Which of the following velocity fields are possible fluid flow cases? Which satisfy the conditions for irrotational flow?
(а) U =x+y+z, v=x-y +z, w=x+y+3
(b)u = xy, v = yz, w = yz + Z
(C)u = x (y + z), V = y(x + z), W= -(x + y)z- I
(d)u = xyz, v = -xyzt, w = 2/2 (xt' - yt)