Describe the necessary steps to create a solid using surface modeling in a modern CAD model
- create wireframe elements (points, lines, planes, curves) in 3D or sketches
- create surfaces from the wireframe geometries (sweep, revolve)
- Trim surfaces together
- Join the surfaces together to a uniform element
- transform into a solid (Thick, closed surface)
- Add fillets
What do C^0, C^1 and C^2 continuity between two curve segments mean?
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
What characterizes a feature (in geometry modeling context)?
- a physical part of a detail
- can be linked to a generic form
- has a specific engineering role (function, manufacturing method, simulation method..)
- has predictable properties)
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
A 3D assembly model consists of:
- parts
- subassemblies
- positioning systems
- input tolerances with range and type of distribution
- critical measures
How does contribution analysis work ?
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))
Why is contribution analysis contribution analysis used for?
It is used to calculate a ranked list of how all input tolerances contributed to the variation in the critical measures.
What is bump-mapping?
A way of using textures to give smooth surface an irregular appearance
How does bump-mapping work?
1,. It works by modifying the surface normal that is used in the illumination model
- The value of the modification is obtained from a texture
- The color (RGB value) of each pixel indicates the surface normal modification
Name two methods for rendering over multiple polygon surfaces!
- Gouraud
2. Phong
How does Gouraud work as a rendering method?
- calculate normal vector for all polygon surfaces
- calculate “mean normal vectors” for the vertices of the polygon
- Mean normal + illumination model –> calculation of intensities (colors) in the vertices
- Intensity values are interpolated line by line over the polygon
How does Phong work as a rendering method?
- Calculate normal vector for all polygon surfaces
- calculate “mean normal vectors” for the vertices of the polygon
- Surface normals are interpolated line by line over the polygon
- Surface normal + illumination model –> calculation of intensities (colors) in each pixel
Describe how a shadow buffer can be used to create shadows!
- Create a buffer corresponding to the depth buffer, containing the distance from the light source to the closest surface
- 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
Mention three benefits of using virtual product models in the product realization process
- Minimizing the costly mistakes with real machines
- finding problems as early as possible in the development process (earlier cheaper to fix)
- Faster development process with efficient tools (time to market)
Mention three advantages with using off-line programming
- avoid costly mistakes with real machines
- faster and more efficient programming
- possibility to make new programs without stopping the production
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
- Different functions uses different software requiring different file formats: problem with file conversion
- Problem with access to right models
what is a digital mockup (DMU) and for what is it used?
- Special type of component based assembly model developed to be able to handle large assemblies (>1000 parts) from different CAD-systems
- C an be used for e.g. packaging studies and assembly simulation but not for e.g. calculation of mass
What type of geometry representation is usually used in a digital mockup (DMU)?
The NURBS-geometry from the CAD-system is simplified to a triangulated surface model
–> large reduction in size
Mention 5 basic needs of engineering information management
- Capture information at the source
- organize information
- distribute the information –> when, where, what, to whom
- Search, re-use, and present information
- secure storage of information over a long time
What is the aim of a PLM system?
PLM systems aim to support the creation and management of all information related to a product throughout its lifecycle
What are the 3 different types of modeling components in a multi-body system dynamic simulation?
- rigid bodies
- constraints (joints, motions)
- Forces (gravity, spring/dampers, friction etc.)
