perform free vibration analysis of plate structures

[ZengLiKun]

dear professor：
    I want to perform free vibration analysis of plate structures.Below I give my  example and output file.The error message of the output file shows that the mass matrix has no non-zero entries, I don't understand where is my problem? Looking forward to your reply.

[ZengLiKun]

here is output file

[Prof. R.L. Taylor]

Your material set needs a density for the mass computation

DENSity MASS rho

should be added

You need to always look at the output file that feap creates.  I gives warnings and errors.  For example with your data the warning in the material set output is that the density is zero.  Always look to see what properties each matrix will require.

[ZengLiKun]

Thank you very much for your reply，My problem was temporarily solved
.

[ZengLiKun]

Dear Professor：
  I'll enter the file after perfecting，and after running it，The information in the output file
  SUBSPACE: Square root of eigenvalues (Hz.)
        2.97376590D-05   4.77934649D-05   6.23329769D-05   5.07859824D-03
        7.24462600D+01   1.62704173D+02   1.81238050D+02   2.32769953D+02
        2.78367818D+02
  2.97376590D-05  of them are the first-order natural frequencies of the structure, am I correct in my understanding?
Thank you very much for your reply.

[Prof. R.L. Taylor]

If subspace converged then these are the frequencies.

[ZengLiKun]

Ok Professor, thank you very much for your reply. But my result subspace  is obviously not convergent, what could be the reason? Also, if I want to simulate the occurrence of cracks on the board, how can I achieve this?

[Prof. R.L. Taylor]

Post your input file so we can check for errors.

You could introduce a crack by having a mesh where nodes do not join along the crack line.  See user manual  for example using block meshing

[ZengLiKun]

This is my adjusted input file and associated output file.Which of my step errors caused the subspace not to converge?

[ZengLiKun]

In addition, can you provide me with some cracked examples so that I can learn quickly? Thank you very much Professor!

[Prof. R.L. Taylor]

When you do free vibration of a shell you must:
(a) have enough b.c. to prevent rigid body motion & eliminate any tangent singularity;
(b) apply a shift to the TANG to allow computation of zero eigenvalues.


Sample mesh with slit attached.