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Problem Formulation
Chapter 2
Lecture 3
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Dr. Mojahid F. Saeed Osman/ISE391/1112
1. Recognizing the need2. Defining the problem
3. Planning the project
4. Gathering information5. Conceptualizing alternative approaches
6. Evaluating the alternatives
7. Selecting the preferred alternative8. Communicating the design
9. Implementing the preferred design
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Formulating Design Problem
The ABET definition of engineering design
states that any engineering design must satisfy
desired needs
3
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Formulating Design Problems(from 9-step model of design process)
Step 1 - Recognizing the Need
Step 2 - Defining the Problem Goals
Objectives
Constraints
B.Hyman/ Fundamentals of Engineering Design Chapter2/Rev.6/26/02
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Hyman/Chapter 2-Problem Formulation/Rev. 6/26/025
Recognizing the Need
Describes a current situation that is unsatisfactory.
Should be written in a negative tone
Establishes improvement in current situation as the ultimate
purpose of the project.
Implies that: We know who is the customer/client is; and
The customer/client knows what their need is
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Recognizing the Need -Automobile Bumper
Problem
There is too much damage to bumpers in low-
speed collisions
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Defining the Problem-Goal
Brief, general, and ideal response to the Need.
Answer the question "How are we going to
address this Need?"
Is so general that we cannot determine when it isachieved.
Its selection establishes the general direction ofthe design effort.
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Goals and Their Associated Design Options
Goal not
selectedGoal
Unavailable Design Options Available Design Options
Fig. 2.2
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Goal for Automobile Bumper Problem
Design an improved automobile bumper
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Scope of Goal Statement
Several potential Goal Statements :
design a child-proof pill bottle that is easier to open
design a child-proof pill container that is easier to open
design a child-proof pill system for dispensing pills
design a child-proof system for dispensing medication
Need Statement:
child-proof pill bottles are too difficultfor people with arthritis to open.
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Need vs. Goal
Need:
Describes the current, unsatisfactory situation
Goal:
describes the ideal future condition
Setting a set of need and goal statement may take severaliterations
Need and goal have to be as simple as possible
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Need vs. Goal
Example
Developing a more efficient air-conditioning system forresidential use
Need
Many houses get uncomfortably hot during summer afternoons.
Two fundamentally different Goals Reduce direct input from summer afternoon sunshine into the house
Increase house ventilation so that hot air escapes
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Rev. 6/26/02 Chapter 2-Problem Formulation 13
Defining the Problem-Objectives
Quantifiable expectations of performance.
Establish operating environment
Indicators of progress toward achieving Goal.
Define the performance characteristics of the design that are of most
interest to the client
Facilitate determination of which alternative designs best meets
expectations.
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Rev. 6/26/02 Chapter 2-Problem Formulation 14
Objectives for Automobile Bumper Problem
Design an inexpensive front bumper so the car can
withstand a 5 mph head-on collision with a fixed concrete
wall without significantly damaging the bumper or other
parts of the car
At the end of the useful life of the bumper, it must be easily
recyclable.
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Itemized List of Objectives
inexpensive
no significant damage to bumper
no significant damage to other parts
easily recyclable
operative
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Rev. 2/19/03 Chapter 2-Problem Formulation 16
Measuring Objectives
Objective Measurement Basis Units
Inexpensive Unit manufacturing cost for a production run of
50,000
SR
No significant damage to bumper Distance bumper is pushed into body inches
No significant damage to other parts Repair cost SR
Easily recyclable Amount of aluminum lb
Retain maneuverability Turning radius ft
Retain braking capability Braking distance ft
Table 2.1
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Rev. 6/26/02 Chapter 2-Problem Formulation 17
Defining the Problem-Constraints
Constraints establish permissible range of the design andperformance parameters
Takes one of three forms:
yes/no constraints The headlight must work
Radiator must not leak
equality constraints
mustbe 18 high inequality constraints
cannot weigh more than 50 lb
must hold at least 50 lbs of steam
mustbe between 12 and 15 long
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Constraints for Automobile Bumper Problem
In order to prevent over-riding bumpers in collisions between
automobiles, the bumpers should be installed 18 up from
the ground.
The weight of the bumper cannot exceed 50 lb.
The mounting brackets on the bumper must be between 8.0
and 12.5 from the center so they match with the bracketsattached to the automobile frame.
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Complete (Revised) Problem Statement for Automobile
Bumper Project
Goal Design an improved front bumper
Objectives (with operating environments, basis for measurement, and units) Inexpensive No significant damaging to bumper No significant damaging to other parts
Easily recyclable Retain maneuverability Retain braking capability
Constraints Should be installed 18 up from the ground. Weight of the bumper cannot exceed 50 lb. Mounting brackets must be between 8.0 and 12.5 from the center Lights must work after collision Radiator must not leak after collision Doors must work after collision
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Trade-offs Between Objectives and Constraints
Restating the problem in a slightly different way can result in
some objectives becoming constraints and vice-versa.
the objective not causing significant damage can bereworded as a constraint not costing more than $200 to
repair.
It may be desirable to include both in the problem statement.
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Rev. 2/19/03 Chapter 2-Problem Formulation 21
Transforming Objectives into Criteria
Objectives
Quantifiable expectations of performance
Criteria Value-free compact descriptors of performance associated
with objectives
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Objectives and Criteria for Automobile
Bumper
Objective Criteria
Inexpensive cost
No significant damage to bumper Amount of damage to bumper
No significant damage to other parts
Easily recyclable
Amount of damage to other parts
Recyclability
Retain maneuverability Maneuverability
Retain braking capability Braking capability
Table 2.2
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