COMSOL - Plane Wave Radiation input not matching Pressure Field

AI Thread Summary
The discussion centers on a model resembling an impedance tube, featuring a cuboid with a membrane and defined inlet and outlet using Integration and Explicit methods. The inlet is set to a pressure amplitude of 20 Pa, while Plane Wave Radiation is applied to both the inlet and outlet. However, the acoustic pressure at the first eigenfrequency is unexpectedly low, measuring approximately 1x10^-11 Pa, raising questions about the accuracy of the pressure settings. The user seeks clarification on why the inlet pressure does not reflect the intended 20 Pa. Additional information or troubleshooting steps are requested to resolve the discrepancy.
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I have a model set up, that is a cuboid, with a membrane half-way along - a bit like an impedance tube setup.

I've used Integration 1 & 2 with Explicit 1 & 2 to define an 'inlet' and 'outlet' at opposing faces of the tube. The Variables for the inlet and outlet are intop1(p0) and intop2(p).

I then added Plane Wave Radiation to the model (inlet & outlet), with the Incident Pressure Field on just the inlet set with a Pressure Amplitude p0 = 20 Pa.

The resulting Acoustic Pressure at the 1st Eigenfrequency shows that the flow direction is correct, but the scale is odd. It shows that the pressure at the inlet is about 1x10^-11 Pa.

How can this be, when I set the inlet pressure to be 20 Pa?

Many thanks.

https://dl.dropboxusercontent.com/u/11341635/Screen%20Shot%202014-08-12%20at%2008.35.20.png
 
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