Читать книгу Computer Aided Design and Manufacturing - Zhuming Bi - Страница 63

Surface modelling aims to create the models for finite, non‐open surface patches of free forms. Note that the boundary surfaces of an object are formed by positioning and joining surface patches with the specified continuity restrictions. A surface modelling method does not represent the topological information of geometric elements such as knitting of boundary surfaces into a watertight volume. Figure 2.24 shows an example of a modelled surface from the surface modelling method. A surface model differs from a solid model since there is no information of the thickness.

Figure 2.24 Surface model example.

Differing from a wireframe model, a surface model has sufficient information to determine hide and shade displays when multiple surfaces are involved; however, a surface model does not include information of volumes or masses. Therefore, it is usually unsuitable to be used in simulations for engineering analysis unless the object is a sheet part with uniform thickness perpendicular to surfaces.