Anyone know them? I heard is related to heart pulse or something.
Perhaps you mean Navier-Stokes? They are non-linear, and generally unpleasant. The set of equations form a dynamical theory, and are the core of fluid mechanics.
Check out http://astron.berkeley.edu/~jrg/ay202/node50.html [Broken]. It saves me repeating a perfectly good source.
Hmm, it seems they also have the name "Napier-Stokes" as you suggested. Never came across that before.
Separate names with a comma.