MAT10 Fluid - Noise Problem



I want to find out how Nastran calculates the noise at end of the fluid (so on the face). is the noise reflected back or is like a total absorbation. I searched in the Guides, but figured out nothing.

To find it out, I made a TOY-Model:


Im calculating the Noise with the Preassure with SOL111. On one face on the bottom of the moddle I have a Structure face where I put a load on. This face is coupled with ACMODL to the Fluid. On all the other outside Faces of the Fluid is no structure. I meassured on 4 Nodes, but all have nearly the same preasure.

So now I'm not smarter than befor this test... I hope you can help me. (I'm using NX NASTRAN 10.2)