Try this. It needs the Fredo6 Plugin and the LibFredo library plugin to work. Download both from the SketchUcation plugin store (NOT the Extension Warehouse) and install them. The plugins are free, but you need to sign up for a free account there.
Draw a quarter circle centred at the origin, centred on the Y axis (use the Arc tool, not the two point arc tool)
Rotate/Copy the arc about the blue axis, by (say) 15° depending on how many segments you want in your niche.
Use the two point arc tool (default shortcut a to make a bulge on the red/green plane between the two large arcs.
Select all the edges, then run the Curviloft/Skin contours option.
Click anywhere in the model to finish (the big green tick should be over a blank area of the screen). Reverse faces if necessary to get the front (white) faces inside.
Rotate/Copy the segment you’ve just created 11x round the blue axis.
Done
PS. Your upload of the model you found hasn’t worked - upload it again.
PPS. I found the clamshell model on the 3D warehouse. Looks as though I drew the initial quarter circles on the wrong axis. Start with a quarter circle on the red green plane, then rotate that about the green axis, select all edges, then run Curviloft to get this.
Then rotate/copy 11x as before, but about green not blue…
