Why should the umbrella surface be made into an arc shape?
In the Hakka customs, girls must wear two umbrellas as dowry when they get married, because the traditional paper umbrellas are round when they are opened, which has the meaning of “consummation”, and the traditional Chinese “umbrella” can be seen Many villains are inside. Therefore, it also has the meaning of “being born early.” The physical shape and font of the umbrella are full of the good wishes of parents to their children.
Of course, there is a scientific basis for making a circle. The umbrella surface can be made into a square or a circle. In order to prevent rain, the side length of the square umbrella surface must be equal to the diameter of the circular umbrella surface. According to the force analysis based on the principle of fluid mechanics, when the umbrella surface receives the wind, the pressure distribution of the front half and the second half is different, and this pressure difference produces a kind of force called air resistance. When the square umbrella surface receives the wind, the pressure difference between the front and rear parts is greater than the pressure difference of the circular umbrella surface, so the resistance received when the square umbrella is driven is greater than the resistance received by the circular umbrella, and it will be very difficult to walk. Therefore, a round shape is chosen as the shape of the umbrella surface.
Why should the curvature of the umbrella surface not be too large?
The characteristics of flowing air are: the flow rate of the flow tube is fast and the flow rate of the thick flow tube is slow. The change of air flow speed will cause pressure change. Bernoulli’s law in physics states that when fluid flows steadily through a pipe, the pressure is low in the place where the flow velocity is fast, and the pressure is high in the place where the flow velocity is slow. If the curved arc of the umbrella surface is too large (close to the plane state), the air flowing through the umbrella surface will be divided into two upper and lower sections. Under the influence of the bulge, the streamline flowing through the upper surface will converge and become dense, the flow tube becomes thinner, and the flow velocity Faster, less pressure; On the lower surface, the streamline is looser, the flow tube is thicker, the flow rate is slower, and the pressure is greater. In this way, the pressure difference between the upper and lower surfaces of the umbrella will cause the umbrella surface to produce upward lift, and vice versa. , It produces downward pressure. Therefore, when used in windy weather, the umbrella will shake up and down, which is difficult to control.
In summary, when making umbrellas, the surface of the umbrella must be made into an arc shape, and the arc must not be bent too large, so it must be properly grasped.