Hi Kumar,

I put this image from your model here because Sandeep is not permitted to open attachments. The top skin is hidden.

You have not sliced this cleanly out of the bulk honeycomb since once cell is not closed.

The proper way to model this is with surfaces at the midplane of each solid face, not with solid bodies.

You ran a Modal analysis without holding the part, which is allowed and simulates how the part would vibrate if it was floating in space. When you do this, you have to request more than six modes, because the first six modes are the rigid body modes. You need to request seven modes to see the first natural frequency, but that might be a little off because of the missing face on one cell and the fact that you should have built it with surfaces instead of solids.

Both SpaceClaim and DesignModeler can extract midsurfaces, but they won't do the all the surfaces at once like my NX CAD system. Can you get a midsurface model from the CAD system that made that geometry?