Maybe you can create some planes down the length of this beam shape to split the body into sweepable and non-sweeapble parts. As you mentioned, the meshing and analysis will be a lot easier (and quicker) if you make midsurfaces from the sweepable sections.
If making midsurfaces is an untentable amount of time for you, maybe you can extract one side. You will have to make sure to specify the correct top or bottom offset in Mechanical for the geometry body properties, and contact setup will require specifying gap and pinball radius.
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