[Felt-users] Possible bug in the htk-elements?

[Dr. T. P. <pe...@io...>]

Hi,

I modified the htk.flt in such a way that the plate is supported on three points
only. For certain locations of the support points I get huge deformations
(-6.3486e+07 m) which are not realistic in my opinion. Furthermore the reaction
forces are wrong.

The following configuration
 _____S_____
|     |     |
|     |     |
------F------
|     |     |
|     |     |
S_____|_____S

does not work (F: force, S: point supports in z) while a slight modification of
the support works:

S __________
|     |     |
|     |     |
------F------
|     |     |
|     |     |
S_____|_____S

Could there be a bug in the htk-elements? I use the 1.13 Windows version. Felt
3.02 on DOS produces similar results.

Best regards


Thomas Peschel


felt-input file:

problem description
title="modified htk sample" nodes=9 elements=4
/* units: m kg s N */

nodes
/* this gives strange results */

1 x=0.0 y=0.0	constraint=support	
2 x=0.25	constraint=free	
3 x=0.5	constraint=support		
4 x=0.0 y=0.25	constraint=free
5 x=0.25 	force=point
6 x=0.5 	
7 x=0.0 y=0.5	constraint=free
8 x=0.25	constraint=support
9 x=0.5	constraint=free

/* for comparison: this works correctly
1 x=0.0 y=0.0	constraint=support	
2 x=0.25	constraint=free	
3 x=0.5	constraint=support		
4 x=0.0 y=0.25	constraint=free
5 x=0.25 	force=point
6 x=0.5 	
7 x=0.0 y=0.5
8 x=0.25
9 x=0.5	constraint=support
 */

htk elements
1 nodes=[1,2,5,4] material=steel
2 nodes=[2,3,6,5]
3 nodes=[4,5,8,7]
4 nodes=[5,6,9,8]
material properties
steel E=2.1e11 G=81.4e9 nu=0.29 kappa=0.85 t=0.001
constraints
free  Tz=u Rx=u Ry=u
support   Tz=c Rx=u Ry=u
forces
point Fz=-1
end


felt output:

** modified htk sample **

Nodal Displacements
-----------------------------------------------------------------------------
Node #      DOF 1       DOF 2       DOF 3       DOF 4       DOF 5       DOF 6
-----------------------------------------------------------------------------
  1             0           0           0 -2.5394e+08  -0.0029851           0
  2             0           0  1.2697e+08 -2.5394e+08   0.0011378           0
  3             0           0           0 -2.5394e+08 -0.00019621           0
  4             0           0  6.3486e+07 -2.5394e+08   0.0013484           0
  5             0           0 -6.3486e+07 -2.5394e+08  -0.0017401           0
  6             0           0  6.3486e+07 -2.5394e+08  -0.0026564           0
  7             0           0 -1.2697e+08 -2.5394e+08   0.0010571           0
  8             0           0           0 -2.5394e+08  -0.0021964           0
  9             0           0 -1.2697e+08 -2.5394e+08  -0.0053933           0

Element Stresses
-------------------------------------------------------------------------------
  1:     0.057877    0.074734   -0.033456      -3.093      -0.882
  2:    -0.042426     0.12531   -0.096462       1.031     -2.3636
  3:     -0.19669    0.087231    -0.01673      -2.062      1.3807
  4:    -0.097236     0.16116   -0.065623     -2.5775       2.053


Reaction Forces
-----------------------------------
Node #     DOF     Reaction Force
-----------------------------------
  1        Tz            0.20568
  3        Tz           -0.16233
  8        Tz            -0.6055