1. There are predefined core materials (foam core like SAN etc & honeycomb can also be modeled) in ansys composite material library.

2. If you want to define your own foam core like PU( which isn't available in earlier versions of ansys) you need to add "ply type" property, among all other properties. You can define  " Homogeneous foam core" as ply type.  

3. simply create fabric of foam core with required thickness in ansys ACP.

4. Apply same rules of Rosette and oriented element set etc. direction wont affect because its a homogeneous material.

5. In the end create solid model.