Thank you. I still feel the stackexchange post misses the forest for the trees (and weeds). Take a look at the NOAA global map showing coasts that have semidiurnal tides (that is, one in roughly ~12 hours) [1].
Most all of the coast of Africa is semidiurnal. So is east coast of North America, a lot of South America. Bay of Bengal, a lot of Europe. If you see the map on the RWU [2] site it shows Greenland and the north coast of Russia (although stretched due to the latitude) are also semidiurnal. This is a major part of the global coastline. The simple mental model explains this. I feel that going to partial differential equations, fourier series, etc. etc. is a little too complicated.
“roughly 12 hours”