Exam 131022 Flashcards
Describe the steps neccessary to create a solid, using surface modeling in modern CAD system
- Create wireframe elements (points, lines,planes, curves) in 3D modeling
- Create surfaces from the wireframe geometries (sweep, revolve,..)
- Trim surfaces together
- Join the surfaces together to uniform element
- Transform into a solid (Thick, Closed surface,..)
- (add fillets)
describe how trimmed parametric surfaces are defined/created
- Parametric surfaces are defined in a similar way as parametric curves but with two parameters u and v
- Parametric curves are defined in the same 2D parametric space
- They are used to create holes (inner trim curves)
- Used to create outer boundary of the surface (outer trim curves) - The trimmed parametric surface is transformed to 3D space
What is the advantage of B-spline curves?
- Better local control of the curve
- order of the polynomial does not increase with the number of control points
- Easier to define joined curve segments
Name three different types of analyses used in CAT (computer aided tolerancing) software!
- variation analysis (with monte carlo simulation)
- contribution analysis
- Stability analysis
Describe how variation analysis with MC works and what it is used for
- calculates with statistical prediction of the variation in critical measures
- statistical method - random data
- Tolerances on parts (inputs) are randomly generated with defined distributions, tolerances and Cp
- Distributions for critical measures (outputs) are generated from thousands of iterations
- All kinematical relations and sensitivities are captured in a 3D assembly model
Describe how contribution analysis works and what it is used for
- calculates a ranked list of how all input tolerances contributes to the variation in the critical emasures
- All input parameters are varied (one at the time) within their tolerances on 3 levels
- Max output is registered
- Contribution is calculated in percentage as %contribution=delta(output)/sum(delta(output))
Describe how stability analysis works and what it is used for
- Can be used to analyze the influence of each part locating scheme on
- variation amplification, color coding
- position stability of parts
- critical product dimension (measures) - It is done by disturbing each locating point with a unit disturbance
- summarizing their contribution with RSS
- Is often used to evaluate different positioning systems
Mention two different methods for advanced 3D computer graphics rendering!
- Ray-tracing
2. Radiosity
Mention how Ray-tracing works as rendering method toghether with pros and cons
- Follow light rays from the observer, one for each pixel
- calculate how the ray is mirrored and refracted (if the object is transparent) when it hits surfaces in the model and save the way in a tree graph
- calculate the intensity at the initial points with illumination models
- use the tree to calculate the intensities at each pixel
- Handles automatically shadows, hidden surfaces and clipping
ADVANTAGE:
- good at transparent objects
- handles specular reflection well
- good at point light sources
DISADVANTAGE:
- unnaturally sharp edges
- bad at diffuse reflection
- not good at global light source
- slow
Mention how Radiosity works as rendering method toghether with pros and cons
- Based on the effect that light sources and surfaces are emitting light
- is done by iterating the emission of light
- In the first step only surfaces with direct light are visible
- in the next step these surfaces emits light to other surfaces
- this is repeated until the result is satisfactory
ADVANTAGE:
- Good at diffuse reflection
- Gives realistic shadows
- Good at global light
DISADVANTAGE:
- Not good at speculat light
- Not good for transparent objects
- Not good at point light sources
- Slow
what are the three different types of coordinate systems used in virtually reality models? what are they used for?
- World coordinate system (w)
- -> only one in each model
- -> the position of other objects are related to this - Object coordinate system (o)
- -> one coordinate system per object in the model
- -> positions the object relative to the world coordinate system or relative to a superseding object - The coordinate system of the observer (virtual observer)
- -> makes it possible to travel around in the model
what are the industrial benefits of using parameterization to reuse engineering knowledge?
- Shorter time
- -> means more iterations, i.e. more design solutions can be evaluated - More iterations means better products
- -> larger amount of designs considered and evaluated in concept phase
- -> knowledge related to lifecycle aspects (design for: assembly, manufacturing, serviceability, environment..) can be integrated in detail design phase
- -> synthesis - analysis loops can be shortened - verification feedback instant
The Method of Influence Coefficient can be used to perform monte carlo variation simulation on non-rigid parts. How does it work?
- when doing a monte carlo variation simulation more than 1000 iterations have to be done
- to do this with traditional FE methods would take too long time
- Therefore, a FE solver is used to create a linearized model of the assembly
- The linearized model is then used in the simulations
- this gives a very large reduction of the simulation time (- a factor 1000)
- If the locators or support points are moved, anew linearization has to be done
Mention reasons for the increased industrial need for IT support for product development
- Shorter lead-times and product lifecycles
- Increased complexity: variants, functions, components
- Collaborative product development
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
