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# Pressure Transfer

# 18. Pressure Transfer

It is a common Sierra/SD use case to run an aerodynamics code, and then need to transfer the structural loads from the aerodynamics code to Sierra/SD to solve the structural problem. For this example, we describe how to transfer pressure loads from other analysis tools to Sierra/SD.

Here we begin with a three dimensional finite element mesh, that is the skin of a “Sierra Test Vehicle,” STV. The STV is composed of Quad4 (2D) elements, each with a set of element variables, including pressure. The STV is a blunt, circular paraboloid that is 3 meters long with a 2 meter diameter. Figure 18.1 shows the pressure output on the transfer mesh `post-surf-mna/surface.e`.

Figure 18.1 Pressures on STV

Before running Sierra/SD, the user should check and see that the desired variables are in the transfer exodus mesh. This can be done in the following way:

    module load sierra
    explore post-surf-mna/surface.e <<< names

The output from explore is shown below, and can confirm that `pressure` exists in the output file. The fields other than `pressure` are not necessary for this example.

    Variables Names:
       Global:
       Nodal:
       Element: Ma            density
                pressure      primitives_1
                primitives_2  primitives_2
                primitives_4  primitives_5
                temperature   velocity_x
                velocity_y    velocity_z
                wall-C_p
       Nodeset:
       Sideset:

Next, we look at the Sierra/SD input file.

    FILE
      geometry_file 'stv_test_model.g'
    END

    TRANSFER 'post-surf-mna/surface.e'
      destination sidesets wetted_surf
      copy variable = pressure
      variable type = element
    END

    FUNCTION read_pressure
      type = exodusread
      sideset = wetted_surf
      exo_var = scalar pressure
      interp = linear
    END

    LOAD 1
      sideset wetted_surf
      pressure 1.0
      function read_pressure
    END

Here we see four distinct sections. As with all Sierra/SD runs, the geometry file is defined as `stv_test_model.g.` This is the standard finite element model with all the geometric complexities of the structural model.

Next, we see the `TRANSFER` Exodus file, `post-surf-mna/surface.e`. This is the transfer mesh, and only contains the shell of the model (2D Quad4 elements). The next three lines copy the element variable `pressure` from the transfer mesh to the sideset `wetted_surf` on the structural mesh.

The `FUNCTION` block defines a function of type `exodusread`, which reads the scalar pressure from the sideset `wetted_surf`. The syntax `interp = linear` tells Sierra/SD to interpolate linearly in time.

Finally, the `LOAD` block defines a pressure load of magnitude 1 on the sideset `wetted_surf,` using the function `read_pressure`.

Figure 18.2 Transfered pressure on structural mesh