FSI with time interval remeshing ?

realanony87 · May 31, 2009, 21:43

Hello,
I am doing a transient FSI simulation of a wing with Ansys Simulation in Workbench and CFX. and due to large deflections (the same order as the length), the mesh quality gets poorer with each time interval.
Is there a way that I can Remesh the region around the wing instead of relying on the mesh interpolator, every X time intervals ? It seems to have been done in the literature with in-house codes but Is there a relatively easy way to do it in the Ansys Suite ?
Thanks

mortazavi · June 1, 2009, 05:53

hi realanony87

sorry I don't know the answer,but :
would you please help me with the error"the connection between cfx and external solver has died unexpectedly" in FSI modeling in CFX????
what does this error means & how can i solve this problem?

realanony87 · June 1, 2009, 09:33

It is probably due to an error from the Structural solver. Check the .out file from Ansys ( not the CFX out file) to see what went wrong. I cannot help you because it could happen due to many reasons.

stumpy · June 2, 2009, 20:59

Remeshing + FSI is not currently possible with ANSYS + CFX. But there's a lots of ways to maintain mesh quality for large deflections. Using a mesh stiffness of "Increase Near Boundaries" with an exponent of say 2 would be a starting point. Then you need to look at where the mesh is folding - and change the mesh motion boundary conditions, or add subdomain mesh motion, or insert sliding interfaces etc to imporve things. Sorry i can't be more specific; the best approach is always case dependent.

Vinzent · September 14, 2010, 06:32

Hello,

to play with mesh stiffness is very usefuel in case of large deflections. How is it possible, to define different mesh stiffnesses of subdomains? I just know this for a whole domain. So I have to control these complicated with if statements. Is there an easier way?

Vinzent

stumpy · September 14, 2010, 10:04

To get a different mesh stiffness in a subdomain you will need if() statements, but the inside()@ function should make this fairly easy, e.g.
if(inside()@subdomain1, meshstiffness1, meshstiffness2)

Vinzent · September 14, 2010, 11:11

stumpy, thank you very much!
this is, what i was searching for.

vinzent

Vinzent · September 17, 2010, 08:29

Hello Stumpy,

when I try to define mesh stiffness with "inside" like your example following error occurs:

##############################################
Error processing expression 'Mesh Stiffness'. Error at position 4. The condition expression in 'if' statement is not logical valued.
Error processing expression: Mesh Stiffness = MS

##############################################

Is there something missing?

Vinzent

stumpy · September 17, 2010, 13:04

The inside() function returns 0 or 1 - I was assuming this was enough for CFX to evaluate if it's true of false, but perhaps not. Try if(inside()@subdomain1 > 0.5, ....

May 31, 2009, 21:43	FSI with time interval remeshing ?	#1
realanony87 New Member Join Date: May 2009 Posts: 21 Rep Power: 17	Hello, I am doing a transient FSI simulation of a wing with Ansys Simulation in Workbench and CFX. and due to large deflections (the same order as the length), the mesh quality gets poorer with each time interval. Is there a way that I can Remesh the region around the wing instead of relying on the mesh interpolator, every X time intervals ? It seems to have been done in the literature with in-house codes but Is there a relatively easy way to do it in the Ansys Suite ? Thanks

September 14, 2010, 06:32	different mesh stiffnesses of subdomains	#5
Vinzent New Member Join Date: Jul 2010 Posts: 22 Rep Power: 16	Hello, to play with mesh stiffness is very usefuel in case of large deflections. How is it possible, to define different mesh stiffnesses of subdomains? I just know this for a whole domain. So I have to control these complicated with if statements. Is there an easier way? Vinzent

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June 1, 2009, 05:53		#2
mortazavi Member SMN Join Date: Jun 2009 Location: CANADA Posts: 71 Rep Power: 17	hi realanony87 sorry I don't know the answer,but : would you please help me with the error"the connection between cfx and external solver has died unexpectedly" in FSI modeling in CFX???? what does this error means & how can i solve this problem?

June 1, 2009, 09:33		#3
realanony87 New Member Join Date: May 2009 Posts: 21 Rep Power: 17	It is probably due to an error from the Structural solver. Check the .out file from Ansys ( not the CFX out file) to see what went wrong. I cannot help you because it could happen due to many reasons.

June 2, 2009, 20:59		#4
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	Remeshing + FSI is not currently possible with ANSYS + CFX. But there's a lots of ways to maintain mesh quality for large deflections. Using a mesh stiffness of "Increase Near Boundaries" with an exponent of say 2 would be a starting point. Then you need to look at where the mesh is folding - and change the mesh motion boundary conditions, or add subdomain mesh motion, or insert sliding interfaces etc to imporve things. Sorry i can't be more specific; the best approach is always case dependent.

September 14, 2010, 10:04		#6
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	To get a different mesh stiffness in a subdomain you will need if() statements, but the inside()@ function should make this fairly easy, e.g. if(inside()@subdomain1, meshstiffness1, meshstiffness2)

September 14, 2010, 11:11		#7
Vinzent New Member Join Date: Jul 2010 Posts: 22 Rep Power: 16	stumpy, thank you very much! this is, what i was searching for. vinzent

September 17, 2010, 08:29		#8
Vinzent New Member Join Date: Jul 2010 Posts: 22 Rep Power: 16	Hello Stumpy, when I try to define mesh stiffness with "inside" like your example following error occurs: ############################################## Error processing expression 'Mesh Stiffness'. Error at position 4. The condition expression in 'if' statement is not logical valued. Error processing expression: Mesh Stiffness = MS ############################################## Is there something missing? Vinzent

September 17, 2010, 13:04		#9
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	The inside() function returns 0 or 1 - I was assuming this was enough for CFX to evaluate if it's true of false, but perhaps not. Try if(inside()@subdomain1 > 0.5, ....