Abstract
Dynamic analyses of vertical hydro power plant rotors require the consideration of the non-linear bearing characteristics. This study investigates the vibrational behavior of a typical vertical machine using a time integration method that considers non-linear bearing forces. Thereby, the influence of support stiffness and unbalance magnitude is examined. The results show a rising influence of unbalance on resonance speed with increasing support stiffness. Furthermore, simulations reveal that the shaft orbit in the bearing is nearly circular for typical design constellations. This property is applied to derive a novel approximation procedure enabling the examination of non-linear resonance behavior, using linear rotor dynamic theory. The procedure considers the dynamic film pressure for determining the pad position. In addition, it is time-efficient compared to a time integration method, especially at high amplitudes when damping becomes small.
Highlights
Hydroelectric power plants are often equipped with vertical rotors
These types of machines are commonly guided by tilting-pad journal bearings due to their excellent stability properties and tunable nominal bearing clearance
For the design and specification of the machine, as well as outstanding operation conditions, the knowledge of the resonance speed is of particular importance
Summary
Hydroelectric power plants are often equipped with vertical rotors. Today, these types of machines are commonly guided by tilting-pad journal bearings due to their excellent stability properties and tunable nominal bearing clearance. For the design and specification of the machine, as well as outstanding operation conditions, the knowledge of the resonance speed is of particular importance. Due to the vertical alignment, no gravity forces are acting on the guide bearings, and the dynamic unbalance forces exceed the static forces in wide ranges of operation conditions, especially with an increasing rotor speed. The bearing stiffness of these nearly statically unloaded bearings significantly increases with the amplitude of shaft orbit and, the dynamic properties of the system depend on the unbalance excitation magnitude. Aside from the impact of thermal effects, this property can be primarily attributed to the nonlinear increase in bearing stiffness
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