ISE391 Lec03 Chap2 Problem Formulation 1

8/3/2019 ISE391 Lec03 Chap2 Problem Formulation 1

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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

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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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8

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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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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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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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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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

ISE391 Lec03 Chap2 Problem Formulation 1

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