Optimal clearance configuration of fluid-film journal bearings for stability improvement

This paper aims to optimize a clearance configuration of fluid-film journal bearings. In order to improve stability of a rotating-machinery system, a performance index is given by summing the squared values of the attitude-angles over a region of eccentricity. A Fourier series is used to represent an arbitrary clearance configuration of a bearing, and the problem is to find the Fourier coefficients to minimize the performance index. The problem is numerically solved by a kind of the conjugate gradient method to yield a unique clearance configuration. The optimal clearance configuration is computed for various ratios of length to diameter of a bearing. A rigid-rotor system is used to verify that the designed bearing improves the system stability compared with that of a full circular bearing and to show that this optimization is more effective for shorter bearings.