Computes value of Friction Factor using Jain(1976)
f = Darcy-Weisbach friction factor
ks = Equivalent sand roughness height (a material property; in feet or meters)
D = Pipe diameter (in feet or meters)
Re = Reynolds number (a flow property)
Jain, A. K., 1976. Accurate explicit equation for friction factor.
ASCE J. of Hyd. Div., 102(HY5) pp. 674-677