전달함수와 진동응답 측정에 의한 원심펌프에서의 유체력 특성에 관한 연구

최복록,박진무,김광은,Choi, Bok-Lok,Park, Jin-Moo,Kim, Kwang-Eun 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.8

Operating excitation forces of the linear vibratory system are normally determined by direct measurement techniques using load cells, strain gauges, etc. But, hydraulic forces of the rotating turbomachinery such as centrifugal pumps are exerted on an impeller due to asymmety of the flow by the interaction between pump impeller and volute. So, investigations of wide range of hydraulic designs and geometric deviations are difficult by direct method. This paper presents a hybrid approach for fourier transformed operational excitation forces, which uses pseudo-inverse matrix of the transfer matrix for the system and the measured vibrational data with standard installed pump. The determination of the transfer function matrix is based on a linear rotor/stationary system and steady state harmonic response in finite element analysis. And, vibrational data is collected in both vertical and horizontal directions at inboard and outboard bearing housings. The results of the process may be enhanced by making acceleration measurements at many more locations than there are forces to be determined.

엔진 배기매니폴드의 배기가스 누설 해석

최복록,Choi, Bok-Lok 한국자동차공학회 2007 한국 자동차공학회논문집 Vol.15 No.3

Exhaust manifold is generally subjected to thermal cycle loadings ; at hot condition, large compressive plastic deformations are generated, and at cold condition, tensile stresses are remained in highly deformed critical zones. These phenomena originate from that thermal expansions of the runners are restricted by inlet flange connected to the cylinder head, because the former is less stiff than the latter and, the temperature of the inlet flange is lower than that of the runners. Therefore, due to the repetitions of thermal deformation, leakage problems could be occur between inlet flange and cylinder head. In this study, we obtained pressure distributions along gasket bead lines from the finite element analysis and compared to the test results. It shows a good agreement between numerical and experimental results.

진동 가진에 의한 엔진 배기계의 파손에 관한 연구

최복록(Bok-Lok Choi),박상준(Sang-Jun Park) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5

This paper present a method for the assesment of vibration fatigues in engine exhaust system. Analysis technologies by virtual model can reduce the no. of physical tests and development cycles. The prediction processes are based on the construction of FE model for the exhaust system, normal mode analysis and frequency response analysis. The analysis results of eigen frequencies are compared with the model test results. And frequency response results of accelerations and stresses at critical locations were also presented. The analysis method could be applied to asses the vibration fatigue for the engine exhaust manifold. It shows a good agreement between numerical and experimental results.

엔진 배기매니폴드의 열응력 발생에 관한 설계 인자들의 이론적 연구

최복록(Bok-Lok Choi) 한국기계가공학회 2007 한국기계가공학회지 Vol.6 No.1

Exhaust manifold is generally subjected to thermal cycle loadings ; at hot condition, large compressive plastic deformations are generated, and at cold condition, tensile stresses are remained in highly deformed critical zones. These phenomena originate from the fact that thermal expansions of the runners are restricted by inlet flange clamped to the cylinder head, because the former is less stiff than the latter and, the temperature of the inlet flange is lower than that of the runners. Since the failure of an exhaust manifold is mainly caused by geometric constraints between the cylinder head and the manifold, the thermal stress can be controlled by geometric factors. The generic geometric factors include the inter distance (2R), the distance from the head to the outlet (L), the tube diameter(d) and the tube thickness (t). This criteria based on elastic analysis up to onset of yield apparently indicate that the pre-stress also reduces the factor; however, high temperature relaxation may reduce this effect at later operation stage.

복합재 코일스프링 개발을 위한 해석 및 실험적 연구

최복록(Bok Lok Choi),오성하(Sung Ha Oh) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5

열적-기계적 반복하중을 받고 있는 엔진 배기매니폴드의 열피로 수명예측

최복록(Bok Lok Choi),장훈(Hoon Chang) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.7

본 연구에서는 열적-기계적 주기하중을 받고 있는 엔진 배기매니폴드에 대해서 열응력 해석방법과 열피로수명 예측과정을 제시하였다. 즉, 파손현상이 복잡한 배기시스템의 효율적인 유한요소 모델링 방법과 온도 의존성 재료의 시험결과를 이용한 해석 데이터 구성, 그리고 열사이클 하중에 대한 열응력 및 파손 예측방법을 디젤엔진의 배기매니폴드에 대해서 나타내었다. 일반적으로 배기매니폴드의 파손 취약부에서는 고온영역에서 큰 압축소성변형이 발생하고 냉각시에는 인장의 잔류응력이 나타난다. 따라서 이같은 응력과 변형률의 이력곡선으로부터 소성변형의 진폭 또는 소성에너지의 크기를 얻을 수 있으며 이를 통해서 피로수명을 예측할 수 있다. In this study, we performed structural and fatigue analyses of the engine exhaust manifold that was subjected to thermo-mechanical cyclic loading. The methodologies used in this study are based on an approach in which the techniques for modeling the exhaust system, the temperature-dependent properties of the material, and thermal cyclic loading are taken into consideration and a reliable strategy is adopted for failure prediction. An application example shows that at an elevated temperature, considerable compressive plastic deformation is observed and that at a low temperature, tensile stresses remain in those parts of the test exhaust manifold where failure is observed. In order to predict fatigue life, mechanical damage is determined on the basis of the stress-strain hysteresis loops by using the classical Coffin-Manson equation and by adopting a method in which the dissipated plastic energy is taken into consideration.

진동응답 측정에 의한 이중 벌류트형 양흡입 원심펌프의 동적특성

최복록(Bok-Lok Choi),박진무(Jin-Moo Park) 한국소음진동공학회 2000 소음 진동 Vol.10 No.3

컴플라이언스 계수에 의한 노즐하중 하에서의 원심펌프의 축단변위에 관한 연구

최복록(Bok-Lok Choi),박진무(Jin-Moo Park),김광은(Kwang-Eun Kim) Korean Society for Precision Engineering 2000 한국정밀공학회지 Vol.17 No.4

복합재 코일스프링 개발을 위한 수치해석 및 실험적 연구

오성하(Sung Ha Oh),최복록(Bok Lok Choi) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.1

본 연구에서는 자동차 코일스프링을 대상으로 CFRP 복합재 재료의 적용가능성을 제시하였다. 기존 강재료를 복합재로 대체해서 대폭적인 경량화를 추구하기 위해서는 재료특성 뿐만 아니라 스프링의 설계인자들도 함께 최적화를 해야 할 것이다. 따라서 먼저 복합재 코일스프링의 전단특성을 고려해서 최대 비틀림강성을 나타내도록 45도로 와인딩한 봉 구조물을 구성하였으며, 예측된 전단탄성계수를 시험결과와 비교한 결과 매우 근사한 값을 나타내었다. 다음으로 45도로 와인딩된 CFRP 복합재 스프링의 소선직경을 결정하기 위해서 비틀림 강성을 강재와 복합재 두 재료에 대해서 동일하게 하였으며, 그 결과, 소선직경은 11.0 mm에서 17.5mm로 재료가 복합재로 변경됨에 따라서 증가되어야 한다. 마지막으로 이 같이 구성된 복합재 코일스프링의 유한요소모델을 구성해서 스프링상수를 계산하였으며, 시험결과와 비교·평가하였다. This paper shows the feasibility of using carbon-fiber-reinforced polymer (CFRP) composite materials for manufacturing automotive coil springs. For achieving weight reduction by replacing steel with composite materials, it is essential to optimize the material parameters and design variables of the coil spring. First, the shear modulus of a CFRP beam model, which has 45° ply angles for maximum torsional stiffness, was calculated and compared with the test results. The diameter of the composite spring was predicted to be 17.5 mm for ensuring a spring rate equal to that when using steel material. Finally, a finite element model of the composite coil spring with 45° ply angles and 17.5 mm wire diameter was constructed and analyzed for obtaining the static spring rate, which was then compared with experimental results.

복합재 판스프링의 재료특성에 따른 스프링 강성변화와 초기 파단하중 예측

오성하(Sung Ha Oh),최복록(Bok Lok Choi) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.12

본 연구에서는 자동차 판스프링을 대상으로 유리섬유 복합재의 적용을 위한 해석적 방법들을 제시하였다. 즉, 판스프링의 정적거동에 영향을 미치는 복합재 재료의 구성 성분비와 섬유각의 변화 등을 고려한 해석을 수행하였다. GFRP 복합재의 기계적 성질들은 ASTM 표준시험 방법을 따라서 직접 측정하였으며, 역해석 방법을 통해서 섬유와 수지 각각의 직교이방성과 등방성 성질들을 시험결과들로부터 재구성하였다. 다음으로 섬유의 방향과 섬유와 수지의 함유량 비와 같은 주요 재료변수들의 변화에 따른 스프링 계수들의 변화를 분석하였다. 마지막으로 초기 파괴하중을 예측하기 위해서 선형 탄성해석과 파손조건식을 이용해서 점진적 파괴해석을 수행하였으며, 그 결과 최초의 손상부위는 전단응력에 의해 판스프링의 모서리 부위에서 발생하였다. This paper presented analysis methods for adapting E-glass fiber/epoxy composite (GFRP) materials to an automotive leaf spring. It focused on the static behaviors of the leaf spring due to the material composition and its fiber orientation. The material properties of the GFRP composite were directly measured based on the ASTM standard test. A reverse implementation was performed to obtain the complete set of in-situ fiber and matrix properties from the ply test results. Next, the spring rates of the composite leaf spring were examined according to the variation of material parameters such as the fiber angles and resin contents of the composite material. Finally, progressive failure analysis was conducted to identify the initial failure load by means of an elastic stress analysis and specific damage criteria. As a result, it was found that damage first occurred along the edge of the leaf spring owing to the shear stresses.