How to output the nodal multi-variable value as CSV file?

[Yulongggggg]

Hi developers, recently, I have been trying to use MOOSE to output all the variables on all the nodes or elements. I want a CSV with every row with the x and y coordinates of every node and corresponding variables (dispx, dispy, stress_xx, material properties etc.), but in MOOSE the displacement is nodal value and the stress, strain and material properties are element value, so if there's a way to change the element value to nodal value or change nodal value to element value so they can have be present in the same CSV file
[Nodalvalue] type = NodalValueSampler sort_by = 'x' variable = 'disp_x disp_y' execute_on = 'TIMESTEP_END' [] [Elemvalue] type = ElementValueSampler sort_by = 'x' variable = 'vonmises_stress stress_xx stress_xy stress_yy strain_xx strain_xy strain_yy' execute_on = 'TIMESTEP_END' []

[GiudGiud]

Hello

You can use the ProjectionAux to project to or from a nodal variable.
This will be good for postprocessing but there will be a projection error in some cases, which you can evaluate using the L2 norm different postprocessors

Guillaume

[GiudGiud]

You can already use these objects instead btw:
QuadraturePointsPositions to gather the quadrature point positions (in the Positions block)
PositionsFunctorValueSampler to sample all the variables (using their functor base class)

[GiudGiud]

I looked and the ElementValueSampler will never be able to output nodal variables.
I recommend you use the PositionsFunctorValueSampler option.

[Yulongggggg]

Hi Giud, I still don't know how to implement this, now I have two CSV files. (1) The element_value file has the coordinate of every quadrature point with variable values like stress and strain but no displacement value. (2) The Nodal_value file has the coordinate of every nodal point but only has the displacement value, is there a way to give every quadrature point the displacement value?

[GiudGiud]

If you do what I mention here, you'll be down to 1 CSV file
add this:

[Positions]
  [all_mesh]
    type = QuadraturePointsPositions
  []

and this

[VectorPostprocessors]
  [point_sample]
    type = PositionsFunctorValueSampler
    functors = 'disp_x disp_y disp_z stress strain'
    positions = 'all_mesh'
    execute_on = TIMESTEP_END
  []
[]

[Yulongggggg]

Thank you so much Guid, I can't image how hard it could be without your help. I used the 'ElementCentroidPositions' instead so I can get the value from every element centroid points. Now I have all the variables just like the image. Just to make sure, there's no way to do the same to all the nodal points, right? Then I will not wasting my time to explore this anymore

[Yulongggggg]

@GiudGiud

[GiudGiud]

You can do that with the Nodal points. You just need to create a new NodalPositions object
for material properties that might give interesting results though, they are not defined on nodes in general.