Wind at U∞ and p∞ flows past a Quonset hut which is a half-cylinder of radius a

Question:

Wind at U∞ and p∞ flows past a Quonset hut which is a half-cylinder of radius a and length L (Fig. P8.48). The internal pressure is pi. Using in viscid theory, derive an expression for the upward force on the hut due to the difference between pi and ps.