Ansys Learning Forum Forums Installation and Licensing Ansys Products Tutorial or Help for 2 way FSI Reply To: Tutorial or Help for 2 way FSI

Paul Hutcheson
Ansys Employee

 

Hi Ashish,

 

  1. Going from Fluent standalone to Fluent within FSI with SyC, you need to reduce iterations per timestep since it is now iterations per coupling iteration. I recommend 3-5 instead of 20. Going from Mechanical standalone to Mechanical within FSI with SyC, you need to set 1 substep and 1 loadstep. Turn off auto timestepping. This is all covered in training. 
  2. Fixing negative volumes depends entirely on what the mesh was trying to do at the time and under what local constraints. I have no idea what it’s doing without seeing an animation or a visual of where the negative volumes are, along with a view of the surrounding mesh to understand the mesh motion in that location. Most often, negative volumes arise due to adjacent walls not having appropriate dynamic mesh zones assigned to them (e.g. symmetry planes with no deforming plane definition allowing nodes to move in plane). It is important to consider how moving walls will affect adjacent walls which are fixed. Or, negative volumes arise due to the motion being too large in one timestep. 1e-7 s seems small to me, but I don’t know the velocity the nodes that went negative were moving at the time or the size of the local cells that went negative. A good rule of thumb is a motion of one cell length per timestep.
  3. If IR, Ball and OR walls are FSI boundaries, i.e. exchanging force and displacement with Mechanical via SyC they have to have System Coupling dynamic mesh zone type set in dynamic mesh panel. The wall velocities in Fluent will affect only the wall shear stress, which will be included in the total force sent to Mechanical. The wall velocities will not affect the motion on the Mechanical side. Displacement is sent from Mechanical to Fluent remember, not the other way around, so make sure set the motion on the solver side that is driving the motion and the other solver will follow.

    To set expectations, I have many commercial customer engagements and unfortunately won’t be able to keep a continuous dialog here. This is a complex analysis, in my opinion too late to tackle with a thesis deadline approaching, but I wish you luck.

 

Paul

 

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