• Journal of Energy Engineering
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• v.13 no.1
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• pp.60-67
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• 2004

The recent movement to deregulated and competitive electricity market reacquires new concepts against existing central dispatch in the system operation and pinning. As power systems tend to be operated more closely to their ultimate ratings, the role of SCOPF (Security Constrained Optimal Power flow) is changed and the importance for real-time security inhancement will be more increased i]1 the new and com partitive electricity market. This paper deals with the application of the SCOPF which makes possible the On-Line application. The security margin of power system truly is changed according to the conditions or configuration of power systems, therefore, the sensitivity factor reiated to the security is recalculated and the application should be updated in accordance with the state of power system. The goal of this paper is to obtain proper security through the effluent usage of the sensitivity and to apply this a1gorithm to system operation. The proposed mechanism has been tested on a sample system and the results show more secure conditions against critical contingencies.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.5
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• pp.2353-2359
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• 2011

The request of Green-IT technology and recommend of computer hardware resource are increasing explosively. So, necessity of Cloud computing is increasing rapidly. Berkeley Univ. announced teens constituent that threat Cloud computing in 2009 and problem for user authentication should be solved as is urgentest among them. So, We wish to propose effective user authentication protocol in Cloud computing environment. Secure safety for user quotation through Kerberos's ticket issue that is existent representative user authentication techniques, and defined authentication procedure of two steps that flow user authentication and service authentication through PKI's. Is uncomplicated structurally more than efficiency for certification protocol and examination result about safety, existent PKI that propose and simplify achievement procedure and system configuration more than Kerberos and reduced response time.

• Korean Institute of Interior Design Journal
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• v.27 no.3
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• pp.14-23
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• 2018

The spatial planning of the elderly care facility plans is analyzed using space syntax in terms of encouraging the social interaction of the residents in this study. First, through the visibility graph analysis, openness and accessibility of space is analysed. Second, the walking behavior of residents through agent analysis model is simulated. Third, the space planning methods for the elderly care facilities are proposed based on the results. The results are as follows. According to the visibility graph analysis, the main corridor has high visual openness and high accessibility. The visual openness and accessibility of the unit living room, where social interaction among residents is possible in each unit, is low. Space planning is needed to increase direct protection and observation of employees to the unit living room. The location of the nurse station that manages the entire floor needs to be located where the openness and accessibility is most high. The nursing station should have a high degree of connectivity to the entire space, so that any accidents can be managed and contact is accessible. Through the agent simulation the flow from the center to each unit space is highest in the corridor space and the inflow to the private rooms and the living room are similar. Therefore, it is necessary to plan the accessibility of the unit living room more for the natural inflow of residents.

• Journal of the Korean Institute of Gas
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• v.4 no.1 s.9
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• pp.40-48
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• 2000

A fuel cell is an electrochemical device continuously converting the chemical energy in a fuel and an oxidant to electrical energy by going through an essentially invariant electrode-electrolyte system. Phosphoric acid fuel cell employs concentrated phosphoric acid as an electrolyte. The cell stack in the fuel cell, which is the most important part of the fuel cell system, is made up of anode where oxidation of the fuel occurs cathode where reduction of the oxidant occurs; and electrolyte, to separate the anode and cathode and to conduct the ions between them. Fuel cell performance is associated with many parameters such as operating and design parameters associated with the system configuration. In order to understand the design concepts of the phosphoric fuel cell and predict it's performance, we have here introduced the simulation of the fuel-cell stack which is core component and modeled in a 3-dimensional grid space. The concentration of reactants and products, and the temperature distributions according to the flow rates of an oxidant are computed by the help of a computational fluid dynamic code, i.e., FLUENT.

• Journal of KIISE
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• v.43 no.11
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• pp.1223-1232
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• 2016

A virtual network technology can provide a network reflecting the requirements of various services. The virtual network can distribute resources of the physical network to each virtual slice. An efficient resource distribution technique is needed to reflect the requirements of various services. Existing bandwidth distribution techniques can only control downlink traffic without taking traffic conditions on the network into account. Downlink and uplink share the same resources in a wireless network. The existing bandwidth distribution techniques assumed that all stations generate saturated traffic. Therefore, the existing bandwidth distribution technique cannot make traffic isolation in a virtual wireless network. In this paper, we proposed a traffic-based bandwidth control techniques to solve these problems. We applied Software-Defined Networking(SDN) to the virtual wireless network, monitored the traffic at each station, and searched for stations that generated unsaturated traffic. We also controlled both uplink and downlink traffics dynamically based on monitoring information. Our system can be implemented with legasy 802.11 clients and SDN-enabled APs. After the actual test bed configuration, it was compared to existing techniques. As a result, the distribution performance of the proposed technique was improved by 14% in maximum.

• Structural Engineering and Mechanics
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• v.68 no.4
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• pp.475-483
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• 2018

Square tubular columns are commonly used in moment resisting frames, while through-diaphragm connection is the most typical configuration detail to connect the H-shaped beam to the column. However, brittle fracture normally occurs at the complete joint penetration weld between the beam flange and the through-diaphragm due to the stress concentration caused by the geometrical discontinuity. Accordingly, three improved types of through-diaphragm are presented in this paper to provide smooth force flow path comparing to that of conventional connections. Tensile tests were conducted on four specimens and the results were analyzed in terms of failure modes, load-displacement response, yield and ultimate capacity, and initial stiffness. Furthermore, strain distributions on the through-diaphragm, the beam flange plate, and the column face were comprehensively evaluated and discussed. It was found that all the proposed three types of improved through-diaphragm connections were able to reduce the stress concentration in the welds between the beam flange and the through-diaphragm. Furthermore, the stress distribution in connection with longer tapered through-diaphragm was more uniform.

• Wind and Structures
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• v.30 no.6
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• pp.633-648
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• 2020

The objective of this work was to investigate the interference effects of two-parallel bridge decks on aerodynamic coefficients, vortex-induced vibration, flutter instability and flutter derivatives. The two bridges have significant difference in cross-sections, dynamic properties, and flutter speeds of each isolate bridge. The aerodynamic static tests and aeroelastic tests were performed in TU-AIT boundary layer wind tunnel in Thammasat University (Thailand) with sectional models in a 1:90 scale. Three configuration cases, including the new bridge stand-alone (case 1), the upstream new bridge and downstream existing bridge (case 2), and the downstream new bridge and the upstream existing bridge (case 3), were selected in this study. The covariance-driven stochastic subspace identification technique (SSI-COV) was applied to identify aerodynamic parameters (i.e., natural frequency, structural damping and state space matrix) of the decks. The results showed that, interference effects of two bridges decks on aerodynamic coefficients result in the slightly reduction of the drag coefficient of case 2 and 3 when compared with case 1. The two parallel configurations of the bridge result in vortex-induced vibrations (VIV) and significantly lower the flutter speed compared with the new bridge alone. The huge torsional motion from upstream new bridge (case 2) generated turbulent wakes flow and resulted in vertical aerodynamic damping H1^* of existing bridge becomes zero at wind speed of 72.01 m/s. In this case, the downstream existing bridge was subjected to galloping oscillation induced by the turbulent wake of upstream new bridge. The new bridge also results in significant reduction of the flutter speed of existing bridge from the 128.29 m/s flutter speed of the isolated existing bridge to the 75.35 m/s flutter speed of downstream existing bridge.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.4
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• pp.272-277
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• 2009

Three dimensional numerical analysis for the coal fired boiler has been performed to investigate the effect of yaw angle variation of the secondary air nozzles on the combustion characteristics and NOx emission. It was found that the prediction gives a good agreement with plant data. The increase in yaw angle up to $20^{\circ}$ have results in the decrease in NOx emission at furnace exit and recirculation flow intensity, together with the increase of unburned carbon in ash. It also has been recognized the remarkably change in configuration of fire ball with increase in yaw angle. The results from this study would be valuable in the case of the combustion modification of the corner firing coal-fired utility boiler.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.5
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• pp.12-18
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• 2006

A new steady approach has been developed to predict the transonic buffet onset of a high speed aircraft. In this paper, the flow is assumed to be steady for the buffet onset. The present study involves the analysis of a distinct change in the variation of various static aerodynamic parameters. These distinct changes indicates the onset of transonic buffet. Among the various aerodynamic parameters considered in this study, the variation in the center of pressure has shown to provide a clearest indicator of transonic buffet onset. This new steady approach can be applied to predict the transonic buffet onset for airfoils with shock induced separation bubble and for large swept wings with small aspect ratios. Good agreements have been obtained compared with unsteady wind tunnel buffet test data. Based on the results obtained the new steady approach, it can be newly suggested that the distinct slope changes of the center of pressure curve can be used as an indicator of buffet onset for the steady experimental method on a full aircraft configuration.

• Proceedings of the KAIS Fall Conference
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• 2012.05b
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• pp.512-516
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• 2012

Recently the Korean government's green energy growth policy has been taken at the national level due to the sufficient supply of renewable energy. Some specific technique should be taken in consideration for the operation of the grid voltage and power quality management. In this case, there may have some chance of operational problems. Typical problems arise when grid-connected solar power produced by Pacific sunshine. The power flow in the reverse direction can create overvoltage on the distribution line and gives value of malfunction on the system. Line voltage and overvoltage adjustment practice can stop these symptoms occurred. Under these circumstances, this paper presents an interconnection test devices for photovoltaic(PV) systems composed of distribution system simulator, PV system simulator and control and monitoring systems using the LabVIEW S/W, and simulates the customer voltage characteristics considering the 3 parameters on the introduction capacity for PV systems, system configuration and Power factor. This paper also proposes a new calculation algorithm for voltage profile to make comparison between calculation values and test device values. The results show that the simulation results for the normal operation characteristics of PV systems which are very practical and effective.