Re:혹시 이런글 아십니까? 아인슈타인 썼다는데..

[太上老君]

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Imaginative because they are constantly carrying out thought experiment,
imagining in their minds how the structures and machines they are
designing will perform when built and put into operation. what if, they
ask themselves, what if these components were longer, shorter,thicker, thinner, in titanium or fiber reinforced
plastic instead of steel, and so on, continually exploring alternatives in their attempts to give the client a
solution which makes the best use of the resources available.
Einstein was a famous exponent of the though experiment. His imagining of what
would happen if he were able to sit on a light ray and travel with the speed of light -
would time stand still? - helped him to the formulation of a four-dimensional space-
time continuum for the theory of relativity. Another question he asked:

would an observer stationary at a point on the earth's surface see a distant flash of
lightning at the same instant as a second observe travelling in a train towards the
place where the flash occurred?

It is said that Sir Henry Royce (of Rolls-Royce fame) could run a new engine in his
mind, and in so doing his imagination would identify potential weaknesses and regions
of wear.
Although these examples are merely a few representatives from a very large pool of
experience, the essential point remains. Successful engineering design demands a high
level of conceptual thinking. Rote learning of techniques of mathematical manipulation
is anathema.
Here are some 'What if'? questions for you, the reader, to think about :

What would happen if a candle were lit in a spacecraft?
How would the 'flame' appear?
Indeed, would there bs a flame?
What would happen if a petrol tanker were to collide with a liquid oxygen tanker at
a busy intersection?
Consider a sphere of any radius(say the radius of the earth). When a central circular
cylindrical hole is drilled completely through this sphere, a solid of revolution of
length L remains.
What is the volume of this remaining solid?
(hint : this volume is a function of L only)
What if all lecture theatres were painted pale blue?red?
What if pay tolls ere introduced on urban arterial roads?
What design problems would immediately arise if a law were passed that all central
business districts were to be 'no passenger' car zones.

Successful designers are realists. Thought experiments are cheap, the only resource
expended is the designer's time. but is this resource sufficient for the task at hand?

the Tacoma narrows suspension bridge in the United States was constructed
according to the best design principles of the time(1940), but failed spectacularly after a
few month's service as a result of severe wind-induced vibrations. In a 65 km/hr cross
wind large swirling air vortices were shed alternately from sharp corners at the top and
bottom of the roadway, acting as a bluff body in a turbulent air steam. The frequency of
the vortex shedding and of the associated dynamic forces coincided with a natural
frequency of torsional oscillation of the bridge structure(Pugsley, 1968). this was a
phenomenon not envisaged by the designers - it was outside their previous experience
and foreign to their conceptual thinking about problems in structural design.
In 1857 the steamship the Great Eastern, designed by the great Victorian engineer,
Isambard Kingdom Brunel, was launched. Approximately 210 meters long and 31500
tonnes at displacement powered by the largest marine steam engines of the time, and
aimed at capturing lucrative transatlantic trade, it was a total failure. It could travel at
only one-third of its designed forward speed due to Brunel's quite unrealistic predictions
of the propulsive power required by large ships to overcome wave making drag(Rolt,
1957).

Inexorably, the laws of nature will take their toll of engineers who flout them or
ignore them.

Designers are optimists. the evolving nature of design problems leads them though
cycles of success and failure. but at any instant the fear of failure, a very human
attribute, is held in check by a balanced and basically optimistic outlook on lift -
positive yet objective.
Early in 1921 Sir John Monash, a distinguished civil engineer and soldier, was
appointed chairman and chief executive officer of the newly formed State Electricity
Commission of Victoria, Australia(S.E.C.). The S.E.C. had been set up to exploit
enormous brown coal deposits in the Latrobe Valley. By late 1921 and early 1922 the
whole enterprise was in crisis. Early mineral exploration and shaft sinkings had
indicated the brown coal to have a moisture content of 45 percent to 48percent. Orders
for boilers, supporting structures and associated equipment were placed on this basis.
However, continued testing revealed moisture contents 65 percent to 68 percent,
unprecedently high values for which existing boiler technology was quite unable to
cope.
In public and before State Parliament Monash brushed aside, even ignored, the
problem until, after two uncertain years of very intensive research and development
within the S.E.C., ways were found of redesigning and modifying the boilers and for
drying the coal on the way to the combustion zones. monash and his boilers and for
running great risks which required steady nerves: if the experiments to adapt failed, the
delay and costs would be incalculable and their secrecy indefensible(Serle, 1982)
So we have a vision of the designer as hero - a person of self-awareness and self-
control, imaginative, realistic and optimistic - as the demands.

A university course in engineering design has two major objectives which are :

1. to instruct young engineers in the methods nd techniques of engineering design. To
this end, general methods of solving design problems and specific techniques for
particular applications are described and explained. by working through a graduated
program of design exercise, the ablility to use these methods and techniques is
developed, and a firm foundation laid for future engineering action; and
2. to develop young engineering ability to combine and apply their knowledge of the
engineering sciences. this knowledge has in turn to be integrated with their own
observations and experiences in the complex situations typical of engineering.

If these objectives are attained, young engineerings successfully develop their capacity
for professional problem solving - and incidentally for problem finding.

What are the attributes of good designers?

first and foremost, they are equaly at home with the general and abstract as with the
specific and concrete. they are masters of the theory of science and the art of
engineering. Doctors can bury their mistakes but designers' errors are exposed for all to
see. The avoidance of error requires unremitting attention to detail, to the checking of
each link in the chain of decisions - all at the cost of much intellectual 'blood, toil,
tear and sweat'.
Designers dream dreams, they see not only the way things are but also the way
things ought to be. Designers have the drive and motivation to create new ideas and then
the courage to eval‎uate their creations criticlly and objectively. The generation and
evolution of ideas demands an emotional commitment, but the intellectual discipline of
their profession ensures that designers keep society they serve.
The vision of great designers encompasses people as well as things; their hopes and
aspirations match the needs of the society they serve.

As well as these attributes designers have knowledge, skills and some attitudes
commensurate with those for whom the design solution must work, as well as attitudes
associated with professional ethics. this includes the knowledge of concept, such as
failure and strength for example. Knowledge of methods includes general design
procedure as well as the detail and specific methods of the relevant engineering
sciences, such as drawing free body diagrams for example. the competent designer
must have a wide range of skill as list below:

Design skill in applying general methods and in organizing work in accordance
with these methods
Skill in foreseeing modes of failure.
Skill in design predictions.
Skill in identifying sources of uncertainty in design predictions.
Note : Judgment in making quantitative allowance for these uncertainties is developed largely by experience. We can, however,
make explicit the methods used by professional engineers to cope with uncertainties.

Skill in solving multi-variable problems. Multi-variable problems arise in engineering designs which are not of a neat mathematical form.
Frequently the number of unknowns exceeds the number of equations relating them; there are inequalities to be satisfied;
some variables are discontinuous. An important question is what is the most efficient strategy for exploring this situation?
Skill in appreasing results. the results of design calculations have to be related to the real world. Questions to be asked are: Are the results of the right order of magnitude?
To what accuracy should they be quoted? What accuracy is justified bearing in mind possible inaccuracies in the data used and practical difficulties of construction and manufacture?
Skill in trial and error calculations. In most cases, direct design or synthesis is not possible. A trial design has to be 'guesstimated', analyzed, and then revised if the analysis reveals faults.
The designer has to be ready to try something and give it a go.

Skill in making approximations, taking legitimate shortcuts in what would otherwise be unnecessarily involved calculations.
This is not a purely computational skill, but depends also on insight into the physical situation being represented mathematically.
It is allied to the ability to recognize key issues and concentrate on them.

Skill in assigning tolerances to design variables. This depends on skill in analogue
simulation in determining the sensitivity of the design to change.

Skill in assigning tolerances to linear dimensions and cylindrical surfaces. This depends on skill in constructing the path equation,
in selecting the appropriate datum for measurement of dimensions, and in avoiding conflicting tolerances.

Competent engineering designers are able to take into account a great variety of problems.
Some of these problems may appear, on the surface, to be quite outside the domain of engineering.
Yet challenges to the designers' skills are found everywhere and they often pervade or daily lives. Some sample challenges are:

Why do sausage skins split parallel to the long axis when barbecued?
Why is corrugated iron corrugated?
What is the purpose of an outrigger on a sailing canoe?
Why do yachtsmen occasionally hang off the side of a yacht on a trapeze when racing?
Why does a piece of chalk fail along a 45 degree helix when twisted in pure torsion?
Why is the Eiffel tower such a distinctive shape?

The real challenge of engineering design is to look at things and see their essential engineering qualities and content.
In the words of Jonathan Swift 'There is none so blind as they that will not see'

Note: Our work in engineering design assumes that certain basic knowledge and skills have already been acquired, namely.

Knowledge of elementary statics, mecahnics of solids and properties of engineering materials; and
skill in reading and interpreting drawings and visualizing in three dimensions, skill in the construction of free body diagrams showing forces in equilibrium,
skill in routine mathematical mampulation and calculation.