modal analysis

[alb2]

Hello,

in a simple 2D model, stiffness and mass given, I am trying to get the same frequency when using a) mass b) mass changed into a force, and in analysis option the convert load to mass option for the modal analysis.

The mass direction is only in the z direction, for the a) option works fine, for the b) I get wrong results

Any help?

Thank you

[Artur.Kosakowski · Accepted solution]

1. Model type should be frame rather than truss (instability if support defined in one node only)

2. Support should be such that it restrains d.o.fs so that there is no instability

3. If you want to convert force into mass you have to define it first (case 3).

I'm attaching the corrected model.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[alb2]

Thanks,

so it means that, first u have to define a load case with the force - new modal analysis  and convert the force to mass of the load case with the force into the modal analysis.

[Artur.Kosakowski]

The order of cases is not important. The rest is as you wrote.