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남재현(Jaehyeon Nam),강재영(Jaeyoung Kang) 한국소음진동공학회 2020 한국소음진동공학회 논문집 Vol.30 No.2
In this study, the friction-induced vibration of the reciprocating device is measured under dust conditions and he dynamic instability mechanism using the analytical finite element model is proposed. In the case of absence of dust, a friction-induced vibration did not occur and the corresponding friction coefficient increased with the increase in revolutions per minute (r/min). In contrast, under the dust condition, a negative slope is developed, in which the friction coefficient decreases with increase in r/min. Consequently, the friction-induced vibration is generated. The results show that this system is excited by the negative slope mechanism, and the dynamics instability is predicted using the analytical finite element model. The numerical results show that the unstable frequency is due to dynamics instability caused by the bending mode of the frictional direction.
마찰곡선을 반영한 인공 고관절 마찰소음 유한요소 해석연구
남재현(Jaehyeon Nam),박기완(Kiwan Park),강재영(Jaeyoung Kang) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.1
본 논문은 복소수 고유치해석을 통하여 세라믹-세라믹 인공고관절 시스템에서의 동적 불안정성을 연구하고자 하였다. 시스템 파라메터 연구를 통해서 모드 연성 기반의 불안정성을 연구하였고, 음의 기울기를 포함하는 유한요소 해석 모델을 구현하여 음의 기울기에 의한 불안정성에 대해 조사하였다. 그 결과 토션이 지배적인 시스템 모드가 음의 기울기에 의해 불안정해 지며, 이는 축하중에 크게 영향을 받는다는 점을 확인하였다. This study investigated the dynamic instability of a ceramic-on-ceramic artificial hip joint system through complex eigenvalue analysis. We examined the mode-coupling mechanism through eigenvalue sensitivity analysis with the variation of system parameters. In addition, we constructed a finite element model including the negative slope of friction curve for investigating the negative-slope mechanism in the hip squeak problem. The numerical results show that the torsion-dominant mode becomes unstable due to the presence of the negative slope while the axial load is the important factor influencing the negative-slope type instability.
남재현(Jaehyeon Nam),강재영(Jaeyoung Kang) 한국소음진동공학회 2021 한국소음진동공학회 논문집 Vol.31 No.1
The aim of the study was to classify the chaotic time-series data with the nonlinear problem using the convolutional neural network (CNN), and to determine and verify the chaotic characteristics from a deterministic system. The classical nonlinear differential equation established by the Rossler model was used, and the chaotic characteristics were determined by the Lyapunov exponent. The chaotic properties was visualized using an unthresholded recurrence plot through the proposed procedure. A simple CNN model was developed to learn the extracted image using the proposed feature-visualization technique. As a result, the chaotic characteristics were classified with an accuracy of 99 % or more.
신희혁(Heehyuk Shin),남재현(Jaehyeon Nam),최성진(Sungjin Choi),강재영(Jaeyoung Kang) 한국소음진동공학회 2019 한국소음진동공학회 논문집 Vol.29 No.3
In this study, the brake squeal of rail or subway brakes is investigated using the numerical finite element method. A complex eigenvalue analysis is applied to determine the squeal modes of the train brake. Because the geometry of the rail brake pad is relatively large, numerous natural modes of the pad exist, leading to its instability. Therefore, it is important to model the system damping including friction and modal damping. The results show that brake squeal noise in the rail is expected to occur at 3000 Hz ~ 8000 Hz and the corresponding squeal modes are found to occur owing to mode coupling in the rail pad. The unstable pad modes are stabilized by the increase in Rayleigh damping.
박기완(Kiwan Park),남재현(Jaehyeon Nam),최성진(Sungjin Choi),남찬혁(Chanhyuk Nam),서선동(Sundong Seo),강재영(Jaeyoung Kang) 한국소음진동공학회 2017 한국소음진동공학회 논문집 Vol.27 No.7
In this paper, squeal analysis for the several surface pattern of the brake pad is conducted. The surface patterns used in this study are the solid-pattern, hexagon-pattern and, hexagon-pattern with rib. In the case of the hexagon-pattern with rib, the effect of the rib thickness on squeal propensity is investigated. From the results of the complex eigenvalue analysis, the hexagon-pattern has a larger positive real part than that of the solid, and its positive real part is reduced as the rib thickness increases. The positive real part of the hexagon-pattern decreased to solid level when the rib thickness increases up to 10 mm. Therefore, it is expected that the hexagon-pattern with the sufficient thickness of the rib can achieve the similar squeal propensity of the solid pad.