**** Entered By: rlange @ 05/25/2006 03:28 PM ****

Q. I want to do a transient FSI problem with ANSYS and CFX but do not want to account for the effect of the deformation of the structure on the flow field, as it is expected to be small. How should I approach this?

A. The two methods to accomplish this are the CFX-Post method and the MFX method.

1. CFX-Post method: Solves the CFD problem by itself first. Then, create an ANSYS cdb file of SURFACE154 elements generated from the surface of the structural model that is to accept the CFX pressures/shear stresses loads. Import the cdb file into CFX-Post (File> ANSYS Import/Export) after the transient is completed and having saved transient results in CFX at suitable intervals, making sure that at least 'Output Boundary flows' are stored in the CFX intermediate transient results files. (see documentation on how to turn on 'Output Boundary Flows' in CFX-Pre, under 'Output Control'.

Once the Results file has been loaded and the surface imported, the load files for ANSYS are created by first accessing the particular time step result in the Time Step selector, and then exporting (File> ANSYS Import/Export). Choose a different name for the export file for each time step.

If this is done in Simulation, one need only choose CFX Pressure as the loading. The user does not have to create the 2D surfaces, as this is done automatically by Simulation. One is prompted to browse for the results file and then choose the appropriate locator and time point. To do a second time point, the load should be deleted (or suppressed) and reapplied, as it cannot be modified once specified.

2. The MFX method: in this case, one sets the ANSYS and CFX problems up as an MFX two-way problem, except that mesh motion is set to None in CFX-Pre under 'Mesh Deformation' in Domain settings. The normal two way FSI load transfer becomes a one way transfer. There will be no reference in CFX to accepting ANSYS displacements because t


**** Entered By: rlange @ 05/25/2006 03:28 PM ****

Q. I want to do a transient FSI problem with ANSYS and CFX but do not want to account for the effect of the deformation of the structure on the flow field, as it is expected to be small. How should I approach this?

A. The two methods to accomplish this are the CFX-Post method and the MFX method.

1. CFX-Post method: Solves the CFD problem by itself first. Then, create an ANSYS cdb file of SURFACE154 elements generated from the surface of the structural model that is to accept the CFX pressures/shear stresses loads. Import the cdb file into CFX-Post (File> ANSYS Import/Export) after the transient is completed and having saved transient results in CFX at suitable intervals, making sure that at least `Output Boundary flows` are stored in the CFX intermediate transient results files. (see documentation on how to turn on `Output Boundary Flows` in CFX-Pre, under `Output Control`.

Once the Results file has been loaded and the surface imported, the load files for ANSYS are created by first accessing the particular time step result in the Time Step selector, and then exporting (File> ANSYS Import/Export). Choose a different name for the export file for each time step.

If this is done in Simulation, one need only choose CFX Pressure as the loading. The user does not have to create the 2D surfaces, as this is done automatically by Simulation. One is prompted to browse for the results file and then choose the appropriate locator and time point. To do a second time point, the load should be deleted (or suppressed) and reapplied, as it cannot be modified once specified.

2. The MFX method: in this case, one sets the ANSYS and CFX problems up as an MFX two-way problem, except that mesh motion is set to None in CFX-Pre under `Mesh Deformation` in Domain settings. The normal two way FSI load transfer becomes a one way transfer. There will be no reference in CFX to accepting ANSYS displacements because there is no mesh motion allowed. So you are not sending the displacements back to CFX once they are calculated in ANSYS. In this approach the stress analysis is done every time step. Generally, this is overkill, as often a stress analyst need pick out only a handful of time steps for the stress calculation.





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