K6ROT

[Torontomississauga]

Hi,

I have a FEM model. With different K6ROT values, the frequencies are different. The 1st frequency with K6ROT equal to 1.0 is about 9 hz lower than the 1st freq. with K6ROT equal to 100. It seems some locations need to be stiffened up. How can I find these locations? Currently I don't see any excess displacements of the elements (except that rotational displacements on 1D elements are hard to see). How can I fix the problem, so that the frequecies are simliar with different K6ROT values? Thank you very much!

 

[rb1957]

is the stiffness of Z-rotations real in your model ? most often the drilling freedom is dummy, no?

 

[Onda]

It is possible that you have connected some bar/beam elements to a single grid point of a shell.
the k6rot influence the drilling stiffness of the shell and influence the TRUE stiffness of the beam.

You should avoid this (if this is the case) connecting more then one grid point to the ends of beams.

 

[Torontomississauga]

I had the same doubt at the beginning. However, it seems not the case here. I've solved the problem by reducing the sensitivity to initial distortion on the flat plate elements. Finally it works!