Converging problem with hyper elastic material

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  • Last Post 22 May 2020
sarbakhshian posted this 24 April 2020

Hi

I'm doing 2-way FSI simulation with hyper elastic materials, i'm trying to use Mooney Rivlin 5 parameter model for hyper elastic behavior. I borrowed all 5 parameters from an article with the same concept, but i'm having a serious converging problem. I have tried to run the simulation with different mesh size and different elements, also with different time step size (increasing and decreasing the step size) but each time Solution information gives me the same Error below:

Distributed sparse solver minimum pivot in absolute value=             
 3.737065875E-02 at node 281725 UZ.                                     
     DISP CONVERGENCE VALUE   =  0.7277      CRITERION=  0.3713E-01
    EQUIL ITER   1 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=  0.7277   
     FORCE CONVERGENCE VALUE  =   5.978      CRITERION=  0.7782E-03
     DISP CONVERGENCE VALUE   =   7.648      CRITERION=  0.3987   
    EQUIL ITER   2 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=   7.648   

 *** ERROR ***                           CP =     619.418   TIME= 221:22
 Element 152312 (type = 6, SOLID186) (and maybe other elements) has     
 become highly distorted.  Excessive distortion of elements is usually  
 a symptom indicating the need for corrective action elsewhere.  Try    
 ramping the load up instead of step applying the load (KBC,1).  You    
 may need to improve your mesh to obtain elements with better aspect    
 ratios.  Also consider the behavior of materials, contact pairs,       
 and/or constraint equations.  Please rule out other root causes of     
 this failure before attempting rezoning or nonlinear adaptive          
 solutions.  If this message appears in the first iteration of first    
 substep, be sure to run shape checking of elements.   

I have already run the same model with elastic materials and it converged with little changes in mesh size. But for the hyper elastic material, nothing seems to effect the converging process. I'm attaching a picture of what happens to the model after the element distortion.

Could anyone help me?

 

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donabbel posted this 27 April 2020

Hey, I'm no expert but I might be able to help a little since I've had similar problems. 

First archive your file without the results and upload it here so we can take a look at it. I can't properly see your mesh but these are a few improvements:

-The mesh is very important for simulations with hyperelastic materials, try meshing it only with hex elements so the element type becomes a solid185. 

-Use keyops(2) = 0 or 1, read the Solution Information since it usually recommends which one to use. 

-Activate the Newton-Raphson Residuals so you can have a better idea about the problematic areas. 

I hope it helps even a little.

 

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sarbakhshian posted this 28 April 2020

thank you very much. i'll check what you said and i will share the results soon

sarbakhshian posted this 22 May 2020

Hi

i just tried your recommended settings but unfortunately couldn't manage to solve the problem. Actually i have no idea how Keyopt number can help me in meshing, i'm just using ansys mesh to mesh the geometry and as far as i searched Keyopt number is helpful when we are using commands. My geometry is kind of complicated so i can not mesh it with all hex elements, i'm using multizone meshing method so ansys mesh uses tetra meshes in some areas, i'm uploading my model here i hope someone can help me

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