[기타] 흡기관 분사식 수소기관의 연소특성에 관한 수치해석적 연구

노경철(Kyoung-chul Ro),김충익(Chung-ik Kim),류홍선(Hong-sun Ryou),이종태(Jong-Tai Lee) 한국자동차공학회 2000 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

Hydrogen fueled engine with external mixture has higher thermal efficiency than directed injection hydrogen fueled engine. It has not required structural change of an existing gasoline engine. But it has low power output and backfire problem in rich mixture relatively.<br/> Thus the numerical analysis is performed on the hydrogen-fueled engine with external mixture for variable equivalence ratios and it is compared with the experimental and numerical result of gasoline engine with external mixture.<br/> It is found that hydrogen fueled engine with external mixture has very shorter delay of combustion period, higher cylinder pressure and higher cylinder temperature than gasoline engine with external mixture.

유량 조절 밸브가 탑재된 진동수주형 파력발전장치의 터빈 내 유동해석을 위한 수치해석 연구

노경철 ( Kyoung-chul Ro ),오재원 ( Jae-won Oh ),김길원 ( Gil-won Kim ),이정희 ( Jung-hee Lee ) 한국산업융합학회 2021 한국산업융합학회 논문집 Vol.24 No.6

In this paper, a numerical analysis was conducted on the effect of the flow control valve of a oscillation water column(OWC) type wave power generator turbine. The OWC wave power turbine operates with compressed air in the air chamber according to the change of wave height. When the wave height changes rapidly, a flow control valve is required due to overload of the turbine and reduced efficiency. Therefore, in this paper, a flow control valve with an opening angle of 60 degrees was installed in the front of the turbine, and the pressure drop, torque, and overall performance were calculated according to the change of turbine RPM and flow rate of turbine inlet. In conclusion, the flow control valve with an opening angle of 60 degrees affects when the turbine rotates at low rotation and the inlet flow rate is large. But it does not have a significant effect on overall turbine performance and it is necessary to find the optimal angle in the future works.

협착을 수반한 분기혈관에서의 주기 가속도 영향에 따른 혈류유동의 수치해석적 연구

노경철(Kyoung Chul Ro),이성혁(Seong Hyuk Lee),유홍선(Hong Sun Ryou) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

The present study are carried out in order to investigate effect of a periodic acceleration force in stenosed and bifurcated blood vessel. The blood flow and wall shear stress are changed under body movement or gravity variation. Numerical studies are performed with different periodic acceleration conditions and a bifurcation angle. It is found that blood flow and wall shear stress are changed about ±12.5% and ±24% as a acceleration phase angle variation with a same periodic frequency. also wall shear stress at inner(after bifurcation) wall is decreased as increasing bifurcation angle.

점탄성 유체해석용 RANS 기반 난류 모델 개발 및 검증

노경철(Kyoung-Chul Ro) 한국산학기술학회 2017 한국산학기술학회논문지 Vol.18 No.3

대동맥이나 협착된 경동맥에서는 심장수축기에 간헐적으로 난류현상이 발생하고 있으며, 혈액의 점성특성으로 인해 기존 난류모델로는 정확한 해석이 어려운 실정이다. 혈류는 점탄성 유체의 성질을 가지고 있어 유체의 전단 변형률 증가에 따라 점도가 감소하는 점탄성 유체이며, 이러한 점탄성 유체는 난류 유동시 저항 감소 현상이 발생한다. 기존의 난류해석 모델들은 점성변화가 없는 뉴턴 유체에 적합한 모델들이 대부분이기 때문에, 점탄성 유체의 저항 감소 현상을 고려한 비뉴턴 유체 해석에 적합한 난류 모델개발이 필요하다. 본 논문은 난류 모델 가운데 수렴성이 좋고 해석시간이 짧은 표준 k-ε 모델을 기반으로 저항 완충 함수를 이용하여 비뉴턴 유체의 저항감소 현상을 해석할 수 있는 수정된 난류모델을 제시하였으며, 이를 기존 난류모델들과 비교하여 제시된 난류 모델을 검증하였다. 새로 제시된 수정된 난류모델은 벽함수 및 점성저층을 고려하지 않았기 때문에 해석시간이 대폭적으로 감소하였으며, 적은 격자수를 이용하여 효율적으로 비뉴턴 유체의 난류 현상을 해석할 수 있기 때문에 향후 혈류해석 및 점탄성유체 해석에 적용할 예정이다. When the systolic blood pressure is high, intermittent turbulence in blood flow appears in the aorta and carotid artery with stenosis during the systolic period. The turbulent blood flow is difficult to analyze using the Newtonian turbulence model due to the viscous characteristics of blood flow. As the shear rate is increased, the blood viscosity decreases by the viscoelastic properties of blood and a drag reduction phenomenon occurs in turbulent blood flow. Therefore, a new non-Newtonian turbulent model is required for viscoelastic fluid and hemodynamics. The main aims of this study were to develop a non-Newtonian turbulence model using the drag reduction phenomenon based on the standard k-ε turbulent model for a general non-Newtonian fluid. This was validated with the experimental data and has a good tendency for non-Newtonian turbulent flow. In addition, the computation time and resources were lower than those of the low Reynolds number turbulent model. A modified turbulent model was used to analyze various turbulent blood flows.

주기 가속도 위상변화에 따른 협착 및 분지 혈관의 혈류 특성에 대한 수치해석적 연구

노경철(K.C. Ro),조성욱(S.W. Cho),이성혁(S.H. Lee),유홍선(H.S. Ryou) 한국전산유체공학회 2008 한국전산유체공학회지 Vol.13 No.3

The present study is carried out in order to investigate the effect of the periodic acceleration in the stenosed and bifurcated blood vessels. The blood flow and wall shear stress are changed under body movement or acceleration variation. Numerical studies are performed for various periodic acceleration phase angles, bifurcation angles and section area ratios of inlet and outlet. It is found that blood flow and wall shear stress are changed about ±20 % and ±24 % as acceleration phase angle variation with the same periodic frequency. also wall shear stress and blood flow rate are decreased as bifurcation angle increased.

점탄성 유체의 난류 해석을 위한 수정된 k-ε 난류모델 개발 및 혈류역학에의 적용

노경철(K.C. Ro),유홍선(H.S. Ryou) 한국전산유체공학회 2010 한국전산유체공학회지 Vol.15 No.4

This article describes the numerical investigation of turbulent blood flow in the stenosed artery bifurcation under periodic acceleration of the human body. Numerical analyses for turbulent blood flow were performed with different magnitude of periodic accelerations using a modified turbulence model which was considering drag reduction of non-Newtonian fluid. The blood was considered to be a non-Newtonian fluid which was based on the power-law viscosity. In order to validate the modified k-ε model, numerical simulations were compared with the standard k-ε model and the Malin's low Reynolds number turbulence model for power-law fluid. As results, the modified k-ε model represents intermediate characteristics between laminar and standard k-ε model, and the modified k-ε model showed good agreements with Malin's verified power law model. Moreover, the computing time and computer resource of the modified k-ε model were reduced about one third than low Reynolds number model including Malin's model.

대용량 변압기용 쿨러의 냉각특성에 관한 수치해석적 연구

노경철(Kyoung-Chul Ro),권기영(Ki-Yeoung Kweon),최원호(Won-Ho Choi) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

The purpose of this study is to evaluate the thermal and hydrodynamic characteristics of the cooler system in a large power transformer. The cooling system consists of a pin-tube, fans and an oil pump. To predict the cooling capacity and the pressure drop according to the oil flow, numerical analysis has been conducted using the commercial finite-volume code, FLUENT and the results are compared with the experimental data. The experimental and numerical results shows a good agreement for all the range of oil flow rate.

노즐 형상 및 분사 압력이 하이브리드 노즐 성능에 미치는 영향 연구

노경철(Kyoung-Chul Ro) 한국산학기술학회 2017 한국산학기술학회논문지 Vol.18 No.12

본 하이브리드 노즐은 국부 지점에 집중적으로 분사하기 위해 소화 약제 주위로 워터미스트를 분사하여 커튼과 같이 약제를 가두어 목표 지점에 살포함으로써 소화 성능이 제고 된다. 본 연구에서는 수치해석 연구를 통해 노즐 기단 각 및 워터미스트 노즐 분사 압력이 하이브리드 노즐 성능에 미치는 영향을 워터미스트 및 소화 약제 액적의 평균 분포 반경을 기반으로 정량적으로 비교 분석 하였다. 워터미스트 노즐 실험 결과를 이용하여 수치해서 기법의 타당성을 검증하였으며, 유동장 내 액적 간 충돌, 병합 및 깨짐 등의 거동을 고려하기 위해 정상상태 2-way interaction Discrete Particle Modeling (DPM) 해석을 수행하였다. 분사 압력이 30 bar에서 60 bar로 증가함에 따라 워터미스트 액적의 평균 분포 반경은 약 40 % 감소하는 반면에 소화 약제의 평균 액적 분포 반경은 약 21 % 감소하였다. 또한 기단 각이 30°에서 60°로 2배 증가하였을 때 소화 약제의 평균 분포 반경은 약 24 % 증가하였다. 결과적으로 하이브리드 노즐은 워터미스트를 분사를 통해 내부에 분사된 소화 약제를 국부지점 집중적으로 분사하는 데 목적이 있으므로 소화 약제 액적의 평균 분포 반경을 고려하여 워터미스트 분사 압력과 기단 각의 설계가 중요할 것으로 판단된다. The fire extinguishing performance of hybrid nozzle systems is improved by injecting an extinguishing agent concentrically into the target site and, in this study, water mist is used as a water curtain to confine the droplets of the agent. In this study, we numerically investigated the effect of the foundation angle and injection pressure on the performance of a hybrid nozzle by evaluating the mean radius of the volume fractions of the agent and water mists. An experiment involving a water mist nozzle was carried out to validate the numerical method and then the droplet behaviors, e.g., stochastic collision, coalescence and breakup, were calculated with 2-way interaction Discrete Particle Modeling (DPM) in the steady state for the hybrid nozzle system. The mean radius of the water mists increased by about 40 %, whereas that of the agent decreased by about 21 %, when the injection pressure was increased from 30 bar to 60 bar. In addition, the mean radius of the agent increased by about 24 % as the foundation angle of the hybrid nozzle head increased from 30° to 60°. As a result, it can be inferred that the injection angle and pressure are important factors for hybrid water mist designs.

조립식 클립형 비닐하우스의 강풍 및 폭설시 구조 안정성 평가

노경철(Ro, Kyoung-Chul) 한국산학기술학회 2014 한국산학기술학회논문지 Vol.15 No.6

본 연구는 폭설 및 강풍 시 조립식 비닐하우스의 구조안정성을 해석하였으며, 내재해 규격 중 가장 엄격한 기준인 적설량 40 cm, 풍속 40m/s를 재해 기준으로 고려하여 적설 하중 및 풍 하중이 비닐하우스 구조에 미치는 영향을 분석하였다. 풍 하중의 경우, 공기역학적 특성에 의해 비닐하우스의 형상에 따른 국부적인 압력 분포 특성이 상이하기 때문에 유체-고체 연성 해석 기법을 적용하였다. 적설하중 및 풍하중 해석 결과에서 비닐하우스 하단지지 파이프와 지붕서까래 체결 부분 근처 에서 가장 큰 응력 및 변형이 발생하며, 적설 하중에 비해 풍 하중 시 구조 안정성이 다소 취약함을 확인하였다. 따라서 본 연구 결과를 기반으로 지지 파이프의 변형을 최소화 하면서 설치 및 유지보수가 용이한 조립식 연결 클립 설계를 위한 기초 자료로 활용할 예정이다. Numerical studies were performed to evaluate the structural safety of a greenhouse under both snow and wind loads. In the case of a wind load, fluid-structure interaction (FSI) method was used to consider the local pressure distributions on the greenhouse-induced by aerodynamic characteristics. The results showed that the maximum stress and deformation occur near the junction of pipe supports and rafters of the roof, where connecting clips are installed. Moreover, the wind load is a more severe condition than a snow load. Overall, these results will be used to design a prefabricated connecting clip with easy installation and low maintenance.

점탄성 유체의 난류 해석을 위한 수정된 k-ε 난류모델 개발 및 혈류역학에의 적용

노경철(K.C. Ro),유홍선(H.S. Ryou) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.5

This article described that a high Reynolds number version of a turbulence model was modified by using drag reduction to analyze the turbulent flows of non-Newtonian fluid with visco-elastic viscosity and it was applied hemodynamics which was representative of visco-elastic fluid. The turbulence characteristics of visco-elastic fluid was expanded viscous sublayer region and buffer layer region by drag reduction phenomenon, and also Newtonian turbulence models does not predict because viscosity was related with shear rate of fluid flow. Hence, numerical simulation using a modified turbulence model was conducted under the same conditions that were applied to obtain the experiment results and previous turbulence models and then the numerical investigation of turbulent blood flow in the stenosed artery bifurcation under periodic acceleration of the human body.