Experimental identification of linear oil-film coefficients using least-mean-square method in time domain

In general sense, under small perturbation the stability of rotor-bearing system can be determined by linear oil-film coefficients of hydrodynamic bearing and oil-film forces can also be expressed by these coefficients. This paper proposes an experimental method to identify these coefficients and presents their characteristics under various operational conditions. A delicate test rig is constructed and experimental data are acquired under various testing conditions. From the experimental data, the relative velocity of the journal and the oil-film forces can be obtained by using a differentiator. The coefficients are identified using least-mean-square method in time domain. Some identified results are compared with the theoretical data. The experimental results indicate that the linear oil-film dynamic coefficients are sensitive to the excitation amplitude. The intensity of sensitivity is varied for different coefficients. From the investigation, it can be concluded that the linear oil-film force model will be invalid once the condition of small perturbation is not satisfied.