Acoustic impedance

Hi all,

I need to model the acoustic impedance response of an elastic tube ( Acoustic-solid interaction) in the frequency domain. The acoustic impedance is :Pressure/volume velocity.

Here is the idea:

The geometry is a simple closed-end elastic tube. The acoustic load is generated by a piston on one end, sliding inside the tube. To have the frequency response, a unit step function of the displacement is applied to the piston (i.e., DZ=U(t)) and the pressure of the air inside the tube is measured in a time domain (i.e., P(t)) in front of the piston.