1. ME886.3 Topic 1: System and System Design (II)

2. Science-based design: making a better system

3. Introduction: System and Design
A system is a set of elements that are connected in a way that meets a principle
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

4. 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.
Specific attributes are prescribed the function or role. For example the function is to support an object. The attribute of this function may be 50 KN – “support an object that is less than 50 KN.

5. Introduction: System and Design
FR(upper id, current id).{Attribute}
FR(1, 2).{Load}
1: FR at Level 1,
2: The second sub-function,
{load}: one attribute that is “load”.
Attribute:
Name | expression |
Specify how good with a function performed
Ex:
Load: >50 KN
Load: <50 KN & > 10 KN
Accuracy: ~0.05
Speed: <50 rmp

6. Introduction: System and Design
CR has two types in terms of the stringency to meet:
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.
CR can be global and local:
Global: a CR is applicable to a group of FRs.
Local: a CR is only applicable to one FR.

7. Introduction: System and Design
Ex:
Global constraint: The total weight of a system is less than 5 N.
Local constraint: color of a pedal must be red.
As regards “using foot to trigger”, it can be either specified with FR or with a separate CR.
To a brake pedal, its function is to trigger the braking mechanism. Suppose that the pedal is required to have a block color.
FR: trigger the braking mechanism.
CR (local): device should be in a black color.

8. Introduction: System and Design
As regards “using foot to trigger”, it can be either specified with FR or with a separate CR.
FR: triggering the braking mechanism with the foot.
FR: triggering the braking mechanism.
CR: with the foot.
Formalism: CR (expression for scope)
Ex:
CR1 (FR1): one CR (CR1) is applicable to FR1,
CR2 (FR1): another CR (CR2) is applicable to FR1 as well,
CR1 (SB-S1): a CR is applicable to sub-system 1,
CR1 (S1): a CR is applicable to system 1.

9. Introduction: System and Design
Design should be said:
To find a mapping from the R space to S space,
where
R: requirement (function, constraint)
S: structure
But not
To find a mapping from the F space to S space,
F: function
If design is conceptualized as an optimization problem, it is a constrained optimization problem.

10. Introduction: System and Design
Idea
Concept
Formalization or mathematics
On a side note, any theory is developed by following the above left logics.
The left logics is further triggered by our curiosity to respond to a question or to solve a problem.

11. Introduction: System and Design
Design parameter (DP):
Description of the structural element to meet both the
functional and constraint requirements
DP: Concave topology

12. Towards a Better System
Science-based Design
General design phase theory
Design theory and methodology
Design modeling and optimization
Towards a Better System

13. 2. General design phase Technical specification of requirement
Concept design
Embodiment design
Detail design

14. Technical specification of requirements
Task: 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>30

15. Concept design Example Requirement: Rotation to translation
Task: Develop the working principle of device under design from the technical specification
Example
Requirement:
Rotation to translation
Working principle is DP
Working principle:
Crank-slider, or
Rack-and-pinion
Remark: for machine design, it refers to kinematic design (principal dimension is given but not material and volume)

16. Remark:
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

17. 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

18. Detail Design Requirement:
Task: 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 description of a piston component ready for manufacturing
DP at this level: detailed information of component for manufacturing

19. FR Total FR may be fulfilled at different design phases 1 3 2 4
Concept design
Embodiment design
Design design

20. Towards a Better System
Science-based Design
General design phase
General design theory and methodology
Design modeling and optimization
Towards a Better System

21. 3. General 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

22. 3. General design theory and methodology
General Axiom 2:
Divide and conquer
Complexity
Simplicity
Problem -0
Problem -1.1
Problem -1.2
One of the motives is to
As we know,
Problem -2.1
Problem -2.2
xiao LIU

23. 3. General design theory and methodology
General Axiom 2:
Divide and conquer
X holds hot water
Requirement:
Design X to hold hot (~100oC) water with hand
Hand grasps X
X holds room temperature water
X resists heat transfer
One of the motives is to
As we know,
xiao LIU

24. 3. General design theory and methodology
X resists heat transfer
Hand grasps X
material
X holds room temperature water
One of the motives is to
As we know,
xiao LIU

25. 3. General design theory and methodology
General Axiom 3:
Generalization of design
Other design problems along with their solutions
Generic design problem
A solution to the current design problem
Current design problem
Remark: The above process is in fact an analogy process to lead to innovation

26. Towards a Better System
Science-based Design
General design process
General design theory and methodology
Design modeling and optimization
Towards a Better System

27. 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

28. 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

29. 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,