How to set BCs for making a FRF of a rail and get a pinned-pinned modeshape with nodes at sleepers?

[omar.el92]

Hi everybody,

I am working on a simulation of a receptance FRF of a railway (mm/N) and i am facing an issue related to the pinned-pinned mode (1052Hz ca.) of a 36m model.

The modeshape should have always the nodes at the sleepers, but what i get is a wavelength slightly different than the sleeper spacing and therefore after 10m ca. from the BC i get the nodes at the midspan.

I have attached a picture that depicts the PP modeshape at the Boundary and in the middle of the model. Since the receptance is computed considering the force applied in the middle of the model, i would have wrong results in the FRF i guess.

I have tried several different BCs (complete hinge of the rail cross section, hinge of only one node in the middle of the cross section, etc) but i always get the same result.

What should be the right BC setting for this kind of simulation?

I am looking forward for your help, i am really struggling on it!

Warm regards,

Omar

 

[Mustaine3]

In simple words - what's the problem? That the rail penetrates these blocks when looking at the eigenmodes?