Theory
Every inlet and outlet is an acoustic port: a flat face where the solution inside the model is matched to the duct modes of the pipe beyond, which are perfectly absorbed (anechoic). At an excited inlet the program also imposes an incoming plane wave with the entered amplitude or power and phase (Excitation input (amplitude or power)).
The transmission loss shown in the report and the result files is the solution with ALL excited inlets driven TOGETHER at their entered amplitudes and phases; the S-matrix of every port and mode is computed in any case. Outlets are never excited: an outlet port is passive, and its termination is set by Outlet: compute a radiation domain.
The port formulation is verified on a straight duct (, no mode coupling) and against the plane-wave transmission loss of an expansion chamber. The TL of several inlets driven together follows the program's power-balance definition, which is consistent with the reference models it was compared against.
Default and rule
- Default
- on for inlets
- Rule
On for every inlet; off (not offered) for outlets.
- Source
Only excited inlets enter the computation. The modal power of the incident wave uses the port's own density and sound speed, with the mean-flow factor of (Morfey, 1971) when mean-flow convection is on.
Valid range on / off; at least one inlet must be excited
No excitation
The acoustic computation does not start when no inlet is excited.
Two inlets
With two excited inlets of equal amplitude, the reported TL is that of both driven together; the TL of each inlet alone (with the other an anechoic exit) is in the port-power file.