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Ansys FAQ

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This article contains answers for Ansys related FAQ. Please feel free to add questions and answers here!




Solver related questions


FSI (Fluid Structure Interaction)


Which programms are necessary to solve a FSI simulation?

Beginning with Ansys 11.0, Ansys Workbench with Simulation and CFX are required.

Which Ansys licenses are required for FSI in Ansys?

Working with Ansys 10.0 or older, a Muliphysics and a CFX license are required. Ansys 11.0 requests an Ansys Product and a CFX license.

What kind of coupling methods are possible?

One-way or two-way FSI coupling.

Is it possible to perform a steady-state FSI simulation?

Yes, Ansys 11.0 enables steady state and transient FSI simulations as well.

What is the general procedure for a FSI simulation in Ansys 11.0?

1. Define the Solid setup in Ansys Simulation (Ansys Workbench). This includes an Fluid-Solid-Interface.

2. Write an Ansys Input File (.inp) of this setup.

3. Define the Fluid setup in Ansys CFX-Pre. A link to the Ansys Input File is required.

4. Write an Ansys Definition File (.def) of this setup.

5. Solve the Definition File with Ansys CFX-Solver.

6. Postprocess the data in CFX-Post.

CFX Setup

Ansys Setup


How do I start an FSI simulation in Ansys 11.0?

Start the CFX Solver Manager and load the .def File. Ansys will load the .inp file automatically.

Is it necessary to define the Ansys Insallation Root in "Define Run" in Ansys 11.0?

On a Windows PC it is not, on Unix it is necessary.

Is it possible to stop a running FSI simulation in Ansys 11.0?

No, the "Stop"-button does not work for FSI simulations.

Is it possible to write back-up files of a FSI simulation in Ansys 11.0?

The solver terminates with the error message "A negative volume appeared". What went wrong?

This error often appears with FSI simulations. Normally it comes together with a large deflection simulation of the solid part. Mostly the CFD-mesh deformation is too big and negative elements appear. Possible solutions might be

  • a better fluid mesh
  • meshsiffness 1/wall distance
  • smaller timesteps


If I open the FSI simulation in CFX-Post 11.0 only the fluid data are available. Where are the solid data?

CFX-Post only opens the .res file by default. If you want to postprocess fluid and solid data together you have to load the solid data additionally: File -> Load Result -> Load the Ansys .rst or similar data. Now you can postprocess all data in CFX-Post.

Ansys Workbench



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