The parameter <phi0> must be greater than 0 (no solid) and less than 1 (no porosity). The <fluid> tag encloses a description of the fluid, as given in Section 4.14.1↑. The <solid> tag encloses a description of the solid matrix constitutive relation and associated material properties, such as those selected from the list provided in Sections 4.1↑-4.7↑. The <permeability> tag encloses a description of the permeability constitutive relation and associated material properties, as may be selected from the list presented in Section 4.8.2↑. To simulate the special case of zero friction between the fluid and solid (such as in the fluid-FSI material), it is permissible to set the permeability to zero.

Example:

<material id="2" name="Material2" type="biphasic-FSI">
  <phi0>0.25</phi0>
  <fluid type="fluid">
    <density>1e-9</density>
    <k>1e+09</k>
    <viscous type="Newtonian fluid">
      <mu>1</mu>
      <kappa>0</kappa>
    </viscous>
  </fluid>
  <solid type="neo-Hookean">
    <density>2e-9</density>
    <E>200</E>
    <v>0</v>
  </solid>
  <permeability type="perm-const-iso">
    <perm>0.005625</perm>
  </permeability>
</material>