• Journal of KSNVE
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• v.9 no.6
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• pp.1247-1258
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• 1999

This paper presents vibration control of a CD-ROM(compact disc-read only memory) drive feeding system consisting of a new type of CD-ROM mount using an electro-rheologocal(ER) fluid. Chemically treated starch particles and silicon oil are used for EF fluid, and its field-dependent yield stresses are experimentally distilled under both the shear and the flow modes. On the basis of the yield stress, an appropriate size of ER CD-ROM mount adapted to conventional feeding system is designed and manufactured. Vibration isolation performance of the proposed mount is evaluated in the frequency domain and compared with that of conventional rubber mount. The ER CD-ROM mount is then installed to the drive feeding system and the system equation of motion is derived. The skyhook controller is then incorporated with the fuzzy technique to improve the performance of ER CD-ROM mount. A set of fuzzy parameters and control rules are obtained from a relation between vertical displacement and pitching motion of the feedng system. Followingthe formulation of the fuzzy-skyhook controller, computer simulation is undertaken in order to evaluate vibration suppression of the CD-ROM drive feeding system subjected to various excitations.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2010.04a
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• pp.346-350
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• 2010

도시화재의 연소 확대성상을 모델화하기 위해 화재실의 개구를 통하여 분출하는 열기류의 온도 평가 실험을 실시하였다. 실험은 축소모형 형태로 개구 조건과 화원조건에 의해 진행이 되었다. 실험 결과 온도분포 Trajectory는 개구종횡비 n에 의해 횡정(橫井)의 연구결과와 비교하여 n=2일때를 제외하고는 다른 경향을 나타냈다. 동일 조건에서 분출화재보유열량 $Q_{ef}$은 개구 조건이 횡장창($B0.2m{\times}H0.1m$)이고, 단일개구일 때 가장 높은 값을 나타냈다. 또한, 분출화재의 발생 한계 발열속도 $Q_{verit}$에서도 굴웅아(堀雄児)의 연구와 유사한 결과를 보이며, 다른 개구조건보다 횡장창($B0.2m{\times}H0.1m$)일 때 높은 값을 나타냈다.

• Journal of IKEEE
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• v.23 no.3
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• pp.878-882
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• 2019

XOR(exclusive-OR)-XNOR(exclusive NOR) circuit is a basic component of 4-2 compressor for high performance arithmetic operation. In this paper we propose an energy efficient XOR-XNOR circuit. The proposed circuit is reduced the internal parasitic capacitance in critical path and implemented with 8 transistors. The circuit produces a perfect output signals for all input combinations. Compared with the previous circuits, the proposed circuit has a 14.5% reduction in propagation delay time and a 1.7% increase in power consumption. Therefore, the proposed XOR-XNOR is reduced power-delay- product (PDP) by 13.1% and energy-delay-product (EDP) by 26.0%. The proposed circuits are implemented with standard CMOS 0.18um technology and verified through SPICE simulation with 1.8V supply voltage.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2003.05a
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• pp.8-13
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• 2003

Historically, IP-based internets have been able to provide a simple best-effort delivery service to all applications they carry. Best effort treats all packets equally, with no service level, packet loss, and delay. But the needs of users have changed. The want to use the new real-time, multimedia, and multicasting applications. Thus, there is a strong need to be able to support a variety of traffic with a variety of quality-of-service requirements. The DiffServ architecture, proposed by the Internet Engineering Task Force(IETF), has become the most viable solution for provising QoS over IP networks. The DiffServ architecture does not specify any handling method between AF out-profile packets and BE packets. This paper propose a mechanism for supporting inter class fairness in the DiffServ architecture. Ⅰ proposed a modified Weighted Round Robin method to protect the BE traffic from AF out-profile packets in the core routers. The proposed technique is evaluated through simulation. Simulation results indicate that the proposed method provides better protection not only for BE packets from AF out-profile packets, but also for the AF in-profile packets in congested networks.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2881-2892
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• 2024

Annular flow refers to a special type of two-phase flow pattern in which liquid flows as a thin film at the periphery of a pipe, tube, or conduit, and gas with relatively high velocity flows at the center of the flow section. This gas also includes dispersed liquid droplets. The liquid film flow rate continuously changes inside the tube due to two processes-entrainment and deposition. To determine the liquid holdup, pressure drop, the onset of dryout, and heat transfer characteristics in annular flow, it is important to have proper knowledge of flow characteristics. Especially a better understanding of entrainment fraction is important for the heat transfer and safe operation of two-phase flow systems operating in an annular two-phase flow regime. Therefore, the objective of this work is to develop a computational model for the simulation of the annular two-phase flow regime and assess the various existing models for the entrainment rate. In this work, Computational Fluid Dynamics (CFD) in ANSYS FLUENT has been applied to determine annular flow characteristics such as liquid film thickness, film velocity, entrainment rate, deposition rate, and entrainment fraction for various gas-liquid flow conditions in a vertical upward tube. The gas core with droplets was simulated using the Discrete Phase Model (DPM) which is based on the Eulerian-Lagrangian approach. The Eulerian Wall Film (EWF) model was utilized to simulate liquid film on the tube wall. Three different models of Entrainment rate were implemented and assessed through user-defined functions (UDF) in ANSYS. Finally, entrainment for fully developed flow was determined and compared with the experimental data available in the literature. From the simulations, it was obtained that the Bertodano correlation performed best in predicting entrainment fraction and the results were within the ±30 % limit when compared to experimental data.

• Journal of the Korea Organic Resources Recycling Association
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• v.32 no.2
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• pp.37-48
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• 2024

Wastewater treatment plants (WWTPs) are obligated to reduce carbon emissions as a part of public sector greenhouse gas (GHG) emission reduction targets. However, Sewage Statistics(2022) shows that CO₂ emissions per wastewater treatment volumes have decreased by only 3.03 % compared to 2020, which is far from enough to meet the Nationally Determined Contribution (NDC) targets. This study aimed to find operational conditions of biological reactors that minimize total carbon footprint (CFP). Total CFP considers both direct emissions from biological processes and indirect emissions from energy consumption. A study was conducted using a computer simulation program which is called as EQPS for a 4-stage BNR WWTP. The results showed that total CFP was reduced by 10.97% compared to the design condition when the mixed liquor recirculation (MLR) was set to 100 % of the influent flow. The N₂O emission factor (EF) of the target WWTP was calculated to be 0.138-0.199 %, which is significantly lower than the IPCC default value of 1.6 %. This study proposes a method to minimize total CFP in WWTPs by optimizing biological reactor operation and emphasizes the need for further research on N₂O emission reduction.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.6
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• pp.1070-1077
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• 2022

The International Maritime Organization has recently strengthened its marine environment regulations. The energy efficiency index has long been an important indicator of ship design, and now, energy efficiency is being enforced for existing ships as well as new ships. To increase the energy efficiency of existing ships, methods such as retrofitting the bow bulb, selecting an optimized trim during ship operation, and installing an energy saving device have been applied. In this study, the ship resistance was numerically simulated using computational fluid dynamics (CFD) under various bow and stern trim conditions. In addition, the bulb was redesigned to further improve the resistance performance under the selected trim conditions. When the improved bulb was applied, the effective horse power increased by approximately 5%. It is, however, necessary to verify whether the redesigned bulb can reduce ship resistance in waves.

• Journal of the Korea Organic Resources Recycling Association
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• v.31 no.2
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• pp.19-38
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• 2023

Nitrous oxide, one of the six greenhouse gases from Kyoto protocol, is known to be emitted in biological nitrification and denitrification reactions at wastewater treatment plant. In this study, EQPS which is a computer program that can simulate nitrous oxide gas emission amount at wastewater treatment plants is used. The MLE process which treats wastewater from combined sewer is studied. Operational variables which are MLR, water temperature at reactor and primary clarifier by-pass percentage are changed to define the condition which produces the least amount of nitrous oxide gas. 200 % of MLR, 20 ℃ of water temperature at bioreactor and 15 % of primary clarifier by-pass percentage are shown the least nitrous oxide emission factor. Also, it is found that the deep aeration tank produces less amount of nitrous oxide gas since less air is required to meet oxygen demand in this type of aeration tank.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.5
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• pp.647-655
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• 2021

The IMO (International Maritime Organization) is discussing the improvement of energy ef iciency of ships in order to reduce greenhouse gas emissions from ships. Currently, by applying an ORC power generation system using waste heat generated from ships, high energy conversion efficiency can be expected from ships. This technology uses an organic medium based on Freon or hydrocarbons as the working fluid, which evaporates at a lower temperature range than water. Through this, it is possible to generate steam (gas) and generate power at a low and low temperature relatively. In this study, the analysis of heat flow between the refrigerant and waste heat in the ORC power generation system, which is an organic Rankine cycle, is analyzed using 3D simulation techniques to determine the temperature change, velocity change, pressure change, and mass change of the fluid flowing of the WHRU (Waste Heat Recovery Unit) inside and the outside the structure. The purpose of this study is to analyze how the mass change affects the structure, and this study analyzed the heat transfer of the heat exchanger from the refrigerant and the exhaust gas of the ship's main engine in the ORC power generation system using this technique.