Course Description. Spring

Course Description

• AE4375: advanced treatment for undergrads; focus on

learning and aplying CAD to engineering; CAD modeling

projects.

• AE6380: graduate course on CAD focusing on how tools

can be integrated into engineering design processes; CAD

modeling and integration projects.

• Course Outline: see class web page

• Class Schedule: see class web page

– TTh 8-9:30: lectures on geometric modeling; surface and solid models; CAD processes; integration

– CATIA Workbook: hands-on training in AE Computer Lab – CAD projects: illustrate CAD principles; reinforce training – Geometric modeling with Matlab: illustrate principles

Course Details

• Grading:

– Projects (CAD, Matlab, homework) 60%

– Midterm exam 15%

– Final exam 25%

• Course web page:

http://www.ae.gatech.edu/classes

• Academic personnel

– Course instructor: Prof. J. Craig

(x4-3042, [email protected])

– Lab instructor: Patrick Roberts

Product Development Process

• Example: aircraft wing

– Product function

• generate lift

• support static/dyn loads • be of low cost

• etc.

– Process model

• CFD (aerodynamics) • FEM (structural analysis) • Mfg. cost model • etc. – Product model • geometric model • mfg models – tolerances – assembly – feature-based geo. Product Function Product Function Design Process Models Design Process Models Design Process Models Design Process Models Product Model Product Model Design Process Design Process Mfg Process Mfg Process Factory Model Factory Model Production synthesis

Kinds of Design Models

• Product development models

– Generic product knowledge (Design Process Models) – Product models (geometric & non-geometric)

– Generic mfg process models (with physics-based and economic

models)

– Factory models (specific instances)

• Non-geometric models

– wiring schematics

– hydraulic piping diagrams – flowcharts

Some Non-geometric Models

Hydraulic Components

Other Issues

Chronological Issues: Hierarchical Issues: Conceptual Detail Conceptual Preliminary •Nongeometric •Simple •System definition •Subsystem partitioning •MDO •Geometric models •Manufacturing System Conceptual Subsystem 2 Subsystem 1 Component 1 Component 2

CAD Fundamentals

• Geometric modeling systems

– User interface – Geometry representation – Topology representation – Manipulation procedures – Database method – Data exchange

• Why 3D models aren’t more widely used in design:

– Conceptual design is concerned with functions performed by

geometry; not by the geometry itself

– Preliminary design is concerned with subsystem interface geo. – Detailed design IS concerned with microscopic geometry!

– Geo. models do not include “design intent”

– Geo. models do not identify mfg. or functional or geo. features – Tolerances are not easily handled

CAD Fundamentals - cont’d

• Why 2D drawings are still

widely used:

– They include lots of

non-geometric information in notes

– Can be sketched easily on

paper

– Familiar system

• 2D dwgs are difficult:

– Not always unambiguous – Need human interpretation

– Can’t readily be interpreted by

Basic Descriptive Geometry

• How do you draw a 3D object in 2D space (on paper)?

– Projections (axonometric, oblique, persepctive) – Multiview projections

– Conventions (1st angle vs 3rd angle)

Axonometric

Perspective

A Simple Example - Desk

Isometric Dimetric Oblique Projections Perspective Projections One Point Two Point Three Point Cavalier Cabinet

A Simple Example - Desk (cont’d)

Conventional Multi-view Orthographic Projection

Rear _{Left Side} Front Top

Right Side

Basic 3D Models

• Wireframes

– easiest of all to create – nothing hidden

– visually ambiguous – topological problems?

Wireframe Problems

Basic 3D Models

• Surface models

– accurate surface def’n – enclose a volume

– topologically difficult

to handle…

Tabulated Cylinder

(swept surface) Surface of Revolution

Ruled Surface

Swept Surface

Basic 3D Models

Basic 3D Models

• Volumes

– combine surfaces together – topology is a problem

– boundary representation

Basic 3D Models

• Boundary models (b-rep)

– aka: graph-based models – graph nodes & edges

• Rules:

– faces bounded by single loop or ring of edges

– edge joins exactly 2 faces and is terminated by vertices

– at least 3 edges meet at each vertex

– Euler’s Rule applies:

V-E+F=2

extended

Basic 3D Models

• Solid models

– Notion of inside vs outside – Analytical models (extend

surface to 3-parameters)

– Spatial decomposition or cell

enumeration

– Constructive solid geometry

(CSG)

– B-rep

Basic 3D Models

Basic 3D Models

This is a “simple” CSG object...

This is a much more comples CSG object!

(can you see why this is so?)

Solid models can have problems...

All points are surrounded by “valid” regions of the surface of the object. Some of thse points are on degenerate (2D or 1D) extensions of the object. NOTE:

By restricting the types of boolean operations that are allowed, we can avoid most of these degeneracies.

NOTE:

By restricting the types of boolean operations that are allowed, we can avoid most of these degeneracies.

Basic 3D Models

A “feature-based” approach

This is much easier to relate to common manufacturing operations and avoids creating parts that are impossible to

Basic 3D Models

Solid models are useful to show other aspects of a product - assembly.