• Journal of KIISE:Information Networking
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• v.36 no.4
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• pp.275-285
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• 2009

RFID technology using the smart tag technology as a part of the sensor network is currently in the spotlight. But there are still many problems in applying the technology in a ubiquitous environment, induding at the point when anybody can read the tag information and the authentication between the tag and the reader, and security problems in very low-cost smart tag implementation. The proposed scheme is designed to enhance security and efficiency related to various services required in RF networks, based on the reliable peripheral devices for users of passive RFID tag. Using passive RFID tag, which has been applied to authentication transactions in existing papers, this study also proposed an appropriate management scheme that is suitable for a dynamic environment and setting a temporary group to provide various services. also proposed scheme is support RFID grouping, temporary group of service and security servicce, improved efficiency of communication.

• Smart Structures and Systems
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• v.24 no.1
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• pp.83-94
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• 2019

Passive negative stiffness dampers (NSDs) that possess superior energy dissipation abilities, have been proved to be more efficient than commonly adopted passive viscous dampers in controlling stay cable vibrations. Recently, inertial mass dampers (IMDs) have attracted extensive attentions since their properties are similar to NSDs. It has been theoretically predicted that superior supplemental damping can be generated for a taut cable with an IMD. This paper aims to theoretically investigate the impact of the cable sag on the efficiency of an IMD in controlling stay cable vibrations, and experimentally validate superior vibration mitigation performance of the IMD. Both the numerical and asymptotic solutions were obtained for an inclined sag cable with an IMD installed close to the cable end. Based on the asymptotic solution, the cable attainable maximum modal damping ratio and the corresponding optimal damping coefficient of the IMD were derived for a given inertial mass. An electromagnetic IMD (EIMD) with adjustable inertial mass was developed to investigate the effects of inertial mass and cable sag on the vibration mitigation performance of two model cables with different sags through series of first modal free vibration tests. The results show that the sag generally reduces the attainable first modal damping ratio of the cable with a passive viscous damper, while tends to increase the cable maximum attainable modal damping ratio provided by the IMD. The cable sag also decreases the optimum damping coefficient of the IMD when the inertial mass is less than its optimal value. The theoretically predicted first modal damping ratio of the cable with an IMD, taking into account the sag generally, agrees well with that identified from experimental results, while it will be significantly overestimated with a taut-cable model, especially for the cable with large sag.

• Nuclear Engineering and Technology
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• v.56 no.8
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• pp.3286-3297
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• 2024

Traditional text-based system engineering, which has been used in the design and application of passive residual heat removal system (PRHRS) for lead-cooled fast reactors, is prone to several problems such as low development efficiency, long iteration cycles, and model ambiguity. This study aims to effectively address the abovementioned problems by adopting a model-based system engineering (MBSE) method, which has been preliminarily applied to meet the design requirements of a PRHRS. The design process has been implemented based on the preliminary design of the system architecture and consists of three stages: top-level requirement analysis, functional requirements analysis, and design requirements synthesis. The results of the top-level requirements analysis and the corresponding use case diagram can determine the requirements, top-level use cases, and scenario flow of the system. During the functional requirements analysis, the sequence, activity, and state machine diagrams are used to develop the system function model and provide early confirmation. By comparing these sequence diagrams, the requirements for omissions and inconsistencies can be effectively checked. In the design requirements synthesis stage, the Analytic Hierarchy Process is used to conduct preliminary trade-off calculations on the system architecture, after which a white box model is established during the system architecture design. Through these two steps, the analysis and design of the system architecture are ultimately achieved. The resulting system architecture ensures the consistency of the design requirements. Ultimately, a functional hazard analysis was conducted for a specific incident to validate case requirements and further refine the system architecture. Future research can further reduce the design risk, improve the design efficiency, and provide a practical reference for the design and optimization of PRHRS in digital lead-cooled fast reactors.

• Journal of Electrical Engineering and Technology
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• v.6 no.6
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• pp.817-823
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• 2011

This paper introduces an efficient voltage multiplier circuit for improved voltage gain and power efficiency of radio frequency identification (RFID) tags. The multiplier is fully integratable and takes advantage of both passive and active circuits to reduce the required input power while yielding the desired DC voltage. A six-stage voltage multiplier and an ultralow power voltage regulator are designed in a 0.13 ${\mu}m$ complementary metal-oxide semiconductor process for 2.45 GHz RFID applications. The minimum required input power for a 1.2 V supply voltage in the case of a 50 ${\Omega}$ antenna is -20.45 dBm. The efficiency is 15.95% for a 1 $M{\Omega}$ load. The regulator consumes 129 nW DC power and maintains the reference voltage in a 1.1% range with $V_{dd}$ varying from 0.8 to 2 V. The power supply noise rejection of the regulator is 42 dB near a 2.45 GHz frequency and performs better than -32 dB from 100 Hz to 10 GHz frequencies.

• Journal of Power Electronics
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• v.14 no.2
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• pp.203-216
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• 2014

In the conventional dc-dc converter, a pair of additional diode and the adjacent passive component capacitor/inductor can be added to the circuit with an X-shape connection, which generates a family of new topologies. The novel circuits, also called diode-assisted dc-dc converter, enhance the voltage boost/buck capability and have a great potential for high step-up/step-down power conversions. This paper mainly investigates and compares conventional dc-dc converter and diode-assisted dc-dc converter in wide range power conversion from the aspects of silicon devices, passive components requirements, electro-magnetic interference (EMI) and efficiency. Then, a comprehensive comparison example of a high step-up power conversion system was carried out. The two kinds of boost dc-dc converters operate under the same operation conditions. Mathematical analysis and experiment results verify that diode-assisted dc-dc converters are very promising for simultaneous high efficiency and high step-up/step-down power conversion in distributed power supply systems.

• Advances in aircraft and spacecraft science
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• v.7 no.4
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• pp.309-333
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• 2020

The proposed study aims to numerically investigate the performance of hydrofoils in the context of amphibious aircraft application. In particular, we also study the effectiveness of a slotted hydrofoil in minimizing the cavitation phenomenon, to improve the overall water take-off performance of an amphibious aircraft. We use the ICON A5 as a base model for this study. First, we propose an approach to estimate the required hydrofoil surface area and to select the most suitable airfoil shape that can minimize cavitation, thus improving the hydrodynamic efficiency. Once the hydrofoil is selected, we perform 2D numerical studies of the hydrodynamic and cavitating characteristics of a non-slotted hydrofoil on ANSYS Fluent. In this work, we also propose to use a slotted hydrofoil to be a passive method to control the cavitation performance through the boundary layer control. Numerical results of several slotted configurations demonstrate notable improvement on the cavitation performance. We then perform a multiobjective optimization with a response surface model to simultaneously minimize the cavitation and maximize the hydrodynamic efficiency of the hydrofoil. The optimization takes the slot geometry, including the slot angle and lengths, as the design variables. In addition, a global sensitivity study has been carried and it shows that the slot widths are the more dominant factors.

• KIEAE Journal
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• v.15 no.3
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• pp.21-28
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• 2015

Purpose: In this study, we analyzed the energy performance levels and high-performance technology trends through the case studies of foreign high-performance buildings. Method: Buildings built within 10 years were selected for the analysis of recent trends. we analyzed the buildings of U.S.A, Germany and Japan using LEED certified buildings, Passive House certified buildings and CASBEE certified buildings database for the case study of foreign high-performance buildings. A total of 20 high-performance buildings including 14 cases in U.S.A, 4 cases in Germany and 4 cases in Japan were selected. Annual energy consumption levels for 20 high-performance buildings were collected with the actual energy consumption data or data from simulation programs officially recognized by DOE. Annual energy consumption were compared with the energy performance standard of the office buildings in the CBECS database, ASHRAE Standard 90.1-2004 and Building Energy Efficiency Rating System in Korea. Result: The order of the green strategies applied in the main categories are Renewable Energy(63%), Indoor Environment Control(51%), Envelope Improvement(44%) and HVAC System & Control(28%). Specified strategies most widely used in the sub-categories are high-performance Insulation (70%), High Efficiency Heating, Cooling Source Equipment(85%), Photovoltaic&Solar Thermal(80%) and Daylighting(80%).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.9
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• pp.851-857
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• 2010

In this study, an experiment was performed to obtain the optimum design of a passive micromixer for effective mixing by using a microsized device and rectangular obstacles; a low Reynolds number was maintained in the microchannel. The experiment was carried out by varying the number, size, and location of the rectangular obstacles. Further, the Y-channel's shape was optimized for maximizing the mixture ratio, which has limit qualification that an allowed value of pressure drop. The increase in the efficiency of mixing was observed to be greater than that in the case of circular obstacles by approximately 2.5%.

• Journal of the Korean Solar Energy Society
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• v.32 no.3
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• pp.129-137
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• 2012

This thesis introduced an azimuth tracking prismatic daylighting system. The system improved several issues of the previous passive prismatic daylighting system: low efficiency at sunrise and sunset, glare effect and polarized. The system was developed to track the movement of sun with azimuth tracking device, and it has its own power from the attached solar cells. We compared the with previous passive one in terms with system efficiency and daylighting factors(DF).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.12
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• pp.1168-1173
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• 2012

In this paper, we propose a protection architecture of passive optical network (PON) system by using two optical line terminals (OLTs). Using this scheme, the network can sustain services to access area and restores normal operation in faulty conditions. Unlike existing systems, the proposed one increases the efficiency of the system by operating both OLTs using different wavelengths in normal condition. During protection mode, a Shared-bandwidth allocation scheme is employed to maximize the utilization efficiency. Performance analysis shows that the proposed scheme can provide reliability to Ethernet-based PON system very efficiently.