25 Sep 2018
— Edited @
03 Nov 2021
I am trying to run a simple cantilever beam in a dynamic gravity load only analysis.
The beam is 16m long, and clamped on KP1 (left side) and KP2 is the free end.
I followed Example 4 from the examples folder to run the static case, which I have included here for reference, worked fine (as expected)
However, I am getting an error stating the following
ERROR RETURN FROM MC23A BECAUSE
MATRIX IS STRUCTURALLY SINGULAR, RANK =332
ERROR RETURN FROM MA28A/AD BECAUSE ERROR RETURN FROM MC23A/AD
Failure of MA28AD with iflag=-1
I understand that most issues with singular matrices occur due to insufficient Boundary conditions, however, in the attached files, I have specified that KP1 is clamped (dofs 1-6 are 0), and KP2 is free (dofs 7-12 are 0). In this case, what are the other B.C. I am missing?
In the GEBT manual, I saw that the total degrees of freedon for dynamic analyses is 18 (including momenta), so I ran another analysis where the dofs 13-18 of KP1 are 0 as well. I got the same error message, so I am quite confused.
Is there another reason for this error message?
Any and all help with this issue would greatly be appreciated!
Static works, dynamic doesn't
2 KBClick to download
26 Sep 2018
I tested your files and they gave the same error messages as what you posted. The issue might be the flexibility matrix, though I am not sure why the same matrix works for static and steady state analysis, but not for transient analysis. One way to work around this is that try to calculate the shearing stiffness and complete the six diagonal entries.
26 Sep 2018
Hello Su Tian,
Thank you for your reply. I went through my input file to see if I can find an error, but as far as my understanding (I am very new to the GEBT solver), it seemed correct. Were you able to find any mistake with this input file?
Also, I input the stiffness matrix based on properties ignoring shear effects due to the beam being very thin (5mm x 7cm x 16m). I know the dimensions and beam physical properties, so would I be able to use VABS to generate perhaps more accurate mass and stiffness matrices?
01 Oct 2018
Your input file looks fine to me as well. You can contact Dr. Yu for the access to VABS. I think you should be able to use the online version on cdmHub.
01 Oct 2018
Thank you for the advice. The file began to work after I had calculated the non-zero values for the shear stiffness of the beam. I had some issues where the solution would fail halfway due to "reaching a local minimum", but after increasing the size of the time-steps, it ran successfully.