inse6400 complex systems

8/17/2019 INSE6400 Complex Systems

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Structure of Complex System

The American Mathematician Warren WeaverIn 1948 defines three types of problems:◦ Problems of Simplicity: a few variables

◦ Problems of Disorganized Complexity: billions or

trillions of variables.◦ Problems of organized complexity: Moderate

numbers of variables

System Engineer raises the question of howdeep that understanding of a broadknowledge needs to be in the developmentof a complex system

System Engineer must recognize suchfactors as program risks, technologicalperformance limits, and interfacingrequirements, and make trade-off analysesamong design alternatives.

System building block provide an importantinsight by examining the structuralhierarchy of modern systems.

System Complexity

What Makes a System Complex?

How does Complexity evolve?

What are the ways of dealing with Complexity?

Are we gaining or losing?

• Complex: composed of interconnected or interwoven parts.

– Does not stipulate the number of interconnected parts. A

complex system may consist of a small number of parts

connected in complicated ways.

– A large number of disconnected parts is not complex system,

for example a large collection of books.

– The items that distinguish a complex system from a

collection of parts are the connections.

– The manifestation of a complex system is the dependence

upon the interfaces. – Different configurations of interfaces lead to much different

systems, different arrangements of parts constitute the same

collection

What Characterizes Complexity?

What Makes a System Complex?

1. Impossible for an individual to comprehend all of the

design; exceeds human intellectual capacity

2. Complexity is Inherent, not Accidental

– Complex problem domains• Needs and requirements change and evolve

• Difficulty expressing needs and requirements

• Expansion of previous system

– Difficulty managing development• Systems are becoming increasingly large & complex

• Coordination of large team efforts very costly

Simplification Approaches◦ Decomposition:

Algorithmic imperative: by progressive steps in ahierarchical process

Object-oriented: by tangible entities which exhibitwell-defined behaviors

◦ Abstraction:

Extraction of essential elements

Inherent in models and modeling

1.Complex Systems decomposition◦ How decompose, lots of ways, pending idea?

◦ Where do you “cut”?

◦ Decomposition is hierarchical; what defines the

levels & depths?◦ Align with specialties, functional vs. physical?

2.Every cut creates an interface◦ What are the characteristics of the interfaces

(internal/external), complexity, testability,responsibility?

3.Optimality◦ What constitutes the “best” decomposition?

◦ What is good enough?

◦ How do we recover from a bad choice?

4.What are the implications for integration &testing?◦ How do we handle testing of internal interfaces?

Are We Gaining or Losing?

• Arguably, hardware capabilities are increasing at anexponential rate.

• Software is becoming a larger part of modern systems than

it has been in the past and software is more complex

and more “opaque.”

• Technology is compounding with complex systems being

embedded in other complex systems.

• Systems engineering practices and procedures and products

appear to be evolving at a much slower rate.

Hierarchic systems are common in bothnatural and man-made systems◦ Physics: atom nucleus neutron, proton,

electron

◦ Organization: director manager general staff

◦ Book: chapter section paragraph

Model of Complex System:

◦ Consists of a number of major interacting elements◦ Majority of systems are developed by an integrated acquisition

process

Definition of System Level:

System → Subsystems → Components → Subcomponents → Parts

System – serves as parts of more complex aggregates or super-systems and perform a significant useful service with only the aidof human operators and standard infrastructure ( e.g. highways,fueling stations, communication lines, etc)

Subsystem- performs a closely related subset of the overall systemfunctions

Component- refer to a range of mostly lower level, middle ofsystem level. Perform elementary functions.

Parts- perform in combination with other parts

Systems Communicationsystems Informationsystems Materialprocessingsystem

Aerospacesystem

Sub-systems Signal networks Databases Materialpreparation

Engines

Components Signal receivers Data displays Powertransfer

Thrustgenerators

Sub-components

Signal amplifiers Cathode raytubes

Gear trains Rocketnozzles

Parts Transformer LED Gears Seals

• System Engineer’s Domain

- Extends down through the component level

- Is as detailed as a system engineer usually needs togo

- Extends across several system categories

• Design Specialist’s Domain

- Extends from the part level up through the

component level- Overlaps the domain of the systems engineers

- Is usually limited to a single technology/discipline

Knowledge domain of systems engineer and design specialist

System Decomposition

Enterprise

System/

Functional Options

Subsystem

Component/

Building Blocks

Subcomponents

Domain of theSystems Engineering

Domain of the

Technical Specialist

External Systems

Building Blocks –The Concept

• A library of commonly occurring system elements

• A means for classifying system constituents according to:

– functional characteristics

physical characteristics

• A useful tool for modeling system architecture and its

synthesis

• Useful for visualizing potential architectures of system

concepts

Functional elements◦ Signal elements: sense and communicate

information

◦ Data elements: interpret, organize, and manipulate

information◦ Material elements: provide structure and

transformation of materials

◦ Energy elements: provide energy and motive power

Physical elements◦ Electronic, electro-optical, electro-mechanical,

mechanical, thermo-mechanical, software

Signal Functional Elements

Functional Element Physical Examples

Input signal TV camera

Transmit signal Radio transmitter

Transduce signal Antenna

Receive signal Radio receiver

Process signal Image processor

Output signal TV display, speaker

Data Functional Elements

Functional element Physical Examples

Input data Keyboard

Process data CPUControl system Windows, UNIX

Control Processing Word Processor, analysis program

Store data Magnetic disk

Output data Printer, display

Material Functional Elements

Support material Airframe, auto body

Store material Container, enclosure

React material Autoclave, smelter

Form material Milling machine, foundry

Join material Welding, riveting

Control position Auto tool feed, power steering

Energy Functional Elements

Generate thrust Rocket, turbojet

Generate torque Gas turbine

Generate electricity Power plant, solar cells

Control temperature Furnace, refrigerator

Control motion Transmission, power brakes

Functional Element: Signal, Data, Material, Energy

Physical Building Blocks

Category Component Examples

Electronic Receiver, transmitter

Electro-optic Optical sensing, fiber optics

Electro-mechanical Electric generator, data storage,transducer

Mechanical Container, material processor,material reactor

Thermo-mechanical Jet & rotary engine, Heating & AC

Software Operating system, applications firmware

Physical Elements: Electronics, EO, EM, Mechanics, TM, Software

- Identifying actions capable of achievingoperational outcomes- Facilitating functional partitioning and

definition

- Identifying subsystem and componentinterfaces- Visualizing the physical architecture of the

system- Suggesting types of component

implementation technology- Helping software engineers acquire

hardware domain knowledge

Summary of Building Blocks

• Provides a structured view of the necessary knowledge base

for systems engineers

• Provides a mechanism for deductive decomposition offunctional architectures to components

• Provides a structured view of a wide variety of systems

• Provides ingredients for modeling system architecture

• Provides a strong link to the concept of object-oriented design

• Building Blocks are fundamental to the concept ofmodularization, which in turn, is fundamental to successfulsystem design.

Not easy to identify what is part of the systemand what is part of the environment

Determining criteria◦ Developmental control: do we have control over the

entity’s development? ◦ Operational control: will the tasks and missions

performed by the entity be directed by the owner of thesystem?

◦ Functional allocation: are we “allowed” to allocatefunctions to the entity in the functional definition?

◦ Unity of purpose: is the entity dedicated to the system’ssuccess

Key concept: control

Human users and operators are often treatedas external entities◦ Focus on the operator interface

◦ Still important in a functional aspect

Examples◦ Network of roads and service stations

automobile

◦ Electrical power grid data processing system

Display the external entities and theirinteractions with the system

External entities: sources for inputs into thesystem and destinations of outputs from the

system Interactions: represented by arrows, the direction

or flow of a particular interaction◦ Application or company-specific labels can be used

Five categories: data, signals, materials, energy andactivities

The system: represented by an oval in the center

Inputs and outputs◦ Operate on external stimuli and/or materials in such a manner as

to process these inputs in a useful way

System operators◦ Emphasize human-machine interface◦ Complex to define and test

Operational maintenance◦ Affect system readiness and operational reliability◦ Provide access for monitoring, testing and repair requirements

Threats◦ Either natural (e.g., salt water) or man-made (e.g., thief)

Support systems◦

Part of the infra-structure on which the system depends forcarrying out its mission

System housing: provide protection Shipping and handling environment

◦ Transport from the manufacturing site to the operating site

Instrument landing

system (ILS)

Interfaces◦ External and internal

◦ Identification and description of interfaces as partof system concept definition

◦ Coordination and control of interfaces to maintainsystem integrity

◦ Three types: connectors, isolators and converters

Interactions◦

Take place via interfaces

Type Electrical Mechanical Hydraulic Human

machine

Interactionmedium

Current Force Fluid Information

Connectors Cableswitch

Jointcoupling

Pipe valve Displaycontrol

panelIsolators RF shield

insulatorShock mountbearing

Seal Coverwindow

Converter Antenna

A/Dconverter

Gear train

piston

Reducing

valvepump

Keyboard

Though interface elements are relatively simple,

a large fraction of system failures occurs at

interfaces.38

A set or arrangement of systems that resultswhen independent and useful systems areintegrated into a larger system that deliversunique capabilities.

Characteristics◦ Operational independence of the individual system◦ Managerial independence of the individual system◦ Geographic distribution◦ Emergent behavior (not necessarily related to

component system)◦ Evolutionary development◦ Self-organization and adaptations

An airport

support trucks

baggage-handling equipment

Air traffic control Satellites,

Radars

aircraft

Shuttle bus

Consists of Multiple SoSs

Enterprise “anything that consists ofpeople, processes, technology, systems, and

other resources across organizations andlocations interacting with each other and theirenvironment to achieve a common mission orgoal

Example Government agencies and departments

Cities and countries

Chapter 3:“Structure of complex systems” ,

“Systems Engineering: Principles and Practice”

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