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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,
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