Convergence of CFX field in FSI analysis

nasdak · June 28, 2009, 13:37

Hello friends

I do the fluid-structure interaction of the aortic valve and blood. I managed the negative element volume and analysis go ahead. I have only one problem. During every coupled interaction I have no convergence for CFX filed.

*** ANSYS BINARY FILE STATISTICS
BUFFER SIZE USED= 16384
122.938 MB WRITTEN ON ELEMENT SAVED DATA FILE: ANSYS.esav
162.000 MB WRITTEN ON ASSEMBLED MATRIX FILE: ANSYS.full
59.125 MB WRITTEN ON RESULTS FILE: ANSYS.rst

//the end of the structure calaculation - everything is fine.

FOURTH SYNCHRONIZATION POINT OF MASTER CODE:
LOAD TRANSFER AT THE END OF SOLUTION

FIFTH SYNCHRONIZATION POINT OF MASTER CODE:
GET SLAVES LOCAL CONVERGENCE

FIELD SOLUTION CONVERGENCE

CONVERGENCE OF FIELD SOLVER: ANSYS. . . . . TRUE
CONVERGENCE OF FIELD SOLVER: CFX. . . . . FALSE

//not converged ??

SURFACE LOAD TRANSFER CONVERGENCE

CONVERGENCE FOR FIELD 2 ACROSS INTERFACE 0
UX DISP CONVERGENCE. . . . . . 0.70735
UY DISP CONVERGENCE. . . . . . 0.72570
UZ DISP CONVERGENCE. . . . . . 0.70866

CONVERGENCE FOR FIELD 1 ACROSS INTERFACE 1
FX FORCE CONVERGENCE. . . . . 0.68833
FY FORCE CONVERGENCE. . . . . 0.69597
FZ FORCE CONVERGENCE. . . . . 0.68933

FIFTH SYNCHRONIZATION POINT OF MASTER CODE:
SERVE SLAVES THE GLOBAL CONVERGENCE
1

Have you ever seen similar problem ?? Or may you have same idaes what's wrong??

regards

Chris

ghorrocks · June 28, 2009, 20:16

Hi,

FSI adds another dimension of things to check over a normal static CFD simulation. Have you checked it converges OK without FSI with some geometries typical of what you will get in the simulation? Have you checked the FSI motion updates are small enough that you are resolving the motion properly?

Glenn Horrocks

nasdak · June 29, 2009, 02:17

Glenn

I've checked it but only for the first state of geometry, and the fluid converged. During the simulation I had a problem with negative volume element then I decrease the substep. Now the deformation is close to 0.1 mm and I think the FSI motion is small enough. May I should decrease the time of the substep again ? I must admit that I have a quite poor mesh.

June 28, 2009, 13:37	Convergence of CFX field in FSI analysis	#1
nasdak New Member chris Join Date: May 2009 Posts: 18 Rep Power: 17	Hello friends I do the fluid-structure interaction of the aortic valve and blood. I managed the negative element volume and analysis go ahead. I have only one problem. During every coupled interaction I have no convergence for CFX filed. *** ANSYS BINARY FILE STATISTICS BUFFER SIZE USED= 16384 122.938 MB WRITTEN ON ELEMENT SAVED DATA FILE: ANSYS.esav 162.000 MB WRITTEN ON ASSEMBLED MATRIX FILE: ANSYS.full 59.125 MB WRITTEN ON RESULTS FILE: ANSYS.rst //the end of the structure calaculation - everything is fine. FOURTH SYNCHRONIZATION POINT OF MASTER CODE: LOAD TRANSFER AT THE END OF SOLUTION FIFTH SYNCHRONIZATION POINT OF MASTER CODE: GET SLAVES LOCAL CONVERGENCE FIELD SOLUTION CONVERGENCE CONVERGENCE OF FIELD SOLVER: ANSYS. . . . . TRUE CONVERGENCE OF FIELD SOLVER: CFX. . . . . FALSE //not converged ?? SURFACE LOAD TRANSFER CONVERGENCE CONVERGENCE FOR FIELD 2 ACROSS INTERFACE 0 UX DISP CONVERGENCE. . . . . . 0.70735 UY DISP CONVERGENCE. . . . . . 0.72570 UZ DISP CONVERGENCE. . . . . . 0.70866 CONVERGENCE FOR FIELD 1 ACROSS INTERFACE 1 FX FORCE CONVERGENCE. . . . . 0.68833 FY FORCE CONVERGENCE. . . . . 0.69597 FZ FORCE CONVERGENCE. . . . . 0.68933 FIFTH SYNCHRONIZATION POINT OF MASTER CODE: SERVE SLAVES THE GLOBAL CONVERGENCE 1 Have you ever seen similar problem ?? Or may you have same idaes what's wrong?? regards Chris

June 29, 2009, 02:17		#3
nasdak New Member chris Join Date: May 2009 Posts: 18 Rep Power: 17	Glenn I've checked it but only for the first state of geometry, and the fluid converged. During the simulation I had a problem with negative volume element then I decrease the substep. Now the deformation is close to 0.1 mm and I think the FSI motion is small enough. May I should decrease the time of the substep again ? I must admit that I have a quite poor mesh. Last edited by nasdak; June 29, 2009 at 02:51.

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June 28, 2009, 20:16		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Hi, FSI adds another dimension of things to check over a normal static CFD simulation. Have you checked it converges OK without FSI with some geometries typical of what you will get in the simulation? Have you checked the FSI motion updates are small enough that you are resolving the motion properly? Glenn Horrocks