Reply To: Response of a system to an excitation on the frame

[peteroznewman]

1.       One mistake was the springs in your model were not arranged along the Y axis. I changed them to be along the Y axis which caused the first mode to be non-zero.

2.       I tried to get your model to run, but could not so I decided to put the work in to convert the geometry to beams and shells.  I assigned everything Aluminum. I didn’t check what the material assignments were in your original model, but the beams and shells have the same cross-section and thickness as your original geometry.  There were a few minor tweaks to get the edges and vertices to line up.

3.       I didn’t spend any time comparing modes from your model to my model. I greatly reduced the number of bonded contacts and joints, so you model may have had extra stiffness where it didn’t belong due to those.

4.       I wanted a lightly damped structure that would ring out past 0.5 s so I put in 1% damping ratio for all frequencies, and then I put another 1% damping ratio at 190 Hz because I wanted the damping to increase linearly from low to high frequencies to damp out the high frequency modes more quickly and let the low frequency modes have lower damping.

5.       I considered the frequency content of the force pulse, which had a period of 0.008 s or 125 Hz. So a maximum time step would be 1/20 of that or 0.0004 s. The highest mode requested in Modal was a bit higher than 250 Hz or a period of 0.004 s to see that mode properly rendered you would want a maximum time step 1/20 of that or 0.0002 s.  You already had 0.0001 s so I kept what you had.

6.       You can run my beam and shell model as a Full Transient. All you have to do is delete the link between the Solution cell of Modal and the Setup cell of Transient Structural.