Tenta 101020 Flashcards
Describe the different components of the formula and what they are used for
Pi: control points, defines the curve
Bin: weight functions, defines how the different control points affect the curve
n: order of the curve
n+1: number of control points
What is the main 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
NURBS is the most commonly used type of curves In modern CAD systems. What geometrical forms can be presented with NURBS but not with Bézier or B-spline?
Bézier and B-splines can not represent conical and circular forms exactly
What cracterizes a feature (in the geometry modeling context)?
- A physical part of a detail
- it can be linked to a generic form
- it has a specific engineering role (function, manufacturing method, simulation method)
- has predictable properties
what characterizes a geometrically robust design?
A geometrically robust design is a design that allows manufacturing and assembly variation without jeopardizing function or aestetics
how does Monte Carlo simulation works?
Model consist of:
- 3D assembly model with defined locating schemes
- Input tolerances with range and type of distribution
- critical measures
simulation:
- Randomly assign one value for each input within its defined tolerance
- assemble the model according to the defined locating schemes
- calculate the critical measures and store the result
- Repeat this at least 1000 times
- calculate the distribution of the critical measures
How does stability analysis work and what is it used for?
Sensitivity analysis is used to identify sensitive areas and sensitivity factors and guides optimization of locator position.
Model consists of:
- 3D assembly model with defined
- Critical measures (not necessary for part stability)
Simulation:
- Each locating point is distrurbed with a unit disturbance
- The amplification to the output, color-coding, part position or critical product dimension is calculated
- The amplification for each individual locating point is summarized with RSS to give a value for the locating scheme
Bump-mapping as a way of using textures to give a smooth surface an irregular appearance. Describe how it works!
- It works by modifying the surface normal that is used in the illumination model
- The value of the modification is obtained from a texture
Name two methods for rendering over multiple polygon surfaces!
- Gouraud
2. Phong
Describe how Gouraud works!
- Calculate normal vector for all polygon vectors
- Calculate mean normal vectors for the vertices of the polygon
- Mean normal + illumination model –> calculation of intensities in the vertices
- intensity values are interpolated line by line over the polygon
Describe how Phong works
- calculate normal vector for all polygon surfaces
- calculate mean normal vectors for the vertices of the polygon
- surface normal are interpolated line by line over the polygon
- surface normal + illumination model –> calculation of intensities in each pixel
Describe how so called shutter glasses can be used to obtain stereo projection on an ordinary computer screen
- Gives 3D by blocking one eye at the time
- This is synchronized with the computer which alternates between view for the left and the right eye respectively
- The view are calculated with perspective projective
- The view for the left eye is calculated by moving the picture half the distance of the eyes to the left
- For the right eye the picture is moved the same distance to the right
Problems related to using CAD-systems in different functions within the company?
- Different functions uses different software requiring different file formats: problem with file conversion
- Problem with access to the right models
Describe the concepts of computer based and feature based assembly modeling
Component based assembly modeling
- The position of the part in the assembly is determined by specifying its position and orientation in global or relative coordinates
Feature based assembly modeling:
- Associates form features on different parts and handles restrictions on form, position, orientation etc. between mating form features
what is a digital mockup (DMU) and what is it used for?
A Digital mockup (DMU) is a special type of component based assembly model developed to be able to handle large assemblies (>1000 parts) from different CAD-systems
- can be used for e.g. packaging studies and assembly simulation but not for e.g. calculation of mass etc.
