March 4, 2021 at 4:45 pm

Erik Kostson

Ansys Employee

You are more than welcome - just to finish of this discussion, and perhaps this will help others - to the points that a vibroacoustic modal analysis predicts acoustic and / or structural modes if we have a structure present . In the right image below there is a room which is 3 m by 2.5 by 2 (the plate inside the room is 1 x 0.5 x 0.01), so the first acoustic mode along the longest direction, should be f=(343m/s)/(2*3m) = 57 Hz, and that is what we get (see highlight with red in the right image below). The plate mode is 52 Hz which is a free bending mode in that model (highlight in blue in the right image below), and is exactly like the pure structural modal analysis (52 Hz, left image highlighted in blue) and as expected. Of course since the structure is not fixed anywhere in the pure structural modal analysis in the left image below, it also has 6 rigid body modes before we get the 52 Hz plate bending mode.nnn