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Superwinds Caused By Global Warming
Transcript of keynote speech by Donald Burfitt-Dons continued
Why should we be so wary of Super Winds?
If we just go on what NOAA have concluded and draw
the conclusion that there is a similar amount of extra energy being
released now in ETCs as has occurred in recent tropical cyclones, a
15% increase in wind strengths we can reach some rough and ready estimates.
Frank Burrow might give us a scientifically more elegant explanation,
but by going to the formula which explains how those great big fat aeroplanes
can actually get airborne we can see why.
10. F=Constant x Velocity Squared.
Good Old Boy Bernoulli got it right and the vital thing
here is the squaring value. Basically as the wind doubles the force
quadruples. Of course, to be scientifically correct some assumptions
are made and it’s not exactly right but near enough for all practical
purposes.
As the wind channels over roofs and between buildings the forces at
work are quite similar to the airflow over an aerofoil section.
Therefore, if we get a fifteen percent increase in
wind strength we are likely to get a 30 % increase in aerodynamic force
at work. That’s not good news for roofs and tiles. Roof trusses
are designed not to resist being pulled upwards but exactly the opposite.
Load is assumed to act downwards with factorisation for snow additions,
etc. Roof plates on which the trusses sit are tied down every two metres
on new buildings but that is a recent change to the building code and
the majority of houses in the country predate that. With a 30 % increase
in lift and as much as 50% in peak gusts you have a perfect formula
for the whole box and dice getting airborne in superwinds. Add in broken
windows allowing cyclone strength winds through the buildings, and I
suugest the results will not be pretty. Continued Donald
Burfitt-Dons talks about the impact of ETCs on aircraft
