Tenta 111022 Flashcards
Describe the steps necessary to create a solid, using surface modeling in a modern CAD system
- create wireframe elements (points, lines, planes, curves) in 3D or sketches
- create surfaces from the wireframe geometries (sweep, revolve)
- Trim the surfaces together
- join the surfaces together to a uniform element
- transform into a solid (Thick, Closed, Surface)
- Add fillets
Curves used in geometry modeling can be of different order. What are the advantages and disadvantages of higher order curves?
Advantage:
- Higher precision
Disadvantage:
- risk for corrupt curves
- increased calculation time
What characterizes a feature?
- a physical part of detail
- can be linked to a generic part
- has 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 and for what is it used?
It is used to calculate a ranked list of how all input tolerances contributes to the variation in the ciritcal measures
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 measures
- Contribution is calculated in percentage %contribution=100*delta(outout)/sum(delta(output))
Describe with text, figures and equations the four steps for collision detection between two objects defined by triangle surfaces
- Do a fast coarse “mini-max-test” with bounding boxes/spheres to determine if a collision might be possible at all
- If yes, check if any of the points on body A is inside body B.
- Test if any of the edges on body A intersects with an infinite plane defined by some of the polygons on body B.
- -> test if the endpoints of the edge are on different sides of the plane. This is done by using the equation of the plane. - If yes, calculate the intersectionpoint between the edge and the plane:
- -> use the equation for the line between the points and the equation of the plane - Check if the intersection point is on the polygon:
- -> calculate the area of the three sub triangles defined by the intersection point and the original vertices of the triangle
- -> If all these areas have the same sign, intersectionpoint is inside the triangle and it is an collision
- -> to speed up the calculation this can be done in 2D by projecting the triangle on a plane
Describe the 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 buffer for the point that is being drawn
- -> Compare the value in the shadow buffer with the distance from the light source to P
- -> It 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 need for costly physical prototypes
- Finding problems as early as the possible in the development process (easier and cheaper to fix)
- Faster development process with efficient tools (time to market)
Give 2 examples of usage of ergonomic simulation with computer manikins
- Evaluation of user interfaces
2. Evaluation of concept for manual assembly
Mention 3 advantages of using off-line programming
- Avoid costly physical prototypes
- Faster and more efficient programming
- possibility to make new programs without stopping the production
Describe some problems with using geometry models in a number of different functions/departments?
- Different function uses different softwares requiring different file formats: problem with file conversion
- Problem with access to the right models
What type of geometry representation is usually used in a digital mockup (DMU)?
triangulated surface model
What is the aim of a PLM system?
PLM system aim to support the creation and management of all information related to a product throughout its lifecycle
Mention three things that a Product Data Management (PDM) database should provide
- A database vault for secure storage of information
- Product structure management
- Process management
What are half spaces and how can they be used to create geometric primitives?
Real, analytical functions f(x,y,z) defined in 3D which splits the space in two half spaces
- One half space where f(x,y,z)< 0
- One half space where f(x,y,z) >0
- Example: Cylindrical half space x^2+ y^2-r^2<0
Solid primitives are created by combining half spaces with Boolean operators
Construction of the cylinder: H1=x^2+y^2-r^2<0 H2=z>0 H3=z-h<0 C=H1 H2 H3
