Estimating the static load on the fluid bearings of a flexible machine from run-down data

A series of recent papers has discussed the problem of parameter identification for rotating machinery. Two techniques have been developed to identify the foundation parameters, the unbalance distribution and the state of bend. In this paper, the method based on the non-linear optimisation of the fit between the measured and model behaviour is extended to evaluate the steady load in oil film bearings. This is an important practical problem since these steady loads have a strong influence on the bearing’s dynamic characteristics. After developing the theory, two distinct examples are simulated and corrupted with noise. In simulation it is shown that the technique is capable of yielding accurate results. It is demonstrated that a measurement of absolute shaft motion is required to give predictions that are sufficiently accurate to be useful. This is not an undue restriction since most modern machines are equipped with proximity probes. The experimental verification of the method is planned on a new rig, currently under construction.