[Jernej Pirnar]

Hi all,

I am interested in Fluid Structure Interaction and I am trying to simulate dynamics of flexible tube in the case of the interior air flow. I use Ansys software package (CFX + Ansys Mechanical APDL).
Let me first briefly introduce my approach.

• Originally cylindrical shaped tube is stretched to get deformed shape. FE model of the deformed tube is exported and it is the basis for creating fluid mesh in ICEM CFD. Output elastic strain (EPEL) is saved via the INISTATE,WRITE command and applied later to prestress the model.
• The deformed tube FE model is imported back into Ansys Mechanical APDL, where the new constraints, fluid-solid interface and MFX setup are defined for the additional FSI (2-way) simulation. Also the initial stress state (imported FE deformed model do not have any stress state), based on the previous static structural analysis is established. Structural part of the FSI simulation (transient) setup is written (MFWR) in the .inp file.
• Fluid mesh is made with ICEM CFD as mentioned. Fluid part of the FSI simulation setup is made in CFX-Pre, and the CFX definition .def file is written.

Definition of the fluid side part of the simulation is made without any problem, but I get stuck with the structural part, when I try to apply the prestress (INISTATE,READ) obtained in the previous static structural analysis. I have already done the FSI simulation without initial stress applied and it has been finished successfully. So, obviously prestressing is the cause the solution fails (in the very first coupling step). Ansys.err file states that the structure FE mesh becomes highly distorted, what is confirmed, when the .rst file is checked. In the initial state file .ist I write only Output elastic strain (EPEL), since the linear elasticity material model is used. Initial state data is written in the Global cartesian coordinate system (INISTATE,WRITE,1,,,,0,EPEL). SOLID186 element type is used and it supports the application of the INISTATE command.

Does anybody have some experience and can give some advice on the topic I described?

Thanks in advance.

Jernej