How Things are Designed and How Things Move

Robert Love, Venkat Jayaraman

June 26, 2008SSTP Seminar – Lecture 3

Overview

• Organizational Details• Presentation– Design, CAD, Automobiles, Mechanisms, Dynamics

• Discussion• Activity– Brief CAD sketch– Aircraft Dynamics

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Design• Carnegie Mellon definition:

– "Design is the process of taking something from its existing state and moving it to a preferred state"

1. Problem or need is identified, often by a customer with specifications

2. Solution is designed– Conceptual Design (brainstorming, trade studies)– Preliminary Design (testing, initial modeling, performance, cost)– Detailed Design (more testing, end is final product)

3. Realization of design (production)4. Implementation to meet need5. Generally sequential, iterative

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Design in a Nutshell

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Design

• What are some methodologies?– Bio-Inspired, ergonomic, aesthetic , usability– KISS principle-No Rube Goldberg Machines!– User centered vs. Use-centered – Form vs. Function– Best way to catch a mouse?

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• Engineering drawing• CAD software• Computer aided machining• Computer aided engineering• How automobiles move

– Engine System– Manual transmission system

Overview

• Convey the following information– Geometry– Dimensions – Tolerances– Material – Finish

Engineering drawing

Why Use CAD?

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• Drawing complex parts by hand not easy• Ease of modifications• Standards • Cost Reduction

• Drafting – Autocad, Alibre, Solidedge layout• Solid Modelling – Pro E, Solidworks, Ideas,

Solidedge, Unigraphics• Analysis – Ansys, CATIA,Nisa, Nastran

CAD softwares

• CAM – Programming tool that helps manufacture physical model using CAD softwares.

• Implemented by CNC machines• CAD drawing -> G-Code ->

Computer controlled manufacturing processes such as turning and drilling

Computer aided manufacturing

• Use of information technology in tasks such as analysis, simulation and design

• CAE areas covers– Stress analysis on components - FEA (Finite element analysis) – Thermal and fluid flow analysis -CFD (Computational fluid dynamics)– Mechanical event simulation– Optimization

• Phases of CAE– Pre-processing – defining the model and environmental factors to be applied

to it – Analysis solver – High performance computers– Post processing – Visualization of results

Computer Aided Engineering (CAE)

• Engine system – Converts gasoline into motion• Four major strokes – Intake, Compression, Power and

exhaust

Engine system

Main parts of engine are

Piston

Crankshaft

Connecting rod

Valves

Ports

Sump

Spark plug

• Increasing stroke displacement• Increasing compression ratio• Cramming more air fuel mixture into

each cylinder• Cooling the incoming air• Allowing intake and exhaust mixture

to flow more easily• Lighter parts

Increasing Engine Power

• Transmits the motion from the engine to the wheels

Manual transmission

Mechanisms

• Def: Some combination of parts and linkages to perform a function

• Types of Mechanisms– Linear Motion– Rotary Motion– Intermittent Motion– Reciprocating Motion– Oscillating Motion– Irregular Motion

• Examples

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Analyzing Things

• Statics– Description of behaviors without

movement

• Dynamics– Kinematics: study of motion without

respect to the forces applied– Kinetics: study of motion under the

influence of forces

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Simplified Models

• Important Concepts:– Inertial Reference Frame vs. Body

Fixed Reference Frame– Right vs. Left Handed Coordinate

System– Scalars, Vectors and Matrices,

Coordinate Transformations, Transport Theorem

– Identify Degrees of Freedom– Dealing with Forces: Newton’s Laws– Tip: Look for symmetry!– Tip: Note assumptions!

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Flight Dynamics

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How many degrees of freedom does an aircraft have?

References• http://www.victorpest.com/mouse_instructions.htm• http://www.blendernation.com/wp-content/uploads/2007/01/mousetrap_30.jpg• http://www.aiaadbf.org/• http://en.wikipedia.org/wiki/Mechanism_(technology)• http://images.google.com/imgres?imgurl=http://upload.wikimedia.org/wikipedia/

commons/thumb/5/5d/Atlas_V_551_with_New_Horizons_on_Lauch_Pad_41.jpg/396px-Atlas_V_551_with_New_Horizons_on_Lauch_Pad_41.jpg&imgrefurl=http://commons.wikimedia.org/wiki/Image:Atlas_V_551_with_New_Horizons_on_Lauch_Pad_41.jpg&h=599&w=396&sz=65&hl=en&start=2&um=1&tbnid=NMIKH-Os41g_KM:&tbnh=135&tbnw=89&prev=/images%3Fq%3Datlas%2BV%26um%3D1%26hl%3Den%26safe%3Dactive%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-US:official%26sa%3DN

• http://www.flying-pig.co.uk/mechanisms/index.html• http://ocw.mit.edu/OcwWeb/Mechanical-Engineering/index.htm• http://www.grc.nasa.gov/WWW/K-12/airplane/rotations.html

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