{"id":304771,"date":"2023-09-04T08:25:55","date_gmt":"2023-09-04T08:25:55","guid":{"rendered":"\/forum\/forums\/reply\/304771\/"},"modified":"2023-09-04T08:46:11","modified_gmt":"2023-09-04T08:46:11","slug":"304771","status":"publish","type":"reply","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/304771\/","title":{"rendered":"Reply To: Non-linear convergence problems"},"content":{"rendered":"

<p> <\/p><p> <\/p><p>Hi Peter, thanks for the response. I’ve simplified the model down to it’s symmetry planes and it seems to run when the solid and shell moduli are similar in magnitude – even without applying any pressure to the shell walls. However, in reallity the solid modulus is actually significantly smaller than the shell modulus – approx. 1 kPa compared to 300MPa (shell elements have orthotropic properties, 300MPa parallel to facesheet, 1 kPa normal to facesheet).  I have attempted to fit a Mooney-Rivlin hyperelastic model to some experimental data. However, this has not helped with convergence.<\/p><p>The command snippet is the following:<\/p><div>!   Commands inserted into this file will be executed just prior to the ANSYS SOLVE command.<\/div><div>!   These commands may supersede command settings set by Workbench.<\/div><div> <\/div><div>!   Active UNIT system in Workbench when this object was created:  Metric (um, kg, uN, s, V, mA)<\/div><div>!   NOTE:  Any data that requires units (such as mass) is assumed to be in the consistent solver unit system.<\/div><div>!                See Solving Units in the help system for more information.<\/div><div> <\/div><div>\/PREP7<\/div><div> <\/div><div>! Define an element type with the desired real constant (CPT216)<\/div><div>ET, 9991, CPT216<\/div><div>KEYOPT, 9991, 12, 1<\/div><div>!KEYOPT,9991,6,1<\/div><div>! Select the solid elements you want to modify (SOLID186)<\/div><div>ESEL, S, TYPE,, 1, 69<\/div><div>! Modify the selected elements to use the specified element type (9991)<\/div><div>EMODIF, ALL, TYPE, 9991<\/div><div> <\/div><div>ESEL, NONE<\/div><div> <\/div><div> <\/div><div>TB,HYPER,99999,,,MOONEY<\/div><div>TBDATA,1,-0.0042, 0.0044, 0 !c1 , c2 = material constants characterizing the deviatoric deformation of the material, c2=incompressibility parameter<\/div><div>FPX=1e5 ! PERMEABILITY<\/div><div>ALPHA=1 ! BIOT coeffient<\/div><div>TB,PM,99999,,,PERM <\/div><div>TBDATA,1,FPX,FPX,FPX<\/div><div>TB,PM,99999,,,BIOT ! BIOT COEFFICIENT<\/div><div>TBDATA,1,ALPHA<\/div><div> <\/div><div> <\/div><div>ESEL, NONE<\/div><div> <\/div><div> <\/div><div>! Define orthotropic elastic material for shell elements <\/div><div>MP,EX,88888,300 ! YOUNG’S MODULUS<\/div><div>MP,EY,88888,0.001<\/div><div>MP,EZ,88888,0.001<\/div><div>MP,GXY,88888,150<\/div><div>MP,GXZ,88888,0.001<\/div><div>MP,GYZ,88888,0.001<\/div><div>MP,NUXY,88888,0 ! POISSON’S RATIO<\/div><div>MP,NUXZ,88888,0<\/div><div>MP,NUYZ,88888,0<\/div><div> <\/div><div>ALLSEL, ALL<\/div><div> <\/div><div>! Select the solid elements you want to modify and assign material 1<\/div><div>ESEL, S, TYPE,, 9991<\/div><div>MPCHG, 99999, ALL<\/div><div> <\/div><div>ALLSEL, ALL<\/div><div> <\/div><div>! Select the shell elements you want to modify and assign material 2<\/div><div>ESEL, S, TYPE,, 70, 189<\/div><div>MPCHG, 88888, ALL<\/div><div> <\/div><div>ALLSEL, ALL<\/div><div> <\/div><div>! impervious (fluid flow flux=0)<\/div><div>NSEL,S,LOC,Y,1000 ! select top surface nodes<\/div><div>NSEL,A,LOC,Y,0   ! select bottom surface nodes<\/div><div>SF,ALL,FFLX,0    ! Set surface force (fluid flow flux) to zero<\/div><div>ALLSEL, ALL<\/div><div> <\/div><div>ESEL, NONE<\/div><div> <\/div><div> <\/div><div>! permeable (fluid pressure=0) on sides of cylinder to allow fluid flow<\/div><div>CSYS, 5  ! change coordinate system to cylindrical with cartesian y as axis of rotation<\/div><div> <\/div><div>NSEL,S,LOC,X,3250  ! select nodes at radius=3250um<\/div><div>D,ALL,PRES,0  ! set fluid pressure to zero <\/div><div> <\/div><div>ALLSEL, ALL<\/div><div> <\/div><div> <\/div><div>!CMSEL,S,internal_free_draining,node<\/div><div>!D,ALL,PRES,0<\/div><div> <\/div><div> <\/div><div>CSYS, 0  ! change coordinate system back to global coordinates<\/div><div> <\/div><div> <\/div><div>ALLSEL, ALL<\/div><div> <\/div><div>! Continue with the solution phase<\/div><div>\/SOLU<\/div><div> <\/div><div> <\/div><div>Any ideas how I could get this model to run with such large differences in stiffness between the solid matrix and reinforcing shell elements?<\/div><div> <\/div><div>Thanks in advance.<\/div><div> <\/div><div><\/div><div><\/div><div><\/div><div> <\/div><p> <\/p><p>Here is a linke to the archive file – can’t figure out how to attach it to the comment:<\/p><p> <\/p><p>https:\/\/livemanchesterac-my.sharepoint.com\/:u:\/g\/personal\/fraser_shields_postgrad_manchester_ac_uk\/Eeew5xpFBGJPhyT0oSj4tRYB3mcMUJdEk-aWrWNkDLMmoA?e=Xc1juw<\/p><\/p>\n","protected":false},"template":"","class_list":["post-304771","reply","type-reply","status-publish","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t