I have a solid as shown in the picture. I want to draw a 3D sketch (eg, like a sine/cosine-wave) on the highlighted surface based on its equation. I tried using Spline on surface but do not achieve what exactly I need. If I use the equation driven curve option I am unable to place it on the surface since I do not know the equation for the surface/curves. Can someone give me some pointers on how I can proceed on this problem?