• Registered: 16-10-2010
  • Posts: 407

Topic: Linear stability analysis on shell elements?

Dear all,
can you tell if shell elements support LinearStability analysis?
From this manual page I read nlgeo = 0. Does it mean no support or does it refer to what?

When trying to run the following file, a strange error about matrix size is displayed.

lstabMITC4.out
-> linear stab. of mitc4 elements
LinearStability nroot 3 rtolv 9.99999974737875E-05
domain 3dShell
OutputManager tstep_all dofman_all element_all
ndofman 33 nelem 20 ncrosssect 2 nmat 1 nbc 23 nic 0 nltf 2 nset 23
node 1 coords 3 0 0 0 
node 2 coords 3 250 0 0 
node 3 coords 3 500 0 0 
node 4 coords 3 750 0 0 
node 5 coords 3 1000 0 0 
node 6 coords 3 1250 0 0 
node 7 coords 3 1500 0 0 
node 8 coords 3 1750 0 0 
node 9 coords 3 2000 0 0 
node 10 coords 3 2250 0 0 
node 11 coords 3 2500 0 0 
node 12 coords 3 0 0 -250 
node 13 coords 3 250 0 -250 
node 14 coords 3 500 0 -250 
node 15 coords 3 750 0 -250 
node 16 coords 3 1000 0 -250 
node 17 coords 3 1250 0 -250 
node 18 coords 3 1500 0 -250 
node 19 coords 3 1750 0 -250 
node 20 coords 3 2000 0 -250 
node 21 coords 3 2250 0 -250 
node 22 coords 3 2500 0 -250 
node 23 coords 3 0 0 -500 
node 24 coords 3 250 0 -500 
node 25 coords 3 500 0 -500 
node 26 coords 3 750 0 -500 
node 27 coords 3 1000 0 -500 
node 28 coords 3 1250 0 -500 
node 29 coords 3 1500 0 -500 
node 30 coords 3 1750 0 -500 
node 31 coords 3 2000 0 -500 
node 32 coords 3 2250 0 -500 
node 33 coords 3 2500 0 -500 
mitc4shell 1 nodes 4 1 2 13 12  crossSect 2 mat 1  boundaryLoads 2 4 1 
mitc4shell 2 nodes 4 2 3 14 13  crossSect 2 mat 1  boundaryLoads 2 5 1 
mitc4shell 3 nodes 4 3 4 15 14  crossSect 2 mat 1  boundaryLoads 2 6 1 
mitc4shell 4 nodes 4 4 5 16 15  crossSect 2 mat 1  boundaryLoads 2 7 1 
mitc4shell 5 nodes 4 5 6 17 16  crossSect 2 mat 1  boundaryLoads 2 8 1 
mitc4shell 6 nodes 4 6 7 18 17  crossSect 2 mat 1  boundaryLoads 2 9 1 
mitc4shell 7 nodes 4 7 8 19 18  crossSect 2 mat 1  boundaryLoads 2 10 1 
mitc4shell 8 nodes 4 8 9 20 19  crossSect 2 mat 1  boundaryLoads 2 11 1 
mitc4shell 9 nodes 4 9 10 21 20  crossSect 2 mat 1  boundaryLoads 2 12 1 
mitc4shell 10 nodes 4 10 11 22 21  crossSect 2 mat 1  boundaryLoads 2 13 1 
mitc4shell 11 nodes 4 21 22 33 32  crossSect 2 mat 1  boundaryLoads 2 14 1 
mitc4shell 12 nodes 4 20 21 32 31  crossSect 2 mat 1  boundaryLoads 2 15 1 
mitc4shell 13 nodes 4 19 20 31 30  crossSect 2 mat 1  boundaryLoads 2 16 1 
mitc4shell 14 nodes 4 18 19 30 29  crossSect 2 mat 1  boundaryLoads 2 17 1 
mitc4shell 15 nodes 4 17 18 29 28  crossSect 2 mat 1  boundaryLoads 2 18 1 
mitc4shell 16 nodes 4 16 17 28 27  crossSect 2 mat 1  boundaryLoads 2 19 1 
mitc4shell 17 nodes 4 15 16 27 26  crossSect 2 mat 1  boundaryLoads 2 20 1 
mitc4shell 18 nodes 4 14 15 26 25  crossSect 2 mat 1  boundaryLoads 2 21 1 
mitc4shell 19 nodes 4 13 14 25 24  crossSect 2 mat 1  boundaryLoads 2 22 1 
mitc4shell 20 nodes 4 12 13 24 23  crossSect 2 mat 1  boundaryLoads 2 23 1 
# fictitious section for LumpedMass elements
SimpleCS 1 thick 0 drillstiffness 0
SimpleCS 2 thick 300 drillstiffness 1e12
IsoLE 1 d 0 E 30000 n 0.3 tAlpha 0.0012
BoundaryCondition 1 loadTimeFunction 1 DOFs 6 1 2 3 4 5 6  values 6 0 0 0 0 0 0  set 1
BoundaryCondition 2 loadTimeFunction 1 DOFs 6 1 2 3 4 5 6  values 6 0 0 0 0 0 0  set 2
BoundaryCondition 3 loadTimeFunction 1 DOFs 6 1 2 3 4 5 6  values 6 0 0 0 0 0 0  set 3
ConstantSurfaceLoad 4 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 5 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 6 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 7 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 8 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 9 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 10 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 11 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 12 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 13 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 14 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 15 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 16 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 17 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 18 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 19 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 20 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 21 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 22 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantSurfaceLoad 23 loadType 3 loadTimeFunction 2  csType 1 Components 6 0 0 1.00000000376832 0 0 0
ConstantFunction 1 f(t) 1.0
ConstantFunction 2 f(t) 1.0
set 1 nodes 1 1
set 2 nodes 1 12
set 3 nodes 1 23
set 4 elementedges 2 1 1
set 5 elementedges 2 2 1
set 6 elementedges 2 3 1
set 7 elementedges 2 4 1
set 8 elementedges 2 5 1
set 9 elementedges 2 6 1
set 10 elementedges 2 7 1
set 11 elementedges 2 8 1
set 12 elementedges 2 9 1
set 13 elementedges 2 10 1
set 14 elementedges 2 11 1
set 15 elementedges 2 12 1
set 16 elementedges 2 13 1
set 17 elementedges 2 14 1
set 18 elementedges 2 15 1
set 19 elementedges 2 16 1
set 20 elementedges 2 17 1
set 21 elementedges 2 18 1
set 22 elementedges 2 19 1
set 23 elementedges 2 20 1

which is related to a strange behaviour of NLStructuralElement :: computeInitialStressMatrix, in which stress_ident, stress_identFull are not resized properly and indx is never computed before using it.

  • Registered: 25-06-2013
  • Posts: 241

Re: Linear stability analysis on shell elements?

Dear Giovanni,

the MITC element doesn't support LinearStability. To do so, you would need to implement the initial stress stiffness matrix as is done in beam2d.C. The implementation of the  computeInitialStressMatrix works just for continuum elements like bricks, but not for structural elements like shells.

Martin

  • Registered: 16-10-2010
  • Posts: 407

Re: Linear stability analysis on shell elements?

Dear Martin, thanks for the explanation, it is clear now.