In this video?
It looks to me to be some sort of fluid mechanics equation, but I can’t pinpoint which one. I’m sure someone will fill in the gap, soon, though. ETA: It looks like some form of the Navier-Stokes equations to me, if you want to try fishing around.
It looks like the incompressible form of the Navier-Stokes momentum equation where rho is 1 and, due to incompressibility,
abla . u = 0.
The only part that eludes me is the variable a on the RHS, because every version I can find has another instance of u there. Otherwise everything fits with minor naming tweaks.
“It looks complicated, must be Navier-Stokes …”
Do we add this to the perennial reference list that includes
Rio, by Duran Duran
Carmina Buranda
Powerhouse
Carmina Burana. I think your brain has crossed that with Carmen Miranda. 
The shirt has a logo and company name on the sleeve. Converge Software. Poking around, I find convergecfd.com, which has the same logo and also the company name Convergent Science. They describe themselves as "Convergent Science is an innovative, rapidly expanding computational fluid dynamics (CFD) company. ", which makes fluid dynamics the right field.