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김원현(Won Hyun Kim),박태선(Tae Seon Park) 한국전산유체공학회 2009 한국전산유체공학회지 Vol.14 No.3
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 geometric 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 the flow mixing is promoted by the development of vertical 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 cf inner nozzle, but the outer pipe length has no effect on the frequency variation.
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.
입구유동 가진이 있는 층류 후향계단 유동에서 열전달에 대한 프란틀수 효과해석
김원현(Won Hyun Kim),박태선(Tae Seon Park) 대한기계학회 2012 大韓機械學會論文集B Vol.36 No.9
입구유동 가진이 있는 층류 후향계단 유동에서 Pr수의 변화에 따른 열전달 특성변화를 조사하기 위하여 비정상 수치해석을 수행하였다. 입구는 가진주파수와 가진진폭의 변화에 따른 교란이 주어졌고, 온도함수의 물성치가 적용되었다. 열전달 변화에 대한 다양한 특징들이 열경계층 변화에 의해서 설명되 었다. 물성치가 일정한 경우와 비교하였을 때, 물성치가 온도의 함수성이 있는 경우 Pr < 1인 조건에서 열전달은 감소하였고, 반대로 Pr < 1인 조건에서 열전달은 증가하였다. 또한 가진진폭이 증가함에 따라 계단 후류 바닥면에서 열전달도 증가하였다. 그렇지만 가진주파수 변화의 경우 St < 0.2 조건에서 열전달이 크게 증가하는 특정주파수 영역이 존재하였다. 특히, 열전달의 증가는 재부착 길이의 rms값의 변동정도와 밀접한 관련이 있음을 보여주었다. The wall heat transfer of backward-facing step laminar flows with different Prandtl numbers and a pulsating inlet is investigated by unsteady simulations. The inlet is perturbed by the variation of frequency and amplitude. Temperature-dependent transport properties are adopted. Various characteristics of the wall heat transfer are explained by the variation of the thermal boundary layer. For Pr < 1, the wall heat transfer of temperature-dependent properties is decreased compared to that of constant properties, whereas it increases for Pr < 1. In addition, the wall heat transfer increases depending on the pulsating amplitude. However, the results of frequency variation for St < 0.2 show that the heat transfer is strongly enhanced at a specific frequency. In particular, the increase in the wall heat transfer is strongly related to the root mean square of the fluctuations of the reattachment length.
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.
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.
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.