Campbell Diagram with 3D Rotor Dynamics Model

Athanasios Besikiotis
Athanasios Besikiotis New Altair Community Member
edited November 2023 in Community Q&A

Hi to everyone,

I am writing to inquire about an issue that I am facing in Hypermesh 2023, as I am doing my diploma thesis. I am trying to run a Campbell analysis on a Rotor Dynamics model with 3D elements. I have combined the examples (1) OS-E: 0325 3D Rotor Dynamics Model and (2) OS-V: 1000 Complex Eigenvalue Analysis of Rotor Bearing System, in order to plot the Campbell diagram. Unfortunately, the diagram is wrong as the frequencies do not change in respect with the rotor speed (it can be seen in the following image).

image

Does anyone know how it can be done?

I would appreciate your assistance in this issue.

Also, I have attached the 2 files that I am using for my analysis.

Tagged:

Best Answer

  • Xiaolei
    Xiaolei
    Altair Employee
    edited November 2023 Answer ✓

    Hi Athanasios, 

    I had a look at the two model. And the below is my understanding. 

    If you check the out file of rotor dynamic analysis, you will see the frequencies doesn't change with speeds(Ex. mode # 5 as below). So it's not an issue of post-process, instead there is something that is not set up properly. 

     Mode #: 5 
     -------------------------------------------------------------------------------
     Step  Rotor speed   Eigenvalue  Eigenvalue     Frequency    Damping     Whirl 
               (RPM)         (Re)        (Im)          (Hz)
     -------------------------------------------------------------------------------
       1    0.000E+00  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       2    4.000E+03  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       3    8.000E+03  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       4    1.200E+04  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       5    1.600E+04  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       6    2.000E+04  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR

    In the model reduction run, you only 2 dofs(3 and 6) were defined as interface dofs, which is not common. I believe you should retain all 6 dof of the each interface nodes. Then in residual run, you should see similar results as the tutorial. The below is the results of mode # 5 that I have. 

     Mode #: 5 
     -------------------------------------------------------------------------------
     Step  Rotor speed   Eigenvalue  Eigenvalue     Frequency    Damping     Whirl 
               (RPM)         (Re)        (Im)          (Hz)
     -------------------------------------------------------------------------------
       1    0.000E+00  -1.18374E+00  1.18393E+02    1.884E+01    2.000E-02  BACKWARD
       2    4.000E+03  -1.18908E+00  1.18387E+02    1.884E+01    2.009E-02  BACKWARD
       3*   8.000E+03   6.32597E-01 -8.18396E+01    1.303E+01   -1.546E-02  FORWARD
       4*   1.200E+04   1.17646E+00 -8.76505E+01    1.395E+01   -2.684E-02  FORWARD
       5*   1.600E+04   1.35686E+00 -9.12636E+01    1.453E+01   -2.974E-02  FORWARD
       6*   2.000E+04   1.50605E+00 -9.38318E+01    1.493E+01   -3.210E-02  FORWARD

    Thanks. 

    Xiaolei

Answers

  • Xiaolei
    Xiaolei
    Altair Employee
    edited November 2023 Answer ✓

    Hi Athanasios, 

    I had a look at the two model. And the below is my understanding. 

    If you check the out file of rotor dynamic analysis, you will see the frequencies doesn't change with speeds(Ex. mode # 5 as below). So it's not an issue of post-process, instead there is something that is not set up properly. 

     Mode #: 5 
     -------------------------------------------------------------------------------
     Step  Rotor speed   Eigenvalue  Eigenvalue     Frequency    Damping     Whirl 
               (RPM)         (Re)        (Im)          (Hz)
     -------------------------------------------------------------------------------
       1    0.000E+00  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       2    4.000E+03  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       3    8.000E+03  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       4    1.200E+04  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       5    1.600E+04  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       6    2.000E+04  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR

    In the model reduction run, you only 2 dofs(3 and 6) were defined as interface dofs, which is not common. I believe you should retain all 6 dof of the each interface nodes. Then in residual run, you should see similar results as the tutorial. The below is the results of mode # 5 that I have. 

     Mode #: 5 
     -------------------------------------------------------------------------------
     Step  Rotor speed   Eigenvalue  Eigenvalue     Frequency    Damping     Whirl 
               (RPM)         (Re)        (Im)          (Hz)
     -------------------------------------------------------------------------------
       1    0.000E+00  -1.18374E+00  1.18393E+02    1.884E+01    2.000E-02  BACKWARD
       2    4.000E+03  -1.18908E+00  1.18387E+02    1.884E+01    2.009E-02  BACKWARD
       3*   8.000E+03   6.32597E-01 -8.18396E+01    1.303E+01   -1.546E-02  FORWARD
       4*   1.200E+04   1.17646E+00 -8.76505E+01    1.395E+01   -2.684E-02  FORWARD
       5*   1.600E+04   1.35686E+00 -9.12636E+01    1.453E+01   -2.974E-02  FORWARD
       6*   2.000E+04   1.50605E+00 -9.38318E+01    1.493E+01   -3.210E-02  FORWARD

    Thanks. 

    Xiaolei

  • Athanasios Besikiotis
    Athanasios Besikiotis New Altair Community Member
    edited November 2023
    Xiaolei Song_21874 said:

    Hi Athanasios, 

    I had a look at the two model. And the below is my understanding. 

    If you check the out file of rotor dynamic analysis, you will see the frequencies doesn't change with speeds(Ex. mode # 5 as below). So it's not an issue of post-process, instead there is something that is not set up properly. 

     Mode #: 5 
     -------------------------------------------------------------------------------
     Step  Rotor speed   Eigenvalue  Eigenvalue     Frequency    Damping     Whirl 
               (RPM)         (Re)        (Im)          (Hz)
     -------------------------------------------------------------------------------
       1    0.000E+00  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       2    4.000E+03  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       3    8.000E+03  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       4    1.200E+04  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       5    1.600E+04  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR
       6    2.000E+04  -2.69370E+00  2.16674E+02    3.448E+01    2.486E-02  LINEAR

    In the model reduction run, you only 2 dofs(3 and 6) were defined as interface dofs, which is not common. I believe you should retain all 6 dof of the each interface nodes. Then in residual run, you should see similar results as the tutorial. The below is the results of mode # 5 that I have. 

     Mode #: 5 
     -------------------------------------------------------------------------------
     Step  Rotor speed   Eigenvalue  Eigenvalue     Frequency    Damping     Whirl 
               (RPM)         (Re)        (Im)          (Hz)
     -------------------------------------------------------------------------------
       1    0.000E+00  -1.18374E+00  1.18393E+02    1.884E+01    2.000E-02  BACKWARD
       2    4.000E+03  -1.18908E+00  1.18387E+02    1.884E+01    2.009E-02  BACKWARD
       3*   8.000E+03   6.32597E-01 -8.18396E+01    1.303E+01   -1.546E-02  FORWARD
       4*   1.200E+04   1.17646E+00 -8.76505E+01    1.395E+01   -2.684E-02  FORWARD
       5*   1.600E+04   1.35686E+00 -9.12636E+01    1.453E+01   -2.974E-02  FORWARD
       6*   2.000E+04   1.50605E+00 -9.38318E+01    1.493E+01   -3.210E-02  FORWARD

    Thanks. 

    Xiaolei

    Hi Mr Xiaolei,

    First of all thank you very much for your reply. If I understood correctly, what you suggest is to have the ASET1 entry such as in the following image (in the whole_3D_model_detailed_version1.fem model), in order to define all the dofs of each interface node as an interface dof. 

    image

    Doing so I found the same results of mode # 5 that you have. 

    Thank you very much.

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