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 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

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.

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

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.

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.

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.

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.

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.

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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,