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Note that it is important to turn off "Thick Shells and Beams" under "Display" before exporting the model as an .stl file. If "Thick Shells and Beams" are turned on, Ansys will export a solid body, not a surface model, and the rest of the steps to calculate the volume of the deformed trachea will not work properly.

Also: turn the displacement scaling to 1 before exporting the deformed geometry as an .stl file

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