wire frame model.pptx

cad

1. wire frame model

2. wire frame model A wire frame model is a visual presentation of a three dimensional   object used in  3D computer graphics. The wire frame model representation contains only vertex and edge information. Most of the solid modeling software such as AutoCad , Proe etc. provided option for wireframe representation of solid model.

3. wire-frame representation A wire-frame representation of a three-dimensional object consists of a finite set of points and connecting edges, which define the object. The term ‘edge’ does not necessarily imply that it is a straight-line segment. An edge may well be an arc of a circle or any other well-defined space curve, which is required for a ‘good’ wire-frame representation.

4. For complex models, a large number of lines may overlap each other. If the model is complicated, it becomes ambiguous and difficult to understand . Figure : An ambiguous wire-frame object

5. Solid model Solid modeling is based on complete, valid and unambiguous geometric representation of physical object. Complete :points in space can be classified.(inside/ outside) Valid :vertices, edges, faces are connected properly. Unambiguous : there can only be one interpretation of object.

6. Euler- Poincaré Formula Euler- Poincaré Formula can be used for check the validness of a solid. A formula : V -E + F -(L -F) -2(S -G) = 0 Where , V : the number of vertices E : the number of edges F : the number of faces G : the number of holes that penetrate the solid , G enus S : the number of shells L : the number of loops

7. For Example: A cube : eight vertices ( V = 8), 12 edges ( E = 12) and six faces ( F = 6), no holes and one shell ( S =1); L = F (each face has only one outer loop) V-E+F-(L-F)-2(S-G) = 8-12+6-(6-6)-2(1-0) = 0

8. Solid model representation Constructive solid geometry (CSG): Objects are represented as a combination of simpler solid objects (primitives). The primitives are such as cube, cylinder, cone , sphere etc . A complete solid model is constructed by combining these “instances” using set specific, logic operations (Boolean)

9. Constructive solid geometry (CSG)- Boolean operation Union The sum of all points in each of two defined sets. (logical “OR”). Also referred to as Add, Combine, Join, Merge .

10. Difference The points in a source set minus the points common to a second set. (logical “NOT”) Set must share common volume Also referred to as subtraction, remove, cut.

11. Intersection Those points common to each of two defined sets (logical “AND”) Set must share common volume Also referred to as common, conjoin

12. Hidden line or hidden surface removal A common requirement of CAD package in solid modeling is to hide the portion of a line or -surface that lies behind another surface or solid object. This process is called hidden line or hidden surface removal. The lines are to be shown as dotted or dashed lines.

13. FEM

14. The conventional analytical methods for solving stresses and strains becomes are very complex and almost impossible when the part geometry is intricate. In FEM becomes a very convenient means to carry out the analysis.

15. Steps in FEM Identify the problem, sketch the structure. calculating various properties for each element such as geometry, material properties, constraints,loading and apply Boundary condition. Interpreting the results.