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열충격 하중 하에서의 엔진 배기매니폴드의 역학적 거동에 관한 연구
최복록(Boklok Choi),김원섭(Wonseop Kim),이경우(Kyungwoo Lee),장훈(Hoon Chang) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
In this study, we investigated the thermally induced fatigue behaviors and gas sealing mechanism of the exhaust manifold under thermo-mechanical cyclic loads. At first, full engine model was considered to identify the critical locations and their results were compared to failure areas of the engine bench test. And the equivalent system model was proposed based on the mechanical behaviors of the full engine model. The weak areas of both FE models show a good agreement with the experimental crack locations. As a result, a simplified modelling methodology was verified to estimate the thermo-mechanical behaviors of the exhaust manifold under thermal shock test condition.
최복록(Boklok Choi) 한국자동차공학회 2007 한국 자동차공학회논문집 Vol.15 No.1
This paper presents the low cycle thermal fatigue of the engine exhaust manifold subject to thermomechanical cyclic loadings. The analysis includes the FE model of the exhaust system, temperature dependent material properties, and thermal loadings. The result shows that at an elevated temperature, large compressive plastic deformations are generated, and at a cold condition, tensile stresses are remained in several critical zones of the exhaust manifold. From the repetitions of thermal shock cycles, plastic strain ranges could be estimated by the stabilized stress-strain hysteresis loops. The method was applied to assess the low cycle thermal fatigue for the engine exhaust manifold. It shows a good agreement between numerical and experimental results.
모터링 내구시험을 상사한 비정상 온도이력을 받고 있는 엔진 터보차져의 열적 거동해석
최복록(Boklok Choi),방인완(Inwan Bang),장훈(Hoon Chang) 한국자동차공학회 2011 한국 자동차공학회논문집 Vol.19 No.6
Fatigue cracks of the turbocharger are often observed for high performance engines under thermal shock tests. Maximum exhaust gas temperature of recently developed gasoline engines could reach approximately 950℃. It's very important to estimate transient temperature histories during thermal shock cycles to predict the stress and the fatigue life of the turbocharger. With these temperature profiles, temperature-dependent material properties and boundary conditions, we could identify critical locations by the application of finite element simulation technologies. In this paper, we applied the reliable analysis approach to the actual turbocharger to predict the weak locations due to the repetitions of plastic strains and compared the results with the crack locations under physical engine test.
배기매니폴드의 열응력 해석을 위한 배기계 모델 구성에 관한 연구
최복록(Boklok Choi),이경우(Kyungwoo Lee),장훈(Hoon Chang) 한국자동차공학회 2010 한국 자동차공학회논문집 Vol.18 No.6
In this study, we investigated the efficient FE modelling techniques for thermal stress analysis of the exhaust manifold subject to thermo-mechanical cyclic loadings. At first, full engine model was considered to identify the critical locations and their results were compared to failure site shown by the engine bench test. And the equivalent system model was proposed based on the mechanical behavior of the full engine model. The weak areas of both FE models show a good agreement with the experimental crack location. As a result, a simplified modelling methodology was verified to estimate the thermo-mechanical behaviors of the exhaust manifold under thermal shock test condition.
최복록(Boklok Choi),강성종(Sungjong Kang) 한국자동차공학회 2011 한국 자동차공학회논문집 Vol.19 No.4
Firstly, FEM model for the body frame of a fuel cell vehicle was built up and design optimization results based on different schemes were exhibited. One scheme was to minimize weight while maintaining the normal mode frequencies and the other was to increase the frequencies without weight change. Next, for a rear frame model, shape parameter study on collapse characteristics such as peak resistance load and absorbed energy was carried out. Also, the stiffness of frame mounting brackets was predicted using inertance calculation and the durability of those mounting brackets for vehicle system loads was evaluated. Finally, for a representative mounting model, the influence on durability due to thickness change was analyzed.
CFD/FEM 에 의한 엔진 배기 매니폴드의 열피로 특성 해석
최복록(Boklok Choi),박재인(Jaein Park),장훈(Hoon Chang),박관흠(Kwanhum Park) 한국자동차공학회 2002 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2002 No.5_3
This paper presents a numerical method for the engine exhaust manifold subject to severe cyclic thermomechanical loading. The analyses based on the geometry of the exhaust manifold, temperature dependent material properties as well as nonlinear stress-strain relationship, proper boundary conditions, and temperature distribution data equivalent to the thermal cycles. As a result of nonlinear thermal stress analysis, compressive plastic deformations occurred during heating process since the thermal expansion of the manifold was restricted by less expanded inlet flange and cylinder head. And, tensile stress remained when the manifold was cooled down to the ambient temperature. From these repetitions of heating and cooling, we can obtain the stress-strain hysteresis loop in a critical zone. The estimated plastic strain range was often used as the crack initiation criteria. This method was applied to assess the characteristics of the low cycle thermal futigue for the "A" engine exhaust manifold. The results show a good agreement between numerical analysis and experimental results.
소형 가솔린 엔진용 터보차저의 기계적 마찰손실에 대한 이론적 계산 및 실험적 검증
이인범(Inbeom Lee),홍성기(Seongki Hong),김구성(Kusung Kim),최복록(Boklok Choi) 한국자동차공학회 2017 한국 자동차공학회논문집 Vol.25 No.5
The rotating shaft of a turbocharger is usually supported by two oil-lubricated journal bearings and a thrust bearing. The turbocharger rotor is the main cause of mechanical friction losses, which strongly influence the efficiency and performance of a high-speed turbocharger. In this paper, we investigated the mechanical friction losses of a turbocharger bearing system by using analytical and experimental methods. The SAE 10W-30 grade engine oil was used for lubricating the turbocharger rotor bearings of the 1.4 L gasoline engine. Petroff’s equation and the CFD method were used to calculate the mechanical friction loss, and the analytical results were verified by the experimental results that used calorimetric measurement techniques. Meanwhile, in order to measure the mechanical friction loss of pure radial journal bearings, the experiment was conducted in the operating ranges without axial thrust loads. Based on the analytical and experimental results, it was found that the mechanical friction loss was mainly induced by oil-lubricated journal bearings, and its magnitude varied in the form of a parabolic function with respect to the turbocharger’s rotation speed. In addition, the theoretical results were in good agreement with the experimental results.
이인범(Inbeom Lee),홍성기(Seongki Hong),김영철(Youngchul Kim),최복록(Boklok Choi) 한국자동차공학회 2016 한국 자동차공학회논문집 Vol.24 No.6
This paper deals with an analytical and experimental investigation to predict the axial thrust load that results from turbocharger operating conditions. The Axial forces acting on the turbocharger thrust bearing are caused by the unbalance between turbine wheel gas forces and compressor wheel air forces. It has a great influence on the friction losses, which reduces the efficiency and performance of high-speed turbocharger. This paper presents the calculation procedure for the axial thrust forces under operating conditions in a turbocharger. The first step is to determine the relationship between thrust forces and strains by experimental and numerical methods. The analysis results were verified by measuring the strains on a thrust bearing with the specially designed test device. And then, the operating strains and temperatures were measured to inversely calculate the thrust strains which were compensated the thermal effects. Therefore it’s possible to calculate the magnitudes of the thrust forces under operating turbocharger by comparing the regenerated strains with the rig test results. It will possible to optimize the design of a thrust bearing for reducing the mechanical friction losses using the results.