Towards Rotordynamic Analysis with COMSOL Analysis with COMSOL
Multiphysics
Martin Karlsson
Excerpt from the Proceedings of the 2012 COMSOL Conference in Boston.
Background
� Rotordynamic analysis are carried out with special purpose rotordynamic codes
� Rotating equipment is supported by a structure and is � Rotating equipment is supported by a structure and is physically coupled with it
� In special cases – a combined analysis might be needed
� Simulation driven design
2
Objective
� What is needed to perform separate as well as combined rotordynamical and structural analysis of rotating equipment?
3
Rotordynamical modelling
� Timoshenko beam elements
� Added mass and inertia due to disks
� Gyroscopic effect� Gyroscopic effect
� Sign of the frequency
4
Multiphysical interactions
� Oil film stiffness and damping
� Fluid-rotorinteractions of seals and impellers
� Electromechanical interactions in electrical machines� Electromechanical interactions in electrical machinesand active magnetic bearings
5
Typical analysis
4
5
6x 10
4 Campbell Diagram [Offset rotor on rigid bearings]
Und
ampe
d na
tura
l fre
quen
cies
[cp
m]
Second bacwards natural mode
Critical speed
Second forwards natural mode
Line of synchronous excitation
6
0 1 2 3 4 5 6
x 104
0
1
2
3
4
Rotor speed [rpm]
Und
ampe
d na
tura
l fre
quen
cies
[cp
m]
First backwards natural mode
Critical speed
Critical speed
First forwards natural modeCritical speed
Implementation of rotordynamics
� Gyroscopic effect
� Rotordynamical coefficients
� Rotordynamical analysis by parametric sweep� Rotordynamical analysis by parametric sweep
� Calculations of rotordynamical coefficients
9