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Block Lanczos solver failure. Stress stiffness matrix contains all zeroes.

Block Lanczos solver failure. Stress stiffness matrix contains all zeroes.

Block Lanczos solver failure. Stress stiffness matrix contains all zeroes.

(OP)
Hello!

Im new here.
My ADPL to study Torsional Buckling on Angle Shapes is giving this error:

"Block Lanczos solver failure. The assembled stress stiffness matrix
contains all zeroes. No load factor solution is possible."

The ADPL is this:
!+++++++++++++++++++++++++++++
!APDL-Flambagem Torsional
!+++++++++++++++++++++++++++++

finish
/clear,nostart
/filname,flambagem-torsional
/TITLE,Flambagem-Torsional
/REP,FAST

!+++++++++++++++++++++
!Dimensões do elemento
!+++++++++++++++++++++

vao=1000 !(comprimento da coluna)
b=90 !(base da cantoneira)
d=90 !(altura da cantoneira)
t=10 !(espessura da cantoneira)
forca=100 !(força aplicada a peça)
*SET,centx,(0.5*t*(d*t)+(0.5*(b-t)+t)*(b*t-t**2))/(d*b-(d-t)*(b-t))
*SET,centz,(0.5*t*b*t+(0.5*(d-t)+t)*(d-t)*t)/(d*b-(d-t)*(b-t))

!++++++++++++++++
!Divisão da Malha
!++++++++++++++++

div_secao=5 !(número de divisões da malha do modelo referentes a seção)

div_compr=20 !(número de divisões da malha do modelo referentes ao comprimento da coluna)

!++++++++++++++++++++++++++
!Propriedades do Material
!++++++++++++++++++++++++++

/prep7

ET,1,SHELL181

MP,EX,1,210000 !Módulo de Elasticidade do Aço

MP,PRXY,1,0.3 !Cieficiente de Poisson do Aço

!++++++++++++++++++++
!Montagem do Elemento
!++++++++++++++++++++

/VIEW,1,1,1,1
/ANG,1

k,1,b,0,0
k,2,0,0,0
k,3,0,vao,0
k,4,b,vao,0
k,5,0,0,d
k,6,0,vao,d

*DO,I,1,3
L,I,I+1
*ENDDO
L,4,1
*DO,I,2,3
L,I,I+3
*ENDDO
L,5,6

AL,1,2,3,4
AL,2,5,6,7


!+++++++++++++++++
!Montagem da Malha
!+++++++++++++++++

LESIZE,1,,,div_secao
LESIZE,3,,,div_secao
LESIZE,5,,,div_secao
LESIZE,6,,,div_secao
LESIZE,2,,,div_compr
LESIZE,4,,,div_compr
LESIZE,7,,,div_compr

AMESH,all

!++++++++++++++++++++++++++++++++++++++++
!Definição da Espessura do Elemento Shell
!++++++++++++++++++++++++++++++++++++++++
sect,1,shell,,
secdata, t,1,0.0,3
secoffset,MID
seccontrol,,,, , , ,

EPLOT

!++++++++++++++++++++
!Criação do Centróide
!++++++++++++++++++++

*GET,NODMAX,NODE,,COUNT

NN1=NODMAX+1
NN2=NODMAX+2

N,NN1,centx,0,centz ! gera no no centro da coluna
N,NN2,centx,vao,centz ! gera no no centro da coluna

NPLOT

LSEL,S,LOC,Y,vao,vao ! seleciona a linha do topo da coluna
NSLL,S,1 ! seleciona os nos pertencentes a essa linha
CM,NODES_UP,NODE ! nomeia esses nos

LPLOT

allsel

LSEL,S,LOC,Y,0,0 ! seleciona a linha da base da coluna
NSLL,S,1 ! seleciona os nos pertencentes a essa linha
CM,NODES_DOWN,NODE ! nomeia esses nos

allsel

LPLOT

ET,2,MASS21 ! cria elemento de massa
TYPE,2
R,1
REAL,1

e,NN1 ! define elemento por conectividade de no
e,NN2

cmsel,s,NODES_UP !Seleciona os Nós do NODES_UP
nsel,a,,,NN2 ! adiciona a selecao o nó NN2
cerig,NN2,all ! define uma regiao rigida

allsel

cmsel,s,NODES_DOWN
nsel,a,,,NN1 ! adiciona a selecao o nó NN1
cerig,NN1,all ! define uma regiao rigida

allsel

F,NN2,FY,-1

NSELL,ALL

FINISH ! Fecha /PREP7

!++++++++++++++++++++
!Criação dos Apoios
!++++++++++++++++++++

/SOLUTION

ANTYPE,STATIC
PSTRES,ON
!eqslv,sparse

LSEL,S,LOC,Y,0,0 ! seleciona a linha da base da coluna
NSLL,S,1 ! seleciona os nos pertencentes a essa linha
nsel,a,,,NN1 ! adiciona a selecao o nó NN2
D,ALL, , , , ,UX,UY,UZ,ROTX,ROTY,ROTZ,

!LSEL,S,LOC,Y,vao,vao ! seleciona a linha do topo da coluna
!NSLL,S,1 ! seleciona os nos pertencentes a essa linha
!D,ALL, , , , ,UX,UY,UZ,ROTX,ROTY,ROTZ,

EPLOT

NSELL,ALL

SOLVE
FINISH

/SOLU
ANTYPE,BUCKLE
PSTRES,ON
BUCOPT,LANB,1
SOLVE
FINISH

/SOLU

/SOLU
EXPASS,ON
MXPAND,1
SOLVE
FINISH

/POST1
SET,LIST
SET,LAST
/VIEW,1,1,1,1
/ANG,1
/REP,FAST
PLDISP
FINISH"

Anyone can help me to solve this error message?

RE: Block Lanczos solver failure. Stress stiffness matrix contains all zeroes.

Check the warning before first solve, CE 68 to 132 are deleted.

"Contraint equation XX has specified degree of freedom (dof) constraint at all nodes/dof. Constraint equation deleted."

I guess your problem might come from these deletions.

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