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

Possible codes for combined analysis

� ABAQUS

� ANSYS

� NASTRAN� NASTRAN

� COMSOL Multiphysics

7

COMSOL Multiphysics

8

Implementation of rotordynamics

� Gyroscopic effect

� Rotordynamical coefficients

� Rotordynamical analysis by parametric sweep� Rotordynamical analysis by parametric sweep

� Calculations of rotordynamical coefficients

9

Gyroscopic effect

10

Rotordynamic coefficients

11

Excitations

Solvers

13

Couple a rotor model to a structural model

14

Example of results –foundation – support – rotor mode shape

15

Example of results- Campbell plot

16

Calculation of rotordynamical coefficients

17

Conclusions

� Possible to design an engineering tool in order to carry out coupled rotordynamical and structural analysis

� Possible to identify rotordynamical coefficients using numerical methods

� Further implementation needed for a complete 3D-rotordynamical analysis

18