[PayarRadfar]

Hi Everyone,

I was wondering if there is a possibility, probably using UDF, to give a boundary condition as pressure to velocity ratio? I am modelling human Aorta and if this is possible it fixes lots of problems we have in the project.

So at the moment lets just consider a simple case, a pipe with one end as Velocity inlet and the other as pressure outlet. Now is it possible to change the pressure outlet to an outlet which is a ratio of pressure to velocity?

Thank you and sorry if the question is dumb!

[`e`]

You could use the DEFINE_PROFILE macro for assigning a boundary condition as a function of the pressure and velocity. However, it would be interesting as to whether or not the simulation would converge. Are there any references with a similar approach, or is there a physical explanation for this boundary condition?

[PayarRadfar]

Originally Posted by `e`

You could use the DEFINE_PROFILE macro for assigning a boundary condition as a function of the pressure and velocity. However, it would be interesting as to whether or not the simulation would converge. Are there any references with a similar approach, or is there a physical explanation for this boundary condition?

Hi there,

Thank you for the response. Alright I will have a look see if I can get it working.

Yes there is a physical explanation. I am doing an FSI simulation and there is another vibration approach for modelling blood pressure and velocity in human aorta and arteries by which it defines pressure and velocity at every point as a addition of two waves back and forward waves. Essentially P = P_b + P_f. This approach does take into account of the stiffness of Aorta/arteries and it is very interesting to compare the values with an FSI simulation as well as the lab results.

It would be interesting to see if we could apply similar approach and see whether it converges or not.

[PayarRadfar]

Originally Posted by `e`

You could use the DEFINE_PROFILE macro for assigning a boundary condition as a function of the pressure and velocity. However, it would be interesting as to whether or not the simulation would converge. Are there any references with a similar approach, or is there a physical explanation for this boundary condition?

Hi "e",

I am trying to do what you told me earlier. However, I dont know how to tell the code that for example: F_PROFILE(f, ft, i) = "Velocity of the Face" * 6360.0;

Can you please advise me how I can call it? I tried C_U (c,t) But it has an error which I think is due to the fact that C_U is the cell variable not face!

Also ultimately, do you know how I could give it different ratio values at different times? e.g. 6360 at first second 10,000 at 2nd second etc.

Sorry for bothering you with simple questions. I have mainly coded in MATLAB before and do not have much experience.

Regards

[`e`]

Remember that velocity is a vector component of (x-direction), (y-direction) and (z-direction) in 3-D Cartesian coordinates. Each of these components can be retrieved at faces with F_U(f,t), F_V(f,t) and F_W(f,t) respectively. For example, with applying a boundary condition dependent on :

F_PROFILE(f,t,i) = F_U(f,t) * 6360.0;

For time dependence, you could use conditional cases (like in MATLAB) for discrete time intervals, or use an equation for a continuous time dependence, for example:

F_PROFILE(f,t,i) = F_U(f,t) * (3.0 + 2.0*CURRENT_TIME);