• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.46 no.12
• /
• pp.986-993
• /
• 2018

Lateral thrust jet has better maneuverability performance than the control surface like the conventional fin for attitude control or orbital transition of guided weapons. However, in the supersonic region, a jet interaction flow occurs due to the lateral thrust jet during flight, and a complicated flow structure is exhibited by the interaction of the shock wave, boundary layer flow, and the vortex flow. Especially, hit-to-kill interceptors require precise control and maneuvering, so it is necessary to analyze the effect of jet interaction flow. Conventional jet interaction analyses were performed under low altitude conditions, but there are not many cases in the case of medium altitude condition, which has different flow characteristics. In this study, jet interaction flow analysis is performed on the lateral jet controlled interceptor operating at medium altitude. Based on the results, the structural characteristics of the flow field and the changes of aerodynamic coefficient are analyzed.

• New & Renewable Energy
• /
• v.18 no.2
• /
• pp.73-81
• /
• 2022

This study was aimed at designing a condenser, as a component of the organic Rankine cycle system for ships. The condenser was manufactured through press molding to achieve a bent shape to enhance the heat transfer performance, considering the shape of the heat transfer plate used in a brazing plate heat exchanger. The heat transfer plate was made of copper-nickel alloy. The required heat transfer rate for the condenser was 110 kW, and the maximum number of layers was set as 25, considering the characteristics of high-temperature brazing. Computational fluid dynamics techniques were used to perform the thermal fluid analysis, based on the ANSYS CFX (v.18.1) commercial program. The heat transfer rate of the condenser was 4.96 kW for one layer (width and length of 0.224 and 0.7 m, respectively) of the heat transfer exchanger. The fin efficiency pertaining to the heat transfer plate was approximately 20%. The heat flow analysis for one layer of the heat exchanger plate indicated that the condenser with 25 layers of heat transfer plates could achieve a heat transfer rate of 110 kW.

• International Commerce and Information Review
• /
• v.18 no.4
• /
• pp.263-281
• /
• 2016

The Importance of SEP (Standard Essential Patents) Procurement Operation is on the side of Governmental and Public both to accelerate the national trade negotiation competitiveness. To operate cooperative system of SEP creation and management, Government should monitor the effect and performance periodically to public sectors. and To achieve the support objectives, it should establish the virtuous circle infrastructure between R&D and economic performance on SEP. This can make the SEP enhancement to pursue the international competitiveness on Intellectual Property Rights. Especially the specific support approach to each phase of the SEP declaration matrix is essential to consolidate the possibility of SEP creation and acquisition. In this study, the concepts of SEP to accelerate the national trade negotiation competitiveness and the prior research were verified through the investigation of market trend and current state of affair analysis. Through the analysis of international and domestic situation of SEP procurement and management, We have found the results as follows. First of all, the leading conglomerates and the Government should focus on the secondary and tertiary industries to create and acquire SEPs to accomplish the effectiveness of selection and concentration. In second, the SMEs and Univ. Labs should focus on the quaternary sector of the economy to retain the competitiveness of speed and challenge on SEP related. From this study, the appropriateness of the tailored-support management model should be institutionalized, and the results implied an research in order to examine the suitability among the current SEP to enhance the competitiveness of national trade research issues.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.44 no.8
• /
• pp.38-44
• /
• 2007

This paper describes a 12 bit 80MHz CMOS D/A converter for wireless transceiver. Proposed circuit in the paper employes segmented structure which consists of four stage 3bit thermometer decoders. Proposed D/A converter is manufactured 0.35um CMOS n-well digital standard process and measurement results show a ${\pm}1.36SB/{\pm}0.62LSB$ of INL/DNL and $46pV{\cdot}s$ of glitch energy. SNR and SFDR are measured to be 58.5dB and 64.97dB @ Fs=80MHz and Fin=19MHz with a total power consumption of 99mW. Such results proved that our work has low power consumption, high linearity, low glitch and improved dynamic performance. Therefore, our work can be appled to various high speed and high performance circuits.

• Journal of KIISE:Computing Practices and Letters
• /
• v.10 no.6
• /
• pp.484-498
• /
• 2004

In this paper. we propose a novel performance monitoring scheme for heterogeneous SOAP nodes. The scheme is basically based on two-level (kernel-level and user-level) packet filtering of TCP flows. By TCP flow, we mean a sequence of raw packet streams on a TCP transaction. In this scheme, we detect and extract SOAP operations embedded in SOAP messages from TCP flows. Therefore, it becomes possible to monitor heterogeneous SOAP nodes deployed on diverse SOAP-based middlewares such as .Net and Apache AXIS. We present two implementation mechanisms for the proposed scheme. The first mechanism tries to identify SOAP operations by analyzing all fragmented SOAP messages on TCP flows. However, a naive policy would incur untolerable overhead since it needs to copy all packets from kernel to user space. The second mechanism overcomes this problem by selectively copying packets from kernel to user space. For selective copying, we use a kernel-level packet filtering method that makes use of some representative TCP flags.(e.g. SIN, FIN and PSH). In this mechanism, we can detect SOAP operations only from the last fragment of SOAP messages in most cases. Finally, we implement a SOAP monitoring system using a component ca]led SOAP Sniffer that realizes our proposed scheme, and show experimental results. We strongly believe that our system will play a vital role as a tool for various services such as transaction monitoring and load balancing among heterogeneous SOAP nodes.

• Journal of Practical Agriculture & Fisheries Research
• /
• v.4 no.1
• /
• pp.128-137
• /
• 2002

This study was conducted to develop the heat exchanger by utilizing the heat energy of underground water(15℃), which might be used for cooling and heating system of the agricultural facilities. We developed the heat exchanger by using the parallel type plat fin tube made of Aluminum(Al 6063), which was named Aloo-Heat(No. 0247164, offered by Korean Intellectual property Office). The trial manufactures were made from Aloo-heat which was 600mm, 700mm length respectively, and It were welded to the end "U" type in order to direct flow of the underground water. The performance test was carried out under the condition of open space and room temperature with the change of flow rate of the underground water and air. The results are as follows. 1. The trial manufactures had convection heat value from 33 to 156 W/m²℃, and It was coincided with design assumption. 2. The amount of energy transfer was increased with the increment of the area of heat transfer, the air flow, the gap of temperature inlet & outlet the underground water and the air. 3. The heat value was 6,825W when the air flow was 6,000m³/h and the gap of temperature between inlet and outlet of the underground water was 6℃, and It dropped from 25.8℃ to 23.2℃(-2.6℃ difference). The convection heat value was 88.5W/m²℃. 4. The heat value was 2.625W when the air flow was 4,000m³/h and the gap of temperature between inlet and outlet the underground water was 2℃, and It dropped from 27℃ to 22.5℃(-4.5℃ difference). The convection heat value was 33.6W/m²℃. 5. Correlation values(R²) of the testing heat values of the trial manufacture type I, II, and III were 0.9141, 0.8935, and 0.9323 respectively, and correlation values(R²) of the amount of the air flow 6,000m³/h, 5,000m³/h, 4,000m³/h were 0.9513, 0.9414, and 0.9003 respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.12 no.12
• /
• pp.1098-1125
• /
• 2000

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigerating Engineering in 1998 and 1999 has been done. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environment. The conclusions are as follows. 1) A review of the recent studies on fluid flow, turbomachinery and pipe-network shows that many experimental investigations are conducted in applications of impingement jets. Researches on turbulent flows, pipe flows, pipe-networks are focused on analyses of practical systems and prediction of system performance. The results of noise reduction in the turbomachinery are also reported. 2) A review of the recent studies on heat transfer analysis and heat exchanger shows that there were many papers on the channel flow with the application to the design of heat exchanger in the heat transfer analysis. Various experimental and numerical papers on heat exchanger were also published, however, there were few papers available for the analysis of whole system including heat exchanger. 3) A review of the recent studies on heat pump system have focused on the multi-type system and the heat pump cycle to utilize treated sewage as the heat source. The defrosting and the frosting behaviors in the fin-tube heat exchanger is experimentally examined by several authors. Several papers on the ice storage cooling system are presented to show the dynamic simulation program and optimal operation conditions. The study on the micro heat pipes for the cooling of high power electronic components is carried out to examine the characteristics of heat and mass transfer processed. In addition to these, new type of separate thermosyphon is studied experimentally. 4) The recent studies on refrigeration/air conditioning system have focused on the system performance and efficiency for new alternative refrigerants. New systems operating with natural refrigerants are drawing lots of attention. In addition to these, evaporation and condensation heat transfer characteristics of traditional and new refrigerants are investigated for plain tubes and also for microfin tubes. Capillary tubes and orifice are main topics of research as expansion devices and studies on thermophysical properties of new refrigerants and refrigerant/oil mixtures are widely carried out. 5) A review of the recent studies on absorption cooling system shows that numerous experimental and analytical studies on the improvement of absorber performance have been presented. Dynamic analysis of compressor have been performed to understand its vibration characteristics. However research works on tow-phase flow and heat transfer, which could be encountered in the refrigeration system and various phase-change heat exchanger, were seemed to be insufficient. 6) A review of recent studies on duct system shows that the methods for circuit analysis, and flow balancing have been presented. Researches on ventilation are focused on the measurement of ventilation efficiency, and variation of ventilation efficiency with ventilation methods by numerous experimental and numerical studies. Furthermore, many studies have been conducted in real building in order to estimate indoor thermal environments. Many research works to get some information for cooling tower design have been performed but are insufficient. 7) A review on the recent studies on architectural thermal environment and building mechanical systems design shows that thermal comfort analysis is sitting environment, thermal performance analysis of Korean traditional building structures., and evaluation of building environmental load have been performed. However research works to improve the performance of mechanical system design and construction technology were seemed to be insufficient.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.35 no.2
• /
• pp.145-152
• /
• 2011

The performance of flat-tube radiators with louvered fins was numerically investigated for different tube insertion lengths. The results of numerical analysis using CFX-11 were compared with experimental results. In this study, three types of flat-tube radiators with louvered fins were considered. An experiment was conducted to validate the numerical results. Flow rate ratio (FR) and Stotal were introduced to understand the uniformity of flow distribution easily. The results of numerical analysis revealed that the heat transfer rate and pressure drop increased as the mass flow rate increased. Further, the results showed that the heat transfer rate of sample 3 with h/D = 0.5 was higher than that of the other samples. The pressure drop increased as the insertion length toward the header part increased, and the pressure drop in the case of sample 3 appeared to be the highest. The factor Stotal showed that the uniformity of the flow distribution in the case of sample 1 with h/D = 0 was higher than that in the case of the other samples.

• Journal of Service Research and Studies
• /
• v.7 no.2
• /
• pp.17-41
• /
• 2017

The purpose of this research is to investigate the factors that impact customer satisfaction and loyalty in mobile payment services. Specifically, this research (1) studies the influence of company reputation on customer satisfaction and loyalty, (2) examines service quality dimensions that increase customer satisfaction, and (3) assesses switching barriers as moderators in influencing customer loyalty. Findings of this empirical research reconfirm the point of view that company reputation, service quality, and switching barriers are crucial for customer satisfaction in mobile payment services. The research methodologies that were used to verify the hypothesis in this study included customized surveys and structural equation modeling. The results demonstrated that company reputation significantly affects customer satisfaction and loyalty. Additionally, the results indicated that only two of the five total service qualities, ease of use and the security/privacy qualities, have positive influences on customer satisfaction. Customer satisfaction has also proven to be a significant influence on loyalty. Lastly, the results showed that among the factors of switching barriers, the factors of lost performance costs, sunk costs, setup costs, the attractiveness of alternatives, and service recovery have moderating effects on the relationships between customer satisfaction and loyalty. Base on the results, this research recommends that firms aim at devising integrated strategies that make switching barriers act as complements to customer satisfaction.

• Convergence Security Journal
• /
• v.18 no.1
• /
• pp.19-31
• /
• 2018

As the ICT technologies advance, the unprecedently large amount of digital data is created, transferred, stored, and utilized in every industry. With the data scale extension and the applying technologies advancement, the new services emerging from the use of large scale data make our living more convenient and useful. But the cybercrimes such as data forgery and/or change of data generation time are also increasing. For the data security against the cybercrimes, the technology for data integrity and the time verification are necessary. Today, public key based signature technology is the most commonly used. But a lot of costly system resources and the additional infra to manage the certificates and keys for using it make it impractical to use in the large-scale data environment. In this research, a new and far less system resources consuming signature technology for large scale data, based on the Hash Function and Merkle tree, is introduced. An improved method for processing the distributed hash trees is also suggested to mitigate the disruptions by server failures. The prototype system was implemented, and its performance was evaluated. The results show that the technology can be effectively used in a variety of areas like cloud computing, IoT, big data, fin-tech, etc., which produce a large-scale data.