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Hello everyone,
For the cylinder model, i compared the outlet flowrate between the rigid and deformable one, but there is a big difference between them, so i want to know if it is normal, for the defomable one i got it based on the final step result of the rigid one, and pick the fifth cycle when the flowrate tends to be periodical stable. Thanks so much.

Jianfei Song

Hi Jianfei,

Thank you for your question! What you are seeing is indeed normal for a deformable wall simulation relative to a rigid one. In a rigid simulation, the walls are completely fixed all the flow that comes in MUST go out. For a cylinder model with a single inflow and single outflow, you should observe the outflow waveform looking exactly like the inflow waveform.

For a deformable wall simulation, the walls can now expand and contract. So when flow comes into the domain, that flow can either go out the outlets OR it can expand the walls in the model. Similarly, when there is little flow in the inlet (i.e. after time 0.4 seconds in your plots) the cylinder walls can then contract and expel flow through the outlet even if there is not much inflow. So the behavior you are seeing is normal. You can adjust the shape of the flow waveform by changing the material properties. Raising the Young's modulus and raising the thickness will push your solution towards more rigid behavior. Note that the method SimVascular uses for deformable wall simulations (called the Coupled-Momentum Method) is only reliable for deformations that are <10% of the cylinder/vessel radius.

One thing you need to be careful of is that it takes pulsatile deformable simulations longer to reach a "periodically steady" state where it forgets any initial transient behavior. We recommend running pulsatile deformable simulations for at least six cycles so that any initial transients are no longer part of the solution.

Hope that helps!