2019-07-16 程序

2 Procedure

2.1 1:100 Scale Model

The dimensions of the 1:100 scale model constructed were 24 in. long, 9 in. wide,

and 6 in. high, with five vertical arches, each spaced 3 in. apart. The cross sections of

the arches in the model had an outside diameter of 0.25 in. Figure 3.1 shows the

constructed model.

Figure 3.1: 1:100 Scale Model

Each end of the modeled structure was comprised of three arches, all with

common base points. Each arch was rotated, in plane, 30° with respect to the adjacent

arches. The plane of the final arch was oriented horizontally. Therefore, the three end

arches created a quarter of a paraboloid. The shape of each arch was formulated using

the following parabolic function: y=/28.125

The model was constructed using the same arch orientations and curvatures as the

structure represented.

Materials

The materials for the model were chosen to approximate as closely as possible the

types of materials used in the structures represented, as well as for practicality in

construction of the model. Two bases were used for the model and are shown in Figure

3.2. Both were made from 0.5 in. thick plywood. The bases could be attached to each

other with 5 bolts and wing nuts. The lower of the two bases was rectangular in shape

and attached to brackets on the wind tunnel framework. The upper base was circular and

the model was attached directly to it.

The arches were made of soft copper tubing having an outside diameter of 0.25 in.

and a thickness of 0.03 in. The membrane was a flexible plastic material designed for

landscaping that was 0.004 in. thick with a grainy texture and black in color. Tension

tests on the membrane material estimated its modulus of elasticity as 3.6 ksi (see

Appendix A).