Georgia Tech
Aerospace Systems Engineering
A Modern Approach
Dr. Daniel P. Schrage
Professor and Director,
Center of Excellence in Rotorcraft Technology(CERT)
Center for Aerospace Systems Analysis (CASA)
School of Aerospace Engineering
Georgia Tech
Course Materials
• Primary Text, Dieter, “Engineering Design:
A Materials and Processing Approach”, 3rd
Edition, McGraw Hill, 2000
• Secondary Text,”Systems Engineering
Fundamentals” Defense Systems
Management College, 1998
School of Aerospace Engineering
Georgia Tech
The Product Design Process
(Chapter 1, Dieter)
•
•
•
•
•
•
•
•
•
•
Introduction and Importance of Product Design
The Design Process – A Simplified Approach
Considerations of a Good Design
Detailed Description of Design Process
Marketing
Organization for Design
Computer-Aided Engineering
Designing to Codes and Standards
Design Review
Technological Innovation and the Design Process
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Some Important Concepts
• Design: “ to fashion after a plan” (Webster Dictionary)
leaves out the essential fact that to design is to create
something that has never been
• Synthesis: “pulling together”
• Ability to design is both a science and an art
The science “can be learned” through techniques &
methods
The art is best “learned by doing” design
• Discovery: “getting the first sight of, or the first knowledge
of something”, as when Columbus discovered America
• Invention: requires the design be a step beyond the limits
of existing knowledge (beyond the state of the art). Some
designs are truly inventive, but most are not
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Integrated Synthesis and Analysis
Varying Fidelity of Synthesis, Sizing& Analysis
Safety
Safety
Economics
Aerodynamics
Aerodynamics
Geometry
Economics
Synthesis & Sizing
Mission
S&C
S&C
Manufacturing
Integrated Routines
Table Lookup
Structures
Conceptual Design Tools
Approximating Functions
Direct Coupling of Analyses
Performance
Manufacturing
Increasing
Sophistication and
Complexity
(First-Order Methods)
Propulsion
Performance
Structures
Preliminary Design Tools
(Higher-Order Methods)
Propulsion
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Definition of Design
(per Dieter)
• Design establishes and defines solutions to
and pertinent structures for problems not
solved before, or new solutions to problems
which have previously been solved in a
different way
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Good Design requires both Synthesis & Analysis
• Typically, we approach complex problems like design by
decomposing the problem into manageable parts or
components
– Because we need to understand how the part will perform in service
we must be able to calculate as much about the part’s behavior as
possible by using the appropriate disciplines of science and
engineering science and the necessary computational tools
– This is called Analysis and usually involves the simplification of
the real world through models
– Synthesis involves the identification of the design elements that
will comprise the product, its decomposition into parts, and the
combination of the part solutions into a total workable system
• In the typical design you rarely have a way of knowing the
correct answer. Hopefully, your design works, but is it the
best, most efficient design that could have been achieved
under the conditions? Only time will tell
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The Four Challenges (C’s) of the
Design Environment
• Creativity
– Requires creation of something that has not existed
before or not existed in the designer’s mind before
• Complexity
– Requires decisions on many variables and parameters
• Choice
– Requires making choices between many possible
solutions at all levels, from basic concepts to smallest
detail of shape
• Compromise
– Requires balancing multiple and sometimes conflicting
requirements
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Product Design Process
• Engineering design process can be applied to several
different ends
– Design of Products, whether they be consumer goods
and appliances or highly complex products such as
missile systems or jet planes
– Another is a complex engineered system such as an
electric power generating station or a petrochemical
plant
– Yet another is the design of a building or bridge
• The principles and methodology of design can be usefully
applied in each of these situations. However, the emphasis
in Dieter’s book is on product design and in this course is
complex product design, specifically Aerospace Systems
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Dieter’s Book Goal
• Provide insight into the current best
practices for doing product design
• The design process should be conducted so
as to develop quality cost-competitive
products in the shortest time possible
• Is necessary, but insufficient for Aerospace
Systems Design
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Japanese Auto Industry and The U.S. Auto Industry
U.S. Company
Japanese
Company
+3
Months
Job #1
1-3
Months
14-17
Months
90%
Total Japanese
Changes Complete
20-24
Months
Number of Engineering Product
Changes Processed
Japanese/U.S. Engineering Change Comparison
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The Quality Engineering Process
provides Recomposition Methods & Tools
Knowledge Feedback
Customer
Seven
Management
and Planing
Tools
Quality
Function
Deployment
Robust
Design Methods
(Taguchi, Six Sigma, DOE)
Statistical
Process
Control
Off-Line
Off-Line
Off-Line
On-Line
•Needs
• Identify
Important
Items
•Variation
Experiments
•Make
Improvements
•Hold Gains
•Continuous
Improvement
Having heard the “voice of the customer”, QFD prioritizes where improvements
are needed; Taguchi provides the mechanism for identifying these
improvements
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Traditional Design & Development Using only a Top
Down Decomposition Systems Engineering Process
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IPPD Environment for System Level Design Trades and
Cycle Time Reduction
CONCEPTUAL
DESIGN
(SYSTEM)
SYSTEM
PROCESS
RECOMPOSITION
SYSTEM
FUNCTIONAL
DECOMPOSITION
Process
Trades
Product
Trades
PRELIMINARY
DESIGN
(PARAMETER)
COMPONENT
PROCESS
RECOMPOSITION
Process
Trades
PRELIMINARY
DESIGN
(PARAMETER)
INTEGRATED
PRODUCT
PROCESS
DEVELOPMENT
DETAIL
DESIGN
(TOLERANCE)
COMPONENT
FUNCTIONAL
DECOMPOSITION
Product
Trades
DETAIL
DESIGN
(TOLERANCE)
Process
Trades
Product
Trades
PART
PROCESS
RECOMPOSITION
PART
FUNCTIONAL
DECOMPOSITION
MANUFACTURING
PROCESSES
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Typical System Life Cycle Cost
100%
75%
Cumulative
Percent
of LCC
Life Cycle Cost
Effectively Rendered
Unchangeable for
a Given Design
•
•
•
50%
25%
0%
Con Exp
CC04264506.ppt
•
•
•
PD & RR
E&MD
Life Cycle Cost
Actually Expended
Production, Deployment,
Operations and Support
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Ramifications of the Quality Revolution
• Decisions made in the design process cost very
little in terms of the overall product cost but have
a major effect on the cost of the product
• Quality cannot be built into a product unless it is
designed into it
• The design process should be conducted so as to
develop quality cost-competitive products in the
shortest time possible
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Georgia Tech
Design Process Paradigm Shift
(Research Opportunities in Engineering Design, NSF Strategic Planning Workshop Final
Report, April 1996)
•
•
•
•
•
A paradigm shift is underway that
attempts to change the way complex
systems are being designed
Emphasis has shifted from design for
performance to design for
affordability, where affordability is
defined as the ratio of system
effectiveness to system cost +profit
System Cost - Performance
Tradeoffs must be accommodated
early
Downstream knowledge must be
brought back to the early phases of
design for system level tradeoffs
The design Freedom curve must be
kept open until knowledgeable
tradeoffs can be made
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Static vs Dynamic Products
• Some products are static, in that the changes in
their design concept take place over a long time
period; rather, incremental changes occur at the
subsystem and component levels (most air
vehicles are static)
• Other products are dynamic, like
telecommunications systems and software, that
change the basic design concept fairly frequently
as the underlying technology changes (avionics
and mission equipment & software are dynamic)
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Georgia Tech
Simplified Design Process
•
•
•
•
•
Definition of the Problem
Gathering Information
Generation of Alternative Solutions
Evaluation of Alternatives
Communication of the Results
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Georgia Tech Generic IPPD Methodology
COMPUTER-INTEGRATED ENVIRONMENT
QUALITY
ENGINEERING METHODS
PROCESS DESIGN DRIVEN
ESTABLISH
THE NEED
DEFINE THE PROBLEM
SYSTEMS
ENGINEERING METHODS
REQUIREMENTS
& FUNCTIONAL
ANALYSIS
SYSTEM DECOMPOSITION
&
FUNCTIONAL ALLOCATION
ESTABLISH
VALUE
ROBUST DESIGN
ASSESSMENT &
OPTIMIZATION
GENERATE FEASIBLE
ALTERNATIVES
SYSTEM SYNTHESIS
THROUGH MDO
PRODUCT DESIGN DRIVEN
7 M&P TOOLS AND
QUALITY FUNCTION
DEPLOYMENT (QFD)
TOP-DOWN DESIGN
DECISION SUPPORT PROCESS
EVALUATE
ALTERNATIVE
ON-LINE QUALITY
ENGINEERING &
STATISTICAL
PROCESS
MAKE DECISION
SYSTEM ANALYSIS
&
CONTROL
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Detailed Description of Design Problems
(Morris Asimow’s Morphology of design)
•
•
•
•
•
•
•
Phase I. Conceptual Design
Phase II. Embodiment Design (Preliminary Design)
Phase III. Detail Design
Phase IV. Planning for Manufacture
Phase V. Planning for Distribution
Phase VI. Planning for Use
Phase VII. Planning for Retirement of the Product
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Discrete Steps in Engineering Design Process
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Design Depends on Individual Who Defines Problem
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Classification of Products Based on Market
• Platform Product
– Is built around a preexisting technological subsystems, e.g. Apple
Macintosh operating systems
– Is similar to a technology-push product
• Process-Intensive Products
– Manufacturing process places strict constraints on the properties of
the product
– Examples are automotive sheet, steel, food products,
semiconductors chemicals and paper
• Customized Products
– Variations in configuration and content created in response to a s
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The Total Materials Cycle
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The Systems Engineering Process
Process Input
• Customer Needs/Objectives/
Requirements
- Missions
- Measures of Effectiveness
- Environments
- Constraints
• Technology Base
• Output Requirements from Prior
Development Effort
• Program Decision Requirements
• Requirements Applied Through
Specifications and Standards
Requirements Analysis
• Analyze Missions & Environments
• Identify Functional Requirements
• Define/Refine Performance & Design
Constraint Requirement
System Analysis
& Control
(Balance)
Requirement Loop
Functional Analysis/Allocation
• Decompose to Lower-Level Functions
• Allocate Performance & Other Limiting Requirements to
All Functional Levels
• Define/Refine Functional Interfaces (Internal/External)
• Define/Refine/Integrate Functional Architecture
• Trade-Off Studies
• Effectiveness Analysis
• Risk Management
• Configuration Management
• Interface Management
• Performance Measurement
- SEMS
- TPM
- Technical Reviews
Design Loop
Synthesis
Verification
• Transform Architectures (Functional to Physical)
• Define Alternative System Concepts, Configuration
Items & System Elements
• Select Preferred Product & Process Solutions
• Define/Refine Physical Interfaces (Internal/External)
Related Terms:
Customer = Organization responsible for Primary Functions
Primary Functions = Development, Production/Construction, Verification,
Deployment, Operations, Support Training, Disposal
Systems Elements = Hardware, Software, Personnel, Facilities, Data, Material,
Services, Techniques
Process Output
• Development Level Dependant
- Decision Data Base
- System/Configuration Item
Architecture
- Specification & Baseline
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Systems Engineering, Its Purpose
To satisfy a mission need with a system
that is cost effective, operationally
suitable, and operationally effective.
CC04264864.ppt
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Systems Engineering Objectives
• Translate customer needs into balanced system/subsystem
design requirements and product
• Integrate technical inputs of the entire development
community and all technical disciplines into a coordinated
program effort
• Transition new technologies into product and abatement
program
• Ensure the compatibility of all functional and physical
interfaces
• Verify that the product meets the established requirements
• Conduct a formal risk management and
CC04264865.ppt
School of Aerospace Engineering
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What Is a System?
• A system is a collection of components
(subsystems) that
– Interact with one another
– Have emergent capabilities - capabilities above
and beyond what the same collection of
components would if they did not interact
– Interacting components implies architecture
CC04264792.ppt
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Elements of a System
• Elements
–
–
–
–
–
Equipment Hardware
Software
Facilities
Personnel
Data
• All elements are interrelated
CC04264867.ppt
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System Element Constituents
• Equipment Hardware
–
–
–
–
–
–
–
–
CC04264868.ppt
Mission hardware
Ground equipment
Maintenance equipment
Training equipment
Test equipment
Special equipment
Real Property
Spares
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System Element Constituents (cont.)
• Software
– Instructions
– Commands
– Data
• Facilities
–
–
–
–
CC04264869.ppt
Industrial
Operational
Training
Depot
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Systems Engineering Principles Apply to All Acquisition
Phases at All Levels of the Engineering Hierarchy
Levels in the
System Hierarchy
System of
systems
System
Segment
Subsegment
Item
CED - Concept Exploration/Definition
PDRR - Program Definition & Risk Reduction
CC04264029.ppt
P/D
EMD
PDRR
CED Acquisition
Phases
EMD - Engineering/Manufacturing Definition
Pre-CED
P/D - Production/Deployment
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Systems Engineering In IPD
IPD
Concurrent
Product
Development Teams
Systems
Systems
Engineering
Engineering
Process
Process
CC04264871.ppt
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Ability to Influence Cost
High
CED
PDRR
EMD
Production.
Deployment
Low
Time
CC04264872.ppt
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System Element Constituents (cont.)
• Personnel
–
–
–
–
Training
Tasks
Number
Types and skills
• Data
– Parts Manuals
– Maintenance Manuals
– Operating Manuals
CC04264870.ppt
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Systems Thinking
CC04264790.ppt
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Roles of Systems Engineers*
• Requirements Owner • Customer Interface
• Technical Manager
• System Designer
• Information Manager
• System Analyst
• Process Engineer
• Validation/Verification • Coordinator
Engr
• Classified Ads SE
• Logistics/Ops
*Source: Twelve Roles of Systems
Engineer
Engineers, Sarah Sheard
• Glue Among URL: www.software.org/pub/externalpapers/
Subsystems
CC04264791.ppt
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What Is a System?
• A system is a collection of components
(subsystems) that
– Interact with one another
– Have emergent capabilities - capabilities above
and beyond what the same collection of
components would if they did not interact
– Interacting components implies architecture
CC04264792.ppt
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Examples of Systems
• Aircraft engine vs a collection of parts
• Aircraft with engines and avionics
• Air traffic control with aircraft, airfields,
radars, controllers, CCS
• Air transportation with air traffic control,
airlines, passengers, cargo, maintenance,
pickup and delivery
CC04264793.ppt
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More Complex Systems
Systems of Systems*
• Individual systems can operate on their
own
• Systems of systems not owned and
controlled as a whole by single entity
*Mark Maier, “Architecting Principles for Systemsof-Systems”, Journal of the International Council
on Systems Engineering, Vol I, 1998
CC04264794.ppt
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Examples of Systems of
Systems
•
•
•
•
•
CC04264795.ppt
Internet
Auto and truck transportation
Air Defense System – maybe
National Airspace System (NAS)
Future Combat Systems (FCS) for
the Objective Force Brigade (Unit
of Action)
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Technical Director Is the Systems
Thinker
• If not, objectives, approaches, and
decisions will not reflect systems
thinking
• Technical Directors who don’t think
systems inhibit systems thinking on
their project
CC04264796.ppt
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Why Is Systems Thinking
Good?
• Intractable problems often have solutions in
the design space of the larger system
• Solutions in the larger systems space are
often less costly or less risky
• Integration with external systems are
addressed
early in the development
CC04264797.ppt
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A Community Example
• The Problem (or so they thought)
– Trees, fuels and other natural resources are
being used up, so we need to recycle them
• The Solution (or so they thought)
– Collect selected trash separately and sell it to
recycling facilities
CC04264798.ppt
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A Dose of Reality
• Separate trash collections for recycleable
would double the cost
• Market for recycled newspaper and
aluminum
cans was saturated
• Unsold recycleables would have to be
stored -- at additional cost
CC04264799.ppt
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Starting to Think Systems
• Who currently collects
trash?
• From whom?
• What is done with the
trash?
CC04264800.ppt
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Answers and More Questions
• Two trash collectors
– One collects from homes
– One collects from businesses
• Does the collector from businesses separate
the recycleables?
• Both put trash in land fills
• Both pay to put trash in land fills
• How much does it cost to put trash in a land
fill?
CC04264801.ppt
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The Land Fills as Part of the
System
• $17* per ton to dump trash in the land fill
• Expected to reach $30 per ton in 15 years
• Land fills charge $150 per ton in New
York
Gee, maybe we should think about
conserving the land fills?
CC04264802.ppt
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A Systems Solution
• Two collections per week
– One for recycleables
– One for non-cycleable trash
• Slight increase in fees for storing
recycleables
Market demand of recycled paper
and aluminum increase soared in 5
years
CC04264803.ppt
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Consequences of Systems
Thinking
• The original objective (saving
resources)
was satisfied
• Current costs were contained
• Future cost containment made the
slight
increase saleable to the public
CC04264804.ppt
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Dieter Chapter 2:
Need Identification and Problem Definition
• Of all the steps in the engineering design process, problem
definition is the most important
• Before the Problem-Definition Step: Design projects
commonly fall into one of five types:
–
–
–
–
–
Variation of an existing product
Improvement of an existing product
Development of a new product for low-volume production run
Development of a new product for mass production
One-of-a-kind- design
• Identifying Customer Needs
• Gathering Information from Customers
School of Aerospace Engineering
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Dieter Chapter 2:
Need Identification and Problem Definition
•
•
•
•
•
Constructing a Survey Instrument
Benchmarking
Customer Requirements
Quality Function Deployment
Product Design Specification
– The basic control and reference document for the design and
manufacture of the product
– In-Use Purposes and Market
– Functional Requirments
– Corporate Constraints
– Social, Political and Legal Requirements
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Presentation Outline
• Synthesis and Sizing of Aerospace Vehicles
• Maneuverability and Agility Considerations
for Aerial Vehicles
• Autonomous Vehicle Considerations
• Summary and Conclusions
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Synthesis and Sizing of Aerial Vehicles
• For Aerial Vehicles Synthesis and Sizing provides the
Closure between Mission Requirements and Geometric
Configuration Solutions
• A Fuel and Thrust/Power Balance Approach is used which
allows for analytical design optimization (min. GW, etc.)
through the coupling of a few critical design parameters
(FW~aspect ratio, wing loading; RW~disk loading)
• Maneuverability and Agility can be related to Energy
Principles (differences between Thrust/Power Available
and Thrust/Power Required), Handling Qualities and the
design of the Flight Control System
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Maneuverability and Agility
Considerations for Aerial Vehicles
• Fixed Wing Fighter Aircraft normally have a good high speed
capability, good maneuverability at normal combat speeds (medium to
high subsonic and transonic speeds), high specific excess power, good
to excellent avionics, and the ability to employ guns and a wide range
of air-to-air missiles. To achieve these capabilities, their optimum
maneuvering speeds are usually rather high, impacting on low speed
maneuverability
• Rotary Wing Aircraft have excellent low speed capability due to the
rotor hub control moments which provides excellent control power in
any axix. This allows rotary wing aircraft to fly Nap-of-the-Earth and
stress aggressive concealed movement to take full advantage of
masking provided by trees and terrain and attacking from a position of
advantage at maximum standoff range
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Summary and Conclusions
• Aerial Vehicle Design and Performance is highly
dependent on the Mission identified and use of a Fuel and
Thrust/Power Synthesis Approach
• For high speed, high altitude, high maneuvering attack
missions, such as Suppression of Enemy Air Defense
(SEAD), Fixed Wing Aerial Vehicle are the Choice
• For low speed, low altitude, high agility(along with
vertical takeoff and landing (VTOL)capability)
reconnaissance and attack missions, such as Urban
Warfare, Rotary Wing Aerial Vehicles are the Choice
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Technological Innovation and The Design Process
• The advancement of technology has three phases:
– Invention: The creative act whereby an idea is conceived
– Innovation: The process by which an invention or idea is brought
into successful practice and is utilized by the economy
– Diffusion: The successive and widespread initiation of successful
innovation
• The technological innovation activity can considered to be:
Ident. Of
Mkt Need
Product
idea
Develop
ment
Pilot
lot
Trial
sales
Commerc
Exploitation
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Successful products delineate four factors that
lead to success
1.
Product planning and research: Products where adequate
time was spent in problem definition & concept development
2.
Product superiority: Having a superior high-quality product
that delivers real value to the customer makes all the differences
between winning and losing
3.
Quality marketing: High in importance is how well the
marketing activities were executed from concept of the idea to the
launch of the product in the marketplace
4.
Proper organizational design: Successful products are most
often developed by a cross-functional team, led by a product
champion, supported by top management, and accountable for the
entire project from beginning to end
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Product and Process Cycles
• Product Life Cycle and Cash Flow Analysis
• Technology Development Cycle and S- Curves
• Process Development Cycle
– Uncoordinated development
– Segmental development
– Systematic development
• Producition and Consumption Cycle
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Societal Considerations in Engineering
• Characteristics of an Environmentally
Responsible Design
• Five roles of government in interacting with
technology
• Technology Identification, Evaluation and
Selection (TIES)
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Dieter: Chapter 3
Team Behavior and Tools
• A team is a small number of people with complementary skills who are
committed to a common purpose, performance goals, and approach for
which they hold themselves mutually accountable
Differences between a working group and a team
Working Group
-Strong, clearly focused leader
-The group,s purpose is the
Same as the broader org.msn.
- Individual work products
- Runs efficient meetings
Team
-Individual & mutual accountability
- Specific team purpose that the team
Itself develops
- Collective work products
- Encourages open-ended discussion
and active problem-solving meetings
- Measures its effectiveness
- Measures performance directly by
indirectly by its influence
assessing collective work products
-Discusses,decides and delegates - Discusses, decides and does real work
together
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Dieter: Chapter 3
Team Behavior and Tools
• What It Means to be an Effective Team Member
–
–
–
–
Take responsibility for the success of the team
Be a person who delivers on commitments
Be a contributor to discussions
Give your full attention to whomever is speaking and demonstrate this by asking
helpful questions
– Develop techniques for getting your message across to the team
– Learn to give and receive useful feedback
• The following are characteristics of an effective team:
–
–
–
–
–
–
Team goals are as important as individual goals
The team understands the goals and is committed to achieving them
Trust replaces fear and people feel comfortable taking risks
Respect, collaboration and open-mindedness are prevalent
Team members communicate readily; diversity of opinions are encouraged
Decisions are made by consensus and have the acceptance and support of the
members of the team
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Dieter: Chapter 3
Team Behavior and Tools
• TEAM ROLES: Within a team members assume different
roles in addition to being an active team member
• TEAM DYNAMICS:Students of team behavior have
observed that most teams go through five stages of
development
• EFFECTIVE TEAM MEETINGS: Students who complain
about design projects taking too much time often are really
expressing their inability to organize their meetings and
manage their time effectively
• PROBLEMS WITH TEAMS: A well-functioning team
achieves its objectives quickly and efficiently in an
environment that induces energy and enthusiam
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Dieter: Chapter 3
Team Behavior and Tools
• PROBLEM SOLVING TOOLS
• TIME MANAGEMENT
• PLANNING AND SCHEDULING
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Dieter: Chapter 5
Concept Generation and Evaluation
• With a clear product design specification developed in
Chap. 2 we have arrived at the point where we are ready to
generate design concepts, evaluate them, and decide which
one will be carried forward to a final product
• The principle that grades this work is that put forth by the
American architect-engineer Louis Henri Sullivan, “form
follows function”
• By this we mean, if the functions of the design are clearly
understood, then its appropriate form or structure will be
easier to determine
School of Aerospace Engineering
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Dieter: Chapter 5
Concept Generation and Evaluation
• A design concept is an idea that is sufficiently developed
that it can be evaluated in terms of physical realizability,
i.e., the means of performing each major function has been
determined
• The process that is applied in this chapter will result in the
generation of multiple design concepts
• Then, with a set of design concepts we will subject them to
an evaluation scheme to determine the best concept or
small subset of best concepts
• Finally, a decision process will be used to decide on the
best concept to develop into the final design
School of Aerospace Engineering
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Dieter: Chapter 5.2 -Creativity and Problem Solving
– Creative thinkers are distinguished by their ability to synthesize new
combinations of ideas and concepts into meaningful and useful forms
– A characteristic of the creative process is that initially the idea is only
imperfectly understood
– Usually the creative individual senses the total structure of the idea but
initially perceives only a limited number of the details
– The creative process be viewed as moving from an amorphous idea to a
well-structured idea, from the chaotic to the organized, from the implicit
to the explicit
– Engineers, by nature and training, usually value order and explicit detail
and abhor chaos and vague generality
– To achieve a truly creative solution to a problem a person must utilize two
thinking styles: vertical or convergent thinking and lateral or divergent
thinking
– Vertical thinking is the type of analytical though process reinforced by
most engineering courses where one moves forward in sequential steps
after a positive decision has been made about the idea
– In lateral thinking your mind moves in may different directions,
combining different pieces of information into new patterns (synthesis)
until several solution concepts appear
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Dieter: Chapter 5.3 -Creativity Methods
5.4 – Creative Idea Evaluation
• Mental Blocks: Perceptual blocks, Emotional blocks, Cultural blocks,
Environmental blocks, Intellectual blocks
• Brainstorming: Carefully define the problem at the start; Allow 5
minutes for each individual to think the problem on their own before
starting the group process; SCAMPER checklist to aid in
brainstorming
• Synectics: technique for creative thinking which draws on analogical
thinking – Direct analogies, Personal analogies, Symbolic analogies,
Fantasy analogies
• Force-Fitting Methods: SCAMPER is one of most widely used
methods
• Mind Map: Concept map
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Dieter: Chapter 5.5: Theory of Inventive Problem
Solving (TRIZ)
• Developed in Russia, starting around 1946, Genrich
Altshuller,etc. Studied over 1.5 million patents
• They organized the problem solutions from the patent
literature into five levels:
– Level 1: Routine design solutions (~30%)
– Level 2: Minor corrections to an existing system (~45%)
– Level 3: Fundamental improvements which resolve contradiction
(~20%) This is where creative design solutions would appear
– Level 4: Solutions based on appln of new scientific principle to
perform the primary functions of the design (~4%)
– Level 5: Pioneering inventions based on rare scientific discovery
(<1%)
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Dieter: Chapter 5.6: Conceptual Decomposition
• Two chief approaches to conceptual decomposition:
– Decomposition in the physical domain
– Decomposition in the functional domain – the great advantage of
functional decompostion is that the method facilitates the
examination of options that most likely would not have been
considered
• Decomposition in the Physical Domain: an important
emerging design consideration is product architecture –
scheme by which the functional elements of the product
are arranged into physical building blocks
• Functional Decomposition: system’s functions are
described as a transformation between an initial state and a
desired final state; originated with the German school of
design methodology
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Dieter: Chapter 5.7: Generating Design Concepts
• Concept Development
• Morphological Chart
• Combining Concepts
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Dieter: Chapter 5.8: Axiomatic Design
• Axiom 1: The independence axiom
– Maintain the independence of functional
requirements (FRs)
• Axiom 2: The information axiom
– Minimize the information content
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Dieter: Chapter 6
Embodiment (Preliminary) Design
• Many U.S. writers divide the design process into 3 phases:
– Conceptual Design
– Preliminary (Embodiment) Design
– Detail Design
• Others call embodiment design “analytical design” because it is the
design phase where most of the detailed analysis and calculation
occurs
• Dieter adopts the terminology conceptual design, embodiment design,
and detail design because they seem to be more descriptive of what
takes place in each of these design phases
• Moving the setting of dimensions and tolerances into embodiment
design (from detail design) is in keeping with the current trend for
utilizing CAE so as to move the decision making as early as possible in
the desing process to compress the product development cycle
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Dieter: Chapter 6
• Three different forms of design:
– Routine design: the attributes that define the design and the
strategies and methods for attaining them are well known
– Innovative design: not all attributes of the design may be known
beforehand, but the knowledge base for creating the design is
known
– Creative design: neither the attributes of the design nor the
strategies for achieving them are known ahead of time
• The Conceptual design phase is most central to innovative
design
• At the opposite pole is selection design or catalog design,
which is more central to routine design
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Dieter: Chapter 6
Product Architecture
• Product architecture is the arrangement of the physical elements of a
product to carry out its required functions
• It is in the Embodiment design phase that the layout and architecture of
the product must be established by defining what the basic building
blocks of the product should be in terms of what they do and what their
interfaces will be between each other. Some organizations refer to this
as system-level design
• There are two entirely opposite styles of product architecture, modular
and integral:
– Modular: components (chunks) implement only one or a few functions
and the interactions are well defined
– Integral: implementation of functions uses only one or a few components
(chunks) leading to poorly defined interactions between components
(chunks)
• In integral product achitectures components perform multiple functions
• Products designed with high performance as a paramount attribute
often have an integral architecture
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Dieter: Chapter 6
Product Architecture
• A modular design makes it easier to evolve the design over time, to
adapt it to the needs of different customers, to replenish components as
they wear out or are used up, and to reuse the product at the end of its
useful life by remanufacture
• Modular design may even be carried to the point of using the same
component in multiple products, a product family
• Integral desing is often adopted when constraints of weight,k space, or
cost require that performance be maximized
• There is a natural tension between component integration to minimize
costs and product architecture
• The best approach is to consider integration of components only within
a single chunk (set of components) of the product architecture
• Thus, the product architecture has strong implications for
manufacturing costs
• A modular architecture tends to shorten the product development cycle
becasuse module can be deveolped independently provided there is not
coupling of functon betgween modules, and provided that interfaces
are well laid out and understood
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Dieter: Chapter 6
Product Architecture
• Four step process for establishing the product architecture
– Create a schematic diagram of the product (FFBD, Schematic
Block Diagram)
– Cluster the elements of the schematic (DSM, DeMAID)
– Create a rough geometric layout (3-view drawing)
– Identify the fundamental and incidental interactions
(Interrelationship Diagraph, Compatibility Matrix)
• SEE EXAMPLES FROM TEXT
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Dieter: Chapter 6
Configuration Design
• In configuration design we establish the shape and general dimensions
of components. Exact dimensions and tolerances are established in
parametric design
• The term component is used in the generic sense to include specialpurpose parts, standard parts, and standard assemblies or modules
• A part is a designed object that has no assembly operations in its
manufacture
• A standard part is one that has a generic function and is manufactured
routinely w/o regard to a particular product (bolts, washers, etc.)
• A special-purpose part is designed and manufactured for a specific
purpose in a specific product line
• An assembly is a collection of two or more parts
• A subassembly is an assembly that is included within another assembly
or subassembly
• A standard assembly or standard module is an assembly or
subassembly which has a generic function and is manufactured
routinely (electric motors, pumps, etc.)
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Dieter: Chapter 6
Configuration Design
• Steps in starting Configuration design:
– Review the PDS
– Establish the spatial constraints that pertain to th product or the
subassembly being designed. Most have been set by the product
architecture
– Create and refine the interfaces or connections between
components
– Maintain functional independence in the design of an assembly or
component
– Answer the following questions:
• Can the part be eliminated or combine with another part?
• Can a standard part or module be used
• Generally, the best way to get started with configuration design is to
just start sketching alternative configurations of a part
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Dieter: Chapter 6
Parametric Design
• In configuration design the emphasis was on starting with
the product architecture and then working out the best form
for each component
• In parametric design the attributes of parts identified in
configuration design become the design variables for
parametric design
• A design variable is an attribute of a part whose value is
under the control of the designer
• Robustness means achieving excellent performance under
the wide range of conditions that will be found in service
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Dieter: Chapter 6
Parametric Design
• Read Table 6.2: Questions for revealing part configuration
design risks
• Failure Modes and Effects Analysis (FMEA)
• Design for Reliability
• Robust Design
• Tolerances
• Design Guidelines for Best Practices
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Dieter: Chapter 7
Modeling and Simulation
• The Role of Models in Engineering Design
–
–
–
–
–
–
–
Descriptive model
Predictive model
Static or dynamic
Deterministic or probabilistic
Iconic-analog-symbolic
Simulation
The Prototype
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Dieter: Chapter 7
Modeling and Simulation
• Mathematical Modeling
– The components of a system are represented by idealized elements
that have the essential characteristics of the real components and
whose behavior can be described by mathematical equations
– Techniques for treating large and complex systems by isolating the
critical components and modeling them are at the heart of the
growing discipline called systems engineering
– Important simplification results when the distributed properties of
physical quantities are replaced by their lumped equivalents.
– A system is said to have lumped parameters if it can be analyzed in
terms of the behavior of the endpoints of a finite number of
discrete elements
– Once the chief components of the system have been identified, the
next step is to list the important physical and chemical quantities
that describe and determine the behavior of the system
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Dieter: Chapter 7
Modeling and Simulation
• Dimensional Analysis
– Buckingham Pi Theorem
• Similitude and Scale Models
– Scale models
– Geometric similarity
• Model dimension = scale factor x prototype dimension
– Static similarity-same portion as geometric dim under cons. stress
– Kinematic similarity- ratio of time proportionality
– Dynamic similarity- fixed ratio of forces
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Dieter: Chapter 7
Modeling and Simulation
• Simulation
– Finite-Difference Method
• A method of approximate solution of partial differential equations
– Monte Carlo Method
• A way of generating information for a simulation when events occur
in a random way
– Geometric Modeling on the Computer
• From it initiation,CAD has promised 5 important benefits to the
engineering design process
– Automation of routine design tasks
– Ability to design in 3D
– Design by Solid Modeling
– Electronic transfer of the design db to manuf (CAD/CAM)
– A paperless design process
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Dieter: Chapter 7
Modeling and Simulation
•
•
•
•
Surface Modeling
Methods of Generating Solids
Constraint-Based Modeler and Features
Finite-Element Analysis
– Types of Elements
– Steps in the FEA Process
• Preprocessing: Geometry, Matl constit reln, FE mesh, Bndy Conds
• Postprocessing: Data interpret., Error estim., Design optim
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Dieter: Chapter 7
Modeling and Simulation
• Computer Visualization
– Dynamic Analysis
– Interactive Product Simulation
• Rapid Prototyping
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Dieter: Chapter 8
Materials Selection and Materials in Design
• The selection of the correct materials for a design is a key step in the
process because it is the crucial decision that links computer
calculations and lines on an engineering drawing with a working
design
• Materials, and the manufacturing processes which convert the material
into a useful part, underpin all engineering design
• The adoption of concurrent engineering methods has brought materials
engineers into the design process at an earlier stage, and the
importance given to manufacturing in present day product design has
reinforced the fact that materials and manufacturing are closely linked
in determining final product performance
• The extensive activity in materials science worldwide has created a
variety of new materials and focused our attention on the competition
between six broad classes of materials: metals, polymers, elastomers,
ceramics, glasses, and composites
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Relation of Materials Selection to Design
– An incorrectly chosen material can lead not only to failure of the
part but also to unnecessary life-cycle cost
– Selecting the best material for a part involves more than selecting a
material that has the properties to provide the necessary
performance in service; it is also intimately connected with the
processing of the material into the finished part (Fig. 8.1)
– As design proceeds from concept design, the material and process
selection becomes more detailed
– Figure 8.2 compares the design methods and tools used at each
design stage with the materials and processes selection
– Thus, material and process selection is a progressive process of
narrowing from a large universe of possibilities to a specific
material and process selection
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Dieter: Chapter 8
Materials Selection and Materials in Design
• General Criteria for Selection: Materials are selected on
the basis of four general criteria:
–
–
–
–
Performance characteristics (properties)
Processing characteristics
Environmental profile
Business considerations
• The chief business consideration that affects materials
selection is the cost of the part that is made from the
material
• This considers both the purchase cost of the material and
the cost to process it into a part. A more rational basis for
selection is life cycle cost (LCC), which includes the cost
of replacing failed parts and the cost of disposing of the
material at the end of its useful life
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Performance Characteristics of Materials
– The performance or functional requirements of material usually is
expressed in terms of physical, mechanical, thermal, electrical, or
chemical properties
– Material properties are the link between the basic structure and
composition of the material and the service performance of the part
(Figure 8.3)
– We can divide structural engineering materials into metals,
ceramics, and polymers; Further division leads to the categories of
elastomers, glasses, and composites; Finally, there is the
technology driving class of electronic, magnetic, and
semiconductor materials
– The chief characteristics of metals, ceramics, and polymers are
given in Table 8.1
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Performance Characteristics of Materials
– The ultimate goal of materials science is to predict how to improve
the properties of engineering materials by understanding how to
control the various aspects of structure
– Figure 8.4 relates various dimensions of structure with typical
structural elements
– The first task in materials selection is to determine which material
properties are relevant to the situation
– Figure 8.5 shows the relations between some common failure
modes and the mechanical properties most closely related to the
failures
– The material properties usually are formalized through
specifications: Performance and Product specifications
– Table 8.2 provides a fairly complete listing of material
performance characteristics
– Figure 8.6 illustrates the generic tree that is developed by
expanding the category of fatigue properties
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Dieter: Chapter 8
Materials Selection and Materials in Design
• The Materials Selection Process
– The problem is not only often made difficult by insufficient or
inaccurate property data but is typically one of decision making in
the face of multiple constraints without a clear-cut objective
function
– A problem of materials selection usually involves one of two
different situations
• Selection of the materials for a new product or design
• Reevaluation of an existing product or design to reduce cost,
increase reliability, improve performance, etc.
– It generally is not possible to realize the full potential of a new
material unless the product is redesigned to exploit both the
properties and the manufacturing characteristics of the material
– In other words, a simple substitution of a new material without
changing the design rarely provides optimum utilization of the
material
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Materials selection for a new product or new design: The steps that
must be followed are:
–
–
–
–
–
Define the functions that the design must perform
Define the manufacturing parameters
Compare the needed properties and parameters with large database
Investigate the candidate materials in more detail
Develop design data and/or a design specification
• Materials substitution in an existing design
– Characterize the currently used material in terms of performance,
manufacturing requirements, and cost
– Determine which characteristics must be improved for enhanced product
function
– Search for alternative matls & processing routes
– Compile a short list of matls & processing routes and use these to estimate
the costs of manufactured parts
– Evaluate the results of Step 4 & make a recommendation for a
replacement material
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Design Process and Materials Selection
– There are two approaches to determing the material-process
combination for a part
• Material first approach: the designer begins by selecting a material
class and narrowing it down
• Process first approach: the designer begins by selecting the
manufacturing process
– While materials selection issues arise at every stage in the design
process, the opportunity for greatest innovation in materials
selection occurs at the conceptual design stage
– Ashby Charts: Figure 8.7a: Young’s modulus vs density; Figure
8.7b: Strength vs density
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Materials Selection in Embodiment (Preliminary) Design
– Detailed materials selection is typically carried out in the
embodiment design phase using the process illustrated in Fig. 8.8
– When the material process selection is deemed adequate for the
requirements, the process passes to a detailed specification of the
material and the design
– Once the component goes into production, the early runs will be
used to fine tune the manufacturing process and to gauge the
market receptivity to the product
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Sources of Information on Materials Properties
– The purpose of this section is to provide a guide to material
property data that are readily available in the published technical
literature
– Scatter or variability of material property results is considerable,
however, it is rare to find a property data presented in a proper
statistical manner by a mean value and the standard deviation (See
Chap. 10)
– Obviously, for critical applications in which reliability is of great
importance, it is necessary to determine the frequency distribution
of both the material property and the parameter that describes the
service behavior
– Figure 8.9 shows that when the two frequency distributions
overlap, there will be a statistically predictable number of failures
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Sources of Information on Materials Properties
– Conceptual Design
• Typical material selection references, such as Ashby scheme
– Embodiment (Preliminary) Design
• Design decisions are being made on the layout and size of parts and
components
• Design calculations require materials properties for a narrower class of
materials but specific to a particular heat treatment or manufacturing process
• These data are typically found in handbooks and computer dbs.
– Detail Design
• Very precise data is required
• This goes beyond just material properties to include information on
manufacturability, cost, the experience in other applns, avail in the sizes and
forms needed, and issues of repeat. of properties & QA
• Two often overlooked factors are whether the manufacturing process will
produce different properties in different directions in the part, and whether the
part will contain a detrimental state of residual stress after manufacture
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Economics of Materials
– Ultimately the decision on a particular design will come down to a
trade-off between performance and cost
– Where performance doesn’t dominate the manufacturer must
provide a value to cost ratio that is no worse, and preferably better,
than the competition
– By value we mean the extent to which the performance criteria
appropriate to the application are satisfied. Cost is what must be
paid to achieve that level of value
– Because cost is such an overpowering consideration in material
selection we need to give this factor additional attention
- Scarcity
- Cost & amount of energy required to process
- Basic supply & demand for the material
- Increases in properties, like yield strength, beyond those of the
basic material are produced by changes in structure brought about
by compositional changes and additional processing steps
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Methods of Materials Selection
– There is no method or small number of methods of materials
selection that has evolved to a position of prominence
– Since the final choice is a trade-off between cost and performance
(properties), it is logical to attempt to express that relation as
carefully as possible
– Figure 8.10 shows the costs of substituting lightweight magterials
to achieve weight saving (fuel economy) in automobiles
– It is important to realize that the cost of a material expressed in
dollars per pound may not always be the most valid criterion
– Total LLC is the most appropriate cost to consider
– Consideration of factors beyond just the initial materials cost leads
to relations like the relation shown in Figure 8.11
– A classic situation regarding cost is the choice between two or
more materials with different initial costs and different expected
lives. This is a standard problem in the field of engineering
economy (See Chap. 13)
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Selection with Computer-Aided Databases
– Use of a Merit Factor approach similar to an OEC
• Material Performance Indices
– A materials performance index is a group of material properties
which governs some aspect of the performance of a component
• Decision Matrices
– Pugh Selection Method
– Weighted Property Index
• Materials Selection by Expert Systems
• Value Analysis
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Dieter: Chapter 8
Materials Selection and Materials in Design
• Design for Brittle Fracture: An important advance in
engineering knowledge has been the ability to predict the influence of
cracks and crack-like defects on the brittle fracture of materials
through the science of fracture mechanics
• Design for Fatigue Failure: Materials subjected to a repetitive
or fluctuating stress will fail at a stress much lower than required to
cause fracture on a single application of load
• Infinite-life design
• Safe-life design
• Fail-safe design
• Damage-tolerance design
– Design for Corrosion Resistance
– Designing with Plastics
– Designing with Brittle Materials
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Dieter: Chapter 9
Materials Processing and Design
• Role of Processing in Design
– Producing the design is a critical link in the chain of events that
starts with a creative idea and ends with a successful product in the
marketplace
– A serious problem has been the tendency to separate the design and
manufacturing functions into separate organizational units
– More conventional manufacturing is divided into (1) process
engineering, (2) tool engineering, (3) work standards, (4) plant
engineering, and (5) administration and control
– We ordinary think of modern engineering in terms of the
automotive assemble line, but mass production manufacturing
systems account for less than 25 percent of metal pars
manufactured
– The major opportunity for greatly increasing manufacturing
productivity in small-lot manufacture
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Dieter: Chapter 9
Materials Processing and Design
• Classification of Manufacturing Processes
– Solidification (casting) processes
– Deformation processes
– Material removal or cutting (machining) processes
– Polymer processing
– Powder processing
– Joining processing
– Heat treatment and surface treatment
– Assembly processes
• Types of Process Systems
– Job shop- Assembly line
– Batch - Continuous flow
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Dieter: Chapter 9
Materials Processing and Design
• Factors Determining Process Selection
– Cost of manufacture and life cycle cost
– Quantity of parts required
– Complexity – shape, form, size
– Material
– Quality of part
– Availability, lead time, and delivery schedule
• Design for Manufacturability (DFM)
– DFM Guidelines (Min tot # of parts; Standardize
comps; Use common parts across product lines; Design
parts to be multifcnl; Design parts for ease of fab.;
Avoid too tight tolerances; Avoid secondary opns;
Utilize the special characteristics of processes)
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Dieter: Chapter 9
Materials Processing and Design
• Design for Assembly (DFA)
– The assembly process consists of two operations,
handling followed by insertion
– There are three types of assembly, classified by the
level of automation
– A list of DFA guidelines are:
•
•
•
•
•
•
Min. the tot. no. of parts
Min. the assembly surfaces
Avoid separate fasteners
Min. assembly direction
Max. compliance in assembly
Min handling in assembly
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Dieter: Chapter 9
Materials Processing and Design
• Early Estimation of Manufacturing Cost
– The decisions about materials, shape, features and tolerances that
are made in the embodiment phase of design determine the
manufacturing cost of the product
– It is not often possible to get large cost reductions once production
has begun because of the high cost of change at this stage of the
product life cycle
– Therefore, we need a way of identifying costly designs as early as
possible in the design process
– One way is to include knowledgeable manuf psnl on IPT
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Dieter: Chapter 10
Engineering Statistics
• Statistics and Design
– Since in engineering design we typically deal with poorly defined
situations or are forced to use data that have low precision, it is
easy to appreciate how the proper application of statistical analysis
can help greatly with engineering design
– At least four major aspects of statistical analysis are important in
engineering design
• Hypotheses tests
• Confidence limits
• Analysis of variance
• Statistical design of experiments
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Dieter: Chapter 10
Engineering Statistics - Probability
• A basic underlying assumption of probability theory is that
it deals with random events
• A random event is one in which the conditions are such
that each member of the population N has an equal chance
of being chosen
• A special and precise system of language and notation is
used in probability theory
• Two events A and B are said to be independent if the
occurrence of either one has no effect on the occurrence of
the other
• Two events that have no elements in common are said to
be mutually exclusive events
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Dieter: Chapter 10
Engineering Statistics – Errors and Samples & Frequency
Distribution
• The act of making any type of experimental observation
involves two types of errors:
– Systematic errors (which exert a nonrandom basis)
– Experimental,or random, errors
• When a large number of observations are made from a
random sample, a method is needed to characterize the
data
– Histograms,
– Frequency Distribution
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Dieter: Chapter 10
Engineering Statistics – Measures of Central Tendency &
Dispersion
• A frequency distribution can be described with numbers
that indicate the central location of the distribution and
how the observations are spread out from the central
location (dispersion)
– Arithmetic mean, or average
– Mode and Median
– Standard Deviation
– Range
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Dieter: Chapter 10
Engineering Statistics – Types of Distributions
• Normal and Lognormal Distributions
– Many physical measurements follow the symmetrical, bell-shaped
curve of the normal, or Gaussian, frequency distribution
• Weibull Distribution
– Widely used for many engineering problems because of its
versatility, since many random variables follow a bounded,
nonsymmetrical distribution, such as fatigue life of components
• Gamma Distribution
– Used to describe random variables that are bounded at one end
• Exponential Distribution
– Special case of the gamma distribution for η = 1
• Distributions for Discrete Variables
– The normal and other distributions discussed deal with continuous
random variables;however, there are important engineering
problems in which the random variable takes on only discrete
values
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Dieter: Chapter 10
Engineering Statistics – Sampling Distributions
• The central problem in statistics is relating the population
and the samples that are drawn from it
• This problem is viewed from two perspectives:
– What does the population tell us about the behavior of the samples
– What does a sample or series of samples tell us about the
population form which the sample came
•
•
•
•
Distribution of Sample Means
t Distribution
Distribution of Sample Variances
F Distribution
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Dieter: Chapter 10
Engineering Statistics – Statistical Tests of Hypotheses
and Statistical Intervals
• The statistical decision-making process can be put on a
rational, systematic basis by considering various
statistically based hypotheses
– Null hypothesis Ho: μ = μo
– Alternative hypothesis H1: μ < μo
• Interval estimation is commonly used to make probability
statements about the population from which a sample has
been drawn or to predict the results of a future sample
from the same population
– Confidence Interval
– Prediction Interval
- Tolerance Interval
- Rejection of Outliers
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Dieter: Chapter 10
Engineering Statistics – Analysis of Variance
• When we have three or more samples treatments we can
use a statistical procedure call the Analysis of Variance
(ANOVA) which is important in design of experiments
• With ANOVA we determine:
– The total spread of results between the different treatments
– The spread of results within each treatment
• One-Way Classification
• Two-Way Classification
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Dieter: Chapter 10
Engineering Statistics – Statistical Design of Experiments
• The greatest benefit can be gained from statistical analysis when the
experiments are planned in advance so that data are taken in a way that
will provide the most unbiased and precise results commensurate with
the desired expenditure of time and money
• This can best be done through the combined efforts of a statistician and
the engineer during the planning stage of the project
• Probably the most important benefit from statistically designed
experiments is that more information per experiment will be obtained
than with an unplanned experimentation
• A second benefit is that statistical design results in an organized
approach to the collection and analysis of information
• Still another advantage of statistical planning is the credibility that is
given to the conclusions of an experimental program when the
variability and sources of experimental error are made clear by
statistical analysis
• Finally, an important benefit of statistical design is the ability to
discover interactions between experimental variables
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Dieter: Chapter 10
Engineering Statistics – Statistical Design of Experiments
• In general, there are three classes of statistically designed
experiments
– Blocking designs use blocking techniques to remove the effect of
background variables from experimental error
– Factorial designs are experiments in which all levels of each factor
in an experiment are combined with all levels of every other factor
– Response surface designs are used to determine the empirical
functional relation between factors (independent variables) and the
response (performance variable). The central composite design and
rotatable designs are frequently used for this purpose
• Factorial Design
• Fractional Factorial Designs
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 10
Engineering Statistics – Regressional Analysis
• Regression analysis is the statistical technique for
establishing such relationships between two or more
variables
– Functional relation: emphasis is on prediction
– Association: correlation between variables, which vary jointly
•
•
•
•
Method of Least Squares
Linear Multiple Regression Analysis
Nonlinear Regression Analysis
Linearization Transformation
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 10
Engineering Statistics – Response Surface Methodology
• A powerful statistical procedure that employs factorial
analysis and regression analysis has been developed for the
determination of the optimum operating condition.
• Response surface methodology (RSM) has two objectives:
– To determine with one experiment where to move in the next
experiment so as to continually seek out the optimal point on the
response surface
– To determine the equation of the response surface near the optimal
point
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety
• A hazard (unsafe condition) is the potential for human,
property, or environmental damage
• A risk is the likelihood, expressed either as a probability or
as a frequency, of a hazard’s materializing
• Risk assessment has become increasingly important in
engineering design as the complexity of engineering
systems has increased
• Reliability is a measure of the capability of a part or a
system to operate without failure in the service
environment. It is always expressed as a probability
• Safety is relative protection from exposure to hazards. A
thing is safe if its risks are judged to be acceptable
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety
• Regulation as a Result of Risk
– In a democracy when the public perception of a risk reaches
sufficient intensity, legislation is enacted to control the risk
• Standards
– Standards are one of the most important ways in which the
engineering profession makes sure that society receives a
minimum level of safety and performance
• Risk Assessment
– The assessment of risk is an imprecise process involving judgment
and intuition
– Three classifications of level of risk
• Tolerable risk
• Acceptable risk
• Unacceptable risk
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety: Probabilistic Approach to
Design
• Conventional engineering design uses a deterministic
approach
• It disregards the fact that material properties, the
dimensions of the components, and the externally applied
loads are stochastic in nature
• In conventional design these uncertainties are handled by
applying a factor of safety
• In critical design situations, such as aircraft, space, and
nuclear applications, however, there is a growing trend
toward using a probabilistic approach to better quantify
uncertainty and thereby increase reliability
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety: Probabilistic Approach to
Design
• There are three typical approaches for incorporating
probabilistic effects in design
– The use of a factor of safety
– The use of the absolute worst case design
– The use of probability in design
• The use of probability in design
Pf = P(σ > Sy)
The reliability R is defined as
R = 1-Pf
See Example in Text
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety: Probabilistic Approach to
Design
• Variability in Material Properties
– The mechanical properties of engineering materials exhibit
variability
– Fracture and fatigue properties show greater variability than do the
static tensile properties of yield strength and tensile strength
– Conservative design values for material properties are required in
the design of minimum weight
• Probabilistic Design
– Review the illustrated example of a crank that must support a
single static load
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety: Probabilistic Approach to
Design
• Safety Factor
– The use of a safety factor is far simpler but with much less
information content
– Using a safety factor is a form of “derating” but the extent of
reduction from the true capacity is not known
• Absolute Worse Case Design
– In absolute worse case (AWC) design the variables are set at either
the lowest or largest expected values
– AWC design, like the use of safety factor, is an approach that
accounts for the statistical nature of the design environment in a
deterministic way
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety: Reliability Theory
• Reliability is the probability that a system, component, or
device will perform without failure for a specified period
of time under specified operating conditions
• The discipline of reliability engineering basically is a study
of the causes, distribution, and prediction of failure
• Definitions
– Mean life: The average life of the number of components put on
test or in service, measured over the entire life curve out to
wearout
– Mean time between failures (MTTF): The sum of survival time (up
time) for all of the components divided by the number of failures
– Mean time between failures (MTBF): The mean time between two
successive component failures. MTBF is similar to MTTF, but it is
applied for components or systems that are repaired
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety: Reliability Theory
• Constant Failure Rate
– The probability distribution of reliability is a negative exponential
distribution
– Although an individual component may not have an exponential
reliability distribution, in a complex system with many
components the overall reliability may appear as a series of
random events and the system will follow an exponential reliability
distribution
• Variable Failure Rate
– Mechanical failures and some electronic components, e.g. relays
and thermionic devices, do not exhibit a period of constant failure
rate
– The most common practice is to consider that failure is distributed
according to the Weibull function
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety: Reliability Theory
• System Reliability
– Most mechanical and electronic systems comprise a collection of
components
– The overall reliability of the system depends on how the individual
components with their individual failure rates are arranged
– It is obvious that if there are many components exhibiting series
reliability, the system reliability quickly becomes very low
– A system in which the components are arranged to give parallel
reliability is said to be redundant; there is more than one
mechanism for the system functions to be carried out
– In a system with full active redundancy all but one component may
fail before the system fails; See Aircraft Example for partial redun.
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety: Reliability Theory
• Maintenance and Repair
– If a failed component can be repaired while a redundant
component has replaced it in service, then the overall reliability of
the system is improved
– If components subject to wear can be replaced before they have
failed, then the system reliability will be improved
– Preventive maintenance is aimed at minimizing system failure
– Repairing a failed component in a series system will not improve
the reliability, since the system is not operating
– However, decreasing the repair time will shorten the period during
which the system is out of service
– Maintainability is the probability that a component or system that
has failed will be restored to service within a given time
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety: Design for Reliability
• The design strategy used to ensure reliability can fall
between two broad extremes
– Fail-safe approach
– “the one-horse shay” approach
– Absolute worse-case approach
• Two major areas of engineering activity determine the
reliability of an engineering system
– Provision for reliability must be established during the earliest
design concept stage, carried through the detailed design
development, and many steps in manufacture
– Once the system becomes operational, it is imperative that
provision be made for its continued maintenance during its service
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety: Methods and Techniques
• Failure Mode and Effects Analysis (FMEA)
– Team-based methodology for identifying potential problems with
new or existing designs
• Fault Tree Analysis (FTA)
– A technique that provides a systematic description of the
combinations of possible occurrences in a system that can result in
failure or severe accidents
• Defects and Failure Modes
–
–
–
–
Hardware failure
Software failure
Human failure
Organization failure
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 11
Risk, Reliability, and Safety: Design for Safety
• Safety may well be the paramount issue in product design
• There are three aspects to design for safety
– Make the product safe, i.e. design all hazards out of the product
– If above not possible, then design in protective devices
– If Step 2 cannot remove all hazards, then warn the user of the
product with appropriate warnings like labels, flashing lights, and
loud sounds
• Guidelines for Design for Safety
– Be familiar with these
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 13
•
•
•
•
•
•
•
•
•
•
Economic Decision Making
The major engineering infrastructure that built this nation –
the railroads, major dams, waterways, and air
transportation – required a methodology for predicting
costs and balancing them against alternative courses of
action
Mathematics of Time Value of Money
Depreciation
Taxes
Profitability of Investments
Other Aspects of Probability
Inflation
Sensitivity and Break-Even Analysis
Uncertainty in Economic Analysis
Benefit-Cost Analysis
School of Aerospace Engineering
Georgia Tech
Dieter: Chapter 14
Cost Evaluation
• An engineering design is not complete until we have a good idea of the
cost required to build the design or manufacture the product
• Categories of Costs
• Methods of Developing Cost Estimates
• Cost Indexes
• Cost-Capacity Factors
• Estimating Plant Cost
• Design To Cost
• Manufacturing Costs
• Value Analysis in Costing
• Overhead Costs
• Activity-Based Costing
• Product Profit Model
• Learning Curve
• Cost Models
• Life Cycle Costing
School of Aerospace Engineering
Georgia Tech
Exam #2: Life Cycle Design
Considerations
• Primary Text Chapters
– Chap 6: Embodiment Design
– Chap 7: Modeling and Simulation
– Chap 8: Materials Selection & Materials in Design
– Chap 9: Materials Processing & Design
– Chap 10: Engineering Statistics
– Chap 11: Risk, Reliability, and Safety
– Chap 13: Economic Decision Making
– Chap 14: Cost Evaluation
• Secondary Text Chapter
– Chap 13: Modeling and Simulation
School of Aerospace Engineering