[CIG-SHORT] How to obtain initial stresses on the node of the hex geometry

[Brad Aagaard]

Farhan,

You can get the basis functions evaluated at the quadrature points for 
any simulation by turning on the relevant journal. For tri or tet cells, 
it is fiatsimplex and for quad or hex cells it is fiatlagrange.

For example:

[pylithapp.journal.info]
fiatlagrange = 1

Here is the output from a quad simulation. Note how these values match 
those in the python script you mentioned.


  -- Basis fns @ quad pts ):
  -- [[ 0.62200847  0.16666667  0.0446582   0.16666667]
  [ 0.16666667  0.62200847  0.16666667  0.0446582 ]
  [ 0.16666667  0.0446582   0.16666667  0.62200847]
  [ 0.0446582   0.16666667  0.62200847  0.16666667]]

Here is the output from a hex simulation:

  -- Basis fns @ quad pts ):
  -- [[ 0.49056261  0.13144586  0.03522081  0.13144586  0.13144586 
0.03522081
    0.00943739  0.03522081]
  [ 0.13144586  0.03522081  0.13144586  0.49056261  0.03522081  0.13144586
    0.03522081  0.00943739]
  [ 0.13144586  0.49056261  0.13144586  0.03522081  0.03522081  0.00943739
    0.03522081  0.13144586]
  [ 0.03522081  0.13144586  0.49056261  0.13144586  0.00943739  0.03522081
    0.13144586  0.03522081]
  [ 0.13144586  0.03522081  0.00943739  0.03522081  0.49056261  0.13144586
    0.03522081  0.13144586]
  [ 0.03522081  0.00943739  0.03522081  0.13144586  0.13144586  0.49056261
    0.13144586  0.03522081]
  [ 0.03522081  0.13144586  0.03522081  0.00943739  0.13144586  0.03522081
    0.13144586  0.49056261]
  [ 0.00943739  0.03522081  0.13144586  0.03522081  0.03522081  0.13144586
    0.49056261  0.13144586]]

Regards,
Brad



On 08/12/2016 02:32 AM, Farhan Javed wrote:
> Hi,
>
> I am trying to output the initial stresses on the hex nodes for the 3D
> geometry of the region using density contrast.There is a available
> python script i.e. generate_statedb.py for 2D gravity problem. If I
> output the average initial stresses on the cell center, and re-run the
> simulation, It should give me zero deformation, but It gives very high
> displacement values. I need these initial stresses due to density
> contrast to constrain the equilibrium or near equilibrium conditions at
> the beginning of a simulation. Please can you guide me how to write a
> matrix for hex geometry as It was provided for quad4 cell in the
> generate_statedb.py python script. I am copying the part of the basis
> function for quad4 cell provided in the script:
>
> # Basis functions for quad4 cell evaluated at quadrature points. Use
> # to compute coordinate of quadrature points in each cell from
> # coordinates of vertices. Note the order must correspond to the order
> # of the data at the quadrature points in the output.
>
> qpts = numpy.array([[ 0.62200847,  0.16666667,  0.0446582,   0.16666667],
>                     [ 0.16666667,  0.62200847,  0.16666667,  0.0446582 ],
>                     [ 0.16666667,  0.0446582,   0.16666667,  0.62200847],
>                     [ 0.0446582,   0.16666667,  0.62200847,  0.16666667]],
> dtype=numpy.float64)
>
>
>
>
>
>
>
> Thanks you in advance.
>
>
> Farhan Javed
>
>
>
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