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ME886.3

Topic 1: System and System Design (II)

Science-based design: making a better system

Introduction: System and Design

A system is a set of elements that are

connected

An element may further be decomposed into

smaller elements; in this case, the element may

be called subsystem

Design is a decision-making process starting

from requirements to system structures

Introduction: System and Design

Requirement consists of functional requirement

(FR) and constraint requirement (CR).

FR: A function or functions a device or system has to achieve or a role or roles a device or system has to play.

CR: A condition or situation where a device or system achieves a required function.

CR has two types:

A condition must be met; for instance, the pedal of a bike must be in black color

A condition has a range; for instance, the cost of a system under design must be less than X dollars

Introduction: System and Design

Design parameter (DP):

Description of the structural element to meet both the functional and constraint requirements

Introduction: System and Design

Science-based Design

1. General design phase theory

2. Design theory and methodology

3. Design modeling and optimization

Towards a Better System

2. General design phase

Conceptual design

Embodiment design

Detailed design

Conceptual design

Develop a technical specification.

Technical specification: a document of customer’s requirement in the technical term.

Example

Customer’ s requirement:

Need a drill to penetrate common steel

Technical specification:

Be able to penetrate into the material with HRC>30This is also called DP

Conceptual design

Develop solution principle

What is solution principle: solution versus solution principle

Example

Requirement:

Rotation to translation

Solution principle:

- Crank-slider- Rack-and-pinion

Remark: for machine design, it refers to kinematic design (principal dimension is given but not material and volume)

Solution principle is DP

Making a statement of what without including the means to achieve it

Realize the rotation to translation through a linkage

Means

The means restrict the possibility of having the means of rack and pinion

Embodiment Design

Requirement:

FR: To materialize a crank-slider kinematic linkage for load of 50 KNCR: To make device as light as possible

Embodiment crank-slider linkage:

Layout is DP

Detailed Design

Develop a complete specification for each individual component ready for manufacturing

Requirement:

FR: To specify geometrical details ready for manufacturingCR: To be easy for manufacturing and assembly

Detailed piston component ready for manufacturing

Details for manufacturing are DP

Science-based Design

1. General design phase

2. Design theory and methodology

3. Design modeling and optimization

Towards a Better System

3. Design theory and methodology

General Axiom 1:

Making what to do and how to do separately. In particular while describing what it is, not be affected by how to realize it

Example (Rotation to translation)

Requirement statement:

When a rotary motor turns, it connects with a rod which further transfers motion to a slider to realize a translation …….

Requirement statement:

When a rotary motor turns, it connects with a rod which further transfers motion to a slider to realize a translation …….

The above statement has violated Design Axiom 1The above statement has violated Design Axiom 1

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Problem -0

Problem -1.1 Problem -1.2

Problem -2.1 Problem -2.2

Com

plex

ityS

impl

icity

3. Design theory and methodology

General Axiom 2: Divide and conquer

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Hold hot water

Requirement:

hold hot (~100oC) water with hand

Grasp water

Hold normal waterResist heat exchange

General Axiom 2: Divide and conquer

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Grasp water

Hold normal water

Resist heat exchange

Ceramic material

3. Design theory and methodologyGeneral Axiom 3: Generalization of design

Current design problem

Generic design problem

Other design problems along with their solutions

A solution to the current design problem

Remark: The above process is in fact an analogy process to lead to innovation

Science-based Design

1. General design process

2. Design theory and methodology

3. Design modeling and optimization

Towards a Better System

4. Design modeling and optimization

1. Mathematical model for design objects at a

different level (conceptual object, embodiment

object, detailed object)

2. Variables defined for structural features, and

mathematical relations defined for the whole

structure along with its behavior

3. Varying of the variables to seek the best behavior

5. Designer’s cognitive process

1. Team-based brain storm and white-box communication

2. Diversification in team composition and in task management

3. Confidence

4. Removal of unnecessary constraints

6. Summary

Design is a marriage of human designers and science-based processes,

Science-based processes are: general design process, design theory and methodology, and modeling and optimization,

Design theory and methodology has three general axioms.

Designer’s cognitive process includes four guidelines,