• 한국지열·수열에너지학회논문집
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• 제13권1호
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• pp.1-6
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• 2017

In this paper, the flow characteristics of water in the water supply pipes of a WBC array were evaluated. We simulated the flow velocities and pressures for a standard pipe, an expansion pipe with a concentric reducer, and an expansion pipe with an eccentric reducer using computational fluid dynamics. In the case of the standard pipe, when the inlet flow velocities were 0.5 m/s and 2.0 m/s, the maximum flow velocities at the center of the WBC array were 0.54 m/s and 2.74 m/s, respectively, which were the greatest values among those of all the pipe models considered. In the case of the expansion pipe, the maximum flow velocities at the center of the WBC array were almost the same under the same conditions regardless of the type of reducer. The pressure losses in the pipe due to the concentric and eccentric reducers were found to be (165.09 ${\times}$ inlet $velocity^{1.6677}$) and (210.98 ${\times}$ inlet $velocity^{1.6478}$), respectively. The coefficient of determination at this time was greater than 0.99 and was the same for both the models. As a simulation result, it was found that in order to reduce the pressure loss when pipe with WBC array is connected with a conventional pipe, diameter of the pipe with WBC array at that section should be enlarged by one step, and then connected to the conventional pipe with a concentric reducer.

• Ocean and Polar Research
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• 제28권4호
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• pp.385-393
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• 2006

Screening performance of the existing intake screens (drum and travelling screen) on mass impingement of marine animals, a euphausiid, Euphausia pacifica and a scyphozoan medusae, Aurelia aurita that have often clogged intake screens of the Uljin Nuclear Power Plant, was tested. The maximum tolerable densities of marine animals in the inflowing seawater upon the screen were estimated with two different approaches. First the maximum density of jellyfish was calculated from (1) passing amount of seawater per unit time through the screens and (2) the covered area of animals on the screens clogged. The maximum density of krill tolerable in the drum screen was cited from a simulated record of Uljin NPP, then those in the travelling screens were also calculated using the data of drum screen and ratio of seawater amount passing through the screens under the condition of 0.5m water column (W.C.) of the differential pressure (AP) produced by screens, an established permissible limit of ${\Delta}P$. Secondly, the screening performances were also tested by hydrodynamic measurements with various screen models in a circulating water channel equipped with a speed-controlling pump and a differential pressure gauge. From the first approach, the maximum tolerable densities of drum and travelling screen were calculated as 2.0 and $1.5ind/m^3$ for the Jellyfish and 900 and $680ind./m^3$ for the euphausiid, respectively. These densities estimated from the second approach were 2.1 and $0.8ind/m^3$ for the jellyfish and 1059 and $504ind/m^3$ for the euphausiid, respectively. These estimates were compared with the data from historic clogging events to evaluate the practical performance of these intake screens. The comparisons suggest a newly improved intake-screen of which performance should be at least seven times (approximately) better than the existing ones ior the krill and 3.2 times for the jellyfish, respectively, for preventing mass impingement, and for maintaining the condition of the differential pressure between the screens below 0.3 m W.C.

• 한국해양공학회지
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• 제35권4호
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• pp.296-304
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• 2021

Research on the development of marine renewable energy is actively in progress. Various studies are being conducted on the development of wave energy converters. In this study, a numerical analysis of wave-energy extraction performance was performed according to the body shape and scale of the sloped oscillating water column (OWC) wave energy converter (WEC), which can be connected with the breakwater. The sloped OWC WEC was modeled in the time domain using a two-dimensional fully nonlinear numerical wave tank. The nonlinear free surface condition in the chamber was derived to represent the pneumatic pressure owing to the wave column motion and viscous energy loss at the chamber entrance. The free surface elevations in the sloped chamber were calculated at various incident wave periods. For verification, the results were compared with the 1:20 scaled model test. The maximum wave energy extraction was estimated with a pneumatic damping coefficient. To calculate the energy extraction of the actual size WEC, OWC models approximately 20 times larger than the scale model were calculated, and the viscous damping coefficient according to each size was predicted and applied. It was verified that the energy, owing to the airflow in the chamber, increased as the incident wave period increased, and the maximum efficiency of energy extraction was approximately 40% of the incident wave energy. Under the given incident wave conditions, the maximum extractable wave power at a chamber length of 5 m and a skirt draft of 2 m was approximately 4.59 kW/m.

• 대한의용생체공학회:의공학회지
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• 제30권5호
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• pp.393-400
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• 2009

The present study developed a new technique with no physical object on the flow stream but enabling the air flow measurement and easily incorporated with the devices for cardiopulmonary resuscitation(CPR) procedure. A turbulence chamber was formed in the middle of the respiratory tube by locally enlarging the cross-sectional area where the flow related turbulence was generated inducing energy loss which was in turn converted into pressure difference. The turbulence chamber was simply an empty enlarged air space, thus no physical object existed on the flow stream, but still the flow rate could be evaluated. Computer simulation demonstrated stable turbulence formation big enough to measure. Experiment was followed on the proto-type transducer, the results of which were within ${\pm}5%$ error compared to the simulation data. Both inspiratory and expiratory flows were obtained with symmetric measurement characteristics. Quadratic curve fitting provided excellent calibration formula with a correlation coefficient>0.999(P<0.0001) and the mean relative error<1%. The present results can be usefully applied to accurately monitor the air flow rate during CPR.

• International Journal of Fluid Machinery and Systems
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• 제9권3호
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• pp.194-204
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• 2016

Floating ring seals offer an opportunity to reduce leakage flows significantly in rotating machinery. Accordingly, they have been applied successfully to rotating machinery within the last several decades. For rocket turbopump applications, fundamental behavior and design philosophy have been revealed. However, further work is needed to explore the rotordynamic characteristics associated with rotor vibrations. In this study, rotordynamic forces for floating ring seals under rotor's whirling motions are calculated to elucidate rotordynamic characteristics. Comparisons between numerical simulation results and experiments demonstrated in our previous report are carried out. The three-dimensional Reynolds equation is solved by the finite-difference method to calculate hydrodynamic pressure distributions and the leakage flow rate. The entrance loss at the upstream inlet of the seal ring is calculated to estimate the Lomakin effect. The friction force at the secondary seal surface is also considered. Numerical simulation results showed that the rotordynamic forces of this type of floating ring seal are determined mainly by the friction force at the secondary seal surface. The seal ring is positioned almost concentrically relative to the rotor by the Lomakin effect. Numerical simulations agree quite well with the experimental results.

• 센서학회지
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• 제18권4호
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• pp.294-300
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• 2009

Cardiopulmonary resuscitation(CPR) is performed by artificial ventilation and thoracic compression for the patient under emergent situation to maintain at least the minimum level of respiration and blood circulation for life survival. Quality of the pre-hospital CPR not only significantly affects the patient's survival rate but also minimizes side effects caused by CPR. Good quality CPR requires monitoring respiration, however, traditional respiratory air flow transducers cannot be used because the transducer elements are located on the flow axis. The present study developed a new technique with no physical object on the flow stream but enabling the air flow measurement and easily incorporated with the CPR devices. A turbulence chamber was formed in the middle of the respiratory tube by locally enlarging the cross-sectional area where the flow related turbulence was generated inducing energy loss which was in turn converted into pressure difference. The turbulence chamber was simply an empty enlarged air space, thus no physical object was placed on the flow stream, but still the flow rate could be evaluated. Both inspiratory and expiratory flows were obtained with symmetric measurement characteristics. Quadratic curve fitting provided excellent calibration formula with a correlation coefficient>0.999 (P<0.0001) and the mean relative error<1 %. The present results can be usefully applied to accurately monitor the air flow rate during CPR.

• 한국추진공학회지
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• 제23권6호
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• pp.51-58
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• 2019

본 연구에서는 소형 무인기에 사용되는 초소형 가스터빈 엔진의 연소기를 3D 프린팅으로 제작하고, 시험 설비와 리그를 제작하여 연소기 단품 성능시험을 수행하였다. 연소기 성능시험은 두 가지 부하조건에서 당량비를 조절하여 각 부하조건 별 4가지 시험조건에서 수행하였다. 성능시험 결과 연소기의 압력손실과 출구온도분포는 우수하였지만, 연소가스에서 다량의 UHC와 CO가 검출되어 연소효율은 일반적인 가스터빈 연소기에 비해 아주 낮음을 확인하였다. 성능시험을 통해 획득한 정량적 성능데이터는 향후 3D 프린팅 기술로 성능이 개선된 연소기의 설계와 제작에 활용 할 예정이다.

• 한국표면공학회지
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• 제51권4호
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• pp.249-255
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• 2018

High temperature and low temperature gaseous nitriding was performed in order to study of the surface hardening and wear properties of the nitrided AISI 410 Martensitic stainless steels. High temperature gaseous nitiridng (HTGN) was carried out using partial pressure $N_2$ gas at $1,100^{\circ}C$ for 10 hour, and Low temperature gaseous nitiridng (LTGN) was conducted in a gas mixture of NH3 and N2 at $470^{\circ}C$ for 10 hour. The nitrided samples were characterized by microhardness measurements, optical microscopy and scanning electron microscopy. The phases were identified by X-ray diffraction and nitrogen concentration was analyzed by GD-OES. The HTGN specimen had a surface hardness of about $700HV_{0.1}$, $350{\mu}m$ of case depth. A ${\sim}50{\mu}m$ thick, $1,250HV_{0.1}$ hard nitrided case formed at the surface of the AISI 410 steel by LTGN, composed nitrogen supersaturated expanded martensite and ${\varepsilon}-Fe_{24}N_{10}$ iron nitrides. Additionally, the results of the wear tests, carried out LTGN specimen was low friction coefficient and high worn mass loss of ball. The increase in wear resistance can be mainly attributed to the increase in hardness and to the lattice distortion caused by higher nitrogen concentration.

• Nuclear Engineering and Technology
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• 제26권1호
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• pp.126-139
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• 1994

본 연구에서는 BETHSY 실험장치에서 수행한 6" 소형 냉각재 상실사고(LOCA) 실험을 최적 열수력 코드인 CATHARE2 V1.2와 RELAP5/MOD3를 이용하여 계산했다. 본 연구의 주 목적은 소형 LOCA시 관심을 가지는 주요 물리현상인 이상 임계유동, 감압과정, 노심수위 감소, loop seal clearing 등에 대한 두 코드의 소형 LOCA 계산모의능력을 평가하는 것이다. 두코드는 이상 유동현상의 전개 경향이나 발생시점을 비교적 잘 예측하는 것으로 나타났고, CATHARE2의 경우가 실험과 더 잘 일치했다. 그렇지만 두 코드는 loop seal clearing 현상, loop seal clearing 발생후의 노심수위, accumulator 유량거동 등의 예측에는 약간의 편차를 보였는데, 편차의 정도는 RELAP5가 CATHARE2보다 더 큰 것으로 나타났다. 두 코드의 편차요인을 보다 상세히 분석하기 위하여 계면 마찰력, mesh크기, 파단노즐 junction에서의 방출계수(Discharge coefficient)등에 대하여 민감도분석을 수행하였다. 그 결과 CATHARE2의 경우는 계면 마찰력을 증가시킴으로써 감압과정시 일차계통의 질량분포, 즉 증기 발생기 입구 공동(SG inlet plenum)에서의 차압과 Cross√er leg의 차압이 개선되었으며, 증기발생기 외측 열전달계수를 증가시킴으로써 중기발생기의 압력변화를 개선할 수 있었다. RELAP5의 경우는 어떤 하나의 입력변수를 변화시켜서 과도기의 결과를 개선할 수 없었으며 다만, 계면 마찰력 모델링에 여전히 많은 불화실성이 내포되어 있음을 확인했다.확인했다.

• 한국산학기술학회논문지
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• 제10권12호
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• pp.3546-3552
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• 2009

본 연구에서는 천정 설치형 공조기 적용을 위해 연구가 활발히 진행되고 있는 알루미늄 평행류 증발기 해석 프로그램을 개발하여 190mm*650mm*25mm(W*H*D) 크기의 열교환기를 해석하였다. R410A냉매의 분배비가 일정하고 상하로 유동하는 2, 3 패스의 경우와 3 패스이고 분배비율(1:1:1, 1:2:2)을 달리할 때, 열교환 성능을 예측하였다. 계산 결과, 2 패스가 3 패스보다 국소 전열량이 30% 정도 높았지만, 건도에 따른 열전달계수는 25% 낮았으며, 3 패스의 경우, 분배비 1:1:1 보다 1:2:2가 냉매 압력손실이 높게 나타났다. 본 해석에서는 패스당 냉매가 균일하게 분포하는 것으로 가정하였으므로, 패스별로 불균일하게 유동되는 실제의 경우보다 열교환성능을 과대 예측하는 것으로 판단된다.