## Fluids

#### pre-stretch soft material first, then apply voltage to change shape to do FSI

• Mark_
Subscriber

Hello,

I'm doing my project using dielectric elastomer material. I'm using 2020 r2 workbench to do simulation. I wanna finish pre-stretch and apply voltage in Transient structural part. Then combine with Fluid Flow (fluent) to finish FSI.

I have some problems right now.

1. how should I set the pre-stretch for the material. I can finish the pre-stretch in static analysis very quickly. But it runs very slow in Transient structural part, and some elements will be highly distorted during this step after a few steps. How should i do pre-stretch for this model? i also need to do Two-way FSI, so I don't think I can do the pre-stretch not considering the fluid influence. Or do you have any ideas to avoid the fluid influence during the pre-stretch? The shape after pre-stretch is not decided, so the model for the water is built based on the non pre-stretch shape of the soft material. But actually, i need to finish the pre-stretch first then put it in the water, then apply voltage. Any ideas to finish these steps?
2. I also have some questions about how to increase the calculation peed for anays. Just as I said above, the calculation speed is very quickly for static analysis. but even with same setting in Transient structural analysis, the speed is very slow. how should I increase the speed?
3. Do you have any tutorials for dielectric elastomer material with pre-stretch using workbench?

Best regards.

• Stephen Orlando
Ansys Employee
Hi Mark Pre-stressing can be rather complicated to set up especially with elastomer materials. One method is the following:
Set up your 2-way FSI case in the non-stressed state with Transient Structural and Fluent transient.
In Transient Structural turn time integration off
Set the End Time in Transient Structural to be the total time of the entire simulation
In Fluent, turn off the flow equations so only the dynamic mesh is solved
Initialize Fluent with pressure = 0.
Run System Coupling so that your model becomes pre-stressed. I imagine this pre-stressing comes from the applied voltage, but I'm not sure exactly how you're stressing the material.
Extend the System Coupling run time.
Turn on the Fluent flow equations.
Turn time integration on in Transient Structural.
Restart the run.