Oceanography
Tidal Harmonics (M₂+S₂+K₁)
η = cos(2πt/12.42) + ½cos(2πt/12) + 0.3cos(2πt/24)

Superposing the principal lunar (M₂), solar (S₂) and diurnal (K₁) constituents reproduces the semidiurnal tide whose M₂/S₂ interference drives the fortnightly spring–neap beat.
Computed & rendered in pure C# on the frozen OnlyCSharp 1.8 library — animation baked to GIF with the library's own
Gif encoder (no GPU, no ffmpeg, no external packages).