal return sludge alternatively flowed into each alternative reaction tank at every 2 hours. In the batch-operated alternative reaction tank, the initial concentration of nitrate rapidly decreased from 2.3 to 0.4 mg/L for only 20 minutes after stopping the inflow, followed by substantial release of phosphorus up to 4 mg/L under anaerobic condition. Jar test showed that the minimum alum doses to reduce the initial $PO_4$-P below 0.2 mg/L were 2 and 9 mol-Al/mol-P in the wastewater and the activated sludge from the membrane tank, respectively. It implies that a pre-coagulation in influent is more cost-efficient for phosphorus removal than the coagulation in the bioreactor. On the result of NUR test, there were little difference in terms of denitrification rate and contents of readily biodegradable COD between raw wastewater and pre-coagulated wastewater. When adding alum into the aerobic tank, alum doses above 26 mg/L as $Al_2O_3$ caused inhibitory effects on ammonia oxidation. Using the two-stage coagulation control based on pre-coagulation, the P concentration in the MBR effluent was kept below 0.2 mg/L with the alum of 2.7 mg/L as $Al_2O_3$, which was much lower than 5.1~7.4 mg/L as $Al_2O_3$ required for typical wastewater treatment plants. During the long-term operation of MBR, there was no change of the TMP increase rate before and after alum addition.

• Journal of Environmental Science International
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• v.28 no.11
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• pp.1005-1017
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• 2019

Environmental factors and changes in phytoplankton community structure before (August 5, 2017), during (August 18 and 25) and after (August 30 and September 15) freshwater input were analyzed to investigate the effects of freshwater input from Ganwol and Bunam lakes located in the upper part of Cheonsu Bay. Due to the large amount of freshwater input in the Cheonsu Bay, the surface salinity of the bay decreased by more than 8 psu, and the thermocline existing in the bay during August weakened. In addition, hypoxic phenomena occurred temporarily in the bay as the low oxygen water mass from the freshwater lakes flowed into the bay, and chemical oxygen demand, nutrients, and N/P increased with freshwater inflow. The density of phytoplankton during the freshwater inflow increased owing to their input from the freshwater lakes. Diatom species (Eucampia zodiacus) dominated the phytoplankton community in the bay before freshwater input; nanoflagellates, chlorophyta, cyanobacteria, and diatoms (Pseudonitzschia delicatissima, Chateocceros spp.) entered during freshwater input; and after freshwater inflow ended, diatoms (Chateocceros spp.) again became predominant indicating a return to previous conditions. The amount of phytoplankton standing crops increased sharply due to the inflow of freshwater species into the bay on the second day of discharge compared to before freshwater input; pre-discharge conditions were restored at most stations except at some sites close to the Bunam Lake three days after discharge. Therefore, the large amount of freshwater flowing into the bay affects not only the geochemical circulation in the bay but also the phytoplankton community structure. In particular, the high concentration of nutrients in the freshwater lake affect the marine ecosystem of the bay during August.

• Proceedings of the Korean Geotechical Society Conference
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• 1993.10a
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• pp.51-56
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• 1993

This paper presents the FEM anlysis results performed to assess the applicability of Horizontal Jet Grout Roofing, and of ground improvement methods for tunneling in soft ground. Horizontal Jet Grount Roofing Method is applicable to ensure the stability of tunnel face in non-cemeted alluvial strata under high ground water pressure. For applying this method, to ensure the reliability, the Horizontel Jet Grout Roofing should be double lined with pre-grouting to reduce the water inflow during the jet grouting.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.5
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• pp.1169-1177
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• 2018

Modern society is a period of rapid digital transformation. This digital-centric business proliferation offers convenience and efficiency to businesses and individuals, but cyber threats are increasing. In particular, cyber attacks are becoming more and more intelligent and precise, and various attempts have been made to prevent these attacks from being discovered. Therefore, it is increasingly difficult to respond to such attacks. According to the cyber kill chain concept, the attacker penetrates to achieve the goal in several stages. We aim to detect one of these stages and neutralize the attack. In this paper, we propose a method to detect anomalous traffic caused by an agent attacking an external attacker, assuming that an agent executing a malicious action has been introduced in advance due to various reasons such as a system error or a user's mistake.

• Journal of The Korean Society of Agricultural Engineers
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• v.63 no.4
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• pp.97-104
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• 2021

Despite the practical limitations of calculating the amount of inflow and supply related to the operation of agricultural reservoirs, the role of agricultural reservoirs is gradually being emphasized. In particular, as interest in disaster safety has increased, the demand for preliminary measures to prepare for disasters has been rising, for instance, pre-discharging agricultural reservoirs for flood control. The aim of this study is to analyze the plans for the flood season reservoir operation considering pre-discharge period and water level limit. Accordingly, we optimized the simulation of daily storage using the ratio correction factor (RCFs) and analyzed the amount of inflow and supply using K-HAS. In addition we developed the drought determination coefficient (k) as a indicator of water availability and applied it for supplementing the risk level criteria in the Drought Crisis Response Manual. The results showed that it would be difficult to set the water level limit during the flood period in the situation of little water supply for flood control in agricultural reservoirs. Therefore, it is necessary to operate the reservoir management regulations after measures such as securing additional storage water are established in the future.

• Journal of Ocean Engineering and Technology
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• v.22 no.5
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• pp.61-68
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• 2008

In Jinhae-Masan bay, a typical semi-dosed bay in Korea, the water quality is severely deteriorated because of the dosed topographic character and the inflow of nutrients from the land. There have been attempts to apply a water quality model dealing with the entrophication phenomenon and the oxygen-deficient mass in the bay in summer, but there have been few examples of models that have considered the phenomenon of stratification in the proper order, and then it is performed the model of water quality. Therefore, this study collected and analyzed the pre-observed water temperature data from Jinhae-Masan bay in summer and then constructed a density model using the topographic heat accumulation effect and inflow from the river to examine the temperature stratification. The simulation results show that this model could demonstrate the temperature stratification in the Jinhae-Masan bay very well.