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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.
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.
김원현(Won-Hyun Kim),정건화(Kun-Hwa Jung),이수목(Soo-Mok Lee),류영석(Young-Seok Ryoo) 한국마린엔지니어링학회 2006 한국마린엔지니어링학회 학술대회 논문집 Vol.2006 No.-
Diesel power plant(DPP) with the medium speed diesel engine is operated under the very severe condition in aspect of load and operating time as compared with the marine diesel generator set. So, minimized vibration level have to be insured for the more stable operation of engine and generator. The vibration of generator set mainly comes from the resonance between the rigid modes by resilient mount or distortion modes by structural stiffness and the excitation forces of engine. Then, avoidance of resonance with structural modification is generally well known. In this paper, the first order vibration in non-resonance range and local vibration modes were investigated by impact test, response /ODS(operational deflection shape) measurement and 3D finite element analysis for the additional reduction of vibration. The proposed countermeasures were actually applied and their final effects were verified through the in-situ measurement.
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.