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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

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slide3

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
slide4

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.

slide5

Introduction: System and Design

  • 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
slide6

Introduction: System and Design

Design parameter (DP):

Description of the structural element to meet both the

functional and constraint requirements

slide7

Science-based Design

  • General design phase theory
  • Design theory and methodology
  • Design modeling and optimization

Towards a Better System

slide8

2. General design phase

Conceptual design

Embodiment design

Detailed design

slide9

Conceptual design

Develop a technical specification.

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

Example

Technical specification:

Be able to penetrate into the material with HRC>30

This is also called DP

Customer’ s requirement:

Need a drill to penetrate common steel

slide10

Conceptual design

Develop solution principle

What is solution principle: solution versus solution principle

Example

Solution principle is DP

Solution principle:

- Crank-slider

- Rack-and-pinion

Requirement:

Rotation to translation

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

slide11

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

slide12

Embodiment Design

Requirement:

FR: To materialize a crank-slider kinematic linkage for load of 50 KN

CR: To make device as light as possible

Embodiment crank-slider linkage:

Layout is DP

slide13

Detailed Design

Develop a complete specification for each individual component ready for manufacturing

Requirement:

FR: To specify geometrical details ready for manufacturing

CR: To be easy for manufacturing and assembly

Detailed piston component ready for manufacturing

Details for manufacturing are DP

slide14

Science-based Design

  • General design phase
  • Design theory and methodology
  • Design modeling and optimization

Towards a Better System

slide15

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 …….

The above statement has violated Design Axiom 1

slide16

Complexity

Problem -1.1

Problem -1.2

Simplicity

Problem -2.2

Problem -2.1

3. Design theory and methodology

General Axiom 2:

Divide and conquer

Problem -0

slide17

General Axiom 2:

Divide and conquer

Requirement:

hold hot (~100oC) water with hand

Hold hot water

Grasp water

Hold normal water

Resist heat exchange

slide18

Ceramic material

Resist heat exchange

Grasp water

Hold normal water

slide19

3. Design theory and methodology

General Axiom 3:

Generalization of design

Other design problems along with their solutions

Generic design problem

Current design problem

A solution to the current design problem

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

slide20

Science-based Design

  • General design process
  • Design theory and methodology
  • Design modeling and optimization

Towards a Better System

slide21

4. Design modeling and optimization

  • Mathematical model for design objects at a different level (conceptual object, embodiment object, detailed object)
  • Variables defined for structural features, and mathematical relations defined for the whole structure along with its behavior
  • Varying of the variables to seek the best behavior
slide22

5. Designer’s cognitive process

  • Team-based brain storm and white-box communication
  • Diversification in team composition and in task management
  • Confidence
  • Removal of unnecessary constraints
slide23

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,