Tiago Henrique Machado

Geometric Discontinuities Identification in Hydrodynamic Bearings

During the operation of rotating machines, especially during starts and stops, hydrodynamic bearings can be progressively worn down. In order to prevent an irreversible failure condition of the entire rotating system, it is necessary to precisely detect wear, without disconnect or disassemble the system. The wear can cause significant geometric changes in the bearing wall, changing the nominal radial clearance. Therefore, the discontinuities can influence the dynamic characteristics of the bearing. In this context, the main objective of this paper is to present a numerical model that represents both the hydrodynamic bearing and the geometric discontinuities to be identified. The parameters of depth, angular span and angular position, according to the wear model, are adjusted by the comparison of the numerical and experimental unbalance response of the system considering the rising of the backward component due to the bearing anisotropy increasing.

Experimental validation of a bearing wear model using the directional response of the rotor-bearing system

The present work gives continuity in the analysis of the wear influence on cylindrical hydrodynamic bearings by presenting an experimental validation of the wear model previously proposed by the authors. This validation is carried on using the frequency response of the rotor-bearings system in directional coordinates. For this purpose, a test rig was assembled in order to evaluate the behavior of the rotating system when supported by hydrodynamic bearings with different wear patterns. The experimental measurements are used to validate the wear model, comparing the anisotropy influence on the experimental and numerical responses. The simulated directional frequency responses showed a good agreement with the experimental ones, demonstrating the potential of the proposed wear model in satisfactorily represent its influence on the rotor-bearings system response in the frequency range where the numerical model was validated.

A Compensation Method for Foundation Effects in Rotating Systems Through Shape Optimization

Rotating systems operating in different foundations structures can present distinct dynamic response. In case of a compliant foundation, interaction between machine and its supports leads to a more complex system with additional degrees of freedom. These degrees of freedom introduce new natural frequencies and vibration modes for the system. When these foundation-induced modes are in the rotor operating range of frequency, a serious problem may arise, since a machine cannot be tested for every different foundation type expected in industry environment, especially in preliminary design phase. Furthermore, foundation replacement or adaptation are costly operations. A significant improvement in machine-foundation compatibility is possible by the introduction of some compensation in machine to change these additional critical frequencies. Therefore, this paper proposes a compensation method for foundation effects through finite element analysis and shape optimization. An optimization is used to find a compromise between minimum mass increase and manufacturing time to ensure a low cost shape, as a result the cost of machine adjustments is reduced. The algorithm is designed to be simple enough to run on cheap micro-controllers. Consequently, the complete system can be embedded in the machine for a negligible amount of its total cost. Simulations’ results show the method as effective in compensating the influence of foundations with minor loss of precision due to simplifications required to make the algorithm less computational intensive than a full-fledged solution designed to run in workstations. In this way, the method is promising for future applications in rotating machines present in industrial plants.

Active Control of Rotor Supported by Faulting Journal Bearing

Although hydrodynamic bearings have minimum contact between solid parts, under particular circumstances they might be susceptible to abrasion and wear. In order to mitigate the problem, it is proposed to apply active control methods to reduce the vibration level at critical situations: fluid induced instability and the first bending mode. However, damage in the bearing surface have direct influence over the oil-film pressure and, consequently, in the bearings equivalent coefficients. Although, initially, small variations may lead to minor performance loss, when it becomes more significant close-loop stability may be affected. Therefore, in this paper it is conducted a preliminary study on the effect of journal bearing wear depth effects in active controlled rotors. A structured uncertain model is proposed to include the possible fault coefficients in the model allowing to perform robust stability analysis. Based on the uncertain formulation a robust control solution is designed guaranteeing rotor stability for a certain damage range.