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Old   June 17, 2009, 07:48
Default FSI in Ansys Workbench + CFX v.11
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chris
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Hi everyone

I model the interaction beetwen an aortivc valve and blood (biomechanics). I defined the model of the structure in Simulation and in the next step I modeled the blood in CFX. First I obtain the solution from cfx and than obtain the total mesh displacement for the structure. Everything is fine. The problem appear in secend itearation. I obtain the solution for CFX but something is happening with the structure. The model of the structure converged but the displacment does'nt change, the time of the analysis starts from 0 and the number of the loadstep is 1. Here is the monitor.
Could anybody tell me what's wrong ??

SOLUTION HISTORY INFORMATION FOR JOB: ANSYS.mntr
ANSYS RELEASE 11.0 13:37:04 07/14/2009

LOAD SUB- NO. NO. TOTL INCREMENT TOTAL
STEP STEP ATTMP ITER ITER TIME/LFACT TIME/LFACT MONITOR MONITOR
CPU MxDs MxPl

1 1 1 2 35 0.10000E-04 0.10000E-04 141.61 0.28203E-03 0.78886E-30
1 2 1 1 36 0.10000E-04 0.20000E-04 218.69 0.28203E-03 0.78886E-30

1 3 1 1 37 0.83333E-05 0.28333E-04 298.25 0.28203E-03 0.78886E-30
1 4 1 1 38 0.83333E-05 0.36667E-04 374.12 0.28203E-03 0.78886E-30
1 5 1 1 39 0.83333E-05 0.45000E-04 454.72 0.28203E-03 0.78886E-30


the third and fourth iteration look similar.

Chris (nasdak)
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Old   June 20, 2009, 12:00
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anonymous
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Quote:
Originally Posted by nasdak View Post
Hi everyone

I model the interaction beetwen an aortivc valve and blood (biomechanics). I defined the model of the structure in Simulation and in the next step I modeled the blood in CFX. First I obtain the solution from cfx and than obtain the total mesh displacement for the structure. Everything is fine. The problem appear in secend itearation. I obtain the solution for CFX but something is happening with the structure. The model of the structure converged but the displacment does'nt change, the time of the analysis starts from 0 and the number of the loadstep is 1. Here is the monitor.
Could anybody tell me what's wrong ??

SOLUTION HISTORY INFORMATION FOR JOB: ANSYS.mntr
ANSYS RELEASE 11.0 13:37:04 07/14/2009

LOAD SUB- NO. NO. TOTL INCREMENT TOTAL
STEP STEP ATTMP ITER ITER TIME/LFACT TIME/LFACT MONITOR MONITOR
CPU MxDs MxPl

1 1 1 2 35 0.10000E-04 0.10000E-04 141.61 0.28203E-03 0.78886E-30
1 2 1 1 36 0.10000E-04 0.20000E-04 218.69 0.28203E-03 0.78886E-30

1 3 1 1 37 0.83333E-05 0.28333E-04 298.25 0.28203E-03 0.78886E-30
1 4 1 1 38 0.83333E-05 0.36667E-04 374.12 0.28203E-03 0.78886E-30
1 5 1 1 39 0.83333E-05 0.45000E-04 454.72 0.28203E-03 0.78886E-30


the third and fourth iteration look similar.

Chris (nasdak)
hi am working on these issues from last 1.5 years and found many things which are not bugs but strictly need to follow the procedure.

one simple thing you need to check is if both the geometries (fsi surface especially) lie at exact place within both (fluid and structural ) domain. This you can check in cfx post

Let me know if still you stuck
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Old   June 22, 2009, 07:26
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Hello

Thank you for your answer. I defined my fsi interface in the Ansys Simulation doing the named selection of the inflow and outflow surfaces. In CFX I defined the fsi interface as a boundary condition (wall) and selected the surfaceses.
Now I try to analyze two first steps. I decrease load step time to 0,0001[s] to do first and secend iteration and the bugs looks similar I described. If I increase LS time to 0,01 I get the negative volume element on the begining of secend iteration (CFX calculation). Could you write the most important aspects to define in both structure and CFX simulation. I'm despered.

Thank you

nasdak
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Old   June 22, 2009, 08:44
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chris
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I obtained after the structure calculation, CFX starts and

FIELD SOLUTION CONVERGENCE

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

After this I get no chande in the defomation status of the structure. I checked the fsi interface and I'm fully aware that it is ok.
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