Triphasic Model

[Narissa]

Hello there.

I am new to F.E.M and Febio. I have problem stimulating a triphasic model. I keep getting an error "Max nr of reformations reached". I am trying to create a triphasic model. The 1 x 1 x 1 block is placed in a container. Load applied at the top of the block via an impermeable piston. The bottom of the block is fixed and communicates with NaCl through a filter. I attached the model I created and the input files with relevant values. I read through the manuals and theory, but I am not sure if I applied the BC and IC correctly.

Regards,
Narissa

[ateshian]

Hi Narissa,

In a triphasic model with a charged solid matrix, a Donnan osmotic pressure will develop, which will swell the solid until the solid matrix stress is balanced by the osmotic pressure. The best way to allow this process to occur is to ramp up the fixed charge density from zero to the desired value, while running a steady state analysis. In your model, the fixed charge density is non-zero and constant with time, so you would need to modify that. You can use a multi-step analysis to switch from this initial steady state response to a transient analysis in response to loading.

Also, you have prescribed a pressure on the surface using a step load curve. That could also be problematic for convergence. It may help if you ramped up this pressure from zero to the desired value. You can prescribe this pressure in the second step of a multi-step analysis.

Best,

Gerard

[Narissa]

Hello Gerard,

Thank you for your advice. I considered your advice and here is the results. I am still unsure if I am doing it correctly. Can you please check if I have followed the instruction correctly? Thank you in advance.

Warm regards,
NarissaMPT53.feb

[ateshian]

Hi Narissa,

I am having a hard time figuring out the relevance of the material parameters and concentrations that you chose, because you have adopted a different set of units that I normally use. If you could reformulate your model using the units we recommend in the User Manual, that would help me figure out why your analysis is not reaching a normal termination.

Best,

Gerard