• Journal of Electrical Engineering and Technology
• /
• v.12 no.6
• /
• pp.2187-2195
• /
• 2017

In order to solve the AC optimal power flow (OPF) problem considering the generators' on/off status, it is necessary to model the problem as mixed-integer nonlinear programming (MINLP). Because the computation time to find the optimal solution to the mixed-integer AC OPF problem increases significantly as the system becomes larger, most of the existing solutions simplify the problem either by deciding the on/off status of generators using a separate unit commitment algorithm or by ignoring the minimum output of the generators. Even though this kind of simplification may make the overall computation time tractable, the results can be significantly erroneous. This paper proposes a novel algorithm for the mixed-integer AC OPF problem, which can provide a near-optimal solution quickly and efficiently. The proposed method is based on a combination of the outer approximation method and the relaxed AC OPF theory. The method is applied to a real-scale power system that has 457 generators and 2132 buses, and the result is compared to the branch-and-bound (B&B) method and the genetic algorithm. The results of the proposed method are almost identical to those of the compared methods, but computation time is significantly shorter.

• Journal of the Korea Society of Computer and Information
• /
• v.18 no.12
• /
• pp.113-121
• /
• 2013

In this paper, we design and implement a network weather map system, which provides a macroscopic view on the whole network topology as well as the network link status and utilization. The proposed system also provides distributed NetFlow-based database facility and Web-based query interface, through which network operators can check the detailed network router or link status as well as submit predefined queries to easily find out and locate heavy hitters and/or their usage. We believe that our develop system will be a useful tool for small-to-mid-scale ISPs or network operators, in managing their own networks in a cost-effective way.

• Economic and Environmental Geology
• /
• v.39 no.4 s.179
• /
• pp.485-494
• /
• 2006

This paper summarizes the history of geothermal research in Korea since 1920s and also describes the present status of research on heat flow, origin of thermal waters and geothermal exploitation and utilization. Geothermal research in Korea has been mainly related with hot spring investigation until 1970s. 1t was not until 1980s before heat flow study became continuous by research institute and academia and first nation-scale geothermal gradient map and heat flow map were published in 1996. Also in 1990s, geochemical isotope analysis of Korean hot spring waters and measurements of heat production rate of some granite bodies were made. Attempts to develop and utilize the deep geothermal water has been tried from early 1990s but field scale exploitations for geothermal water was activated in 2000s. Considering recent increase of demands on both deep and shallow geothermal energy utilization, outlook on future goethermal research and development is encouraging.

• Journal of Coastal Disaster Prevention
• /
• v.5 no.4
• /
• pp.173-182
• /
• 2018

As the research about increasing the efficiency of dredging soil transport, the technology, which reduce the friction between pipe wall and fluid in the pipe and disturbed generating pipe blockage, has been developed. So for the purpose of applying this technology to real construction site, main test has been tried at the real scale test in field. As a test result, this paper will show 30% flow efficiency increasing by permitted electro magnetic force to the pipe. And test result was evaluated as a ultra sonic velocity profiler. To propose the design technique and the execution manual of the high efficiency dredging material transport technic, this research have confirmed flow status changing depending on a soil material kind under electro-magnetic field and analyze the effect of electro-magnetic field which affects to each dredged soil material transportation. For achieving this research, EMF(Electro-Magnetic Field) generator is installed on the dredger(20,000HP) and through monitored flow status, dredging soil flow rate and sampled material specification is confirmed. Also dredger operating condition is measured and dredger power for soil transportation, hydraulic gradient and flow rate are compared, as transportation efficiency is calculated by this parameter, it is possible to check transportation efficiency improvement depending on each dredged soil material under electro-magnetic field. To verify the technique of dredged soil transfer using electromagnetic field, which is the core technique of the high efficiency dredged soil transfer, and the technique of expert system for pipeline transfer and the flow state. This could lead to a verification of transfer efficiency according to the characteristics of the dredged soil (sand, clay, silt) and the transfer distance (5km, 10km, 15km), which is planned to be used for a technology development of pump power reduction and long-distance transfer applying the high efficiency dredged soil transfer technology.

• Journal of Korean Neurosurgical Society
• /
• v.62 no.2
• /
• pp.201-208
• /
• 2019

Objective : In patients with internal carotid artery (ICA) occlusion, collateral middle cerebral artery (MCA) flow has a protective role against ischemia. However, some of these patients may experience initial major neurological deficits and major worsening on following days. Thus, we investigated the safety and efficacy of endovascular treatment (EVT) for ICA occlusion with collateral MCA flow by comparing clinical outcomes of medical treatment versus EVT. Methods : The inclusion criteria were as follows : 1) acute ischemic stroke with ICA occlusion and presence of collateral MCA flow on transfemoral cerebral angiography (TFCA) and 2) hospital arrival within 12 hours from symptom onset. The treatment strategy was made by the attending physician based on the patient's clinical status and results of TFCA. Results : Eighty-one patients were included (30 medical treatment, 51 EVT). The EVT group revealed a high incidence of intracranial ICA occlusion, longer ipsilesional MCA contrast filling time, and a similar rate of favorable clinical outcome despite a higher mean baseline the National Institutes of Health Stroke Scale (NIHSS) score. By binary logistic regression analysis, intravenous recombinant tissue plasminogen activator and EVT were independent predictors of favorable clinical outcome. In subgroup analysis based on stroke etiology, the non-atherosclerotic group showed a higher baseline NIHSS score, higher incidence of EVT, and a higher rate of distal embolization during EVT in comparison with the atherosclerotic group. Conclusion : In patients with ICA occlusion and collateral MCA flow, decisions regarding treatment strategy based on TFCA can help achieve favorable clinical outcomes. EVT strategy with respect to etiology of ICA occlusion might help achieve better angiographic outcomes.

• Nuclear Engineering and Technology
• /
• v.50 no.3
• /
• pp.478-487
• /
• 2018

Pyroprocessing technology has been regarded as a promising solution for recycling spent fuel in nuclear power plants. The Korea Atomic Energy Research Institute has been studying the current status of equipment and facilities for pyroprocessing and found that existing facilities are manually operated; therefore, their applications have been limited to laboratory scale because of low productivity and safety concerns. To extend the pyroprocessing technology to a commercial scale, the facility, including all the processing equipment and the material-handling devices, should be enhanced in view of automation. In an automated pyroprocessing facility, a supervised control system is needed to handle and manage material flow and associated operations. This article provides a preliminary design of the supervising system for pyroprocessing. In particular, a manufacturing execution system intended for an automated pyroprocessing facility, named Pyroprocessing Execution System, is proposed, by which the overall production process is automated via systematic collaboration with a planning system and a control system. Moreover, a simulation-based prototype system is presented to illustrate the operability of the proposed Pyroprocessing Execution System, and a simulation study to demonstrate the interoperability of the material-handling equipment with processing equipment is also provided.

• Journal of Korean Neurosurgical Society
• /
• v.59 no.5
• /
• pp.512-517
• /
• 2016

Objective : The pathophysiology of idiopathic Chiari malformation (CM) type 1 is disturbance of free cerebrospinal fluid (CSF) flow and restoration of normal CSF flow is the mainstay of treatment. Additional migration of the medulla oblongata in pediatric patients is referred to as CM type 1.5, but its significance in adult patients is unknown. This study is to compare surgical outcomes of adult idiopathic CM type 1.5 with that of type 1. Methods : Thirty-eight consecutive adult patients (M : F=11 : 27; median, 33.5; range, 18-63) with syringomyelia due to idiopathic CM type 1 were reviewed. Migration of the medulla oblongata was noted in 13 patients. The modified McCormick scale (MMS) was used to evaluate functional status before and one year after surgery. All patients underwent foramen magnum decompression and duroplasty. Factors related to radiological success (${\geq}50%$ decrease in the diameter of the syrinx) were investigated. The follow-up period was $72.7{\pm}55.6$ months. Results : Preoperative functional status were MMS I in 11 patients and MMS II in 14 of CM type 1 and MMS I in 8 and II in 5 of CM type 1.5. Of patients with MMS II, 5/14 patients in group A and 3/5 patients in group B showed improvement and there was no case of deterioration. Radiological success was achieved in 32 (84%) patients and restoration of the cisterna magna (p=0.01; OR, 46.5) was the only significant factor. Conclusion : Migration of the medulla oblongata did not make a difference in the surgical outcome when the cisterna magna was restored.

• Journal of Power Electronics
• /
• v.17 no.6
• /
• pp.1625-1636
• /
• 2017

A power electronic transformer (PET) based on the cascaded H-bridge (CHB) and the isolated bidirectional DC/DC converter (IBDC) is capable of accommodating a large scale battery energy storage system (BESS) in the medium-voltage grid, and is referred to as a power electronic transformer based battery energy storage system (PET-BESS). This paper investigates the PET-BESS and proposes a coordinative control strategy for it. In the proposed method, the CHB controls the power flow and the battery state-of-charge (SOC) balancing, while the IBDC maintains the dc-link voltages with feedforward implementation of the power reference and the switch status of the CHB. State-feedback and linear quadratic Riccati (LQR) methods have been adopted in the CHB to control the grid current, active power and reactive power. A hybrid PWM modulating method is utilized to achieve SOC balancing, where battery SOC sorting is involved. The feedforward path of the power reference and the CHB switch status substantially reduces the dc-link voltage fluctuations under dynamic power variations. The effectiveness of the proposed control has been verified both by simulation and experimental results. The performance of the PET-BESS under bidirectional power flow has been improved, and the battery SOC values have been adjusted to converge.

• Proceeding of Spring/Autumn Annual Conference of KHA
• /
• 2008.04a
• /
• pp.251-255
• /
• 2008

Nowadays the scale of domestic construction becomes large, sophisticated and specialized. It has led to a growing need for the high quality, cost reduction, safety and reduction of work duration. Therefore the importance of construction materials management is emphasized to perform the project successfully. It becomes an current issue about method of construction material management according to the flow of construction progress in the construction field. Therefore, various researches using RFID for efficiency of construction material are being studied. We analyzed the case study using RFID, drew the problems through the investigation of status about the management of material in the field, and then suggested the method of material management using in the apartment building construction field.

• Journal of Wetlands Research
• /
• v.23 no.2
• /
• pp.183-188
• /
• 2021

In the case of small-scale sewage treatment plants, it is reported that the amount of inflow fluctuates and it is difficult to operate the sewage treatment due to the inflow of unknown water due to the aging of sewage pipes. In particular, there are many overall operational problems due to the decrease in water temperature in winter. In this study, the operation status of small-scale sewage treatment facilities located in mountainous areas and water quality changes according to temperature were analyzed. It was found that the concentration of BOD, COD, and SS in effluent water was greatly changed depending on the temperature, and it was found that COD was particularly affected. Accordingly, the water level of the bioreactor was raised by 0.4m in order to temporarily apply measures to lower the water temperature in winter. As a result of comparing and analyzing the results when the bioreactor was covered and operated, a significant improvement effect occurred. In addition, a plan to improve the treatment efficiency of the bioreactor in winter is to extend the residence time of the bioreactor, a plan to expand the bioreactor specification, a new flow control tank and transport it to the outside, and an oxygen-free air diffuser to be used as an aerobic tank in case of an emergency in winter. The improvement plan was suggested. The results of this study are expected to be used as basic data for the operation plan of small-scale sewage treatment facilities in winter.