Solid Modeling Presentation

8/12/2019 Solid Modeling Presentation

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Recall weakness of wireframe and surface

modeling Ambiguous geometric description

incomplete geometric description

lack topological information

Tedious modeling process

Awkward user interface


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To learn how to generate solid models in

CAD

To understand how to use solid modeling

in the design process


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Solid modeling is based on complete, validand unambiguousgeometricrepresentation of physical object.

Complete points in space can beclassified.(inside/ outside)

Valid vertices, edges, faces are connectedproperly.

Unambiguous there can only be oneinterpretation of object


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Analysis automation and integration is possible

only with solid modelshas properties such as

weight, moment of inertia, mass.

Solid model consist of geometric and topologicaldata

Geometry shape, size, location of geometric

elements

Topology connectivity and associativity of geometricelements non graphical, relational information


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Autocad: Initial input defines distances

Inventor:A changeable parameter defines the

position and length of each point

Parts do not have to be redrawnwhen a designvariable is changed late in the design process.

Automatically updating modelsmake it easy to createand compare several different configurations.


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Any changes made to the 3D model automatically are updated

in the projections


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Sketch

Part:.ipt

Assembly:.iam

Drawing:.idw


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3D CAD files can be emailed to 3D rapid prototyping

facilities, who will then mail back a plastic part

Yes, model yourself and your personal action figure may soon

arrive at your door!!!


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Finite Element Analysis (FEA) which analyzes stress in parts

is taught in MAE150 and MAE133.

Interference between parts can also be calculated.


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Great Visualization

Automatic and updating drawings

Model is parametric

Rapid Prototyping3D Analysis


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1. Constructive solid geometry (CSG)

2. Boundary representation (B-rep)

3. Spatial enumeration

4. Instantiation.


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Objects are represented as a combination ofsimpler solid objects (primitives).

The primitives are such as cube, cylinder, cone,torus, sphere etc.

Copies or instances of these primitive shapesare created and positioned.

A complete solid model is constructed bycombining these instances using set specific,logic operations (Boolean)


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Boolean operation each primitive solid is assumed to be a set of

points, a boolean operation is performed on

point sets and the result is a solid model. Boolean operation union, intersection and

difference

The relative location and orientation of the two

primitives have to be defined before theboolean operation can be performed.

Boolean operation can be applied to two solidsother than the primitives.


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Union The sum of all points in each of two defined

sets. (logical OR) Also referred to as Add, Combine, Join, Merge

AB

A B


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intersection

Those points common to each of two defined

sets (logical AND)Set must share common volume

Also referred to as common, conjoin

Constructive solid geometry

(CSG)- boolean operation

ABA B


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When using boolean operation, be careful to

avoid situation that do not result in a valid

solid

Constructive solid geometry

(CSG)- boolean operation

ABA B


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Boolean operation Are intuitive to user

Are easy to use and understand

Provide for the rapid manipulation of largeamounts of data.

Because of this, many non-CSG systems

also use Boolean operations


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Data structure does not define model shape

explicitly but rather implies the geometric shape

through a procedural description

E.g: object is not defined as a set of edges & faces butby the instruction : union primitive1 with primitive 2

This procedural data is stored in a data structure

referred to as a CSG tree

The data structure is simple and stores compactdata easy to manage


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CSG tree stores the history of applying

boolean operations on the primitives. Stores in a binary tree format

The outer leaf nodes of tree represent the

primitives

The interior nodes represent the boolean

operations performed.


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+

-


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More than one procedure (and hence database)can be used to arrive at the same geometry.

-


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CSG representation is unevaluated Faces, edges, vertices not defined in explicit

CSG model are always valid Since built from solid elements.

CSG models are complete and

unambiguous


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CSG is powerful with high levelcommand.

Easy to construct a solid modelminimum step.

CSG modeling techniques lead to aconcise databaseless storage. Complete history of model is retained and can

be altered at any point.Can be converted to the corresponding

boundary representation.


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Only boolean operations are allowed in the

modeling process with boolean operation

alone, the range of shapes to be modeled is

severely restricted not possible to constructunusual shape.

Requires a great deal of computation to derive

the information on the boundary, faces and

edges which is important for the interactivedisplay/ manipulation of solid.


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CSG representation tends to accompany

the corresponding boundary

representation hybrid representation

Maintaining consistency between the two

representations is very important.

Solid Modeling Presentation

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