tailieunhanh - Aeronautical Engineer Data Book Episode 13

Tham khảo tài liệu 'aeronautical engineer data book episode 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Basic mechanical design 231 contains all the changes required to adapt vendor software for custom use. Types of modelling CAD software packages are divided into those that portray two-dimensional or three-dimensional objects. 3D packages all contain the concept of an underlying model. There are three basic types as shown in Figure Wireframe models Although visually correct these do not contain a full description of the object. They contain no information about the surfaces and cannot differentiate between the inside and outside. They cannot be used to link to a CAM system. Surface models Surface models are created conceptually by stretching a two-dimensional skin over the Wireframe model No differentiation between inside and outside Surface model All surfaces and their boundaries are defined and recognized by the model It is possible to get meaningless nonsense models like this Although the model appears solid there is no recognition of what lies inside the surfaces Solid model The model is recognized as a solid object Various techniques of solid modelling include BR Boundary Representation CSG Constructive Solid Geometry FM Faceted Modelling Fig. Types of modelling 232 Aeronautical Engineer s Data Book edges of a wireframe to define the surfaces. They can therefore define structure boundaries but cannot distinguish a hollow object from a solid one. Surface models can be used for geometric assembly models etc. but not analyses which require the recognition of the solid properties of a body finite element stress analysis heat transfer etc. . Solid models Solid models provide a full three-dimensional geometrical definition of a solid body. They require large amounts of computer memory for definition and manipulation but can be used for finite element applications. Most solid modelling systems work by assembling a small number of building block reference shapes. Finite Element FE analysis FE software is the most widely used type of .