Connect Shell elements with solids

Hello Professionals,

I want to fill the shell structure below with solid elements.

The target of my work is to do a topology optimization of the filled shell. In this topology optimization the shell elements would be the no design space and the solids become the design space. I tried to mesh the solids with TetraMesh. But when I enhance the displacement factor to more than 20, the structure of the topology optimization isn't connected to the shell structure around anymore. You can see the in the following picture.

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I also tried to mesh the design space with SolidMap Mesh, but when I want to mesh the solid next to the tube, HyperMesh displays the following.<?xml version="1.0" encoding="UTF-8"?>

Is there any opportunity to connect the shell elements with the solid elements?

Best regards,

Tobias