Exam 2015-10-30

Question 1

Describe the necessary steps to create a solid using surface modeling in a modern CAD model

Answer 1

1. create wireframe elements (points, lines, planes, curves) in 3D or sketches
2. create surfaces from the wireframe geometries (sweep, revolve)
3. Trim surfaces together
4. Join the surfaces together to a uniform element
5. transform into a solid (Thick, closed surface)
6. Add fillets

Question 2

What do C^0, C^1 and C^2 continuity between two curve segments mean?

Answer 2

C^0- continuity
–> Two curves segments are joined without constraints

C^1-continuity
–> The curve segments have the same direction at the common point

C^2-continuity
–> The curve segments have the same curvature at the common point

Question 3

What characterizes a feature (in geometry modeling context)?

Answer 3

1. a physical part of a detail
2. can be linked to a generic form
3. has a specific engineering role (function, manufacturing method, simulation method..)
4. has predictable properties)

Question 4

In order to perform a 3D variation analysis a 3D assembly model is needed. Describe the necessary components and inputs for a 3D assembly model

Answer 4

A 3D assembly model consists of:

1. Parts
2. Sub assemblies
3. Positioning systems
4. Input tolerances with range and type of distribution
5. Critical measures

Question 5

How does contribution analysis work ?

Answer 5

Model consist of:

3D assembly model with defined locating schemes
input tolerances with range and type of distribution
critical measures
Simulation:

All input parameters are varied (one at the time) within their tolerances on 3 levels
Max output is registered for all measured
Contribution is calculated in percent as % contribution=100*delta(output)/sum(delta(output))

Question 6

Why is contribution analysis contribution analysis used for?

Answer 6

It is used to calculate a ranked list of how all input tolerances contributed to the variation in the critical measures.

Question 7

What is bump-mapping?

Answer 7

A way of using textures to give smooth surface an irregular appearance

Question 8

How does bump-mapping work?

Answer 8

1. It works by modifying the surface normal that is used in the illumination model
2. The value of the modification is obtained from a texture
3. The color (RGB value) of each pixel indicates the surface normal modification

Question 9

Name two methods for rendering over multiple polygon surfaces!

Answer 9

1. Gouraud
2. Phong

Question 10

How does Gouraud work as a rendering method?

Answer 10

1. calculate normal vector for all polygon surfaces
2. calculate “mean normal vectors” for the vertices of the polygon
3. Mean normal + illumination model –> calculation of intensities (colors) in the vertices
4. Intensity values are interpolated line by line over the polygon

Question 11

How does Phong work as a rendering method?

Answer 11

1. Calculate normal vector for all polygon surfaces
2. calculate “mean normal vectors” for the vertices of the polygon
3. Surface normals are interpolated line by line over the polygon
4. Surface normal + illumination model –> calculation of intensities (colors) in each pixel

Question 12

Describe how a shadow buffer can be used to create shadows!

Answer 12

1. Create a buffer corresponding to the depth buffer, containing the distance from the light source to the closest surface
2. When drawing the point P on a surface
   - -> find the corresponding position in the shadow suffer for the point that is being drawn
   - -> compare the value in the shadow buffer with the distance from the light source to P.
   - ->If the value is less than the distance: draw only with ambient light

Question 13

Mention three benefits of using virtual product models in the product realization process

Answer 13

1. Minimizing the costly mistakes with real machines
2. finding problems as early as possible in the development process (earlier cheaper to fix)
3. Faster development process with efficient tools (time to market)

Question 14

Mention three advantages with using off-line programming

Answer 14

1. avoid costly mistakes with real machines
2. faster and more efficient programming
3. possibility to make new programs without stopping the production

Question 15

Geometry models created in a CAD-system are used by a number of different functions (departments etc.) within the product development process. Describe some problems related to this

Answer 15

1. Different functions uses different software requiring different file formats: problem with file conversion
2. Problem with access to right models