• Convergence Security Journal
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• v.16 no.2
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• pp.19-23
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• 2016

The design, management, and operation of network infrastructure have evolved during the last few years, leveraging on innovative technologies and architectures. With such a huge trend, due to the flexibility and significant economic potential of these technologies, software defined networking (SDN) and network functions virtualization (NFV) are emerging as the most critical key enablers. SDN/NFV enhancing the infrastructure agility, thus network operators and service providers are able to program their own network functions (e.g., gateways, routers, load balancers) on vendor independent hardware substrate. They facilitating the design, delivery and operation of network services in a dynamic and scalable manner. In NFV, the management and orchestration (MANO) orchestrates other specific managers such as the virtual infrastructure manager (VIM) and the VNF Manager (VNFM). In this paper, we examine the contents of these NFV MANO systematically and proposes a security system in a virtualized environment.

• Journal of KIISE:Computer Systems and Theory
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• v.31 no.11
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• pp.626-634
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• 2004

In a client-server model, network server systems suffer from both heavy communication and computational loads. While communication channels become increasingly speedy, the existing protocol stack architectures still include mainly three performance bottlenecks of protocol stack processing, system call, and network interrupt overheads. To address these obstacles, in this paper we present a host-independent network system where a network interface card (NIC) is utilized in an efficient manner. First, by offloading network-related portion to the NIC, the host can fully utilize its processing power for other useful purposes. Second, it eliminates the system call overhead, such as context-switching and memory copy operations, since the host communicates with the NIC through its user-level libraries. Third, it a] so reduces the network interrupt operation count as the host handles the interrupt in a segment instead of a packet. The experimental results show that the proposed network system reduces the host CPU overhead for communication system by 68-71%. It also shows that the proposed system improves the communication speed by 11-83% under heavy computational and communication load conditions.

• Advances in Energy Research
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• v.7 no.1
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• pp.1-19
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• 2020

Energy consumption of air-conditioning and refrigeration systems is responsible for about 25 to 30% of the energy demand especially in hot seasons. This equipment is mostly electricity dependent and their use in principle affects negatively the environment. Enhancing the energy efficiency of the existing equipment is important as one of the measures to reduce environment impacts. This paper reports the results of an experimental study to evaluate the impacts of the use electronic expansion valve and variable velocity compressor on the performance of vapor compression refrigeration system. The experimental rig is composed of two independent circuits one for the vapor compression system and the other is the secondary fluid system. The vapor compression system is composed of a forced air condenser unit, evaporator, hermetic compressor and expansion elements, while the secondary system has a pump for circulating the secondary fluid, and an air conditioning heat exchanger. The manufacturer's data was used to determine the optimal points of operation of the system and consequently tests were done to evaluate the influence of variation of the compressor velocity and the opening of the expansion device on the performance of the refrigeration system. A fuzzy logic model was developed to control the rotational velocity of the compressor and the thermal load. Fuzzy control model was made in LabVIEW software with the objective of improving the system performance, stability and energy saving. The results showed that the use of fuzzy logic as a form of control strategy resulted in a better energy efficiency.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.269-274
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• 2008

For fitness-for-service analyses of underground natural gas pipelines, engineering assessment methods against possible defects need to be developed. The assessment methods for high pressure pipeline of KOGAS, was developed using the full size pipe burst tests and the finite element analysis. It included the defect assessment methods for a single and multi-corrosion, corrosion in girth welding part, corrosion in seam welding part, the mechanical damage defects as dent and gouge, crack and large plastic deformation of API 5L X65 pipe. In addition, we developed method to assess pipeline integrity by internal and external load to buried pipeline. Evaluation results were compared with other methods currently being applied to the gas pipeline. The program of Windows environment is made for easily using assessment methods. It provides a consistent user interface, so non-professional technician can easily and friendly use the FFS program from company intranet. Several evaluation programs is easily installed using one installer. Each program constitutes a common input interface and the output configuration program, and evaluation result store and can be recalled at any time. The FFS program based on independent evaluation method is used to evaluate the integrity and safety of KOGAS pipeline, and greatly contribute to safe and efficient operation of pipeline. This paper presents experimental, analytical and numerical investigations to develop the FFS methods for KOGAS pipeline, used as high pressure natural gas transmission pipeline within KOREA. Also, it includes the description of the integrated program for FFS methods.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.47 no.3
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• pp.83-89
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• 2010

Scalable routing is one of the key challenges in designing and operating large scale MANETs. Performance of routing protocols proposed so far is only guaranteed under various limitation, i.e., dependent of the number of nodes in the network or needs the location information of destination node. Due to the dependency to the number of nodes in the network, as the number of nodes increases the performance of previous routing protocols degrade dramatically. We propose Cluster Overlay Dynamic Source Routing (CODSR) protocol. We conduct performance analysis by means of computer simulation under various conditions - diameter scaling and density scaling. Developed algorithm outperforms the DSR algorithm, e.g., more than 90% improvement as for the normalized routing load. Operation of CODSR is very simple and we show that the message and time complexity of CODSR is independent of the number of nodes in the network which makes CODSR highly scalable.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1366-1379
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• 2019

High-gain DC/DC converters have become one of the key technologies for the grid-connected operation of new energy power generation, and its research provides a significant impetus for the rapid development of new energy power generation. Inspired by the transformer effect and the ripple-suppressed ability of a coupled inductor, a double-coupled inductor high gain DC/DC converter with a ripple absorption circuit is proposed in this paper. By integrating the diode-capacitor voltage multiplying unit into the quadratic Boost converter and assembling the independent inductor into the magnetic core of structure coupled inductors, the adjustable range of the voltage gain can be effectively extended and the limit on duty ratio can be avoided. In addition, the volume of the magnetic element can be reduced. Very small ripples of input current can be obtained by the ripple absorption circuit, which is composed of an auxiliary inductor and a capacitor. The leakage inductance loss can be recovered to the load in a switching period, and the switching-off voltage spikes caused by leakage inductance can be suppressed by absorption in the diode-capacitor voltage multiplying unit. On the basis of the theoretical analysis, the feasibility of the proposed converter is verified by test results obtained by simulations and an experimental prototype.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.66-72
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• 2019

To improve ride quality and running stability of high speed train(HST), it is important that connection between coaches adopts the articulated bogies by using a gangway ring, unlike the conventional independent bogies assembled with car bodies. Although the gangway ring should be ensured absolute safety against passenger movement between coaches during train operation, there is still a lack of quantitative durability criteria of that. Therefore, in order to improve the passenger safety of HST, it is important to study the test requirements on durability evaluation for the ring. In this study, seven mixed loading cases were derived from the triaxial loading(vertical/lateral/longitudinal) modes. The safety factor of each component is at least 2.4 or more from the results of the finite element analysis. In addition, fatigue safety was evaluated through durability analysis from the viewpoint of strain-life design. Durability tests for the gangway ring carried out a total of 10 million cycles in 4 phases load conditions. After the durability test, the defect of each component was investigated using nondestructive testing techniques.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.4
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• pp.456-465
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• 2019

PHEV(Plug in Hybrid Electric Vehicle) and BEV(Battery Electric Vehicle) equip high voltage batteries to drive motor and vehicle electric system. Those vehicle require OBC(On-Board Charger) for charging batteries and LDC(Low DC/DC Converter) for converting from high voltage to low voltage. Since the charger and the converter actually separate each other in electrical vehicles, there is a margin to reduce the vehicle weight and area of installation by integration two systems. This paper studies a 1.5kW LDC converter that can be integrated into an OBC using an isolated current-fed converter by simplifying the design of LDC transformers. The proposed LDC can control the final output voltage of the LDC by using a fixed arbitrary output voltage of the bidirectional buck-boost converter, so that Compared to the existing OBC-LDC integrated system, it has the advantage of simplifying the transformer design considering the battery voltage range, converter duty ratio and OBC output turn ratio. Prototype of the proposed LDC was made to confirm normal operation at 200V ~ 400V input voltage and maximum efficiency of 91.885% was achieved at rated load condition. In addition, the OBC-LDC integrated system achieved a volume of about 6.51L and reduced the space by 15.6% compared to the existing independent system.