To generate a hexahedral mesh from a tetrahedral mesh in Ansys Workbench, you can follow these general steps:

It's important to note that not all geometries are suitable for generating fully hexahedral meshes, especially complex or irregular shapes. In such cases, transitional elements like tetrahedra or pyramids may be necessary to achieve a suitable mesh.

Hello!

I had a similar experience when attempting to mesh a cylindrical pipe for fluid analysis. By default, ANSYS Workbench often generates a tetrahedral mesh, which is generally considered less desirable compared to a hexahedral mesh in many cases. To overcome this, I opted for the "Automatic" meshing option and selected the entire body. In the details menu, I experimented with four different methods: Hex Dominant, Sweep, Multizone, and Cartesian. The first two methods, Hex Dominant and Sweep, were partially successful in generating hexahedral structures, but they also included some tetrahedral structures. Seeking a purely hexahedral mesh, I then tried the Multizone and Cartesian methods. These methods proved to be effective as they generated a mesh entirely composed of hexahedral elements, without any tetrahedral elements. Overall, the Multizone and Cartesian methods provided the desired hexahedral meshing for my analysis, yielding better results compared to the previous attempts with Hex Dominant and Sweep.

This small experience of mine while doing meshing may help you.