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4.14.4 General Specification of Biphasic-FSI Materials
The material type for a biphasic-FSI material is “biphasic-FSI”. This is a hybrid biphasic material used for modeling dynamic viscous fluid flow and frictional filtration through a porous-deformable solid. In contrast to the standard biphasic material described in Section 4.8↑, this material accommodates fluid viscosity and fluid dynamics; therefore it can be interfaced seamlessly with a fluid-FSI material to allow viscous fluid transport across that interface. The following parameters must be defined:
|<phi0>||solid volume fraction in the reference configuration (||[ ]|
|<fluid>||Specification of the fluid material|
|<solid>||Specification of the porous solid material|
|<permeability>||Specification of the hydraulic permeability|
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.
<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>
The value of <density> in the <fluid> and <solid> materials represents the true mass density of each constituent.