principles of engineering system design dr t asokan [email protected] n
TRANSCRIPT
Principles of Principles of
Engineering System DesignEngineering System Design
Dr T Asokan
Six functions of Design Process
1. 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
T Asokan ED309
Operational Architecture Development
• The development process for the operational architecture ( also known as allocated architecture) is the activity during which the entire design comes together.
• It integrates the requirements decomposition with the functional and physical architectures
• It provides a complete description of the system design and provides the raw materials for the interface definition as well as trade - off decisions.
1. Allocate functions and system-wide requirements to physical subsystems
2. Allocate functions to components
3. Trace system-wide requirements to system and derive component-wide
4. Define and analyze functional activation and control structure
5. Conduct performance and risk analysis
6. Document architectures and obtain approval
T Asokan ED309
Major activities involved in allocated architecture Development
T Asokan ED309
T Asokan ED309
Allocation of engg. functions to components
T Asokan ED309
• Mapping of functions to components is chosen rather than mapping of components to functions
• Allowing two components to be mapped to same function must be avoided
• While allocation:– Try to maximise the fundamental objective– Try to minimize the number and complexity of
interfaces– Maximise early critical testing opportunities – Equalize risks across the physical architecture or – Localize risks in a single element of the physical
architecture
Approaches for solving allocation problem
• Distribution of responsibility between human and computer [Sheridian and Verplank 1978]– Human does all planning, scheduling, optimisation etc.; computer
merely does deterministic execution– Computer provides options, but the human chooses between them and
plans the operation– Computer helps to determine options and suggest one for use, which
human may or may not accept– Computer selects action and carries it out if human approves– Computer does entire task and informs human of what it has done– Computer does entire task and informs human only if requested– Computer performs entire task autonomously, ignoring human
supervisor who must completely trust the computer in all aspects of decision making
• Distribution of functions between humans and machines [Price 1985]– There is no formula for allocation; imagination is crucial to
allocation
– Allocation can be systematized; combining imagination and systematization yields superior results
– Make use of analogous technologies building upon allocation decisions and their results
– Consider future technologies; allocation decision cannot be solely based on what exists now
– Do it in stages and iterate
– Provide interaction between the three design decisions- Physical resources, functional allocation and detailed design
– Assure interdisciplinary communication
• Design Structure Matrix (DSM) for allocation– Design structure matrix is meant to capture
interactions of all sorts between functions so that intelligent combinations of functions into components can be derived
– This is a bottom-up approach to the allocation problem
– Information in the matrix provides a clue as to how to rearrange the items to form clusters
A B C D E F G H I
Engine block A A
Cylinder head
B B
Cam shaft C C
Pistons D D
Connecting rods
E E
Crank shaft F F
Fly wheel G G
lubrication H H
Water pump/cooling
I I
DSM for v-8 engine [ Eppinger, 1997]
A F G D E H
Engine block A A
Crank shaft F F
Fly wheel G G
Pistons D D
Connecting rods
E E
lubrication H I