입구유동 가진이 있는 층류 후향계단 유동에서 열전달에 대한 Prandtl 효과해석

김원현(Won Hyun Kim),박태선(Tae Seon Park) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10

This study the effect on Prandtl numbers on heat transfer of backward-facing step laminar flow with a pulsating inlet. The characteristics of laminar backward-facing step flow with pulsating inlet are investigated using temperature dependent function of dynamic viscosity and thermal conductivity with unsteady flow simulation. In order to analyze the effect of Prandtl numbers on heat transfer are selected for various values of Prandtl numbers, the dimensionless pulsating frequency and amplitude. The result showed that, an improvement in Nusselt number observed for the increasing pulsating amplitude and both heat transfer enhancement and reduction were detected depending on pulsating frequency

동축제트의 와류주파수 및 혼합특성에 대한 수치해석 연구

김원현(Won Hyun Kim),박태선(Tae Seon Park) 한국전산유체공학회 2007 한국전산유체공학회 학술대회논문집 Vol.2007 No.-

This study focuses on the near-field vortical structure and dynamics of coaxial jets. The characteristics of laminar flow and mixing in coaxial jets are investigated using a unsteady flow simulation. In order to analyze the geometic effects on the vortical structure, several cases of different configurations are selected for various values of the velocity ratio of inner jet to outer jet. From the result, it is confirmed that mixing is promoted by the development of vortical structure and the interaction between inner jet and outer jet. This feature is strongly related to the vortex frequency in the shear-layers. The vortex frequency depends on the velocity ratio and the lip thickness of inner nozzle, but the outer pipe length has no effect on the frequency variation.

마이크로 연소기의 난류연소 유동에 대한 비원형 공기 유입구의 영향

김원현(Won Hyun Kim),박태선(Tae Seon Park) 한국연소학회 2014 KOSCOSYMPOSIUM논문집 Vol.2014 No.5

온도변화에 따른 체성분 분석기의 재현성에 관한 연구

김원현 ( Kim Won-hyun ) 인하대학교 교육연구소 2005 교육문화연구 Vol.11 No.-

The purpose of this study is to assess the reliability of bioelectrical impedance body composition analyzer in determination of the % body fat, FFM, fat mass according to the various circumstantial temperatures. For this purpose, 92 subjects(male=36, female=56) were participated. for the assessment of reliability according various temperatures(10℃, 20℃, 30℃), totally 3 times measurements were accomplished repeatedly. As the statistical method, one-way repeated ANOVAs and two-way repeated ANOVAs were used. The results were followed as : There was no significant difference between male and female according temperatures in %body fat, FFM, fat mass, Total body water. The difference of FFM, % body fat according to temperatures and obesity was not shown in female. therefore, the bioelectrical impedance body composition analyzer which we use in field have enough validity regardless environmental temperatures. For the future study, validity depending on various humidities must be researched.

중속 디젤엔진 밸브트레인의 동특성 계측 및 해석

김원현(Won-Hyun Kim),이수목(Soo-Mok Lee),배종국(Jong-Gug Bae),김도중(Do-Joong Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

A valve train dynamics of newly developed medium speed diesel engine was measured and analyzed. OHV-type valve train is represented by 7-DOF lumped mass model and distributed parameter model for the dynamic simulation. Analysis results with the given cam profiles were compared with the measured valve displacements, accelerations and acting forces. Based on these results, dynamic characteristics of valve train were investigated and the performance and safety were also evaluated. To improve the analysis accuracy, contributions of design parameters(mass and stiffness) to the dynamic behavior were investigated with the natural vibration analysis and sensitivity analysis. In addition, model tuning and optimization were performed from the measurement results.

박용 중속 디젤 엔진 밸브트레인의 이상 소음 원인 규명

김원현(Won Hyun Kim),김훈석(Hoon Suk Kim),이수목(Soo Mok Lee) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11

An abnormal noise was detected in the valve train of newly developed medium speed diesel engine during the shop test. The valve train system and cam profiles were designed based on the kinetic and kinematic analyses. And the vibration characteristics of camshaft were also considered. Nevertheless, the impulse noise was generated and it was confirmed that this is due to the crashing of intake valve in closing timing at the initial test. To investigate the root causes, the dynamic behaviors of valve train system and the torsional vibration of camshaft were measured. From these experiments and the additional analysis, it was concluded that the one of the cause of crashing is coincidence of intake valve closing timing and the fuel cam timing. The other one is the maximum acceleration of intake cam which close to maximum operating speed of valve train. In this work, the intake cam profile was modified to reduce the maximum valve acceleration and then the abnormal noise was disappeared.

다공배플 두께가 마이크로 연소기의 유동 및 혼합특성에 미치는 영향

김원현(Won Hyun Kim),박태선(Tae Seon Park) 대한기계학회 2017 大韓機械學會論文集B Vol.41 No.9

다공배플을 가진 마이크로연소기에 레이놀즈응력 난류모형을 이용하여 난류유동 및 혼합특성에 대한 수치해석 연구를 수행하였다. 다공배플은 연소실 내부에 다수의 3차원 와유동을 발생시키는 기하학적 특징을 가지고 있다. 그러한 형상특징 중에서 배플두께를 변화시킬 경우 와유동구조의 다양한 변화가 얻어졌다. 여러 와유동중에서 연료유동으로부터 생성된 와유동은 혼합도 증가에 결정적 역할을 하였다. 연소실 내부의 3차원 와유동구조는 배플두께 변화에 따른 유동의 발달상태에 의존하였다. 특히, 배플두께가 연료유입구 직경보다 작을수록 배플구멍 제트유동의 속도분포는 포물선형태에서 안장모양의 형태로 변하였다. 연소실내부의 재순환영역크기 및 혼합도는 이러한 제트유동구조에 밀접한 상관관계를 가졌다. Flow structure and mixing characteristics in a micro combustor with a multi-hole baffle were numerically studied using the Reynolds stress model. The multi-hole baffle has geometrical features to produce multiple three-dimensional vortices inside combustion chamber. When the thickness of the baffle"s geometrical factors changes, variations of vortical structures occur variously. Among these vortices, the vortex generated from the fuel stream exerts a critical influence on the mixing enhancement. The three-dimensional vortical structure, in its development state, was strongly dependent on the baffle thickness. In particular, as the baffle thickness decreases to values less than the diameter of the fuel hole, the jet stream in baffle holes changes from the parabolic to saddleback profile type. The sizes of recirculation zones inside combustion chamber and the mixing state were closely affected by the structure of the jet streams.

마이크로 프로세서를 사용한 다이렉트 시퀀스 스프레드 스팩트럼 시스템의 동기회로에 관한 연구

방사현(Sa Hyun BANG),김원후(Won Hoo KIM) 한국통신학회 1982 한국통신학회 학술대회논문집 Vol.1982 No.10

난류모델을 이용한 기체수소-액체산소 화염에 대한 수치해석

김원현(Won Hyun Kim),박태선(Tae Seon Park) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.11

초임계조건의 기체수소/액체산소 화염의 난류유동 및 온도장에 대해 난류모델을 이용한 해석이 수행되었다. 실제유체의 연소유동을 해석하기 위하여 화염편모델에 SRK 상태방정식이 도입되었다. 수정된 압력-속도-밀도 연계알고리듬이 초임계유동에 적용되었다. 실험결과를 참조로 6개의 대류항 차분법과 4개의 난류모델의 성능비교가 이루어졌다. 결과로부터 대류항차분법과 난류모델에 대한 예측성이 조사되었다. 선택된 난류모델들은 실제유체 연소유동의 다양한 특징을 고려하기 위해서 수정이 필요함을 나타내었다. Turbulent flow and thermal fields of gaseous hydrogen/liquid oxygen flames at supercritical pressure are investigated by turbulence models. The modified Soave-Redlich-Kwong (SRK) EOS is implemented into the flamelet model to realize real-fluid combustions. For supercritical fluid flows, the modified pressure-velocity-density coupling are introduced. The relative performance of six convection schemes and the predictions of four turbulence models are compared. From the results, the capability of conventional convection schemes for real-fluid combustions and the predictability for each turbulence model are examined. The selected turbulence models are needed to be modified to consider various characteristics of real-fluid combustions.

배플이 부착된 마이크로 연소기의 난류유동 및 연소에 대한 수치해석 연구

김원현(Won Hyun Kim),박태선(Tae Seon Park) 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.5

배플이 있는 마이크로 연소기의 난류유동 및 연소특성이 레이놀즈 응력 모형에 의하여 조사되었다. 형상변화에 따른 난류유동 및 연소에 대한 영향을 살펴보기 위하여, 여러 개의 배플형상이 선택되었다. 유동구조와 온도장의 상관관계가 재순환 영역, 화염크기, 열손실 변화에 의해 조사되었다. 유체간의 혼합은 공기유입구의 직경이 감소하는 경우가 연료유입구의 직경이 감소하는 경우보다 더 빠르게 나타났다. 연료 또는 공기유입구의 직경이 감소함에 따라 연소효율은 증가하였고, 화염길이는 감소하였다. 또한, 공기유입구의 직경이 감소함에 따라 연소온도와 열손실이 증가하고, 반면에 연료유입구의 직경이 감소함에 따라 연소온도와 열손실은 감소되었다. Turbulent flow and combustion characteristics in a micro can combustor with a baffle plate are investigated by a Reynolds Stress Model. In order to examine the geometric effects on the flow and combustion, several configurations are selected for different baffles. The interrelation between the flow structure and the thermal field are inspected by the variation of recirculation region, flame length and heat loss. The flow mixing is faster in case of air hole diameter decreases than fuel hole diameter decreases. As the fuel or air hole diameter decreases, combustion efficiency is enhanced and flame length is decreased. Additionally, as the diameter of air hole decreases, the heat loss and combustion temperature are increased, while the heat loss and combustion temperature are reduced with decreasing the diameter of fuel hole.