Calculating the resultant forces via the pressure and shear stress terms in Navier-Stokes

General Discussion
1

Hello,

I would like to calculate the resultant forces that a viscous fluid exerts on a flat surface, suppose that the object is in 3D, is the total force calculated as follows?:

varFf([u1,u2,u3],[v1,v2,v3]) = int2d(Th, Allfaces)= (pressureN.xv1 + pressureN.yv2 + pressureN.z.v3) + (tau_xy(v1N.y + v2N.x) + tau_xz*(v1N.z + v3N.x) + tau_yz*(v2N.z + v3N.y))

I took into account the pressure and shear stress terms.