1. Engineering System Design
Principles of
Engineering System Design
Dr T Asokan

2. Engineering System Design
Principles of
Engineering System Design
Lecture 4: System Design Process
Dr T Asokan
T Asokan

4. What needs are we trying to fill?
What is wrong with the current situation?
Is the need clearly articulated?
Who are the intended users?
How will they use our products?
How is this different from the present?
What specific capability will we provide?
To what level of detail?
Are element interfaces well defined?
What is the overall plan of attack?
What elements make up the overall approach?
Are these complete, logical, and consistent?
Which elements address which requirements?
Is the allocation appropriate?
Are there any unnecessary requirements?
Are the details correct?
Do they meet the requirements?
Are the interfaces satisfied?
Will the solution be satisfactory in terms of cost and schedule?
Can we reuse existing pieces?
What is our evidence of success?
Will the customer be happy?
Will the users’ needs be met?
Need
Focus of Systems Engineering
From Original Need
To Final Product
The Whole System
The Full System Life Cycle
Operations Concept
Functional Requirements
System Architecture
Allocated Requirements
Focus of Component Engineering
On Detailed Design
And Implementation
Detailed
Design
Implementation
Test & Verification

5. Six functions of Design Process
Define system level design problem : Originating requirements development
2. Develop the system functional architecture
3. Develop the system physical architecture
4. Develop the system operational architecture
5. Develop the interface architecture
6. Define the qualification system for the system

6. Operation, Maintenance Operation, Maintenance
Define
Requirements
Investigate
Alternatives
Full-Scale
Design
Implementation
Integration
& Test
Operation, Maintenance
& Evaluation
Retirement,
Disposal &
Replacement
The system
life cycle
Define
Requirements
Investigate
Alternatives
Full-Scale
Design
Implementation
Integration
& Test
Operation, Maintenance
& Evaluation
Retirement,
Disposal &
Replacement
The system
life cycle
Life cycle
Development phase, manufacturing phase, deployment phase, training phase, operation or maintenance phase, refinement, retirement phase.

7. Define System Level Design Problem
Operational Concept
External Systems
Originating Requirements
Objectives hierarchy
Documentation
Requirement management

8. Define System Level Design Problem
Major Input: Stake holders’ inputs
Major output: Originating requirements, Operational concept

9. Function Inputs Outputs Define system boundary with Ext. systems
Develop operational concept
Stakeholders’ input
Operational concept
Define system boundary with Ext. systems
System boundary, inputs, outputs.
Develop system objectives hierarchy
Oper. Concept, stakeholder input
Objectives hierarchy
Develop, analyse and refine requirements. (originating and system)
Originating and system requirements
Ensure requirements feasibility
System engg. Team input
Design feasibility
Define qualification system requirements
Test system requirements
Obtain approval of system documentation
Originating and system requirements documents

10. An operational concept is a vision for what the system is (in general terms). It is a statement of mission requirements, and a description of how the system will be used.
It includes:
Information about how the system will be developed, operated and retired (from the perspective of the system’s stakeholders).
A collection of scenarios.
Systems interaction with other systems.

11. Operational concepts for landing on the moon
T Asokan ED309

12. Operational Concept Scenario- Example: Passenger lift
Passengers (including mobility, hearing, visually challenged) request up service, receive feed back that their request was accepted, receive input that the elevator car is approaching, and then that an entry opportunity is available, enter elevator car, request floor, receive feedback that their request was accepted, receive feedback that the door is closing, receive feedback about what floor the elevator is stopping, receive feedback that an exit opportunity is available, and exit elevator with no physical impediments.
T Asokan ED309

13. Scenario 2
Emergency situation
Fire
Auto-close
Breakdown
Overload
maintenance
Scenario 3
Scenario 4
Scenario 5

14. Input/output trace for scenario 1
Scenario Description
Input/Output Trace
Passenger
Elevator
Up service request
feedback
Floor request
Input/output trace for scenario 1
Exit opportunity
T Asokan ED309

15. External Systems Diagram
It is the Model of the interaction of the system with other systems (external) in the relevant contexts, thus providing a definition of the system’s boundary in terms of the system’s inputs and outputs.
Purpose: Explicitly define the systems boundary and needed interfaces.
T Asokan ED309

16. Systems/Mechanisms
Elevator System
Passengers
Maintenance personnel
Building
System Function
Provide elevator services
Request and use elevator services
Maintain elevator services
Provide structural support

17. External Systems Diagram Building regulations
Request Elevator Services
Provide Elevator Services
Use Elevator Services
Maintain Elevator Services
Provide structural support
Elevator system
Maintenance Personnel
Building
Passengers
T Asokan ED309

20. Objectives Hierarchy
The hierarchy of objectives that are important to the system’s stakeholders in a value sense.
Stakeholders would be willing to pay to obtain increased performance on any of these objectives.
Developed by defining the natural subsets of the fundamental objectives
T Asokan ED309

21. Usually has two to five levels. Additional information
like value weights, value curves etc. are added for
each objective.
Acts as a corner stone for trade-off studies
To be developed for each phase of the life cycle of
the system.
An important tool in the decision making process

22. T Asokan ED309

23. Originating requirements
Requirements categories
Originating requirements (OR):
Derived from operational needs, operational requirements are those top-level statements defined in language that is understandable to stakeholders, leaving substantial room for design flexibility.
Derived requirements
Defined by system engineering team in engineering terms during the design process.
Mission requirements
Originating requirements
T Asokan ED309

24. Emergent Requirements
Implied Requirements
Requirements not specifically identified in the OR but can be inferred based upon the available information.
Emergent Requirements
Requirements that are not even hinted at in the OR but whose presence is made known by stakeholders later in the system engineering process.
System Requirements
Derived requirements
Component Requirements
Configuration Item Requirements

25. Originating requirements
Mission requirements
Originating requirements
System Requirements
Derived requirements
Component Requirements
Configuration Item Requirements