There are really many possibilities playing with noise, Cosinus, Power …
Grooves …
Micro grooved waving surface
http://www.grasshopper3d.com/forum/topics/how-to-create-smooth-and-stable-waves-using-magfields
http://www.grasshopper3d.com/forum/topics/how-to-generate-a-sine-cosine-function-with-a-gradual-distance
marble turbulence noise v3.gh (34.6 KB)