1. 3D
MODELLING
PART-4
Wikitechy

2. Microsoft most valuable professional
Microsoft web developer advisory council member
Hcl subject matter
expert
Mind cracker most
Valuable professional
Leading lights rising
Star australia champion
HCL Service delivery
Excellence award
Hcl sql knowledge champion
DNS Most valuable member

3. Primitive Instancing
In a hierachical model, there are parts that are exactly the same.
For example, all four wheels of a car can be the same model.
Instead of saving four copies of the model, we save just one primitive model and three instances
If we modify the primitive, we know that the primitive and the instances are identically changed.

4. Sweep Representations
a 2D area swept along a linear path normal to the plane of the area to create a volume
2D/3D along a trajectory through space defines a new object -- sweep

5. More representations Boundary Representations
describe object by its surface boundaries: shared edges have pointers to 2 polygons, etc.
Spatial-partitioning representations
Spatial-Occupancy Enumeration
identical solids called voxels (volume elements) arranged in a fixed regular grid.
Octrees: divide-&-conquer power of subdivision.
Binary Space-partitioning Trees: recursively divide space into pairs of subspaces, each separated by a plane. Originally used in determining visible surfaces in graphics.

6. Physics-based Modeling
Modeling triangular polyhedron: all vertices and the surrounding triangular shapes are congruent

7. Why draw 3D Models? 3D models are easier to interpret.
3D models can be used to perform engineering analysis, finite element analysis (stress, deflection, thermal…..) and motion analysis
3D models can be used directly in manufacturing, Computer Numerical Control (CNC).
Less expensive than building a physical model.
3D models can be altered easily, create more concepts
Can be used for presentations and marketing.
Ken Youssefi

8. Basics of Finite Element Analysis (FEA)
A complex problem is divided into a smaller and simpler problems that can be solved by using the existing knowledge of mechanics of materials and mathematical tools
Why FEA ?
Modern mechanical design involves complicated shapes, sometimes made of different materials that as a whole cannot be solved by existing mathematical tools.
Engineers need the FEA to evaluate their designs

9. Basics of Finite Element Analysis
The process of dividing the model into small pieces is called meshing. The behavior of each element is well-known under all possible support and load scenarios.
The finite element method uses elements with different shapes. Elements share common points called nodes.
mesh
analysis results 9

10. Introduction to Engineering, E10.
Ken Youssefi
Introduction to Engineering, E10.

11. Computer Numerical Control (CNC)
A CNC machine is an NC machine with the added feature of an on-board computer.
A solid model of the part is created. 1
Program is entered into MCU via CDs or created by onboard computer 3 2
The program path is generated by computer
Tool exchanger
Programmed instructions sent to CNC machine 5
Part is machined 6
Programmed path of cutter is displayed 4
Machine Control Unit (MCU)
CNC machine
Ken Yussefi

12. CNC Machines
Machining Centers, equipped with automatic tool changers, are capable of changing 90 or more tools. Can perform milling, drilling, tapping, boring… on many faces.

13. Creating Solid Models Parametric Modeling Concept
Parametric is a term used to describe a dimension’s ability to change the shape of model geometry if the dimension value is modified.
Feature-based is a term used to describe the various components of a model. A part can consist of various types of features such as holes, grooves, fillets, and chamfers.
Parametric models are featured-based,
parametric, solid modeling design program:
SolidWorks, Pro-Engineer, Unigraphics (CSG
and parametric), Autodesk Inventor, …..

14. Design Intent In parametric modeling, dimensions control the model.
Design intent is how your model will react when dimension values are changed.

15. Introduction to Engineering, E10.
Design Intent
The drawing shows the intent of the designer that the inclined plane (chamfer) should have a flat area measuring 2.5 inches and that it should start at a point 1.25 inches from the base of the drawing. These parameters are what the designer deemed significant for this model.
2.50
2.50
1.25
4.00
Remember that the placement of dimensions is very important because they are being used to drive the shape of the geometry. If the 2.5 in. vertical dimension increases, the 2.5 in. flat across the chamfer will be maintained, but its angle will change.
Ken Youssefi
Introduction to Engineering, E10.

16. Design Intent
In this drawing, what is important to the designer is the vertical location and horizontal dimension of the chamfer, rather than the flat of the chamfer.
2.125
2.50
1.25
4.00
2.50
4.00
1.75
30.0O
In the last drawing, the designer calls for a specific angle for the chamfer. In this case the angle of the chamfer should be dimensioned.

17. Introduction to Engineering, E10.
Design Intent
Ken Youssefi
Introduction to Engineering, E10.

18. Parametric Modeling
The true power of parametric modeling shines through when design changes need to be made. The design modification is made by simply changing a dimension. 60 10
 15 30
Pattern: 8 Holes
Since the counterbore is associated with the top surface of the ring, any changes in the thickness of the ring would automatically be reflected on the counterbore depth.

19. Sketching and Features
When discussing the mind-set needed for working with parametric modelers, two topics need to be expanded: Sketching and Features
Sketching
Take the word sketch literally. A sketch should be just that, a sketch.
When sketching it is not necessary to create geometry with accuracy. Lines, arcs, and additional geometry need not be created with exact dimensions in mind.
When the dimensions are added, the sketch will
change size and shape. This is the essence of
Parametric Modeling.
In short, the sketch need only be the approximate size and shape of the part being designed. When dimensions are added, they will drive the size and the shape of the geometry.

20. Sketching and Features
Sketched Feature
2.75
2.5
1.0
.25
.75
Create a 2D sketch.
Create a feature from the sketch by extruding, revolving, sweeping, lofting and blending.
Revolved feature
Extruded feature

21. Creating Solids - Sweep
A Sweep feature requires a profile and a path. The profile will follow the path to create the solid.
Profile (section)
Path (guide)

22. Creating Solids – Loft (different profiles)
Round profile
Square profile
Round profile
Sections (profiles) do not have to be sketched on parallel planes
All sections must be either closed or open

23. Creating Features from Sketches
Loft in SolidWorks

24. Introduction to Engineering, E10.
Applied Feature
Applied feature does not require a sketch.
It is applied directly to the model.
Fillets and chamfers are very common
applied features.
Chamfer
Fillet
Ken Youssefi
Introduction to Engineering, E10.

25. Applied Features
Shell – hollowing out a solid

26. Applied Features - Patterns
Linear (rectangular) pattern

27. Applied Features - Patterns
Linear (rectangular) pattern
Select # of features in dir. 1 and 2
Select direction 1 and 2
Select spacing in dir. 1 and 2
Select feature to pattern

28. Applied Features - Patterns
Circular (polar) pattern
Select axis of rotation
Select # of features
Select spacing between features
Select feature to pattern

29. (National Design Repository)
Motivation
Large databases of 3D models
With the advent of the world wide web, the number of available 3D models has increased substantially.
Many of these models have been collected into large databases, and in this context the challenge has changed from “How do we generate 3D models?” to “How do we find them?”
In particular, the question that I’d like to focus on in this talk is “given a 3D model, how do we find other models in the databases with a similar shape?”
Computer Graphics
(Princeton 3D Se
arch Engine)
Mechanical CAD
(National Design Repository)
Molecular Biology
(Audrey Sanderson)

30. Goal Find 3D models with similar shapes 3D Model Shape Descriptor
The classic approach for searching large databases is to design of an effective shape descriptor.
The descriptor is a structured abstraction of 3D shape allowing for the matching of different models.
In general each model in the database will be represented by its descriptor.
Then, when a query model is presented to the database, its descriptor is computed.
The descriptor is then matched against the descriptors in the database.
Finally, the nearest model, or models, in the database are returned.
In order for the descriptor to work well in practical applications it should satisfy a number of the following conditions:
3D Model
Shape Descriptor
Nearest Neighbor
Model Database

31. Research Challenge Need shape descriptor that is: Discriminating
Concise to store
Quick to compute
Efficient to match
Most importantly, the descriptor should have enough information to distinguish between models in the database that are similar to the query model and models that are different.
Nearest Neighbor
3D Model
Shape Descriptor
Model Database

32. Research Challenge Finding a 3D shape descriptor that is:
Discriminating
Concise to store
Quick to compute
Efficient to match
Because the database will contain descriptors for a large number of 3D models, we would like the descriptors to be small
3D Model
Shape Descriptor
Nearest Neighbor
Model Database

33. Research Challenge Finding a 3D shape descriptor that is:
Discriminating
Concise to store
Quick to compute
Efficient to match
Since we would like searching the database to be efficient, ideally interactive, the initial step of converting the model into its descriptor should be quick
3D Model
Shape Descriptor
Nearest Neighbor
Model Database

34. Research Challenge Finding a 3D shape descriptor that is:
Discriminating
Concise to store
Quick to compute
Efficient to match
Similarly, the retrieval of the most similar model, or models, from the database should be efficient as well.
Nearest Neighbor
3D Model
Shape Descriptor
Model Database

35. Research Challenge Finding a 3D shape descriptor that is:
Discriminating
Concise to store
Quick to compute
Efficient to match
Many possible alignments
In the context of model matching, efficiency is particularly challenging since each model in the database represents multiple copies of a single shape in all possible alignments.
3D Model
Shape Descriptor
Nearest Neighbor
Model Database

36. 3D Model Matching Approaches
Search over all possible alignments
Too slow for large database - - - -
min
Thus when we compare two models we would like them to be optimally aligned.
For example in order to match the volkswagon bug to the toon car, we would like to compare the bug to all possible alignments of the toon car, and then return the match value at the best alignment.
However, trying out all possible alignments, to find the one giving the best match, is too slow and cannot be done in real-time, applications.
Two approaches for addressing this problem have been proposed: - -

37. 3D Model Matching Approaches
Search over all possible alignments
Too slow for large database
Normalize alignment (e.g., with moments)
OK for translation and scale, not for rotation
The first approach is to place each model into a canonical coordinate system and to assume that two models are optimally aligned when each is in its own canonical frame.
For example:
Center of mass can be used to normalize for translation,
Average distance to center can be used to normalize for scale, and
Principal axes can be used to normalize for rotation
While we have found that, in practice, these methods work well for normalizing translation and scale, they do not work as well for rotation, and can result in misalignment between similar models
For example, the small differences in the shape and position of the handles results in very different alignments for the two mugs shown below.
PCA Aligned Models

38. Subscribe to our YouTube Channel
COPYRIGHTS RESERVED FROM :
Learn Technology Videos
Include our WhatsApp number in your group to get regular tech videos
Learn School Education
Subscribe to our YouTube Channel
Learn Interview Tips

39. Website : www.wikitechy.com
COPYRIGHTS RESERVED FROM :
Website :
Include our WhatsApp number in your group to get regular tech videos

40. COPYRIGHTS RESERVED FROM : WWW.WIKITECHY.COM
Thank You..!!!
Include our WhatsApp number in your WhatsApp group to get regular tech videos
Post your Questions / Queries / Doubts in our YouTube Videos. Our expert team will answer it
Website :
More details :