Preformed fibre insulation panels 2438 m 1219 m 25 mm are

Preformed fibre insulation panels 2.438 m * 1.219 m * 25 mm are used to insulate a building. During construction some are left lying flat on grass. If the density of a panel is 100 kg/m3 calculate the minimum wind velocity (in km/hr) at ground level which wil lift the panel and blow it away. Note that the grass under the panel reduces the air velocity to stagnation conditions.

Solution

weight of the panel = desity * volume = 100 kg/m3 * 2.438 m * 1.219 m * 0.025 m = 7.429 kg

area of the panel = A = Length * breadth = 2.971 m^2

lift created L = C* p * V^2 * A / 2    ; assuming C , coefficient of lift = 1 , p , air density , V velocity of wind ,

A panel area

                 the lift created by wind must be equal to the weight to blow away

                           1.225kg/m3 * V^2 * 2.971 / 2 = 7.429 kg

                                     V = 2.020 m/sec or 7.272 km/hr