Compositing model: viscoplastic + simple compressible

Hi everyone. I am running simulations of the lithosphere + upper mantle, and I am currently using the ‘Visco plastic’ material model for the rheological behavior. However, this makes my model incompressible. Therefore, I was thinking of setting a ‘Compositing’ material, where I take all parameters from the ‘Visco plastic’ material model, and the compressibility from a ‘Simple compressible’ material model where I can give a value to the parameter ‘Reference compressibility’. However, when I run the simulation, I notice that density is the same as when I simply setup my material as ‘Visco plastic’. Can anyone give me any suggestions?
Here, for further information, I also enclose the section of my code for materials
Test.prm (3.5 KB)
Thanks a lot!

Dear Alessio,

If I understand your prm correctly, ASPECT assigns density from viscoplastic because that is what you ask it to do:

subsection Compositing
   set Compressibility                 = simple compressible
   set Density                         = visco plastic
   set Entropy derivative pressure     = visco plastic
   set Entropy derivative temperature  = visco plastic
   set Reaction terms                  = visco plastic
   set Specific heat                   = visco plastic
   set Thermal conductivity            = visco plastic
   set Thermal expansion coefficient   = visco plastic
   set Viscosity                       = visco plastic


The Compositing module gives users a lot of freedom, and that also allows for some unnatural model choices. Make sure you understand in which of the governing equation(s) each of the material properties is used, and the implications of your choices on the simulation.

Best wishes,