Problem regarding viewing FSI result in CFD-post

risunny · June 25, 2015, 18:50

Hello,

I have done a fsi simulation using ansys transient structural and Fluent.Then i created a point in the structural domain and selected the transient XY-plot to view mash displacement.But the graph is showing some discontinuity as in the attached figure.I have tried some other points but it gives similar problem.Can anyone help me in this regard?

stumpy · July 16, 2015, 10:18

Next time you need to do this, create a Results Tracker for Displacement in Mechanical. It's easier than trying to post-process a displacement after the fact.

By best guess for the discontinuity is that your point in CFD-Post is at a fixed x,y,z coordinate. Try creating the point at a node number, so it follows the mesh as it moves.

risunny · July 26, 2015, 08:06

Thanks for the help.The problem is solved using node number.I think result tracker can be created with vertex only but my geometry is a hollow cylinder,is there any other way?

I have another query, i have to do a fsi simulation of flow through pipe.The boundary condition is fixed-fixed.The problem is initially i have to apply an axial displacement to create a prestress before fixing one end.But i can not figure out how to do it.

stumpy · July 31, 2015, 16:14

Regarding the results tracker, click "Show Mesh" in the toolbar, then you can pick a mesh node rather than a geometry vertex.

One solution for the pipe pre-stress is to use a displacement in Mechanical that is a function of time, so for the first 1 second the axial displacement is applied, then it is held in place. This would be a single FSI simulation; you would just ignore the solution for the first 1 second.

risunny · November 16, 2015, 14:32

Thank you for previous reply.

I was trying to follow your mentioned process about the pre-stress.During the first second of FSI simulation i supressed the data transfer(force) from fluid to solid.Then i have unsuppressed the data transfer and restarted the simulation in Ansys 14.5.But the problem is CFD-post got crashed every-time i want to see the result after restart and in Ansys 14 the simulation wasn't started after restart.Was the procedure correct?

There was a warning showing that large deformation may invalidate the boundary condition like displacement.In my case large deformation was on,How does this affect the simulation?

July 31, 2015, 16:14		#4
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	Regarding the results tracker, click "Show Mesh" in the toolbar, then you can pick a mesh node rather than a geometry vertex. One solution for the pipe pre-stress is to use a displacement in Mechanical that is a function of time, so for the first 1 second the axial displacement is applied, then it is held in place. This would be a single FSI simulation; you would just ignore the solution for the first 1 second. risunny likes this.

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July 16, 2015, 10:18		#2
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	Next time you need to do this, create a Results Tracker for Displacement in Mechanical. It's easier than trying to post-process a displacement after the fact. By best guess for the discontinuity is that your point in CFD-Post is at a fixed x,y,z coordinate. Try creating the point at a node number, so it follows the mesh as it moves.

July 26, 2015, 08:06		#3
risunny New Member Rashidul Islam Join Date: Jul 2014 Posts: 3 Rep Power: 12	Thanks for the help.The problem is solved using node number.I think result tracker can be created with vertex only but my geometry is a hollow cylinder,is there any other way? I have another query, i have to do a fsi simulation of flow through pipe.The boundary condition is fixed-fixed.The problem is initially i have to apply an axial displacement to create a prestress before fixing one end.But i can not figure out how to do it.

November 16, 2015, 14:32		#5
risunny New Member Rashidul Islam Join Date: Jul 2014 Posts: 3 Rep Power: 12	Thank you for previous reply. I was trying to follow your mentioned process about the pre-stress.During the first second of FSI simulation i supressed the data transfer(force) from fluid to solid.Then i have unsuppressed the data transfer and restarted the simulation in Ansys 14.5.But the problem is CFD-post got crashed every-time i want to see the result after restart and in Ansys 14 the simulation wasn't started after restart.Was the procedure correct? There was a warning showing that large deformation may invalidate the boundary condition like displacement.In my case large deformation was on,How does this affect the simulation?