Parameter identification of a discrete-mass mathematical model of crankshaft oscillations

The article aims at developing a refined discrete-mass mathematical model of free and forced oscillations of a crankshaft. An integrated approach to the transition from a finite-element model to a discrete one was proposed. The algorithm of the corresponding sequential transition was described in detail. The proposed model describes free and forced oscillations of the crankshaft. The developed discrete-mass model considers the natural stiffness anisotropy of the crankshaft, D’Alembert inertia forces of discrete masses, and centrifugal inertia forces from the action of residual imbalances. Other nonlinear loading factors of different nature acting on the journals were considered, such as damping of the oil layer, hydrodynamic rigidity, nonlinear friction, circulating force, and internal friction. Moreover, the proposed model considers the possibility of contact between the rotor and the stator in non-calculated or transient modes. The corresponding components of all the above forces were included in the proposed nonlinear differential equations system describing a double-rigidity rotor’s vibration state. The reliability of the proposed free oscillations model was proven by the relative errors of the first two eigenfrequencies for the discrete-mass model. The obtained eigenfrequencies were compared with the corresponding values obtained using the finite-element analysis. The reliability of the extended model of forced oscillations is proven by reducing it to a linearized form and further comparing it with the existing simplified models of rotor oscillations.