Identification method of dynamic characteristics coefficients of tilting pad bearing in critical speed range of large unit

Abstract

For tilting pad bearing of large unit, it is not easy to identify stiffness and damping coefficients in full-size unit test. Because of many limiting factors in large unit test, the stiffness and damping test methods are not fully applicable to large units, which can be easily implemented in laboratory. The nonexcitation methods are proposed in this paper to identify the stiffness and damping coefficients of tilting pad bearing in the critical speed range of large unit, including direct method and iterative method. Firstly, the rotor speed and vibration during the whole period are obtained. The vibration data of the first-order critical speed range in the startup stage are selected, and the stiffness and damping coefficients of tilting pad bearing are identified through the two methods. The results show that the stiffness and damping coefficients identified through the direct method are generally less than the theoretical values. The identification error of stiffness coefficient is within ±9%, and the identification accuracy of stiffness coefficient is significantly higher than that of damping coefficient. The damping coefficient identified by the iterative method agrees well with the theoretical value, and the identification error is about −3%. In conclusion, the stiffness and damping coefficients of tilting pad bearing in the range of first-order critical speed can be obtained by combining the two identification methods. These identification results are relatively reliable and can basically meet the analysis requirements of important vibration problems of bearing-rotor system.