Use perimeter welds in part or assembly models to connect parallel plates, that may be curved, along the perimeter of one of the plates, as shown here:

Before mesh generation, a sequence of surfaces is automatically created to connect the selected edges of the top plate to the base plate. Creo Simulate adds shell elements to the newly created surfaces. A series of welds on one or more of the perimeter edges of the top plate connects it to the base plate. In this case, the components are touching, but the resulting compressed surfaces are parallel to one another and do not touch. For this type of geometry, you should use a perimeter weld to connect the two plates, or allow Creo Simulate to create automatic midsurface connections. For more information on allowed surfaces, see Guidelines for Surface-Surface Connections and Interfaces (FEM mode).