60 M. M. G. Kuhr et al. EIGENFREQ. in Hz Ͳ ͷͲ ͳͲͲ ͳͷͲ ʹͲͲ Ͳ ͷͲ ͳͲͲ ͳͷͲ ʹͲͲ Ͳ ͳͲʹͲ͵ͲͶͲͷͲ Ͳ ͳͲʹͲ͵ͲͶͲͷͲ݂ ୰୭୲୭୰ ʹ݂ ୰୭୲୭୰ Ͳ ͷͲ ͳͲͲ ͳͷͲ ʹͲͲ Ͳ ͷͲ ͳͲͲ ͳͷͲ ʹͲͲ Ͳ ͳͲʹͲ͵ͲͶͲͷͲ Ͳ ͳͲʹͲ͵ͲͶͲͷͲ Ͳ ͷͲ ͳͲͲ ͳͷͲ ʹͲͲ Ͳ ͷͲ ͳͲͲ ͳͷͲ ʹͲͲ Ͳ ͳͲʹͲ͵ͲͶͲͷͲ Ͳ ͳͲʹͲ͵ͲͶͲͷͲ EIGENFREQ. in Hz EIGENFREQ. in Hz ROTOR SPEED in Hz ROTOR SPEED in Hz݂ ሻ ROTOR + ܭ ூǤǤூǡ ܥ ூǤǤூǡ ܯ ூǤǤூǡ ܭ ݁ ሻ ROTOR + ܭ ூǤǤூǡ ܥ ூǤǤூǡ ܯ ூǤǤூ݀ ሻ ROTOR + ܭ ூǤǤூூǡ ܥ ூǤǤூூǡ ܯ ூǤǤூூܿ ሻ ROTOR + ܭ ூǡ ܥ ூǡ ܯ ூܾ ሻ ROTOR + ܭ ூǡ ܥ ூܽ ሻ ROTOR BEND. MODE 1 TORS. MODE AXIAL MODE BEND. MODE 3 BWW FWW݂ ୡ୰୧୲ ൌʹʹ ǡͶͲ ǡͶͶ ݂ ୡ୰୧୲ ൌʹͶ ǡͶͲ ݂ ୡ୰୧୲ ൌͳͲ ǡͶͲ ݂ ୡ୰୧୲ ൌͳ ǡ͵ ǡͶͲ ݂ ୡ୰୧୲ ൌʹͲ ǡͶͲ ǡͶͶ ݂ ୡ୰୧୲ ൌͳ ǡͳͻ ǡ͵Ͷ ǡͶͲ ǡͷͲ BEND. MODE 2 Fig. 5 Campbell diagrams of the rotor system. The different figures a) to f) indicate different degrees of modelling of the rotordynamic influence of the fluid-filled gaps, ranging froma) the rotor without the annulus, to f) the rotor with a balance piston inducing both forces and moments as well an additional axial stiffness onto the rotor Focussing now on the impact of the annular gap and later the overall balance piston. Figure 5b depicts the Campbell diagram when the rotor system and the stiffness and damping coefficients due to translational motion, i.e. KI and CI, are considered. This level of modelling is typically employed for classical journal bearings with laminar flow conditions, where the influence of flow inertia is negligible. It is shown that there is only a slight change in the eigenfrequencies of the overall
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