Geometric Modelling in Computer Aided Design.pptx

Geometric Modelling in Computer Aided Design is explained in this PPT.

1. Geometric Modelling Modelling- Creating symbolic models of the physical world has long been a goal of mathematicians , scientists, engineers, etc . Geometrical Modelling can be defined as computer friendly and mathematical representation of geometry. Geometric Modelling is the computer-aided design and manipulation of geometric objects. Geometric modelling is only a means not the goal in engineering .

2. ●2D Projections (Drawings) ●Solid Models Constructive Solid Geometry and describes an object as a solid ●Wire Frame Models describe an object using boundary lines ●Surface Models describe an object using boundary surfaces Free-form, Curved, & Sculptured Surface Geometric Modelling Techniques

3. ●Wireframe Modelling (Auto-cad Drawings) • The word “wireframe” is related to the fact that one may imagine a wire that is bent to follow the object edges to generate a model. • Developed in 1960s and referred as “a stick figure” or “an edge representation” • Model consists entirely of points, lines, arcs and circles, conics, and curves . Wireframe Modelling

4. ●Advantages Simple to construct Does not require as much as computer time and memory as does surface or solid modelling. As a natural extension of drafting, it does not require extensive training of users. From the basis for surface modelling as most surface algorithms require wireframe entities (such as points, lines and curves) ●Disadvantages The input time is substantial and increases rapidly with the complexity of the object Both topological and geometric data need to be user-input; while solid modelling requires only the input of geometric data . volume and mass properties, NC tool path generation, cross-sectioning, and interference cannot be calculated. Wireframe Modelling

5. ●Surface Modelling • A surface model is a set of faces. • A surface model consists of wireframe entities that form the basis to create surface entities. • Used to be separated, shape model are now incorporated into solid models. • It is most often used type of model. Surface Modelling

6. ●Examples of Surface Modelling • Surface models define only the geometry, no topology. • Shading is possible. Surface Modelling

7. ●Advantages Less ambiguous Provide hidden line and surface algorithms to add realism to the displayed geometry Support volume and mass calculation, finite element modelling , NC path generation, cross sectioning, and interference detection. ●Disadvantages Require more training and mathematical background of the users Require more CPU time and memory. Awkward to construct. Surface Modelling

8. ●Solid Modelling The solid modelling technique is based upon the "half-space” concept. The object is defined by the volume space contained within the defined boundary of the object. In general speaking, a closed boundary is needed to define a solid object. Solid Modelling

9. ●Solid Modelling Support • Using volume information – weight or volume calculation, centroids, moments of inertia calculation, – stress analysis (finite elements analysis), heat conduction calculations , – system dynamics analysis • Using volume and boundary information – generation of CNC codes, and robotic and assembly simulation. Why Solid Modelling?

10. Geometric Modelling X= r sin θ , Y= r cos θ and Z= h When we give some values to these 3 variables, ie . r=10, θ = Π and h=25 It would be a point (X,Y,Z). X= r sin θ , Y= r cos θ and Z= h But when we vary one parameter say θ then, ie . r=10, - Π≤θ≤Π and h=25 It would be a circle. X= r sin θ , Y= r cos θ and Z= h But when I vary one more parameter say θ and h then, ie . r=10, - Π≤θ≤Π and 0 ≤ h ≤ 25 It would be a cylinder. Let us see one example… What do these equations represents

11. Geometric Modelling X= r sin θ , Y= r cos θ and Z= h If I vary r and θ keeping h=const., ie . ≤ r ≤ 10, - Π≤θ≤Π and h=25 It would be a disk. X= r sin θ , Y= r cos θ and Z= h If I vary all three r, θ and h, ie . ≤ r ≤ 10, - Π≤θ≤Π and 0 ≤ h ≤ 25 It would be a Solid Cylinder. X= r sin θ , Y= r cos θ and Z= h If I vary all three r, θ and h, ie . 5 ≤ r ≤ 10 , - Π≤θ≤Π and 0 ≤ h ≤ 25 It would be a Hollow Cylinder.

12. Modelling Porous Medium Biomedical Applications Modelling Non-homogeneous Materials – varying density – changing composition – multiple phases (solid, liquid ) New challenges to Geometric Modelling

13. Thank You…