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The Nature of Engineering Knowledge September 29, 2010.

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The Nature of Engineering Knowledge September 29, 2010
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Page 1: The Nature of Engineering Knowledge September 29, 2010.

The Nature of Engineering Knowledge

The Nature of Engineering Knowledge

September 29, 2010

Page 2: The Nature of Engineering Knowledge September 29, 2010.

Grand Unified Theory

Page 3: The Nature of Engineering Knowledge September 29, 2010.

Consider an architect’s model of a building; the building and the model are geometrically similar, but different sizes

100 m 1 m

Page 4: The Nature of Engineering Knowledge September 29, 2010.

Measurements on the model can be translated to measurements on the building via scale factors:

100 m 1 m

Quantity Scale Factor

Length of water pipe

Floor Area

Enclosed Volume

Weight

Ratio of Study space toTravel space

Page 5: The Nature of Engineering Knowledge September 29, 2010.

Fw

FrFg

fw

fg

fr

Page 6: The Nature of Engineering Knowledge September 29, 2010.

The Froude Number

Fr = V2/Lg

If the Froude number is the same for a ship and its model, both will behave the same way (e.g., capsize and sink)

Page 7: The Nature of Engineering Knowledge September 29, 2010.

Catamaran model in a towing tank

Page 8: The Nature of Engineering Knowledge September 29, 2010.

Reynolds Number

At a critical value of Reynolds number,flow changes from laminar to turbulent

Re = Inertial ForcesViscous Forces

= ρvlμ

Page 9: The Nature of Engineering Knowledge September 29, 2010.

Reynolds’s Experiment

Page 10: The Nature of Engineering Knowledge September 29, 2010.
Page 11: The Nature of Engineering Knowledge September 29, 2010.

Karman Vortex Street

Characteristic of turbulent flow

Page 12: The Nature of Engineering Knowledge September 29, 2010.

The Mach Number

M = v/c

If the Mach number is the same foran aeroplane and its model, bothwill be in the same sonic regime(e.g., both supersonic)

Page 13: The Nature of Engineering Knowledge September 29, 2010.

NASA’s Supersonic wind tunnel at Glenn Research Center

Page 14: The Nature of Engineering Knowledge September 29, 2010.

Weber Number

Indicates the ratio between inertialforces and surface-tension forces(this is why you can’t design bugs with a towing tank)

We = ρV2lσ

Page 15: The Nature of Engineering Knowledge September 29, 2010.

Water strider on a pond

Page 16: The Nature of Engineering Knowledge September 29, 2010.

Detailed attention to non-dimensional

numbers made pre-CGI monster movies more realistic

Page 17: The Nature of Engineering Knowledge September 29, 2010.

Usefulness of the Non-Dimensional Numbers

Fluid friction in a pipe is affected byits diameter, and by the fluid’s speed and viscosity.

Using Reynolds number, we caninvestigate all these in one seriesof experiments.

Page 18: The Nature of Engineering Knowledge September 29, 2010.

Why aren’t there anynon-dimensional numbersin electrical engineering?

Page 19: The Nature of Engineering Knowledge September 29, 2010.

Laplace’s Equation

…applies to heat conduction and electrostatics.

So an electrostatic problem can model a thermal problem.

Δ2 Φ = 0

d2φdx2

d2φdy2

d2φdz2

+ + = 0

Page 20: The Nature of Engineering Knowledge September 29, 2010.

Teledeltos paper

Page 21: The Nature of Engineering Knowledge September 29, 2010.

Finite-Element Analysis

Page 22: The Nature of Engineering Knowledge September 29, 2010.

Acc

urac

y

Number of elements

Error in Computer Simulations

Page 23: The Nature of Engineering Knowledge September 29, 2010.

Fuzzy Control

Fuzzy logic employs models of systems that

are deliberately imprecise: for example, a

car may be modelled as having three possible speeds, `too slow’, `OK’, `too fast’.

This can yield simple, robust control

algorithms.

Page 24: The Nature of Engineering Knowledge September 29, 2010.

Qualitative Physics

In making predictions about the world, we

employ mental models. These are neither

exact nor numerical, but they work.

Qualitative physics attempts to get computers

to do the same thing.

Page 25: The Nature of Engineering Knowledge September 29, 2010.

Example: what happens if I knock over this glass of water?

Page 26: The Nature of Engineering Knowledge September 29, 2010.

Example: what happens if I knock over this glass of water?

Page 27: The Nature of Engineering Knowledge September 29, 2010.
Page 28: The Nature of Engineering Knowledge September 29, 2010.
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Page 32: The Nature of Engineering Knowledge September 29, 2010.

Conclusions

• Engineering has a range of strategies, not limited to the application of scientific knowledge

• New non-scientific strategies are continuing to be developed, and may be used in preference to older, more scientific methods.


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