Abstract
The study of rotating machinery occupies a prominent position in the context of machines and structures in view of the significant number of phenomena typical in the operation of such equipment. Thus, this project aims to diagnose the wear in hydrodynamic bearings by gradual removal of the coating material, one of the typical problems and inherent to the repeated operation of rotating machines, which can be accentuated in starting and stopping or during the passage through the critical speed of the rotor (the first natural frequency). Due to the anisotropic nature of these components, which have different dynamic characteristics of stiffness and damping in orthogonal directions that define the plane perpendicular to the rotation axis, the frequency response of the rotor-bearing system in directional coordinates, presents a non-null backward component and with growing influence in function of the degree of anisotropy present in the system, in this case, due to the hydrodynamic bearings. As noted in previous works, wear by removing the inner coating material of the bearing further supports the increase of dynamic asymmetry in these components, and thus their influence can be seen in the response of the rotating system in directional coordinates, with the increase backward component of the response of the rotor at the point of positioning of the bearings. Therefore, this wear on the bearings can increase the degree of anisotropy of the system through an increase in the difference between the stiffness and damping coefficients in each direction of the plane perpendicular to the axis of rotation. Consequently, their model allows us to evaluate from what point the anisotropy affects the directional frequency response of the system. Within this context, this project presents a numerical model for identification of some characteristic parameters of this type of wear in lubricated bearings, from the dynamic response of rotor-bearing system in the frequency domain. The identification of the wear parameters will be conducted through a search method to minimize an objective function, which compares the frequency response simulated numerically with that obtained experimentally in an instrumented and monitored test bank in the laboratory. You can work with a single solution to the problem (mono-objective), or with a set of optimal solutions (multi-objective functions), identifying in this case, the characteristic parameters of the present condition of wear in the bearings. It is therefore a diagnosis proposed based in models for fault monitoring and scheduling of maintenance shutdowns. In the modeling of rotor-bearing system, the rotor model is represented by the classical finite elements method and the bearings are modeled by finite volume method. The present in hydrodynamic bearings wear will be modeled as a geometric discontinuity. For this purpose, we will use a numerical method for solving the Reynolds equation, associated with the Bernoulli equation, thereby obtaining the pressure field generated in the oil film inside the bearing. The dynamic coefficients are approximate from a concept similar to a spring-damper system in order to represent the inherent flexibility and damping of the oil film, respecting their linearity of the respective operating ranges of the rotor. The modal analysis of rotor-bearing system in directional coordinates will be used to determine the function of experimental directional frequency response, to be compared with that obtained numerically in the objective function to be minimized. In this minimization process, the search parameters are those that best characterize the wear model in lubricated bearings, through the inherent effects in the forward and backward modes of the rotor.
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