Learning Forum

[Christijaaan]

Hi!

I have an easy system (s. fig.) which is a harmonic torsional excited water filled tube.

Now I want to extract and average the nodal forces to calculate the torsional moment around the tube axis in a user defined cross-section (component, sliced like a salami :) ) in the pipe wall via APDL Postcommands. I tried the following but it didn't work out:

...

direc_axial     = 'Y'
direc_trans_1   = 'Z'
direc_trans_2   = 'X'

CMSEL,S,ebene !Auswahl der Ebene als Komponente
*GET,n_nodes,NODE,,count !Anzahl der Knoten in der Ebene
*DIM,calc_array,ARRAY,n_nodes,13 !Init Array für flächengewichtete R/Im des Drucks und der Fläche (n_nodes x 2)

set,1,i,,IMAG
next_node = 0
*DO,j,1,n_nodes,1
next_node = ndnext(next_node)

calc_array(j,1) = ARNODE(next_node)

!Rotation um Rohrachse
*GET,r_trans1,NODE,next_node,LOC,direc_trans_1
*GET,r_trans2,NODE,next_node,LOC,direc_trans_2
r_abs = sqrt(r_trans1**2 + r_trans2**2) 
u_rot = 1/r_abs*(-r_trans2*u_trans1 + r_trans1*u_trans2) !ACHTUNG: VZ in der Klammer ist entscheidend für die Phase
calc_array(j,11) = u_rot*calc_array(j,1)
!Moment um Rohrachse
*GET,f_trans1,NODE,next_node,RF,direc_trans_1
*GET,f_trans2,NODE,next_node,RF,direc_trans_1
f_rot = 1/r_abs*(-r_trans2*f_trans1 + r_trans1*f_trans2)
m_rot = f_rot*r_abs
calc_array(j,13) = m_rot*calc_array(j,1)
*ENDDO

...

Actually it thought that this should be a hard task... but it turns out to be. Does anybody has some suggestions for an alternative workflow??

Greetings!!!

Christian

[dlooman]

A common, pretty easy way is to select a set of nodes at a cross-section and the elements on only one side of those nodes.  Then fsum, possibly in conjunction with spoint will give you the moment at that location.