• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1055-1060
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• 2009

Noise is one of the major environmental problems in human life. But hot water distributers with the flow rate control valve bring about often noise according to the heating control condition in residential buildings. The sound power level increased as the flow rate and pressure difference increased. And thus, experimental analyses for the flow rate control and the pressure difference control were carried out in this study to reduce the noise emitted from the flow rate control valve. As the results, the flow rate control method using a SMA(Shape Memory Alloy)-valve and the flow rate control system using a pressure difference sensor can be expected to control noise in the region of below 50 dB of sound power level.

• 한국철도학회논문집
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• 제10권4호
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• pp.438-443
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• 2007

This paper proposes an integrated SE process for the development of railway systems with safety assessment included. Although the safety assessment process must be performed with SE process properly with good coordination, the interfaces between the two processes have not been clear. Thus, in many of safety critical system developments in Korea, it is difficult to assess safety in proper development phase. The process model proposed in this paper is based on both the concept of system life cycle and the repetitive use of SE process. In each of development phases, appropriate safety assessment methods are described. Also the evaluation of the integrated system incorporating safety factors is described. The resultant process model is expressed by the Enhanced Functional Flow Block Diagram (EFFBD) using a CASE tool. The model also allows timeline analysis for identifying activity flow and data flow, resulting in the effective management of process. In conclusion, the integrated process enable both the SE process and safety assessment process to cooperate with each other from early development phase throughout the whole system life cycle.

• Tribology and Lubricants
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• 제28권6호
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• pp.278-282
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• 2012

Various bearings such as deep-groove ball bearings, angular-contact ball bearings, and roller bearings are used to support the load and to lubricate between the shaft and the housing. The bearings of potential rolling systems in a turbo pump are the deep-groove ball bearings as comparing with the bearings with rolling elements such as cylindrical rollers, tapered cylindrical rollers, and needle rollers. The deep-groove ball bearings consist of rolling elements, an inner raceway, an outer raceway and a retainer that maintain separation and help to lubricate the rolling element that is rotating in the raceways. In the case of water-lubricated ball bearings, however, fluid friction between the ball and raceways is affected by the entry direction of flow, rotation speed, and flow rate. In addition, this friction is the key factor affecting the bearing life cycles and reliability. In this paper, the characteristics of flow conditions corresponding to a deep-groove ball bearing are investigated numerically, with particular focus on the friction distribution on the rolling element, in order to extend the analysis to the area that experiences solid friction. A simple analysis model of fluid flow inside the water-lubricated ball bearing is analyzed with CFD, and the flow characteristics at high rotation speeds are presented.

• Carbon letters
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• 제28권
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• pp.105-110
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• 2018

Owing to their scalability, flexible operation, and long cycle life, vanadium redox flow batteries (VRFBs) have gained immense attention over the past few years. However, the VRFBs suffer from significant polarization, which decreases their cell efficiency. The activation polarization occurring during vanadium redox reactions greatly affects the overall performance of VRFBs. Therefore, it is imperative to develop electrodes with numerous catalytic sites and a long cycle life. In this study, we synthesized heteroatom-rich carbon-based freestanding papers (H-CFPs) by a facile dispersion and filtration process. The H-CFPs exhibited high specific surface area (${\sim}820m^2g^{-1}$) along with a number of redox-active heteroatoms (such as oxygen and nitrogen) and showed high catalytic activity for vanadium redox reactions. The H-CFP electrodes showed excellent electrochemical performance. They showed low anodic and cathodic peak potential separation (${\Delta}E_p$) values of ~120 mV (positive electrolyte) and ~124 mV (negative electrolyte) in cyclic voltammetry conducted at a scan rate of $5mV\;s^{-1}$. Hence, the H-CFP-based VRFBs showed significantly reduced polarization.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1660-1664
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• 2008

Extra-corporeal Life Support System (ECLS) is the device used in emergency cases to substitute a extracorporeal circulation in open heart surgery, cardiac arrest or in acute cardiopulmonary failure. To obtain the effect of counter-pulsation on hemodynamic response in the ECLS quantitatively, we developed cardiovascular model which consists of 12 compartment model of heldt et al. and 3 compartment model of Schreiner et al. based on windkessel approximation. We compared coronary perfusion, arterial pulse pressure, cardiac output, and left ventricular pressure-volume diagram according to flow configuration such as counter-pulsation, copulsation, and continous flow. When counter-pulsation was applied, 5% higher coronary perfusion, 26% lower pulse pressure, and 2% higher cardiac output than copulsation condition were calculated. We conclude that counter-pulsation configuration in the ECLS is hemodynamically more stable than copulsation and influences the positive effect to recover ventricles.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 추계학술대회 논문집
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• pp.115-116
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• 2013

Recently environmental problems such as greenhouse gas emissions has become a global problem. As a result, the current that can be easily used to Petroleum and coal reserves of fossil energy and environmental issues, coupled with the limitations of this finding for renewable energy to replace the movement is spreading around the world. Among them Energy Storage System with secondary battery technology has been increased interest in, Redox flow batteries, unlike the conventional theory, the life of the rechargeable battery almost no restrictions existing lithium-ion batteries 10 times more than the life of the road. In this paper, power plant or power system, installed in a building that can cope with the rapid increase in demand for power redox flow battery for 100kW PCS will be introduced.

• 한국유체기계학회 논문집
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• 제8권6호
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• pp.40-46
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• 2005

Because of design and manufacturing costs, it is important to predict an expected life of bellows with component stresses of bellows as its design factors and material characteristics. In this study, numerical analyses are carried out to elucidate the thermal and flow characteristics of the bellows-seal gate and globe valves for high temperature (max. $600^{\circ}C$) and for high pressure (max. $104 kgf/cm^2$) conditions. Using commercial codes, FLUENT, which uses FVM and SIMPLE algorithm, and ANSYS, which uses FEM, the pressure and temperature fields are graphically depicted. In addition, when bellows have an axial displacement, thermal stress affecting bellows life is studied. The pressure and temperature values obtained from the flow analyses are adopted as the boundary conditions for thermal stress analyses. As the result of this study, we got the reasonable coefficients for valve and thermal stress for bellows, compared with existing coefficients and calculated values.

• 펄프종이기술
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• 제35권5호
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• pp.37-45
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• 2003

To investigate the influence of the design and operating parameters of the headbox on hydrodynamics, a pilot headbox system and pressure monitoring apparatus were constructed. The pilot headbox system consisted of a circulating water reservoir, centrifugal pump, distributor, turbulence generator and slice. The distributor was designed to function as a pressure attenuator. Flow rate to the headbox and MD and CD velocity profiles in the slice zone were monitored using an ultrasonic flowmeter and Pitot tubes, respectively. As the distance from the step diffusor increased, evener CD velocity profile was observed. Wall effect increased with the increase of the velocity. Flow stability in the headbox was evaluated by injecting a dye at the outlet of the distributor. Application of theoretical analysis based on CFD in designing headboxes is briefly discussed.

• Journal of Information Technology Applications and Management
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• 제20권1호
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• pp.217-240
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• 2013

Noting that compatibility beliefs are important antecedents of technology adoption, the objective of this study was to assess compatibility beliefs that affect users' intention to adopt a mobile entertainment service (MES). We developed a set of key compatibility beliefs: compatibility with life-style, compatibility with social meaning, and compatibility with past flow experiences. We then defined the key dimensions of each construct and developed operational measures for those dimensions. We tested the theorized effects of each of the compatibility constructs on MES adoption. The results support the effects of compatibility beliefs on users' intentions to adopt MES.

• Wind and Structures
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• 제26권3호
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• pp.163-177
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• 2018

Tornadoes are one of the world's deadliest natural phenomena. They are characterized by short life span and danger. It has been observed through post-damage surveys that localities with large numbers of buildings suffer major damage during a tornado attack resulting in huge loss of life and property. Thus,it is important to study interfering buildings exposed to tornado-like vortices. The present study focuses on external and internal pressures developed on building models exposed to translating tornado-like vortices in the presence of an interfering building model. The effects of translating speed and swirl ratio of a tornado-like vortex on external and internal pressures for a principal building in the vicinity of an interfering building are investigated. Results indicate that external and internal pressures are enhanced or reduced depending on the location of the interfering building with respect to the principal building.