ANSYS modelling

[Orangeman]

Hello friends,

I am using ANSYS for the first time, I need to model a a thin-walled circular tube to analyze the buckling of it based on different boundaries conditions. At the moment, below is what I written. When I try to run it, ANSYS shuts down right after the command line-solve.

Thanks

c*** -----------------------------------------------
/PREP7
ANTYPE,STATIC ! STATIC ANALYSIS
PSTRES,ON ! CALCULATE PRESTRESS EFFECTS
nlgeom,on
et,1,shell181
mp,ex,1,20e6
mp,prxy,1,0.33
r,1,1
c*** -------------------------------

k,1,0
k,2,,80
k,3,12
k,4,12,80
l,3,4
arotat,1,,,,,,1,2
eshape,2
esize,1
amesh,all
/solu

nsel,s,loc,y
d,all,all
sfl,8,pres,1
sfl,6,pres,1
sfl,12,pres,1
sfl,10,pres,1
C*** ! controls solution printout
C*** ! print nodal dof solution
OUTPR,,1
solve
finish
/solu
ANTYPE,BUCKLE ! BUCKLING ANALYSIS
BUCOPT,LANB,1 ! USE BLOCK LANCZOS EIGENVALUE EXTRACTION METHOD, EXTRACT 1 MODE
MXPAND,1 ! EXPAND 1 MODE SHAPE
solve
*get,fcr,mode,1,freq
Finish

 

[rickfischer51]

Most of your nodes are unselected. Add the command allsel before the first solve. Also, the ANTYPE, PRSTRS and NLGEOM commands rightfully belong after /SOLU. It appears the program accepted them but I think it best to keep them in Solution to better organize your solution options.

Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[Orangeman]

I have rewrote the program to try to analyze the different modes of buckling but when I compare it to the Pcr = pi*EI / KL^2 formula it doesnt come out right. I was wondering what went wrong for my program.

I set the boundary conditions to K=1 where its fix in end and hinged at the other.


c*** -----------------------------------------------
c*** filename: Perfect Circular Tube under axial load
c*** length = 100 in
c*** diameter= 20 inches
c*** thickness= 2 inches
c*** -----------------------------------------------
/PREP7
C*** ----------------------------------------------------
C*** I added these commands
ANTYPE,STATIC ! STATIC ANALYSIS
c*** ---------------------------------------------------
et,1,shell63
r,1,2 !2in Thickness
mp,ex,1,30e6
mp,nuxy,1,0.3
c*** ------------------------------------------------
csys,1 !Cylinder Coordinate
k,1,0,0,0
k,2,0,0,100
k,3,10,0,0
k,4,10,0,100
l,3,4
arotat,1,,,,,,1,2
c*** ------------------------------------
esize,,8
amesh,all
C*** cartesian coordinates
csys,0
c*** ---------------------------------------------------------------
c*** support end of column in x, y and z directions
c*** DL,line,area,lab, value1
c*** --------------------------------------------------------------
DL,5,1,ux,0
DL,11,4,ux,0
DL,9,3,ux,0
DL,7,2,ux,0
c*** ---------------------------
DL,5,1,uy
DL,11,4,uy
DL,9,3,uy
DL,7,2,uy
c*** --------------------------
DL,5,1,uz
DL,11,4,uz
DL,9,3,uz
DL,7,2,uz
c*** ---------------------------------------------------------------

c*** -------------------------------------------
/SOLU
ANTYPE,STATIC ! STATIC ANALYSIS
PSTRES,ON
c*** unit pressure on top of column
sfl,8,pres,1
sfl,6,pres,1
sfl,12,pres,1
sfl,10,pres,1

C*** ! controls solution printout
C*** ! print nodal dof solution
OUTPR,,1
SOLVE
FINISH
/SOLU
ANTYPE,BUCKLE ! BUCKLING ANALYSIS
BUCOPT,LANB,1 ! USE BLOCK LANCZOS EIGENVALUE EXTRACTION METHOD, EXTRACT 1 MODE
MXPAND,1 ! EXPAND 1 MODE SHAPE
SOLVE
*get,fcr,mode,1,freq
finish