Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

3.1 Engineering Design Process 45

functional design. Before we can consider improving our design, we need to ask ourselves

what criterion we should use to optimize the design. Design optimization is always based on

some particular criterion, such as cost, strength, size, weight, reliability, noise, or performance.

If we use the weight as an optimization criterion, then the problem becomes one of minimiz-

ing the weight of the ladder without jeopardizing its strength. For example, we may consider

making the ladder from aluminum. We would also perform stress analysis on the new ladder

to see if we could remove material from certain sections of the ladder without compromising

the loading and safety requirements.

Another important fact to keep in mind is that optimizing individual components of an

engineering system does not necessarily lead to an optimized system. For example, consider a

thermal-fluid system such as a refrigerator. Optimizing the individual components indepen-

dently — such as the compressor, the evaporator, or the condenser —with respect to some cri-

terion does not lead to an optimized overall system (refrigerator).

Traditionally, improvements in a design come from the process of starting with an

initial design, performing an analysis, looking at results, and deciding whether or not we can

improve the initial design. This procedure is shown in Figure 3.1. In the past few decades, the

optimization process has grown into a discipline that ranges from linear to nonlinear pro-

gramming techniques. As is the case with any discipline, the optimization field has its own

terminology. There are advanced classes that you can take to learn more about the design

optimization process.

Evaluate

results

of analysis

Can the design

be improved?

Perform

analysis

Modify

design

Initial

design

Final

design

No

Ye s

■Figure 3.1

An optimization procedure.

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