CBUSH spring benchmark

Altair Forum User

Dear all,

 

before inserting the CBUSH spring into my model I decided to do a simple benchmark which in the end turned out unlogical (for me).

 

My benchmark model consists of CBUSH element - one end is fixed (1-6 DOF) while the other is loaded with a force of magnitude = 1 (axially in tension), 1D. I am using a PBUSH property with stiffness K = 1 (for axial direction, other K's are defined as RIGID).

 

The results yield a displacement of 10E-4 and not 1, as I expected. I am assuming Force = Stiffness x Displacement.

 

What did I miss here?

 

Thank you all for your time and help!

tinh

oh, reaffirm your input values

displacement is 1 always. i tested it

Altair Forum User

Thank you for your answer!

 

I made a new model with same inputs (K = 1, F = 1) and now the results yield '1'. This is correct. However I cannot find what was wrong with my old model... Please see below the input deck.

 

This is my input file:

 

SUBCASE       1
  LABEL displacement                                                                      
ANALYSIS STATICS
  SPC =        1
  LOAD =        2
  DISPLACEMENT(H3D,ROTA) = ALL

BEGIN BULK

CORD3R         1       1       2       3

GRID           1        0.0     0.0     0.0                            
GRID           2        0.0     0.0     10.0                           
GRID           3        1.0     0.0     0.0                            
GRID           4        0.0     0.0     0.0                            
GRID           5        0.0     0.0     10.0                           

CBUSH          1       1       4       5                               1

PBUSH          1       KRIGID   RIGID   1.0     RIGID   RIGID   RIGID  

SPC            1       4  1234560.0    
FORCE          2       5       01.0     0.0     0.0     1.0    

ENDDATA

 

Any thoughs?

tinh

hi

try comparing with your new deck.

your PBUSH card was able to have problem