Principles of Engineering System Design

1. Principles of Engineering System Design Dr T Asokan asok@iitm.ac.in

2. INTRODUCTION TO SYSTEMS DESIGN Operational Architecture Development Dr T Asokan asok@iitm.ac.in

3. 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 T Asokan ED309

4. 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 definitionas well as trade - off decisions.

5. Major activities involved in allocated architecture Development • Allocate functions and system-wide requirements to physical subsystems • Allocate functions to components • Trace system-wide requirements to system and derive component-wide • Define and analyze functional activation and control structure • Conduct performance and risk analysis • Document architectures and obtain approval T Asokan ED309

6. T Asokan ED309

7. T Asokan ED309

8. Allocation of engg. functions to components T Asokan ED309

10. 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

11. 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

12. 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

13. 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

14. DSM for v-8 engine [ Eppinger, 1997]