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.. "auto_how_to/example_surface_integral.py"
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.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_auto_how_to_example_surface_integral.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_auto_how_to_example_surface_integral.py:


Compute a surface integral over a patch
=======================================

``SurfIntegrate`` weights by face-area magnitude instead of cell volume. On
a boundary patch, that gives you per-patch totals (mass flux, force,
heat flux) as long as the per-face quantity you hand it is the right
integrand.

Here we compute the area of the ``lowerWall`` patch on the damBreak case by
feeding ``area()`` into ``Sum`` — same idea, simpler integrand.

.. GENERATED FROM PYTHON SOURCE LINES 15-17

Open the case
-------------

.. GENERATED FROM PYTHON SOURCE LINES 17-39

.. code-block:: Python


    import os
    import subprocess

    import pyOFTools.patch_pybfoam  # noqa: F401
    from pyOFTools import clone_example

    CASE = clone_example("damBreak")
    subprocess.run(
        ["./Allrun"],
        cwd=CASE,
        check=True,
        env={**os.environ},
        capture_output=True,
        text=True,
    )

    from pybFoam import Time, fvMesh

    time = Time(str(CASE.parent), CASE.name)
    mesh = fvMesh(time)








.. GENERATED FROM PYTHON SOURCE LINES 40-46

Patch area via ``create_patch_surface`` + ``area`` + ``Sum``
------------------------------------------------------------
``create_patch_surface`` returns a sampledSurface spanning the given
patches. Wrap it in a ``SurfaceDataSet`` yourself (there's no builder for
this yet), then ``area()`` writes face-area magnitudes onto the dataset
and ``Sum`` reduces them.

.. GENERATED FROM PYTHON SOURCE LINES 46-63

.. code-block:: Python


    from pyOFTools.aggregators import Sum
    from pyOFTools.builders import area
    from pyOFTools.datasets import SurfaceDataSet
    from pyOFTools.geometry import SampledSurfaceAdapter
    from pyOFTools.surfaces import create_patch_surface
    from pyOFTools.workflow import WorkFlow

    patch_surface = create_patch_surface(mesh, name="lower", patches=["lowerWall"])
    patch_ds = SurfaceDataSet(
        name="lowerWall",
        geometry=SampledSurfaceAdapter(patch_surface),
    )

    patch_area = (WorkFlow(initial_dataset=patch_ds) | area() | Sum()).compute()
    print(f"lowerWall patch area = {patch_area.values[0].value:.6g} m^2")





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    lowerWall patch area = 0.00992797 m^2




.. GENERATED FROM PYTHON SOURCE LINES 64-83

Surface-weighted integral of a sampled field
--------------------------------------------
To compute a flux-like quantity, interpolate a volume field onto the
patch, then use ``SurfIntegrate`` (same as ``sample | Sum`` but weighted
by face area):

.. code-block:: python

   from pyOFTools.aggregators import SurfIntegrate
   from pyOFTools.builders import sample

   flux = (
       WorkFlow(initial_dataset=patch_ds)
       | sample(mesh, "p")
       | SurfIntegrate()
   ).compute()

The surface variant is in :doc:`example_sample_plane` where we also
visualise the sampled field.


.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 10.465 seconds)


.. _sphx_glr_download_auto_how_to_example_surface_integral.py:

.. only:: html

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    .. container:: sphx-glr-download sphx-glr-download-jupyter

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      :download:`Download Python source code: example_surface_integral.py <example_surface_integral.py>`

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