systems design 2013

8/12/2019 Systems Design 2013

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Systems Engineering

Systems Engineering and Analysis

Benjamin S Blanchard & Wolter J Fabrycky


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Design from a systems perspective

A system is an assembly or combination of elements or

parts forming a complex or unitary whole.

(Power system, transportation system ..)

A system is a set of interrelated components functioning

together to achieve some common objective or purpose.


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3

Elements of a system

Black Box Recorders/DataloggersConsist Building:

Car Identification,

Numbering &

Orientation

EP Braking

Seat Reservation Displays

Destination Displays

Public Address

Doors

Engine Controls,

Traction

Maintenance

Automation

Refrigeration

Wayside Systems

Lighting

GPS Location

Signaling

Monitoring &

Diagnostics

HVAC

Dispatch &

Emergency

Communications with

Control Center

Auxiliary Power


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Elements of System

Components (operating parts of system)

Attributes (properties of the components andof the system as a whole)

Relationships (link between components sothat components operate effectively together)


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System and subsystems

A system is made up of components

Many components are broken down intosmaller components

There is a hierarchical level of components

The lower levels are called subsystems

Eg Air transport system

Aircraft, control tower, terminalssubsystems

Equipment, people, software - components


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Classification of systems

Natural systems

High degree of order equilibrium (seasons, the

food chain....

No dead ends, no waste, only continual

recirculation and regeneration

Human-made systems


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Classification of systems

Human-made systems

These are recent systems

Can impact natural systems negativelyegglobal warming


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Engineered systems

Human made systems

Designed to meet some functional purpose orobjective

Operate over a life cycle (identification ofneedphase out and disposal)

Design momentum is increased in recent

timesRequire a combination of resources (facilities,

equipment, materials, people, money...)


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Engineered systems

Composed of subsystems and related

components

Form part of a hierarchy

Are embedded into the natural world


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Product Life Cycle

Conceptual-Preliminary

Design

DetailedDesign &

Development

Productionand/or

Construction

Product use,Phase-out

and Disposal

ACQUISITION PHASE UTILISATION PHASE


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Life cycles of the system.


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Product Life Cycle

The four concurrent life cycles progress in

parallel

This is the basis of concurrent engineering

Life cycle design responds simultaneously to

customer needs and life cycle outcomes


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Technological activities and

interactions within the system life-

cycle process.


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System process activities and

interactions over the life cycle.


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System Design Considerations

Two key considerations:

Customer requirements

Design criteria (derived from key designconsiderations)


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Some system design

considerations.


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Development of Design Criteria

Design-dependent parameters (DDPs)

Parameters that the design must conform to

(weight, reliability, design life, etc...)

Technical performance measures (TPM)

Measures to which the design must perform

technically (availability, efficiency, range and

accuracy, speed....)


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A hierarchy of system design

considerations.


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Design Consideration Hierarchy

Syst

emV

alue

Economic Factors

(Life cycle cost)

Technical Factors(System effectiveness)


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Third Order Economic Considerations

Life

CycleCost

Research &Development Cost

Production Cost

Operation/utilisationcost

Maintenance &

support cost

Retirement &disposal cost


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Third Order Technical Considerations

SystemE

ffectiv

eness

Performance

Operational availability

Reliability/Dependability

Producibility

Supportability

Disposability


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Fourth Order Economic

Considerations

Research cost

Design cost

Data cost

Contractor cost

Manufacturing cost

Test & evaluation costOperating cost

Maintenance cost


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Fourth Order Technical Considerations

Size, weight, and shape

Speed of performance

Reliability

Maintainability

Ergonomics

Safety

Flexibility (adaptability)

Pollutability


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Fifth Order Considerations

Technical Factors

Accessibility

Aesthetics

Controls and displays

Energy consumption

Interchangeability

Inventory levels

Shelf life/ storage

Transportability


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Ergonomics


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Ergonomics


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Ergonomics


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Ergonomics


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Aesthetics


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Aesthetics


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Aesthetics


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Conceptual Design Phase

Identification of Need

System Feasibility Analysis

System Requirements Analysis

System Specification

Preliminary System Design

Advance System

PlanningResearch

TechnologyDevelopment &

Application


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Systems Requirements Analysis

Operational requirements

Maintenance and support requirements

Technical performance measures (TPMs)

Functional analysis and allocation (system

level)

Analysis, synthesis and evaluation


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Operational Requirements

Operational distribution or deployment# of sites and geographic distribution!

Mission profile or scenario

What functions must it perform?

Performance & related parameters

throughput, power output, size, weight Utilisation requirements

duty cycle, up time, down time

Effectiveness requirements

availability, reliability, failure rate

Operational life cycle (horizon)

Spares inventory control

Environment

temperature, shock and vibration, noise, humidity, terrain


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Maintenance and support requirements

Levels of maintenancetype of maintenance and facility location

Repair policies

design may be non-repairable, partially repairable or fully repairable

Organisational responsibilities

customer, supplier, a third party or a combination Logistic support elements

spares, test & support equipment, training etc

Effectiveness requirements

availability of spares, test equipment reliability, level of

training Environment

temperature, shock and vibration, noise, humidity, terrain


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Technical Performance Measures (TPM)

These lead to the desired characteristics that

should be incorporated into the designdesign

criteria

TPM Metric Benchmark Weighting

Velocity

(km/h)

1000 (min) 850 32

Availability

(operational)

95% 90% 45

Size (m) 30 m long

18 m wide

12 m high

20 m long

25 m wide

12 m high

13

Weight (kg) 500 kg 580 kg 10


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Functional Analysis and Allocation

System

Requir

ements

Detailed DesignCriteria

ResourceRequirements


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Functional Allocation

HighL

evelFunctions

Lower Level FunctionSubsystem 1

Lower level functionSubsystem 2

Lower level FunctionSubsystem 3


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Functional Allocation

Tract

ionSy

stem

Power System

Control system

Cooling System

Fault IndicationSystem


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Synthesis, Analysis and Evaluation

Define problem Identify measures (TPMs & DDPs)

Select appropriate evaluation techniques

Develop model to facilitate evaluation process

Acquire input data Evaluate each of the candidates

Perform a sensitivity analysis

Identify potential areas of risk

Make a recommendationTrade off analysis leads into synthesis

Synthesis is design


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This is the single most important engineering

design document.

Defines system functional baseline

Feasibility analysis

Operational requirements

Top level functional analysis

Identifies critical TPMs and DDPs


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System specification leads into one or moresubordinate specifications:

Development specificationpertains toresearch, design & development

Product specificationpertains to inventory thatcan be procured off the shelf

Process specificationpertains to services thatare performed on any component of the system

Material specificationpertains to raw material,mixtures or semi-fabricated materials that areused in the fabrication of a product

systems design 2013

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