Description of the function graph I've need to somehow describe this function:
The most similar function I guessed is the equation of the form y(x) = sin(x) + sin(3x)  (green line) but it doesn't exactly what I needed. Maybe there is someone who knows how to describe it?

I noticed that your graph looks like a sine curve that's been wrapped around a cylinder viewed from above. From that I was able to work out the equation $y = -\sin(e \sin(x))$. Feel free to play around in desmos to modify it to your liking: https://www.desmos.com/calculator/jfwbvrmj7d
Is there any particular application you had in mind for this graph?
