5.2. Non-Uniform Ideal Gas Material

In non-uniform acoustic media, both mass density and sound speed vary with the spatial position and are derived by the ideal gas law.

To set up a non-uniform ideal gas model:

  1. Define the temperature T0 via the TREF command (defaults to 22 °C).

  2. Define the density ρ0 and sound speed C0 at the reference temperature T0 via the MP,DENS and MP,SONC commands.

  3. Define the reference static pressure Psref via the R,,Psref command.

  4. Define the spatial static pressure Ps via the BF,,SPRE command.

  5. Define the spatial temperature via the BF,,TEMP command.

The ideal gas model does not support the MPTEMP and MPDATA commands for mass density and sound speed. Mass density and sound speed are defined at a reference temperature, and the ideal gas model calculates the temperature-dependent nodal mass density and sound speed.

Example 5.3: Defining a Non-Uniform Ideal Gas Model

mp,dens,1,1.21       ! mass density
mp,sonc,1,343        ! sound speed
r,1,pref,psref       ! static reference pressure
tref,22              ! reference temperature
nsel,s,loc,x         ! nodes at x=0
bf,all,spre,101325  ! static pressure on nodes
bf,all,temp,100      ! temperature on nodes

For more information, see Non-uniform Acoustic Media in the Mechanical APDL Theory Reference.