The Nature of Engineering Knowledge

The Nature of Engineering Knowledge

September 29, 2010

Grand Unified Theory

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

100 m 1 m

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

Fw

FrFg

fw

fg

fr

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)

Catamaran model in a towing tank

Reynolds Number

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

Re = Inertial ForcesViscous Forces

= ρvlμ

Reynolds’s Experiment

Karman Vortex Street

Characteristic of turbulent flow

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)

NASA’s Supersonic wind tunnel at Glenn Research Center

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

Water strider on a pond

Detailed attention to non-dimensional

numbers made pre-CGI monster movies more realistic

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.

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

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

Teledeltos paper

Finite-Element Analysis

Acc

urac

y

Number of elements

Error in Computer Simulations

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.

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.

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

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

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.