• 대한기계학회논문집B
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• 제24권3호
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• pp.338-345
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• 2000

A model testing has been performed to investigate the flow characteristics of a vortex chamber, which plays a role of a flow switch and passively controls the discharge flow rate. This method of passive flow control is a matter of concern in the design of advanced nuclear reactor systems as an alternative to the active flow control to provide emergency water to the reactor core in case of postulated accidents like LOCA (Loss-Of-Coolant Accident). By changing the inflow direction in the vortex chamber and varying the flow resistance inside the chamber, the vortex chamber can control passively the injection flowrate. Fundamental characteristics such as discharge flow rate and pressure drop of the vortex chamber are measured, and its parametric effects on the performance of the vortex chamber are also systematically investigated.

• Steel and Composite Structures
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• 제28권6호
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• pp.691-708
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• 2018

An innovative Hybrid Passive Resistive configuration for Truss Girder Frames (HPR-TGFs) is introduced in the present study. The proposed system is principally consisting of Fluid Viscous Dampers (FVDs) and Buckling Restrained Braces (BRBs) as its seismic resistive components. Concurrent utilization of these devices will develop an efficient energy dissipating mechanism which is able to mitigate lateral displacements as well as the base shear, simultaneously. However, under certain circumstances which the presence of FVDs might not be essential, the proposed configuration has the potential to incorporate double BRBs in order to achieve the redundancy of alternative load bearing paths. This study is extending the modern Direct Displacement Based Design (DDBD) procedure as the design methodology for HPR-TGF systems. Based on a series of nonlinear time history analysis, it is demonstrated that the design outcomes are almost identical to the pre-assumed design criteria. This implies that the ultimate characteristics of HPR-TGFs such as lateral stiffness and inter-story drifts are well-proportioned through the proposed design procedure.

• 한국산업정보학회논문지
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• 제16권4호
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• pp.1-7
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• 2011

본 논문에서는 수동형 RFID 시스템을 이용한 무선 전력 전송을 위해 910MHz 대역에서 동작하는 정류회로를 두 종류의 쇼트키 다이오드 HSMS_2822와 HSMS_2852를 사용하여 설계한 후 입력 전력, 부하 저항에 따른 출력 전압을 측정하여 RF-DC 변환 효율을 비교 분석하였다. 입력 전력이 -20~17dBm에서 HSMS_2822를 사용했을 때보다 HSMS_2852를 사용한 경우 변환 효율이 더 높게 나타났다. 제작된 정류회로와 다이폴 안테나를 이용하여 RFID 리더기가 동작할 때 거리에 따른 수선되는 전압과 전류를 측정하였으며, 50cm 떨어진 거리에서 2.5V의 전압과 5.75mA의 전류가 측정되었다.

• Nuclear Engineering and Technology
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• 제38권4호
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• pp.343-352
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• 2006

Convenient analytical tools for evaluation of the aperiodic and the fluctuating instabilities of the passive residual heat removal system (PRHRS) of an integral reactor are developed and results are discussed from the viewpoint of the system design. First, a static model for the aperiodic instability using the system hydraulic loss relation and the downcomer feedwater heating equations is developed. The calculated hydraulic relation between the pressure drop and the feedwater flow rate shows that several static states can exist with various numbers of water-mode feedwater module pipes. It is shown that the most probable state can exist by basic physical reasoning, that there is no flow rate through the steam-mode feedwater module pipes. Second, a dynamic model for the fluctuating instability due to steam generation retardation in the steam generator and the dynamic interaction of two compressible volumes, that is, the steam volume of the main steam pipe lines and the gas volume of the compensating tank is formulated and the D-decomposition method is applied after linearization of the governing equations. The results show that the PRHRS becomes stabilized with a smaller volume compensating tank, a larger volume steam space and higher hydraulic resistance of the path $a_{ct}$. Increasing the operating steam pressure has a stabilizing effect. The analytical model and the results obtained from this study will be utilized for PRHRS performance improvement.

• 전기학회논문지
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• 제65권5호
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• pp.878-882
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• 2016

These days, SFCLs are being developed in order to limit fault current. However, the superconducting elements that limit the fault current have such problems as capacity increase and require auxiliary devices including cooling device. If devices that comprise the current power network can withstand fault current for at least one cycle, it is possible to limit the fault current with current limiting elements by bypassing it on the fault line. In this study, the fault current limiter was configured with current transformer, vacuum interrupter, and current limiting element. Through the experience, it was confirmed that the fault current was limited within one cycle. The superconducting element, as a current limiting element, limited the fault current by 80 % within one cycle from fault occurrence, and the passive element limited it more than 95 %. Also, through the comparison between resistance curve and power consumption curve, it was confirmed that the current limiting element using a passive element was more stable than the superconducting element that required capacity increase and other auxiliary devices. It was considered that the FCL proposed in this study could limit fault current stably within one cycle from fault occurrence by using the existing power technologies such as fault current detection and solenoid valve operating circuit.

• 한국정밀공학회지
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• 제21권11호
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• pp.209-218
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• 2004

The purpose of this paper is to suggest a practical and simple method for the identification of the joint mechanical properties and to apply it to human knee joints. The passive moment at a joint was modeled by three mechanical parts, that is, a gravity term, a linear damper term and a nonlinear spring term. Passive pendulum tests were performed in 5 fat and 5 thin men. The data of pendulum test were used to identify the mechanical properties of joints through sequential quadratic programming (SQP) with random initial values. The identification was successful where the normalized root-mean-squared (RMS) errors between the simulated and experimental joint angle trajectories were less than 10％. The parameter values of mechanical properties obtained in this study agreed with literature. The inertia, gravity and the damping constant were greater at fat men, which indicates more resistance to body movement and more energy consumption fer fat men. The suggested method is noninvasive and requires simple setup and short measurement time. It is expected to be useful in the evaluation of joint pathologies.

• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3196-3206
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• 2021

For the Korean design of the PCCS (passive containment cooling system) in an innovative PWR, the overall thermal resistance around a condenser tube is dominated by the heat transfer coefficient of steam condensation on the exterior surface. It has been reported, however, that the calculated heat transfer coefficients by thermal-hydraulic system codes were much lower than measured data in separate effect tests. In this study, a new empirical model of steam condensation in the presence of a noncondensable gas was implemented into the MARS-KS 1.4 code to replace the conventional Colburn-Hougen model. The selected correlation had been developed from condensation test data obtained at the JERICHO (JNU Experimental Rig for Investigation of Condensation Heat transfer On tube) facility, and considered the effect of the Grashof number for naturally circulating gas mixture and the curvature of the condenser tube. The modified MARS-KS code was applied to simulate the transient response of the containment equipped with the PCCS to the large-break loss-of-coolant accident. The heat removal performances of the PCCS and corresponding evolution of the containment pressure were compared to those calculated via the original model. Various thermal-hydraulic parameters associated with the natural circulation operation through the heat transport circuit were also investigated.

• Corrosion Science and Technology
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• 제17권6호
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• pp.310-316
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• 2018

The effect of passive film on corrosion of metals and alloys in a static corrosive environment has been studied by many researchers and is well known, however few studies have been conducted on the electrochemical measurement of metals and alloys during cavitation corrosion conditions, and there are no test standards for electrochemical measurements 'During cavitation' conditions. This study used commercially additive manufactured(AM) pure titanium in tests of anodic polarization, corrosion potential measurements, AC impedance measurements, and repassivation. Tests were performed in 3.5% NaCl solution under three conditions, 'No cavitation', 'After cavitation', and 'During cavitation' condition. When cavitation corrosion occurred, the passive current density was greatly increased, the corrosion potential largely lowered, and the passive film revealed a small polarization resistance. The current fluctuation by the passivation and repassivation phenomena was measured first, and this behavior was repeatedly generated at a very high speed. The electrochemical corrosion mechanism that occurred during cavitation corrosion was based on result of the electrochemical properties 'No cavitation', 'After cavitation', and 'During cavitation' conditions.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.321-325
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• 2005

Bipolar plate is the main part with MEA in automotive PEMFC. It must have a good electrical conductivity and excellent corrosion resistance, be cost effective. Therefore, stainless steels have been studied by many researchers because of its corrosion resistance and cost benefits. But their properties are not sufficient for the application to bipolar plate for automotive PEMFC. In this work, we have performed stamping using various commercial stainless steels to select candidate material for biploar plate and to derive design parameters for stamping simulation. The results showed that a small curvature at the corner of flow field is more favorable due to easier a plastic deformation. Stamping process was simulated by changing surface condition, and the size and angle of channel. The optimum shape and spring back phenomena were evaluated. Surface coating was applied to increase the corrosion resistance and electrical conductivity of stainless steel. The electrical interfacial resistance was 10 to $15m{\Omega}cm^2$ under clamping force of 150psi. But corrosion resistance of coating on the stainless steel was not good due to the unstableness of microstructure.

• 센서학회지
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• 제9권1호
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• pp.76-82
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• 2000

본 연구에서는 내부전극 접합기술을 이용하여 적층구조의 PTC 서미스터를 제작하였다. 적층구조 PTC 서미스터는 저항, 소형, 대전류 등의 특징을 갖는다. PTC 특성을 조사하기 위하여 첨가제효과, 전압-전류특성, 온도특성, 복합임피던스 특성 등을 측정하였다. 적층구조 PTC서미스터는 저항의 온도특성과 전압-전류특성에서 높은 비선형성을 나타내었다. 적층수가 증가함에 따라 상온저항이 감소되는 특성이 결정립의 효과에 기인됨을 알았다. 전류의 스윗칭 변화는 적층구조가 갖는 열용량의 크기에 비례하였으며, 적층수가 증가할수록 스윗칭 시간이 증가하였다.