To compute the "multi port" transfer matrix, you'll need to compute the local speed of sound. This requires a knowledge of the density.
rho u = -nabla p
where r is the density (kg/m^3) and v is the particle velocity vector (m/s). (Note that the "multi port" equations use volume velocity (m^3/s) and not particle velocity, so the surface integral of the component of v normal to the interface area must be computed.) Assuming a sinusoidal steady state excitation, we get
v = -1/(j rho omega) nabla p
r will normally be about 1.18 km/m^3, but for a porous material it can look like the graph below.
bangerth
commented
3 years ago
From Jason's email:
To compute the "multi port" transfer matrix, you'll need to compute the local speed of sound. This requires a knowledge of the density.
rho u = -nabla p
where r is the density (kg/m^3) and v is the particle velocity vector (m/s). (Note that the "multi port" equations use volume velocity (m^3/s) and not particle velocity, so the surface integral of the component of v normal to the interface area must be computed.) Assuming a sinusoidal steady state excitation, we get
v = -1/(j rho omega) nabla p
r will normally be about 1.18 km/m^3, but for a porous material it can look like the graph below.