Hi ItalicBike,

I changed your Geometry and sliced it up to make a vertex at the Evaluation Point. I changed the BCs to be on geometry instead of nodes. I don't have the sall BC quite the same, you can make 4 planes and 4 slices to make faces where you want to bond to a wall.

I changed your model to be a Modal Superposition method to calculate the Harmonic Response. That is done by linking the Modal Solution cell to the Harmonic Response Setup cell.

That required that I turned off the Damped solver in Modal.

I requested modes up to 750 Hz, which is 1.5 times higher than 500 Hz.

Here are the natural frequencies below 750 Hz:

In Harmonic Response, the Analysis Settings request frequencies between 100 and 500 Hz with 400 data points. You can see five peaks that correspond with the five modes found above. You can see that mode 5 has a bigger response at the evaluation point than mode 4.

If you click on the Solution Information folder for Harmonic Response, the Solution Output text will display. Scroll down till you find the PARTICIPATION FACTOR CALCULATION and look at the Y direction table. The RATIO column shows that mode 1 has the biggest contribution and mode 5 the second biggest to the response at the evaluation point. This is not what the graph above shows because the size of the peaks on the graph strongly depend on the spacing of points along the frequency axis. If you rerun the analysis and put 100 points between 150 and 170 Hz, the height of the maximum in the graph will jump up. The peaks are even more strongly dependent on damping, which is the whole point of your experiment, right?

Another analysis that can be added to this model is a Transient Structural.

This is where the force-time plot you showed in the attachment can be applied to the vertex in the center.

Reply with the data from the graph in a text file or spreadhsheet if you want me to help with that.

The acceleration-time plot at the evaluation point can be made. This would simulate the data an accelerometer would record at that point when the force is briefly applied at the center. You can take that data, transform it to dB, compute the frequency content and plot the Power Spectral Density or FFT magnitude vs. Frequency. However dB is a ratio relative to a reference value. What is the reference value that you would divide the acceleration by to compute dB?