Dynamic analysis and stability conditions in rotating systems with tilting pad journal bearing

• Grant number: 11/22426-4
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2012
• End date: December 31, 2012
• Field of knowledge: Engineering - Mechanical Engineering - Mechanical Engineering Design
• Principal Investigator: Katia Lucchesi Cavalca Dedini
• Grantee: Antonio Carlos Sanches Grijota Piragibe Carneiro
• Host Institution: Faculdade de Engenharia Mecânica (FEM). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil

Abstract

The dynamic analyses of rotating machines involve an elevated degree of complexity. In these analyses, the dynamic behavior of the rotor should be analyzed considering it's interaction with the others components of the same system, as the support structure (or foundation) and the bearings. In a system rotor-bearing-foundation, the vibration applied by the rotor is transferred through the bearings to the supporting structure, in which interacts with the bearings retransmitting the vibration to the rotor. In this way, the bearings have an important role in this system, because this component is responsible to transmit forces between the rotor and the support structure. For this reason, in order to obtain a more realistic dynamic analysis of the system rotor-bearing-foundation, the dynamic behavior of the bearings must be considered in the mathematical model of the complete system. To consider the dynamic behavior of the bearings should determine the non-linear forces generated in these elements by pressure distribution that supports the external load, or yet, in the specific case of hydrodynamic bearings, to accomplish the linear approximation of these forces in a rotation range and acceptable load conditions, estimating the equivalent stiffness and damping coefficients of the bearings that can be applied in the system. This work aims to evaluate the tilting pad bearings' stability condition, because the dynamics characteristics of these bearings allow its application on machines with high rotations and low load. In face of that, the stiffness and damping coefficients of a tilting pad journal bearing are determined and applied in the dynamic analyses of rotating systems supported by these components to evaluate the stability condition of the complete system. In this context, there will be used two distinct approaches in the dynamic analysis of the tilting-pad journal bearing. The first approach is based on the complete model of the hydrodynamic forces, in which are considered the equivalent coefficients of stiffness and damping related to the angular displacement of the pads (a), besides the traditional translational coefficients (x,y) of the axis inside the bearing. The second approach uses the reduced equivalent coefficients, in which a reduction of the dynamic model of the bearing is accomplished in order to obtain equivalent coefficients represented only through the translational coordinates of the axis (x,y). In both approaches, the stability analysis aims to understand the phenomena and evaluate the sensitivity degree of the design parameters involved in this phenomena.(AU)