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Defining permeability as a function of void ratio in Abaqus

Defining permeability as a function of void ratio in Abaqus

Defining permeability as a function of void ratio in Abaqus

(OP)
Hi,

I am using the soils step to model compression of blood vessels. I need to show that applying an extrenal pressure reduces the flow velocity. I have a series of hex elements forming a long cuboid with pore pressure boundary conditions at each end driving the flow.

I understand that Abaqus allows you to define permeability as a function of void ratio. This is from the user manual:

"Data lines to define fully saturated isotropic permeability (TYPE=ISOTROPIC):

First line:

   1.

      k. (Units of LT–1.)
   2.

      Void ratio, e.
   3.

      Temperature, .
   4.

      First field variable.
   5.

      Second field variable.
   6.

      Etc., up to five field variables."

At the moment my code reads:

*Permeability, specific=9.8e-06
 1e-8,4.

I've simply set the value of void ratio to that of my initial void ratio defined using *INITIAL, type=ratio.

At the moment applying a compresive force to the elements does reduce the void ratio but even when it reaches 0 the flow velocity is still the same as with no load and so I am assuming the permeability is constant throughout.

I know the second data entry should define the relationship between void ratio and permeability but I'm unsure as how to implement this. I haven't found anything useful in the user manuals. e.g If I wanted a linear relationship like k=ae

where k is permeability, a is a constant and e is void ratio, how would I write this into the code?

Do I need to define field variables in order to do this or is there a simpler way?

Thanks in advance,

Andy

 

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