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볼의 자이로스코픽 모멘트와 원심력을 고려한 고속 볼베어링의 마찰 토크 해석 및 실험
장진우(Jinwoo Jang),장건희(Gunhee Jang) 한국소음진동공학회 2015 한국소음진동공학회 학술대회논문집 Vol.2015 No.10
A ball bearing is core component to design a rotor-bearing system. Friction loss of ball bearings is one of major energy loss in the rotor-bearing system, and predicting the friction torque of ball bearings is required to design a motor with low power consumption. Force equilibrium equations and geometric compatibility equations of a ball bearing are solved to calculate dynamic characteristics of a ball bearing. Friction torque is calculated by Palmgren and SKF ball bearing friction models with simulated contact angle result. In experiment, power loss of a motor is measured to calculate the friction torque of a ball bearing. The research shows that Palmgren and SKF ball bearing friction models are in good agreement with the experimental result, and the friction torque of a ball bearing is dominantly affected by preload and rotating speed.
클리핑방법을 이용한 non-conformal interface 경계를 갖는 열전도 해석
이주희(Juhee Lee),장진우(Jinwoo Jang),이용준(Yongjun Lee),이상환(Sanghwan Lee),이현균(Hyeonkyun Lee) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
In CFD(Computational Fluid Dynamics) or heat transfer problem using an unstructured grid, it is possible to divide a complex domain into several simple domains. However, the grid points on the interface between two domains are not matched completely so called non-conformal mesh. Thus, mesh handling technique is needed to deal with this problem. Especially, a similar problem occurs in multi-phase or multi-material system. Since fluxes are calculated two neighbor cells sharing a surface in a finite volume method, it is difficult to calculate the proper flux. In order to overcome the problem, we employed the clipping method that calculates the connectivity and geometrical informations between non-conformal cells on the interface. The clipping method is generally used for comptuer graphics and searches the shape information of the overlapped polygons. In this study, we implemented the clipping algorithm that calculates the area and center of overlapped polygons. To validate the clipping method, the 3-dimensional heat conduction with a non-conformal interface was performed and then, it represented the reasonable solutions.
이주희(Lee, Juhee),장진우(Jang, Jinwoo),이용준(Lee, Yongjun),최준혁(Choi, Junhyuck),이상환(Lee, Sanghwan) 한국건축친환경설비학회 2014 한국건축친환경설비학회 논문집 Vol.8 No.6
Heat transfers and related phenomena can be described by the second order partial differential equation, which cannot generally be solved except a simple domain. To make matters worse, the solution significantly dependents on the boundary conditions. The equations with analytical methods are solvable for only a limited number of cases. The known solutions are extremely useful in helping to understand heat transfer phenomena, but they rarely can be applied in engineering or design, because these solutions are not sufficiently practical. The engineer and designer have generally been forced to use numerical methods instead. To obtain an numerical solution, a discretization method, which approximates the differential equations by a system of algebraic equations is used. The approximations are applied to small domains in space and time so the numerical solution provides results at discrete locations in both space and time. The accuracy of numerical solutions is dependent on the quality of discretizations and size of cells used. The higher accuracy, the higher numerical resource are required. The balance between the accuracy and difficulty of the numerical methods is critical. The final linear equations by discretization are solved with matrix solver, which takes the most of the computation time. To reduce the computation time, the effective method for matrix solver is required. This study provides an overview of discretization, and matrix solver for the 3-dimensional numerical heat transfer.
Solid-state drive 강제진동시 dummy solder ball 효과에 의한 피로수명 예측
이주엽(Juyub Lee),장건희(Gunhee Jang),장진우(Jinwoo Jang) 한국소음진동공학회 2014 한국소음진동공학회 학술대회논문집 Vol.2014 No.10
This research proposes a method to estimate the fatigue life of solid-state drive(SSD) due to the effect of dummy solder ball under forced vibration. Mechanical jig is developed to describe the SSD in laptop computer. The jig with SSD is mounted on a shaker, and excited by a sinusoidal sweep vibration within the narrow frequency band around the first resonant frequency until the SSD fails. A finite element model of SSD is also developed to simulate the forced vibration. It shows that the solder joints at the corners of controller package are most vulnerable components and that placing dummy solder balls at those area is effective method to increase fatigue life of SSD.