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Hi everyone.

I am having some issues with the results of my simulation of an aneurismatic aortic arch with deformable wall properties.
As suggested from the guide, I ran a rigid wall simulation to impose the initial condition of the deformable wall simulation.

At first my simulation did not converge, so I have modified the .svpre file by adding two lines (fix_free_edge_nodes_vtp mesh-complete/walls_combined.vtp and deformable_create_mesh_vtp mesh-complete/walls_combined.vtp) as suggested by a previuos post on the forum (viewtopicPhpbb.php?f=188&t=11726&p=3307 ... 6ea480d24b).
Now the simulation converges, but the displacements appear to be too large (up to 2cm), even if the initial displacements calculated from the presolver seem to be correct.

My model is in mm, so I used consistent units of measurments for the wall properties ([Pa] for the Elastic modulus and pressure, [mm] for the thickness and [g/mm^3] for the density), is it correct?

Does anyone have any suggestion?

Thank you for your help,
Valentina

Hi Valentina,

I suggest to make sure that the boundary conditions are in the correct units: velocity, r, rcr, etc.

Cheers,
Dave

Hi Dave,

thank you for your reply.

I checked the units of measurement of the boundary conditions and they should be correct, in the deformable wall simulation I use the same boudary conditions as in the the rigid wall case, where the results have the right order of magnitude.

Is there anything else that I could check?

Thank you for your help,
Valentina

Hi Valentina,

I'm not sure what could be the problem. When doing a simulation I typically first start with a simple geometry (e.g. cylinder or Y-junction tube) and run a simulation with the simplest BCs and examine the results to make sure they make sense. I then increase the complexity of the simulation step by step, switch to deformable wall, add more complex BCs, etc.

If you put your SV Simulations folder somewhere I can download it I'll have a look.

Cheers,
Dave

Hi Dave,

thank you for your suggestion and sorry for the delay in my reply.
I increased the complexity of the simulation step by step and before adding the deformable walls everything seemed to work fine. I am simulating the fluid dynamic of an aneurismatic aorta.

Maybe I am making some mistakes with the units of measure. My model is in mm, so I used:
- 0.00106 g/mm^3 as blood density;
- 0.004 g/(mm*s) as blood viscosity;
- Pa for the pressure (should I have used dyne/mm^2?)
- g/(s*mm^4) for the resistances;
- mm^4*s^2/g for the capacitances;

For the deformable wall I set:
- 2 mm for the thickness;
- 2000000 Pa for the Elastic Modulus;
- 0.5 for the Poisson's ratio;
-0.83 as shear constant;
- 0.00112 g/mm^2 as wall density;
-11411 Pa as Pressure, calculated from a previous simulation.

With these units of measure, I expect the displacements to be in mm (setting mm as Sim Units for the conversion), is that right?

And one last question, regarding the IC file, is it correct to calculate it from a rigid wall simulation with the same boundary condition as the deformable wall one, or should I run a steady rigid wall simulation?

Thank you for your help,
Valentina

Hi Valentina,

Your units look ok.

I would run a steady rigid wall simulation for the IC.

If the rigid wall simulation pressure, velocity and stresses make sense then I'm not sure what is going on, must be something that is not scaled correctly. Upload your SV project (without the imaging data) someplace I can download it and I'll have a look.

Cheers,
Dave