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# Neo Hookean Model

I am modeling a RBC(red blood cell) membrane using shell181 element and

using neo hookean model. But when I try to solve it, it gives error. I

couldnt figure out the cause. Please help me.

This is my input file for creating the model.

/com,structural,,,

/clear,start,,,

/prep7,,,,

k,1,0,0,0.000000405

k,201,0,0,-0.000000405

k,2,0,0.00000005,4.06E-07

k,202,0,0.00000005,-4.06E-07

k,3,0,0.0000001,4.07E-07

k,203,0,0.0000001,-4.07E-07

k,4,0,0.00000015,4.10E-07

k,204,0,0.00000015,-4.10E-07

k,5,0,0.0000002,4.15E-07

k,205,0,0.0000002,-4.15E-07

k,6,0,0.00000025,4.20E-07

k,206,0,0.00000025,-4.20E-07

k,7,0,0.0000003,4.27E-07

k,207,0,0.0000003,-4.27E-07

k,8,0,0.00000035,4.34E-07

k,208,0,0.00000035,-4.34E-07

k,9,0,0.0000004,4.43E-07

k,209,0,0.0000004,-4.43E-07

k,10,0,0.00000045,4.53E-07

k,210,0,0.00000045,-4.53E-07

k,11,0,0.0000005,4.65E-07

k,211,0,0.0000005,-4.65E-07

k,12,0,0.00000055,4.77E-07

k,212,0,0.00000055,-4.77E-07

k,13,0,0.0000006,4.90E-07

k,213,0,0.0000006,-4.90E-07

k,14,0,0.00000065,5.04E-07

k,214,0,0.00000065,-5.04E-07

k,15,0,0.0000007,5.20E-07

k,215,0,0.0000007,-5.20E-07

k,16,0,0.00000075,5.36E-07

k,216,0,0.00000075,-5.36E-07

k,17,0,0.0000008,5.53E-07

k,217,0,0.0000008,-5.53E-07

k,18,0,0.00000085,5.71E-07

k,218,0,0.00000085,-5.71E-07

k,19,0,0.0000009,5.90E-07

k,219,0,0.0000009,-5.90E-07

k,20,0,0.00000095,6.10E-07

k,220,0,0.00000095,-6.10E-07

k,21,0,0.000001,6.30E-07

k,221,0,0.000001,-6.30E-07

k,22,0,0.00000105,6.51E-07

k,222,0,0.00000105,-6.51E-07

k,23,0,0.0000011,6.73E-07

k,223,0,0.0000011,-6.73E-07

k,24,0,0.00000115,6.95E-07

k,224,0,0.00000115,-6.95E-07

k,25,0,0.0000012,7.18E-07

k,225,0,0.0000012,-7.18E-07

k,26,0,0.00000125,7.41E-07

k,226,0,0.00000125,-7.41E-07

k,27,0,0.0000013,7.65E-07

k,227,0,0.0000013,-7.65E-07

k,28,0,0.00000135,7.89E-07

k,228,0,0.00000135,-7.89E-07

k,29,0,0.0000014,8.13E-07

k,229,0,0.0000014,-8.13E-07

k,30,0,0.00000145,8.38E-07

k,230,0,0.00000145,-8.38E-07

k,31,0,0.0000015,8.62E-07

k,231,0,0.0000015,-8.62E-07

k,32,0,0.00000155,8.87E-07

k,232,0,0.00000155,-8.87E-07

k,33,0,0.0000016,9.12E-07

k,233,0,0.0000016,-9.12E-07

k,34,0,0.00000165,9.36E-07

k,234,0,0.00000165,-9.36E-07

k,35,0,0.0000017,9.61E-07

k,235,0,0.0000017,-9.61E-07

k,36,0,0.00000175,9.85E-07

k,236,0,0.00000175,-9.85E-07

k,37,0,0.0000018,1.01E-06

k,237,0,0.0000018,-1.01E-06

k,38,0,0.00000185,1.03E-06

k,238,0,0.00000185,-1.03E-06

k,39,0,0.0000019,1.05E-06

k,239,0,0.0000019,-1.05E-06

k,40,0,0.00000195,1.08E-06

k,240,0,0.00000195,-1.08E-06

k,41,0,0.000002,1.10E-06

k,241,0,0.000002,-1.10E-06

k,42,0,0.00000205,1.12E-06

k,242,0,0.00000205,-1.12E-06

k,43,0,0.0000021,1.14E-06

k,243,0,0.0000021,-1.14E-06

k,44,0,0.00000215,1.16E-06

k,244,0,0.00000215,-1.16E-06

k,45,0,0.0000022,1.18E-06

k,245,0,0.0000022,-1.18E-06

k,46,0,0.00000225,1.19E-06

k,246,0,0.00000225,-1.19E-06

k,47,0,0.0000023,1.21E-06

k,247,0,0.0000023,-1.21E-06

k,48,0,0.00000235,1.23E-06

k,248,0,0.00000235,-1.23E-06

k,49,0,0.0000024,1.24E-06

k,249,0,0.0000024,-1.24E-06

k,50,0,0.00000245,1.25E-06

k,250,0,0.00000245,-1.25E-06

k,51,0,0.0000025,1.26E-06

k,251,0,0.0000025,-1.26E-06

k,52,0,0.00000255,1.27E-06

k,252,0,0.00000255,-1.27E-06

k,53,0,0.0000026,1.27E-06

k,253,0,0.0000026,-1.27E-06

k,54,0,0.00000265,1.28E-06

k,254,0,0.00000265,-1.28E-06

k,55,0,0.0000027,1.28E-06

k,255,0,0.0000027,-1.28E-06

k,56,0,0.00000275,1.28E-06

k,256,0,0.00000275,-1.28E-06

k,57,0,0.0000028,1.28E-06

k,257,0,0.0000028,-1.28E-06

k,58,0,0.00000285,1.28E-06

k,258,0,0.00000285,-1.28E-06

k,59,0,0.0000029,1.27E-06

k,259,0,0.0000029,-1.27E-06

k,60,0,0.00000295,1.26E-06

k,260,0,0.00000295,-1.26E-06

k,61,0,0.000003,1.25E-06

k,261,0,0.000003,-1.25E-06

k,62,0,0.00000305,1.24E-06

k,262,0,0.00000305,-1.24E-06

k,63,0,0.0000031,1.22E-06

k,263,0,0.0000031,-1.22E-06

k,64,0,0.00000315,1.20E-06

k,264,0,0.00000315,-1.20E-06

k,65,0,0.0000032,1.17E-06

k,265,0,0.0000032,-1.17E-06

k,66,0,0.00000325,1.15E-06

k,266,0,0.00000325,-1.15E-06

k,67,0,0.0000033,1.12E-06

k,267,0,0.0000033,-1.12E-06

k,68,0,0.00000335,1.08E-06

k,268,0,0.00000335,-1.08E-06

k,69,0,0.0000034,1.04E-06

k,269,0,0.0000034,-1.04E-06

k,70,0,0.00000345,9.99E-07

k,270,0,0.00000345,-9.99E-07

k,71,0,0.0000035,9.51E-07

k,271,0,0.0000035,-9.51E-07

k,72,0,0.00000355,8.97E-07

k,272,0,0.00000355,-8.97E-07

k,73,0,0.0000036,8.38E-07

k,273,0,0.0000036,-8.38E-07

k,74,0,0.00000365,7.71E-07

k,274,0,0.00000365,-7.71E-07

k,75,0,0.0000037,6.95E-07

k,275,0,0.0000037,-6.95E-07

k,76,0,0.00000375,6.08E-07

k,276,0,0.00000375,-6.08E-07

k,77,0,0.0000038,5.05E-07

k,277,0,0.0000038,-5.05E-07

k,78,0,0.00000385,3.73E-07

k,278,0,0.00000385,-3.73E-07

k,79,0,0.0000039,1.52E-07

k,279,0,0.0000039,-1.52E-07

k,100,0,0.00000391,0

l,1,2,,

l,201,202,,

l,2,3,,

l,202,203,,

l,3,4,,

l,203,204,,

l,4,5,,

l,204,205,,

l,5,6,,

l,205,206,,

l,6,7,,

l,206,207

l,7,8

l,207,208

l,8,9

l,208,209

l,9,10

l,209,210

l,10,11

l,210,211

l,11,12

l,211,212

l,12,13

l,212,213

l,13,14

l,213,214

l,14,15

l,214,215

l,15,16

l,215,216

l,16,17

l,216,217

l,17,18

l,217,218

l,18,19

l,218,219

l,19,20

l,219,220

l,20,21

l,220,221

l,21,22

l,221,222

l,22,23

l,222,223

l,23,24

l,223,224

l,24,25

l,224,225

l,25,26

l,225,226

l,26,27

l,226,227

l,27,28

l,227,228

l,28,29

l,228,229

l,29,30

l,229,230

l,30,31

l,230,231

l,31,32

l,231,232

l,32,33

l,232,233

l,33,34

l,233,234

l,34,35

l,234,235

l,35,36

l,235,236

l,36,37

l,236,237

l,37,38

l,237,238

l,38,39

l,238,239

l,39,40

l,239,240

l,40,41

l,240,241

l,41,42

l,241,242

l,42,43

l,242,243

l,43,44

l,243,244

l,44,45

l,244,245

l,45,46

l,245,246

l,46,47

l,246,247

l,47,48

l,247,248

l,48,49

l,248,249

l,49,50

l,249,250

l,50,51

l,250,251

l,51,52

l,251,252

l,52,53

l,252,253

l,53,54

l,253,254

l,54,55

l,254,255

l,55,56

l,255,256

l,56,57

l,256,257

l,57,58

l,257,258

l,58,59

l,258,259

l,59,60

l,259,260

l,60,61

l,260,261

l,61,62

l,261,262

l,62,63

l,262,263

l,63,64

l,263,264

l,64,65

l,264,265

l,65,66

l,265,266

l,66,67

l,266,267

l,67,68

l,267,268

l,68,69

l,268,269

l,69,70

l,269,270

l,70,71

l,270,271

l,71,72

l,271,272

l,72,73

l,272,273

l,73,74

l,273,274

l,74,75

l,274,275

l,75,76

l,275,276

l,76,77

l,276,277

l,77,78

l,277,278

l,78,79

l,278,279,,,,,,

l,79,100,,,,,,

l,279,100,,,,,,

K,1001,0,0,0.000004, ,,,

K,1002,0,0,-0.000004,,,,

arotat,all,,,,,,1001,1002,360,

After this i use SHELL181 element and neo hookean model. When I try to

solve it it give error ( An error has occured in calculating the element

geometry. This is probably caused by either incorrect model dala or

excessive deformation. Please check your input data for element 19494.)

The DB log file is here

/BATCH

! /COM,ANSYS RELEASE 11.0SP1 UP20070830 09:55:18 11/10/2008

!*

ET,1,SHELL181

!*

R,1,1.6e-6,1.6e-6,1.6e-6,1.6e-6, , ,

RMORE, , , , , , ,

!*

!*

TB,HYPE,1,1,2,NEO

TBTEMP,0

TBDATA,,6.1e-6,0,,,,

TYPE, 1

MAT, 1

REAL, 1

ESYS, 0

SECNUM,

!*

MSHAPE,0,2D

MSHKEY,0

!*

FLST,5,632,5,ORDE,2

FITEM,5,1

FITEM,5,-632

CM,_Y,AREA

ASEL, , , ,P51X

CM,_Y1,AREA

CHKMSH,'AREA'

CMSEL,S,_Y

!*

AMESH,_Y1

!*

CMDELE,_Y

CMDELE,_Y1

CMDELE,_Y2

!*

! /REPLOT,RESIZE

/UI,MESH,OFF

FLST,2,1,3,ORDE,1

FITEM,2,552

!*

/GO

DK,P51X, ,0, ,0,UX, , , , , ,

FLST,2,1,3,ORDE,1

FITEM,2,159

!*

/GO

FK,P51X,FX,1.2e-12

nlgeom,on

FINISH

/SOL

! /STATUS,SOLU

SOLVE

Is it that the way i created the model is wrong? If yes, can someone

suggest me a better way to create the bioconcave model of RBC. Any help

regarding this would be great.

Thanks,

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## Comments

## the loading is not proper

I see the command you given before. The error in the calculation is mainly induced by the very large stress ( or not convergency). In your model, the loading is concetrated on a point, which could induce such error. The constrain is also not proper.

Please revise the loading, then try again.

Ying Li Department of Engineering Mechanics Tsinghua University Beijing, 100084, P. R. CHINA