1. You can use either column, but the conclusion is the same.

2. Base acceleration means the acceleration signal of the base of a shaker table. You can't put this into ANSYS directly. You can integrate that signal and apply a velocity input, or integrate it again and input a displacement. In the light blue plots above, I am plotting the relative displacement between the base and the mass that is connected to the base through a spring and damper.  If you have a displacement input, which is easy to generate in matlab, you can run that simulation in ANSYS. If you probe the Z displacement of a point on the IC, you have to subtract the Z displacement of the input to the faces fastened to the shaker to get the relative displacement.

Instead of actually moving the base, the acceleration signal can be applied to the mass. This is easy to do in ANSYS and then when you probe the Z displacement of a point on the IC, the base has zero displacement, so you don't have to do the subtraction to get the relative displacement.

I wanted to be able to probe a point on the edge of the PCB and a point on the IC so I went into SpaceClaim and split the body.

Now I can get a probe on the edge of the PCB where you saw large flapping and on the IC at the center of one of its edges.

I created a 5 second sine sweep from 80 - 190 Hz sampled at 4 kHz. It took 3 hours, 23 min on 8 cores. Here is the input acceleration spectrogram.

I output the data at 4 kHz also.  Below is the acceleration of the IC point.

Below is the acceleration of the Edge point, note the much higher accelerations occurring on the edge.

You can see the higher frequencies in the response of the edge compared with the IC.

Hope this helps.