Volume 20, Issue 5 (May 2020)                   Modares Mechanical Engineering 2020, 20(5): 1347-1360 | Back to browse issues page

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1- Mechanical Engineering Department, Engineering Faculty, Ardakan University, Ardakan, Iran
2- Mechanical Engineering Faculty, Yazd University, Yazd, Iran , dashti@yazd.ac.ir
3- Mechanical Engineering Faculty, Yazd University, Yazd, Iran
Abstract:   (1516 Views)
The lubricant's ability to maintain the dynamic stability of rotor particularly in special conditions such as operating at critical speeds and instantaneous turbulences in loading or lubricant properties is always one of the most prominent characteristics of the journal bearings. Aspect or length to diameter ratio of bearing is an important factor that in different loading conditions will have an obvious effect on the performance of the trapped lubricant film between the rotor surface and bearings shell. So, the effects of aspect ratio on the damping of rotor disturbances with linear and nonlinear dynamic analysis approaches are studied in this research. Initially, the static equilibrium point of the rotor center in noncircular two, three and four lobe bearings space is obtained using the governing Reynolds equation of micropolar lubrication for different values of aspect ratio. Later, assuming the rotor perturbation as the limit cycle oscillations around the equilibrium point, critical mass and whirl frequency ratio are determined as the linear dynamic stability indexes for recognizing the converging disturbances. In nonlinear analysis model, the simultaneous solving of the lubrication and the rotor motion equations in successive time steps with Runge-Kutta method is done to differentiate the converging or diverging rotor perturbations. Results show that decreasing the aspect ratio improves the stability and the chance of controlling disturbances and returning the rotor center to static equilibrium position. Comparison of linear and nonlinear dynamic analysis results also indicates more cautious behavior and limited stability range of linear model in most of investigated cases.

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Article Type: Original Research | Subject: Computational Fluid Dynamic (CFD)
Received: 2019/03/27 | Accepted: 2020/03/5 | Published: 2021/03/15

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