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Rotordynamics, eigenvalues and frequency domain
Posted 06.04.2014, 08:29 GMT-4 Fluid & Heat, Interfacing, Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers, Structural Mechanics Version 4.4 0 Replies
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I have two questions about rotordynamics modelling.
First of all, I'm modelling a rotor using a parametric sweep on angular velocity to find its eigenvalues.
After that I would like to extract the system matrices (in LiveLink with Matlab) using the command "mphmatrix", but the damping matrix (which includes the gyroscopic matrix) varies with the angular velocity of the rotor.
So, how can I extract system matrices for a certain step of the parametric sweep? (or for every step of the sweep, it's the same!)
My second question is related with rotordynamics too.
I would like to perform a frequency response analysis of a rotor. In my model the rotor is modelled with beams and the bearings with the Lubrication shell interface. There are also some ODEs so I substituted the time derivatives with i*2*pi*freq and -(2*pi*freq)^2.
The problem is that in this way the ODEs generate an error like this:
Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 1547 equations giving NaN/Inf in the matrix rows for the variable mod1.pf.
at coordinates: (-0.0799129,0.00534406,0), (-0.0768651,0.0223399,0), (-0.0788467,0.0139241,0), (-0.0702572,0.0382926,0), (-0.0739908,0.0304943,0), ...
There are 6 equations giving NaN/Inf in the matrix rows for the variable mod1.thx.
at coordinates: (0,0,0), (0,0,-0.07), (0,0,-0.14), (0,0,-1.3), (0,0,-1.37), ...
There are 6 equations giving NaN/Inf in the matrix rows for the variable mod1.thy.
at coordinates: (0,0,0), (0,0,-0.07), (0,0,-0.14), (0,0,-1.3), (0,0,-1.37), ...
There are 6 equations giving NaN/Inf in the matrix rows for the variable mod1.thz.
at coordinates: (0,0,0), (0,0,-0.07), (0,0,-0.14), (0,0,-1.3), (0,0,-1.37), ...
There are 1 equations giving NaN/Inf in the matrix rows for the variable mod1.tilt1.
at coordinates: (0,0,0), ...
There are 1 equations giving NaN/Inf in the matrix rows for the variable mod1.tilt1B.
at coordinates: (0,0,0), ...
There are 1 equations giving NaN/Inf in the matrix rows for the variable mod1.tilt2.
at coordinates: (0,0,0), ...
..................
I made a simple check about ODE in frequency domain: I modelled (with ODE interface) the frequency response of a 1D mass-spring model, and all work well!
My rotor model is quite complex because there are three physics involved; in particular I think the problem could be in the non linearity of the Lubrication shell Interface used to model the bearings.
Any advice?
Thanks a lot
Best regards
Daniele
Hello Daniele Daniele
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