4. A rotating vertical cylinder generates a sideways force just like a sail. The first ship based on this principal was built in 1924 (Flettner ship). The flow around a rotating cylinder described by the velocity potential is = U cos 0(r+ R2 r -)-QR20, where U (the speed of the wind), (the rotation rate), and R (the radius) are constants. FLESTNER-ROraw (a) Calculate the expression for the velocity vector, v = v in terms of R, U and Q. V (b) Plot the (top view) velocity vector on the surface of the cylinder at 45 degree intervals (0 = = 0, л/4 л/2, 3л/4, л, 5л/4, 3π/2, 7л/4 гadians). m, and 2 47.14 1/s]. [Assume U=10.0 m/s, R=0.6