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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,

Comments

Ying Li's picture

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

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