set the outputs of VABS airfoils together and create a (.dat) file to be run at GEBT

  1. chadi amer

    Dear all,

    I'm analyzing a wind turbine blade dynamic analysis to get the mode shapes and natural frequencies,

    so after I inserted all required airfoil cross section data (0m to 5m, having 10 cross-section) into PreVABS and run it at VABS,

    now I need to put VABS output files all together as a (.dat) file to be run in GEBT.

    Any example or tutorial of such case would be very much appreciated, noting that each cross-section is different from the other, regarding cord length pitch axis, etc...


    PS: as we all know VABS has the following data regarding the airfoil cross section data:The 6X6 Mass Matrix, The Mass Center of the Cross Section, The 6X6 Mass Matrix at the Mass Center, The Mass Properties with respect to Principal Inertial Axes, Mass Per Unit Span, Mass Moments of Intertia about x1, x2 and x3 axises, The Principal Inertial Axes Rotated from User Coordinate System, Degree about the positive direction of x1 axis, The mass-weighted radius of gyration, The Geometric Center of the Cross Section Xg2 and Xg3, Classical Stiffness Matrix (1-extension; 2-twist; 3,4-bending), Classical Flexibility Matrix (1-extension; 2-twist; 3,4-bending), The Neutral Axes (or Tension Center) of the Cross Section Xt2 and Xt3, Timoshenko Stiffness Matrix (1-extension; 2,3-shear, 4-twist; 5,6-bending), Timoshenko Flexibility Matrix (1-extension; 2,3-shear, 4-twist; 5,6-bending), and The Generalized Shear Center of the Cross Section in the User Coordinate System Xs2 and Xs3.

    (Aside,this work is a part of my master of science in aerospace engineering thesis, so it has a high importance for me) 



    Kindest Regards,

    B.S Aeronautical Engineer
    M.Sc Aerospace Engineering Student



  2. Su Tian


    There are some supporting documents under the GEBT Tool webpage, including a GEBT manual and several examples with sample input files.

    I am working with VABS and GEBT right now as well. So if you have further questions, we can discuss later.


    Best regards,

    Su Tian

  3. chadi amer

    ok Mr. Tian

    I have read the manual actually but I still find it hard to insert my data corresponding 

    would u please send me an email so we can discuss about it 

    mine is

    there I can show u my files I am working on or u may send me some examples simulating a similar case

    thanks a lot


  4. chadi amer

    Dear sirs, I have managed such a file to run a modal analysis for my wind turbine blade having 10 different crossections but still Im having an error I dont know the reason, can anybody tell please, very urgently 











    -1.0405803491E-13   -1.9771112026E-08    9.3979911387E-08   -1.2698921987E-08   -2.8328015753E-11   -1.0123873627E-11

    -4.5694757922E-08   -4.4892344385E-11   -2.8328015753E-11   -1.1351405996E-10    2.0322494782E-06    6.2063368541E-07

    -8.2146533760E-10   -1.2262430452E-11   -1.0123873627E-11    5.7687841030E-11    6.2063368541E-07    3.4401597992E-07


    -1.9045753866E+00    0.0000000000E+00    0.0000000000E+00    0.0000000000E+00   -2.8330114837E-01    7.8456325172E-01






























    The Error Message was as such at the end of the .txt.ech file


        Failure of MA28AD with iflag=-1  

  5. chadi amer

    and some times if gives me 


    frame number unmatch

    what does the frames resembles here? 

    any body knows ?


  6. Qi Wang

    Hi Chadi,

    My first guess on the this bug is that your boundary conditions are not correct (ncond_pt). In your input file, it reads:

    1 #point conditions 1 2 3 4 5 6 0 0 0 0 0 0 # corresponding value 0 0 0 0 0 0 # corresponding time functions 0 0 0 0 0 0 # indicate whether it is a follower condition

    2 7 8 9 10 11 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

    However, I think key point 2 is not a boundary point; change this key point number to 10 (which I think this is the point at the tip) and try it again.


    Emailed forum response from
  7. chadi amer

    thanks for your opinion sir


    but the error is as such


     I/O error: read number of member frames                                                                                                                                                                                                                                                                     

    I dont really understand what does frames stands for



  8. Qi Wang

    Can you upload your input file as attachment please?

    The data in the post is in poor format that I can’t help debug.


    Emailed forum response from
  9. chadi amer

    can i have your email to send u my file directly and u may check it more carefully ?


    mine is


  10. Wenbin Yu

    Chadi, Please use attachment instead on the board. Our team usually will not be responsive to email questions as we can Q&A to be shared with all other users. 

  11. chadi amer

    ok sir, I didnt realize the icon of attachment at first. thanks

  12. Qi Wang

    Hi Chadi,

    Attached please find the corrected input file for this analysis. There are two mistakes in the original file:

    1. The boundary condition should be applied to boundary points; for this case, the boundary points are 1 and 10.
    2. The nframe tag in your case should be "0". Everything is defined in the global coordinates, thus, no local frame is needed.

    Moreover, you really don't need so many elements for this case. In your original input file, you meshed each segment by 100 elements ( and there are 9 segments in total).



  13. chadi amer

    Thanks a lot Dr. Qi Wang,

    The file u fixed run now perfectly at GEBT now, but I have two questions:

    1- why the eigenvalues shows two values one is positive while the other is negative? and why the first 6 modes are not around zero value Hz since I run the dynamic analysis flag 3 for freefree mode? is it correct that their values are in Hertz although we input the Rpm in rd/s ?

    2- when I run the PostGEBT file for that it shows an error in line 33 which I couldnt fix to see the graphs of the mode shapes? (please see attachment) (while no such error for other examples = no installation mistake)






  14. Qi Wang

    Hi Chadi,

    1 The eigensolver in GEBT returns all the "complex eigen pairs". PostGEBT will generate a file named "NaturalFrequency.pgt" in which only the natural frequencies are documented.

    2 I run the PostGEBT successfully: the natural frequencies are documented in the ".pgt" file and all the corresponding eigenvectors are plotted in ".png" files. 


  15. chadi amer

    :) everything works perfectly now, much appreciation for all your time and patience Dr. Qi


    presents something new to the natural and applied science when its published this February 2015

    Best Regards,

    Chadi Amer


  16. chadi amer

    two small question to add here,

    1-why each member has its own mode for Disp and Force sepeerately but not all the beam as a whole ?because my professor asked me to show all the beam mode shapes related to each natural frequency. 

    2- why the limits of the RPM in rd/s are, 0.000001 and 83 for my case?


  17. Qi Wang

    Hi Chadi,

    The PostGEBT will plot the eigenmodes for each beam at this moment. But you can output the quantities of your interested only by changing the "IO.f90" subroutine in your GEBT download package.

    I don't quite understand what does "the limits" mean in your description.


  18. chadi amer

    Dear Sir,

    The PostGEBT is plotting now the mode shapes (eigenmodes) for each member (of the same beam) separately as we saw,


    - What quantities did you mean here sir? (if number of frequencies and related modeshapes of the output, I know where to edit in the main GEBT input)  

    - for (IO.f90) on which line of its subroutines we are able to fix such issue?


    (why when Im doing the free-free modal analysis I do not see around 0 Hz values for the first 6 natural frequencies? I understood that only flexible mode shapes shows up in such case.)


    my request is mode shapes for the whole beam all together.

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